27/09/2014
Conversores Boost
Conversores Boost (ART247)
Fontes chaveadas, conversores DC/DC e outros circuitos de alimentação utilizam tecnologias diferentes para alterar uma tensão de entrada e com isso obter um valor diferente de tensão de saída com o máximo de estabilidade e eficiência. Nas edições anteriores falamos dos conversores do tipo "charge pump" com especial destaque a linha de componentes da Texas Instruments destinado a este tipo de aplicação. Nesta edição, continuamos com a série falando agora dos conversores do tipo "boost", analisando seu funcionamento e mostrando suas vantagens. Nossa série continuará com aplicações práticas que podem ser de grande utilidade para o projetistas, descrevendo um kit de desenvolvimento na próxima edição.
Os reguladores chaveados possuem uma eficiência que não pode ser encontrada em qualquer outra configuração quando se trata de projeto de fonte de alimentação.
Em outros artigos tratamos dos circuitos "charge pump" que possibilitam a elaboração de alguns circuitos bastante eficientes nesta categoria de aplicações. No entanto eles não são únicos o que nos leva a dar aos projetistas as outras configurações existentes.
Basicamente, existem quatro tipos de conversores DC/DC mais usados nos projetos práticos:
Boost - que fornece uma tensão de saída maior do que a aplicada na entrada
Buck - que fornece uma tensão de saída menor do que a aplicada na entrada
Buck-boost (inversor) em que a tensão de saída tem polaridade oposta a aplicada na entrada.
Fly-back em que temos diversas tensões de saída que podem ser maiores ou menores do que a tensão de entrada.
Na figura 1 mostramos de forma simplificada os quatro tipos de circuitos.
Este artigo vai se dedicar especificamente aos conversores do tipo "boost".
O Indutor
O elemento básico dos conversores do tipo boost é um indutor. Assim, nada melhor do que começarmos nossas explicações pela ação deste componente no circuito.
Ao estabelecermos uma tensão num indutor, de modo que uma corrente possa circular através deste componente, a sua intensidade vai variar com o tempo.
Esta corrente vai ser dada pela expressão:
V = L (di/dt)
O comportamento elétrico de um indutor quando aplicamos tensões que variam tem algumas características interessantes.
A primeira é que só aparece tensão nos terminais do indutor, se aplicarmos neste componente uma tensão que varia com o tempo.
A segunda é que o indutor não responde às variações da tensão instantaneamente. Ele precisa de um tempo para isso.
Finalmente, quanto mais rápida for a variação da corrente num indutor maior será a tensão que aparece nos seus terminais.
Este comportamento dos indutores pode ser melhor visualizado na figura 2.
Veja que o parâmetro mais importante neste comportamento do indutor é di/dt que mede como a corrente varia com o tempo: (é a taxa da variação da corrente).
Veja que a rampa linear no indutor só ocorre quando a se aplica uma tensão constante neste elemento.
Estes fatos são de grande importância para se entender com o funcionam os circuitos do tipo "boost".
De uma maneira mais simples de entender, podemos dizer que da mesma forma que um capacitor armazena energia no campo elétrico entre as armaduras, um indutor armazena energia no campo magnético criado pela corrente, conforme mostra a figura 3.
Quando a tensão é aplicada num indutor as linhas de força se expandem armazenando energia. Quando a tensão deixa de ser aplicada, o campo se contrai com as linhas de força cortando as espiras do indutor e com isso induzindo uma tensão.
Esta tensão será tanto maior quanto mais rápida for a contração do campo o que permite usar este componente para gerar tensões maiores do que a aplicada.
Esta tecnologia é justamente usada nos conversores boost, onde o indutor funciona como uma espécie de reservatório de energia que ainda pode aumentar o valor da tensão aplicada.
Um Conversor Boost na Prática
O projeto das etapas elevadoras de tensão em fontes chaveadas, conversores DC/DC e outras aplicações tem diversos elementos críticos para os quais os projetistas devem estar atentos.
Vamos analisar de maneira rápida como funciona um circuito típico e quais os problemas para os quais o projetista deve estar atento.
Na figura 4 temos o circuito típico de um conversor boost.
Conforme podemos ver, o elemento básico desta etapa é um transistor de efeito de campo de potência de canal N que faz o chaveamento da corrente principal pela carga e pelo indutor.
Podem ser usados outros componentes como, por exemplo, MOSFETs de canal P ou bipolares. No entanto a preferência pelos MOSFETs de canal N está na sua menor resistência entre o dreno e a fonte quando em condução (Rds(on)) que permite controlar correntes mais intensas com menor dissipação de calor.
Na operação, o transistor Q1 é continuamente chaveado, ligando e desligando pela ação do circuito de controle.
Esta ação faz com que seja criada uma corrente pulsante através do diodo e do diodo CR1. Apesar do indutor estar conectado ao capacitor C somente quando o diodo conduz, uma filtragem L/C é obtida de forma efetiva.
A função deste filtro é filtrar o trem de pulsos obtendo assim uma tensão contínua na carga (Vo).
Modos de Operação
No modo contínuo de condução a tensão de saída depende do ciclo ativo e da tensão entrada. Neste circuito as tensões de entrada, saída, corrente de carga e ciclo ativo não devem variar.
Neste modo de operação, a etapa de elevação de tensão (boost) assume dois estados em cada ciclo do sinal de comutação. Estes ciclos são mostrados na figura 5.
No estado ON, o transistor Q1 conduz e CR1 está desligado. No estado OFF o transistor está cortado e CR1 conduzindo.
A representação simplificada da figura 5 possibilita a visualização das correntes nos dois estados.
É importante observar as formas de onda nos diversos elementos deste circuito neste modo de operação. Estas formas de onda são mostradas na figura 6.
Veja que sempre existe uma corrente circulando pelo indutor.
No modo descontínuo, observando as formas de onda mostradas na figura 7.
Para isso consideramos o que ocorre quando a corrente de carga diminui e o modo de condução muda de contínuo para descontínuo.
Quando a corrente de carga cai abaixo de um certo valor, durante uma parte do ciclo de comutação a corrente pelo indutor será zero. A corrente permanecerá nula até o início do ciclo seguinte.
Uma etapa de potência de um conversor "boost" operando nesta modalidade terá três estados diferentes em cada ciclo do sinal de controle, diferentemente de apenas dois estados do modo contínuo.
Para o projetista é importante saber que a resposta de freqüência de uma etapa deste tipo é diferente quando ele opera num ou noutro modo. Isso deve ser levado em conta nos projetos.
Aplicações Práticas
Nas aplicações práticas as etapas de elevação de tensão podem operar tanto no modo contínuo como no modo descontínuo dependendo apenas de como a corrente de carga varia. Assim a escolha do modo de funcionamento depende da aplicação que se tem em mente e ela define os valores dos componentes que devem ser usados..
Alguns componentes deste circuito se tornam críticos, por este motivo, como por exemplo a indutância.
No modo contínuo as etapas normalmente são projetadas para operar com correntes de carga que correspondam a 5 ou 10% da carga total máxima. A faixa de tensões de entrada, tensões de saída e correntes de carga são definidas pelas especificações potência desta etapa.
Existem então procedimentos que devem ser observados para se calcular o valor mínimo que o indutor deve ter para manter a etapa funcionando no modo contínuo.
A seleção do indutor admite muitas opções que vão desde o próprio enrolamento pelo projetista até a utilização de tipos comerciais.
Especial atenção deve ser dada ao tipo de núcleo usado, que pode ser responsável por interferências, conforme mostra a figura 8.
Os tipos de "slug" são os mais baratos mas que têm maior nível de interferências. Os tipos toroidais, por outro lado apresentam menor nível de irradiação de ruído mas são mais caros.
Temos também os tipos de núcleo R-I ou E-E que mantém baixo nível de radiação de ruídos e os tipos "pot core" que possui excelente características de ruído, já que o fluxo magnético fica contido a esta núcleo.
Evidentemente a escolha da tecnologia usada para o indutor está ligada a diversos fatores como a corrente que deve ser conduzida, a potência do estágio, a presença de circuitos sensíveis nas proximidades, custo e outros.
A capacitância de saída é outro ponto para o qual o projetista deve estar atento.
A função do capacitor de saída nas fontes chaveadas com etapas do tipo "boost" é armazenar energia no campo elétrico entre as armaduras.
Esta energia é entregue ao circuito de saída com a finalidade de manter assim a tensão constante na carga.
O principal fator que determina o valor do capacitor de saída é o ripple que deve ser mantido pelas especificações do projeto. Juntamente com o indutor, o capacitor formam um filtro e este filtro deve ter características que mantenha o ripple de saída dentro dos limites exigidos pelo projeto.
O terceiro elemento que deve ser levado em conta no projeto é a corrente de carga.
Na prática devem ser usados capacitores com baixa ESR (equivalent series resistance) e ESL (Equivalent series inductance).
Para aplicações comerciais de baixo custo podem ser usados capacitores de três tecnologias: alumínio de baixa impedância, semicondutor orgânico e tântalo. Os capacitores eletrolíticos de alumínio são os mais baratos mas possuem maior ESR do que os outros.
Os tipos eletrolíticos semicondutores orgânicos se tornaram uma opção interessante nos últimos anos, como os da série OS-COM da Sanyo reunindo baixa ESR e alta estabilidade na faixa de temperatura além de grande capacitância em dimensões reduzidas. Finalmente temos os capacitores de tântalo sólido para montagem em superfície.
O diodo também é um elemento importante no projeto.
Este componente é polarizado de modo a operar com uma condução alternada na velocidade de chaveamento do circuito.
Os diodos usados devem ser de comutação rápida, devem ter uma tensão de ruptura de acordo com o projeto, alta capacidade de corrente e baixa queda de tensão quando polarizados no sentido direto.
A melhor solução para a os projetos de etapas de baixas tensões é um diodo Schottky.
Circuitos Práticos
A Texas Instruments através de sua empresa Unitrode Products possui uma linha de conversores tipo boost que operando a partir de tensões de 1 V podem obter na saída tensões na faixa de 3,3 V a 5 V em diversas configurações práticas.
A família UCC3941 consiste em conversores do tipo "boost" (elevadores de tensão) de baixa tensão que utilizam apenas um indutor e que são otimizados para operar com uma ou duas pilhas alcalinas, aumentando a tensão destas fontes para 3,3 V ou 5 V de saída, ou uma tensão ajustável (dependendo do tipo) com potências de até 500 mW.
A família UCC391 pode ainda fornecer uma saída auxiliar de 9 V com potência de até 100 mW.
A partida sob plena carga pode ser feita com tensões tão baixas como 0,8 V e um máximo garantido de 1 V, e ainda operar com tensões de até 0,4 V se em operação, maximizando a utilização da bateria.
Dentre as possíveis aplicações para esta família de componentes, estão os pagers e assistentes digitais pessoais, que exigem alta eficiência na conversão de tensões.
Os circuitos desta família também podem ser usados com outras fontes de alimentação tais como baterias de Nicad e NiMH.
Na figura 9 temos o diagrama de blocos internos para os componentes desta família já com os componentes externos ligados numa aplicação típica.
Todos os componentes podem ser encontrados em invólucros de 8 pinos do tipo D ou N.
Os componentes desta família são os seguintes:
UCC2941D-3 - 3,3 V - Invólucro SOIC D- -40 a 85oC
UCC3941D-3 - 3,3 V - Invólucro SOIC D - 0 a 70 oC
UCC2941D-5 - 5 V - Invólucro SOIC D - -40 a 85oC
UCC3941D-5 - 5 V - Invólucro SOIC D - 0 a 70 oC
UCC2941-D - ADJ - Invólucro SOIC D - ajustável de 1,3 a 6 V - -40 a 85 oC
UCC3941-D - ADJ - Invólucro SOIC D - ajustável de 1,3 V a 6V - -40 a 85 oC
UCC2941N-3 - 3,3 V - Invólucro DIP N - -40 a 85 oC
UCC3941N-3 - 3,3 V - Invólucro DIP N - 0 a 70 oC
UCC2941N -5 - 5 V - Invólucro DIP N - -40 a 85 oC
UCC3941N-5 - 5 V - Invólucro DIP N - 0 a 70 oC
UCC2941N-ADJ - Invólucro DIP N - Ajustável de 1,3 a 6 V - -40 a 85 oC
UCC3941-ADJ - Invólucro DIP N - AJustável de 1,3 a 6 V - 0 a 70 oC
Características Gerais Para o UCC2941-3
Parâmetro - Valor
Vcc (max) - 3,8 V
Vcc (min) - 0,8 V
Preset Vout (V) - 3,3 V
Vout (max) - 3,3 V
Vout (min) - 3,3 V
Vout - Precisão - 3 %
Corrente de Saída - 200 mA
Eficiência Típica (max) - 85 %
Iq (tip) - 0,08 mA
Current de Shutdown (tip) - 8 uA
Frequência de Chaveamento (max) - 250 kHz
Destaques da Família ICC3941:
* Tensão de entrada de 1 V com partida assegurada sob carga total ou alimentação principal até de 0,4 V
* Faixa de tensões de entrada de 1 V até Vout + 0,5 V
* Potência de saída de 500 mW com tensões de bateria tão baixas como 0,8 V
* Saída secundária de 9 V com um único indutor
* Potência de saída limitada com ajuste externo
* Saída totalmente desconectada em condição de shutdown
* Controle adaptativo do modo de corrente para eficiência ótima
* Corrente de alimentação em shutdown de 0,8 uA
Conclusão
A Texas Instruments disponibiliza um kit de desenvolvimento e é deles que falaremos na próxima edição.
Para saber mais, os leitores que dominam o diodo inglês podem fazer o download do documento "Understanding Boost Power Stages in Swiitchmode Power Supplies - SLVA061 - no site da Texas Instruments - http://www.ti.com
Hablemos de Baterias
Fonte: http://www.decibeleros.com.ve/foro/viewtopic.php?f=9&t=632
Hablemos de Baterias
por ATENCIO77 » Mié Mar 13, 2013 10:25 pm
How to Measure CCA (Cold Cranking Amp)
BU-902a: How to Measure CCA (Cold Cranking Amp)
Ever since Cadillac invented the starter motor in 1912, car mechanics explored ways to measure cold cranking amps. CCA assures that the battery has sufficient energy to crank the engine when cold. To do this without “freezing,” testers look at internal resistance, the gatekeeper of a battery. A starter battery with low resistance assures reasonably good cranking, and a CCA reading of 400 to 500A is sufficient for most starter batteries. According to SAE J537, a CCA reading of 500A delivers 500A at -18°C (0°F) for 30 seconds without dropping below 7.2 volts. Read more about How to Measure Capacity.
Courtesy of BMW
Garages seldom do the full-fletched CCA test; this belongs to laboratories. Instead, device manufacturers offer alternatives and the carbon pile introduced in the 1980s is one of the oldest and most reliable methods. To do a pass/fail test, a fully charged starter battery is loaded with half the rated CCA for 15 seconds at a moderate temperature of 10º C (50º F) and higher. The battery will pass if the voltage stays above 9.6V. Colder temperatures cause the voltage to drop further. The DC load method has the advantage of detecting batteries with a partially shorted cell (low specific gravity) but the device cannot estimate battery capacity.
Mechanics prefer small sizes, and instead of applying the prolonged load that is typical of the carbon pile, device manufactures developed handheld testers that induce a high-current pulse. The Ohm’s law calculates the internal resistance based on the load current and voltage drop. The test conditions and results of this device are similar to the carbon pile.
Meanwhile, non-invasive test methods emerged, meaning that the battery is no longer loaded for measurements. The AC Conductance method reads CCA by injecting a single frequency of 80–90 Hertz to the battery. The units are smaller than invasive devices and the battery does not need to be fully charged. AC Conductance meters cannot read capacity and a partially shorted cell may pass as good.
Critical progress has been made in electrochemical impedance spectroscopy (EIS). Research centers have been using EIS for many years but high equipment cost, long test times and the need for trained professionals to decipher the data have kept this technology in laboratories. Fuzzy logic, advanced digital signal processors and a new algorithm to process the information have simplified this task.
Cadex took the EIS concept one step further and developed multi-model electrochemical impedance spectroscopy or Spectroäfor short. Spectro™ gives more accurate CCA estimation than what is possible with single-frequency AC Conductance, but the most important advantage is the ability to estimate capacity, the leading health indicator of a battery. Here is how it works:
A control signal ranging from 20 to 2000Hz is injected into the battery as if to capture the topography of a landscape. The scanned imprint is then compared against a matrix to derive at the reading. A matrix can be described as a multi-dimensional lookup table; and text recognition, fingerprint identification and visual imaging operate on a similar principle.
CCA works on a basic matrix that covers a broad range of starter batteries. Capacity, on the other hand, requires a complex model. To simplify testing, Cadex has developed a generic matrix that covers most starter batteries, flooded and AGM. The said generic matrix provides pass/fail information based on a capacity setting of 40 percent, which serves as the end-of-life threshold. Battery-specific matrices can be made available that offer numeric capacity values in percent. The test takes 15 seconds and works with a partially charged battery. Figure 1 shows the Spectro CA-12 with Spectro™ technology.
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Figure 1: Spectro CA-12 battery tester
Multi-frequency concept Spectro™ concept displays capacity, CCA and state-of-charge; test time is 15 seconds.
Courtesy Cadex
Patented technology
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“How accurate are the readings,” car mechanics ask? This depends on the tester and method used. For example, the Spectro CA-12 with a generic matrix provides a CCA accuracy of 90 percent; capacity is about 80 percent. The single-frequecy AC Conductance, on the other hand, provides a CCA accuracy of roughly 70 percent with no capacity readout. Such low accuracies may come as a surprise to many and service technicians ask for better than 90 percent. This is impossible with lead acid batteries because of inherited inaccuracies. Capacity fluctuations of +/- 12 percent are common even with highly accurate discharge and charge equipment tested in a controlled laboratory environment. Read more about How to Measure Capacity.
State-of-charge (SoC) also affects accuracy. Figure 2 compares CCA readings at different SoC, taken with the Spectro CA-12 and a device that is based on AC Conductance. While Spectro shows only a slight decrease with depleting charge, AC Conductance reflects a strong departure form the horizontal line; the readings are only similar at a 70 percent SoC. Since most batteries hover at about 70 percent when the car is brought in for service, the CCA readings of the two methods may appear similar.
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Figure 2: CCA accuracy on state-of-charge
The Spectro CA-12 provides stable CCA readings between a SoC of 100–40% (red); the values on AC Conductance drop rapidly with SoC (blue).
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Battery manufacturers are hesitant to endorse new test technologies. It is said that the first digital tester introduced in the early 1990s won approval by agreeing to give slightly higher CCA readings than what a lab test would provide. After all, who knows the true value! Very few service garages would go through a full SAE J537 verification that can take up to a week to complete for one battery. Showing a higher reading will indeed favor market acceptance, but this poses a problem when emerging technologies reveal correct readings that are at lower levels.
It so happened that the battery laboratory of a German luxury car manufacturer performed a comparison test as part of product qualification. The battery testers involved were the Spectro CA-12 and a device based on AC Conductance. With a dedicated matrix, the Spectro CA-12 achieved a CCA accuracy of 97%; capacity came in at 87 percent. In comparison, the AC Conductance unit produced a correct CCA prediction of only 51 percent with no capacity reference.
One can clearly see that a CCA measurement at a low accuracy provides limited information regarding battery aging and end-of-life prediction. Furthermore, the driver can guess CCA on engine cranking. Capacity is the more reliable health indicator and there is some confusion in differentiating between the two. North America focuses on CCA, and RC (reserve capacity) is usually overlooked. Europe, on the other hand, is more in tune with capacity and their batteries are clearly marked with Ah. [Formula for RC to Ah conversion: RC divided by 2 plus 16]
Figure 3 illustrates the bond between capacity and CCA on hand of a fluid-filled container. The liquid represents the capacity, and the tap symbolizes the energy delivery or CCA, best remembered as “pipe size.” While CCA stays stable through most of the battery life, the capacity decreases steadily. The illustration represents the aging process with growing “rock content” that inhibits energy storage. The capacity gradually declines until there won’t be enough “juice” one day to start the engine. Read more about Tracking Battery Capacity and Resistance as part of Aging.
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Figure 3: Relationship of CCA and capacity of a starter battery
Capacity represents energy and is shown as liquid. CCA relates to internal resistance and is responsible for energy delivery, best remembered as “pipe size.” CCA tends to stay high while the capacity diminishes as part of aging.
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Conclusion
No single instrument can evaluate all battery anomalies and rapid testing only gives a rough estimation. There are battery defects that can only be revealed by applying a heavy load, and a micro short in a cell is such a case. A rapid-test might pass the battery as good even though the short has lowered the specific gravity to almost “empty” due to high self-discharge and the engine won’t crank. A carbon pile or hydrometer is best able to find the anomaly but the test must be done after the battery has been removed from the charger for a few days. A charge will cover up the fault and everything will look normal.
There are no ideal battery test instruments; however, scientists predict that the battery industry is moving towards electrochemical impedance spectroscopy to estimate battery performance. While advancements in battery rapid-testing are noteworthy, none is foolproof.
Fonte:http://batteryuniversity.com/learn/article/how_to_measure_cca_cold_cranking_amp
Battery Basics - The Battery Cell Online
Fonte: http://www.thebatterycellonline.co.nz/210364/index.html
The commercial use of the lead acid battery is over 100 years old. The same chemical principal is being used to create energy that our Great, Great, Grandparents may have used.
If you can grasp the basics you will have fewer battery problems and will gain greater battery performance, reliability, and longevity. I suggest you read the entire tutorial, however I have indexed all the information for a quick read and easy reference.
A battery is like a piggy bank. If you keep taking out and putting nothing back you soon will have nothing.
Present day chassis battery power requirements are huge. Look at today’s vehicle and all the electrical devices that must be supplied. Electronics require a source of reliable power. Poor battery condition can cause expensive electronic component failure. Did you know that the average vehicle has 11 pounds of wire in the electrical system? Look at RVs and boats with all the electrical gadgets that require power. I can remember when a trailer or motor home had a single 12-volt house battery. Today it is standard to have 2 or more house batteries powering inverters up to 4000 watts.
Average battery life has become shorter as energy requirements have increased. Life span depends on usage; 6 months to 48 months, yet only 30% of all batteries actually reach the 48-month mark. A Few BasicsThe Lead Acid battery is made up of plates, lead, and lead oxide (various other elements are used to change density, hardness, porosity, etc., like Calcium/Calcium plates) with a 35% sulfuric acid and 65% water solution. This solution is called electrolyte which causes a chemical reaction that produces electrons. When you test a battery with a hydrometer you are measuring the amount of sulfuric acid in the electrolyte. If your reading is low, that means the chemistry that makes electrons is lacking. So where did the sulfur go? It is attached to the battery plates, and when you recharge the battery the sulfur returns to the electrolyte.These topics are covered below in more detail:
1. Safety
2. Battery types, Deep Cycle and Starting
3. Wet Cell, Gel-Cell and Absorbed Glass Mat (AGM)
4. CCA, CA, MCA, AH and RC; what's that all about?
5. Battery Maintenance
6. Battery Testing
7. Selecting and Buying a New Battery
8. Battery Life and Performance
9. Battery Charging
10. Battery Do's
11. Battery Don'ts
The commercial use of the lead acid battery is over 100 years old. The same chemical principal is being used to create energy that our Great, Great, Grandparents may have used.
If you can grasp the basics you will have fewer battery problems and will gain greater battery performance, reliability, and longevity. I suggest you read the entire tutorial, however I have indexed all the information for a quick read and easy reference.
A battery is like a piggy bank. If you keep taking out and putting nothing back you soon will have nothing.
Present day chassis battery power requirements are huge. Look at today’s vehicle and all the electrical devices that must be supplied. Electronics require a source of reliable power. Poor battery condition can cause expensive electronic component failure. Did you know that the average vehicle has 11 pounds of wire in the electrical system? Look at RVs and boats with all the electrical gadgets that require power. I can remember when a trailer or motor home had a single 12-volt house battery. Today it is standard to have 2 or more house batteries powering inverters up to 4000 watts.
Average battery life has become shorter as energy requirements have increased. Life span depends on usage; 6 months to 48 months, yet only 30% of all batteries actually reach the 48-month mark. A Few BasicsThe Lead Acid battery is made up of plates, lead, and lead oxide (various other elements are used to change density, hardness, porosity, etc., like Calcium/Calcium plates) with a 35% sulfuric acid and 65% water solution. This solution is called electrolyte which causes a chemical reaction that produces electrons. When you test a battery with a hydrometer you are measuring the amount of sulfuric acid in the electrolyte. If your reading is low, that means the chemistry that makes electrons is lacking. So where did the sulfur go? It is attached to the battery plates, and when you recharge the battery the sulfur returns to the electrolyte.These topics are covered below in more detail:
1. Safety
2. Battery types, Deep Cycle and Starting
3. Wet Cell, Gel-Cell and Absorbed Glass Mat (AGM)
4. CCA, CA, MCA, AH and RC; what's that all about?
5. Battery Maintenance
6. Battery Testing
7. Selecting and Buying a New Battery
8. Battery Life and Performance
9. Battery Charging
10. Battery Do's
11. Battery Don'ts
12. Self Discharge
13. How long will my battery last?
14. What type of charger and why?
15. AGM vs Gel vs AGM??
16. Battery Standards info+conversion table DIN, SAE, JIS, EN, IEC, IKC and CEI
1. We must think safety when we are working around and with batteries. Remove all jewellery. After all you don't want to melt your watchstrap while you are wearing the watch. The hydrogen gas that batteries make when charging is very explosive. I have had 2 batteries blow up and drench me in sulfuric acid. That is no fun. This is a good time to use those safety goggles that are hanging on the wall. Sulfuric Acid eats up clothing and you may want to select Polyester clothing to wear, as it is naturally acid resistant. I just wear older clothes, after all Polyester is so out of style. When doing electrical work on vehicles it is best to disconnect the ground cable from the battery. Just remember you are messing with corrosive acid, explosive gases and 100's amps of electrical current.
2. Basically there are two types of batteries; starting (cranking), and deep cycle (RV/marine/golf cart). The starting battery (SLI starting lights ignition) is designed to deliver quick bursts of energy (such as starting engines) and have a greater plate count. The plates will also be thinner and have somewhat different material composition. The deep cycle battery generally has less instant energy but greater long-term energy delivery. Deep cycle batteries have thicker plates and can survive a number of discharge cycles. Starting batteries should not be used for deep cycle applications. The so-called Dual Purpose Battery is only a compromise between the 2 types of batteries, although this is changing as technology makes advances. (There are now newer technology batteries available in New Zealand, so shop around and ask questions)
3. Wet Cell (flooded), Gel Cell, and Absorbed Glass Mat (AGM) are various versions of the lead acid battery. The wet cell comes in 2 styles; serviceable, and maintenance free. Both are filled with electrolyte and for deep cycle use, I prefer one that I can add water to and check the specific gravity of the electrolyte with a hydrometer. The Gel Cell and the AGM batteries are specialty batteries that typically cost twice as much as a premium wet cell. However they store very well and do not tend to sulfate or degrade as easily as wet cell. There is little chance of a hydrogen gas explosion or corrosion when using these batteries; these are the safest lead acid batteries you can use. Gel Cell and some AGM batteries may require a special charging rate. I personally feel that careful consideration should be given to the AGM battery technology for applications such as Marine, RV, Solar, Audio, Power Sports and Stand-By Power just to name a few. If you don't use or operate your equipment daily; this can lead to premature battery failure; or if you depend on top-notch battery performance, then spend the extra money. Gel Cell batteries are still being sold, but AGM batteries are replacing them in most applications where they have been used in the past. There is some confusion about AGM batteries because different manufacturers call them different names; some of the popular ones are sealed regulated valve, dry cell, non-spillable, and sealed lead acid batteries. In most cases AGM batteries will give greater life span and greater cycle life than a wet cell battery, although with modern technological advances, this is becoming less so, so consider both when making your decision.
SPECIAL NOTE about Gel Batteries: It is very common for individuals to use the term GEL CELL when referring to sealed, maintenance-free batteries, much like one would use Kleenex when referring to facial tissue or "Xerox machine" when referring to a copy machine. Be very careful when specifying a battery charger, many times we are told by customers they are requiring a charger for a Gel Cell battery when in fact the battery is not a Gel Cell.
AGM: The Absorbed Glass Matt construction allows the electrolyte to be suspended in close proximity with the plate’s active material. In theory, this enhances both the discharge and recharge efficiency. Actually, AGM batteries are a variant of Sealed VRLA batteries. Popular usage; high performance engine starting, power sports, deep cycle, solar and storage battery. AGM batteries are typically good deep cycle batteries and they will deliver their best life performance if recharged before the battery drops below the 50 percent discharge rate. If these AGM batteries are discharged to a rate of 100 percent the cycle life will be 300 plus cycles and this is true of most AGM batteries which are rated as deep cycle batteries.
GEL: The gel cell is similar to the AGM style because the electrolyte is suspended, but different because technically the AGM battery is still considered to be a wet cell. The electrolyte in a GEL cell has a silica additive that causes it to set up or stiffen. The recharge voltages on this type of cell are lower than the other styles of lead acid battery. This is probably the most sensitive cell in terms of adverse reactions to over-voltage charging. Gel Batteries are best used in VERY DEEP cycle application and may last a bit longer in hot weather applications. If the incorrect battery charger is used on a Gel Cell battery poor performance and premature failure is certain.
4. CCA, AH and RC what are these all about? Well these are the standards that most battery companies use to rate the output and capacity of a battery.
Cold cranking amps (CCA) is a measurement of the number of amps a battery can deliver at -18 ° C for 30 seconds and not drop below 7.2 volts. So a high CCA battery rating is good especially in cold weather.
What are Marine Cranking Amps (MCA) or (CA) rates?This is a rating used to describe the discharge load in amperes which a new, fully charged battery at 32 degrees F (0C), can continuously deliver for 30 seconds and maintain a terminal voltage equal or greater than 1.2 volts per cell. It is sometimes referred to as Marine Cranking Amps or Cranking Amps.
Reserve Capacity (RC) is a very important rating. This is the number of minutes a fully charged battery at 25 ° C will discharge 25 amps until the battery drops below 10.5 volts.
An amp hour (AH) is a rating usually found on deep cycle batteries. If a battery is rated at 100 amp hours it should deliver 5 amps for 20 hours, 20 amps for 5 hours, etc.
5. Battery Maintenance is an important issue. The battery should be cleaned using a baking soda and water mix; a couple of table spoons to a litre of water. Cable connection needs to be clean and tightened. Many battery problems are caused by dirty and loose connections. A serviceable battery needs to have the fluid level checked. Use only mineral free water. Distilled water is best. Don't overfill battery cells especially in warmer weather. The natural fluid expansion in hot weather will push excess electrolytes from the battery. To prevent corrosion of cables on top post batteries use a small bead of silicon sealer at the base of the post and place a felt battery washer over it. Coat the washer with high temperature grease or petroleum jelly (Vaseline), then place cable on the post and tighten. Coat the exposed cable end with the grease. Most people don't know that just the gases from the battery condensing on metal parts cause most corrosion.
6. Battery Testing can be done in more than one way. The most popular is measurement of specific gravity and battery voltage. To measure specific gravity buy a temperature compensating hydrometer and to measure voltage, use a digital D.C. Voltmeter. A good digital load tester may be a good purchase if you need to test sealed batteries.
You must first have the battery fully charged. The surface charge must be removed before testing. If the battery has been sitting at least several hours (I prefer at least 12 hours) you may begin testing. To remove surface charge the battery must experience a load of 20 amps for 3 plus minutes. Turning on the headlights (high beam) will do the trick. After turning off the lights you are ready to test the battery.
State of Charge Specific Gravity Voltage
12V 6V
100% 1.265 12.7 6.3
*75% 1.225 12.4 6.2
50% 1.190 12.2 6.1
25% 1.155 12.0 6.0
Discharged 1.120 11.9 6.0
*Sulfation of Batteries starts when specific gravity falls below 1.225 or voltage measures less than 12.4 (12v Battery) or 6.2 (6 volt battery). Sulfation hardens the battery plates reducing and eventually destroying the ability of the battery to generate Volts and Amps.
Load testing is yet another way of testing a battery. Load test removes amps from a battery much like starting an engine would. A load tester can be purchased at most auto parts stores. Some battery companies label their battery with the amp load for testing. This number is usually 1/2 of the CCA rating. For instance, a 500CCA battery would load test at 250 amps for 15 seconds. A load test can only be performed if the battery is near or at full charge.
The results of your testing should be as follows:
Hydrometer readings should not vary more than .05 differences between cells.
Digital Voltmeters should read as the voltage is shown in this document. The sealed AGM and Gel-Cell battery voltage (full charged) will be slightly higher in the 12.8 to 12.9 ranges. If you have voltage readings in the 10.5 volts range on a charged battery, that probably indicates a shorted cell. (12.6 / 6 = 2.1 volts per cell, so 12.6 - 2.1 = 10.5 volts)
If you have a maintenance free wet cell, the only ways to test are voltmeter and load test. Most of the maintenance free batteries have a built in hydrometer that tells you the condition of 1 cell of 6 (usuall cell 2). You may get a good reading from 1 cell but have a problem with other cells in the battery.
When in doubt about battery testing, call the battery manufacturer/supplier. Many batteries sold today have a toll free number to call for help.
7. Selecting a Battery - When buying a new battery I suggest you purchase a battery with the greatest reserve capacity or amp hour rating possible. Of course the physical size, cable hook up, and terminal type must be a consideration. You may want to consider a Gel Cell or an Absorbed Glass Mat (AGM) rather than a Wet Cell if the application is in a harsher environment or the battery is not going to receive regular maintenance and charging. For MOST Motorhome use, I recommend a simple 6 volt battery like the GC2-6Volt coupled to achieve 12 / 24 / 48 volt configuration. Properly maintained these should give you years of good service.
Be sure to purchase the correct type of battery for the job it must do. Remember engine starting batteries and deep cycle batteries are different. Freshness of a new battery is very important. The longer a battery sits and is not re-charged the more damaging sulfation build up there may be on the plates. Most batteries have a date of manufacture code on them. The month is indicated by a letter 'A' being January and a number '8' being 2008. C8 would tell us the battery was manufactured in March 2008. Remember the fresher the better. The letter "i" is not generally used because it can be confused with #1.
Battery warranties are figured in the favor of battery manufacturers. Let's say you buy a 60-month warranty battery and it lives 41 months. The warranty is pro-rated so when taking the months used against the full retail price of the battery you end up paying about the same money as if you purchased the battery at the sale price. This makes the manufacturer happy. What makes me happy is to exceed the warranty. Let me assure you it can be done by almost anyone, but the key is proper maintenance.
8. Battery life and performance - Average battery life has become shorter as energy requirements have increased. Two phrases I hear most often are "my battery won't take a charge, and my battery won't hold a charge". Only 30% of batteries sold today reach the 48-month mark. In fact 80% of all battery failure is related to sulfation build-up. This build up occurs when the sulfur molecules in the electrolyte (battery acid) become so deeply discharged that they begin to coat the battery's lead plates. Before long the plates become so coated that the battery dies. The causes of sulfation are numerous. Let me list some for you.· Batteries sit too long between charges.
· Battery is stored without some type of energy input.
· "Deep cycling" an engine starting battery. Remember these batteries can't stand deep discharge.
· Undercharging of a battery, to charge a battery (let’s say) to 90% of capacity will allow sulfation of the battery using the 10% of battery chemistry not reactivated by the incomplete charging cycle.
· Heat of 37 plus C., increases internal discharge. As temperatures increase so does internal discharge. A new fully charged battery left sitting 24 hours a day at 37 degrees C for 30 days would most likely not start an engine.
· Low electrolyte level - battery plates exposed to air will immediately sulfate.
· Incorrect charging levels and settings. Most cheap battery chargers can do more harm than good. See the section on battery charging and do yourself a favour - buy a decent battery charger. Your batteries will thank you by providing years of power for you.
· Cold weather is also hard on the battery. The chemistry does not make the same amount of energy as a warm battery. A deeply discharged battery can freeze solid in sub zero weather.
· Parasitic drain is a load put on a battery with the key off. More info on parasitic drain will follow in this article.
There are ways to greatly increase battery life and performance. All the products we sell are targeted to improve performance and battery life.
An example: Let's say you have "toys"; an ATV, classic car, antique car, boat, Harley, etc. You most likely don't use these toys 365 days a year as you do your car. Many of these toys are seasonal so they are stored. What happens to the batteries? Most batteries that supply energy to power our toys only last 2 seasons. You must keep these batteries from sulfating or buy new ones. There are products to prevent and reverse sulfation. The PulseTech products are patented electronic devices that reverse and prevent sulfation. Also Battery Equaliser, a chemical battery additive, has proven itself very effective in improving battery life and performance. Other devices such as Solar Trickle Chargers are a great option for standard type batteries maintenance, as is a smart charger for deep cycle batteries.
Parasitic drain is a load put on a battery with the key off. Most vehicles have clocks, engine management computers, alarm systems, etc. In the case of a boat you may have an automatic bilge pump, radio, GPS, etc. These devices may all be operating without the engine running. You may have parasitic loads caused by a short in the electrical system. If you are always having dead battery problems most likely the parasitic drain is excessive. The constant low or dead battery caused by excessive parasitic energy drain will dramatically shorten battery life. If this is a problem you are having, you may want to fit a ‘kill switch’ to prevent dead batteries before they happen. This method will also prevent you from deep cycling your starting/cranking battery.
9. Battery Charging - Remember you must put back the energy you use, immediately. If you don't the battery sulfates and that affects performance and longevity. The alternator is a battery charger. It works well if the battery is not deeply discharged. The alternator tends to overcharge batteries that are very low and the overcharge can damage batteries. In fact an engine starting battery on average has only about 10 deep cycles available when recharged by an alternator. Batteries like to be charged in a certain way, especially when they have been deeply discharged. This type of charging is called 3 step regulated charging. Please note that only special “SMART CHARGERS” using computer technology can perform 3 step charging techniques. You don't always find these types of chargers in parts stores or cheaper 'bulk' outlets. The first step is bulk charging where up to 80% of the battery energy capacity is replaced by the charger at the maximum voltage and current amp rating of the charger. When the battery voltage reaches 14.4 volts this begins the absorption chargestep. This is where the voltage is held at a constant 14.4 volts and the current (amps) declines until the battery is 98% charged. Next comes the Float Step (sometimes called trickle charge). This is a regulated voltage of not more than 13.4 volts and usually less than 1 amp of current. This in time will bring the battery to 100% charged, or close to it. The float charge will not boil or heat batteries but will maintain the batteries at 100% readiness and prevent cycling during long term inactivity. Some gel cell and AGM batteries may require special settings or chargers.
Please note: it will take an inordinate amount of time to fully charge a deeply discharged battery using a cheap "trickle" charger - they are simply not designed for bulk charging batteries, so again I say do yourself and your batteries a favour, buy a decent battery charger, preferably a 'smart' charger.
10. Battery Do's· Think Safety First.
· Do read entire tutorial
· Do regular inspection and maintenance especially in hot weather.
· Do recharge batteries immediately after discharge.
· Do buy the highest RC reserve capacity or AH amp hour battery that will fit your configuration.
11. Battery Don'ts· Don't forget safety first.
· Don't add new electrolyte (acid) - just distilled water.
· Don't use unregulated high output battery chargers to charge batteries.
· Don't place your equipment and toys into storage without some type of device to keep the battery charged.
· Don't disconnect battery cables while the engine is running (your battery acts as a filter).
· Don't put off recharging batteries.
· Don't add tap water as it may contain minerals that will contaminate the electrolyte.
· Don't discharge a battery any deeper than you possibly have to.
· Don't let a battery get hot to the touch and boil violently when charging.
· Don't mix size and types of batteries.
· Don't mix batteries of differing ages - they could wreck each other.
A 12-volt battery is made up of a plastic case containing six cells. Each cell is made up of a set of positive and negative plates immersed in a dilute sulfuric acid solution known as electrolyte, and each cell has a voltage of around 2.1 volts when fully charged. The six cells are connected together to produce a fully charged battery of about 12.6 volts.
That's great, but how does sticking lead plates into sulfuric acid produce electricity? A battery uses an electrochemical reaction to convert chemical energy into electrical energy. Let's have a look. Each cell contains plates resembling tiny square tennis racquets made either of lead antimony or lead calcium. A paste of what's referred to as "active material" is then bonded to the plates; sponge lead for the negative plates, and lead dioxide for the positive. This active material is where the chemical reaction with the sulfuric acid takes place when an electrical load is placed across the battery terminals.
How It Works
Let me give you the big picture first for those who aren't very detail oriented. Basically, when a battery is being discharged, the sulfuric acid in the electrolyte is being depleted so that the electrolyte more closely resembles water. At the same time, sulfate from the acid is coating the plates and reducing the surface area over which the chemical reaction can take place. Charging reverses the process, driving the sulfate back into the acid. That's it in a nutshell, but read on for a better understanding. If you've already run from the room screaming and pulling your hair, don't worry.
The electrolyte (sulfuric acid and water) contains charged ions of sulfate and hydrogen. The sulfate ions are negatively charged, and the hydrogen ions have a positive charge. Here's what happens when you turn on a load (headlight, starter, etc). The sulfate ions move to the negative plates and give up their negative charge. The remaining sulfate combines with the active material on the plates to form lead sulfate. This reduces the strength of the electrolyte, and the sulfate on the plates acts as an electrical insulator. The excess electrons flow out the negative side of the battery, through the electrical device, and back to the positive side of the battery. At the positive battery terminal, the electrons rush back in and are accepted by the positive plates. The oxygen in the active material (lead dioxide) reacts with the hydrogen ions to form water, and the lead reacts with the sulfuric acid to form lead sulfate.
The ions moving around in the electrolyte are what create the current flow, but as the cell becomes discharged, the number of ions in the electrolyte decreases and the area of active material available to accept them also decreases because it's becoming coated with sulfate. Remember, the chemical reaction takes place in the pores on the active material that's bonded to the plates.
Many of you may have noticed that a battery used to crank a vehicle that just won't start, will quickly reach the point that it won't even turn the engine over. However, if that battery is left to rest for a while, it seems to come back to life. On the other hand, if you leave the switch in the "park" position overnight (only a couple of small lamps are lit), the battery will be totally useless in the morning, and no amount of rest will cause it to recover. Why is this? Since the current is produced by the chemical reaction at the surface of the plates, a heavy current flow will quickly reduce the electrolyte on the surface of the plates to water. The voltage and current will be reduced to a level insufficient to operate the starter. It takes time for more acid to diffuse through the electrolyte and get to the plates' surface. A short rest period accomplishes this. The acid isn't depleted as quickly when the current flow is small (like to power a tail light bulb), and the diffusion rate is sufficient to maintain the voltage and current. That's good, but when the voltage does eventually drop off, there's no more acid hiding in the outer reaches of the cell to migrate over to the plates. The electrolyte is mostly water, and the plates are covered with an insulating layer of lead sulfate. Charging is now required.
12. Self Discharge
One not-so-nice feature of lead acid batteries is that they discharge all by themselves even if not used. A general rule of thumb is a one percent per day rate of self-discharge. This rate increases at high temperatures and decreases at cold temperatures. Don't forget that your vehicle, with say a clock, stereo, and CB radio, is never completely turned off. Each of those devices has a "keep alive memory" to preserve your radio pre-sets and time, and those memories draw about 20 milliamps, or .020 amps. This will suck about one half amp hour from your battery daily at 80 degrees Fahrenheit. This draw, combined with the self-discharge rate, will have your battery 50 percent discharged in two weeks if the vehicle is left unattended and undriven.
When A Battery Is Being Charged
Charging is a process that reverses the electrochemical reaction. It converts the electrical energy of the charger into chemical energy. Remember, a battery does not store electricity; it stores the chemical energy necessary to produce electricity.
A battery charger reverses the current flow, providing that the charger has a greater voltage than the battery. The charger creates an excess of electrons at the negative plates, and the positive hydrogen ions are attracted to them. The hydrogen reacts with the lead sulfate to form sulfuric acid and lead, and when most of the sulfate is gone, hydrogen rises from the negative plates. The oxygen in the water reacts with the lead sulfate on the positive plates to turn them once again into lead dioxide, and oxygen bubbles rise from the positive plates when the reaction is almost complete.
Many people think that a battery's internal resistance is high when the battery is fully charged, and this is not the case. If you think about it, you'll remember that the lead sulfate acts as an insulator. The more sulfate on the plates, the higher the battery's internal resistance. The higher resistance of a discharged battery allows it to accept a higher rate of charge without gassing or overheating than when the battery is near full charge. Near full charge, there isn't much sulfate left to sustain the reverse chemical reaction. The level of charge current that can be applied without overheating the battery or breaking down the electrolyte into hydrogen and oxygen is known as the battery's "natural absorption rate." When charge current is in excess of this natural absorption rate, overcharging occurs. The battery may overheat, and the electrolyte will bubble. Actually, some of the charging current is wasted as heat even at correct charging levels, and this inefficiency creates the need to put more amp hours back into a battery than were taken out. More on that later.
13. How Long Will My Battery Last?
There are many things that can cause a battery to fail or drastically shorten its life. One of those things is allowing a battery to remain in a partially discharged state. We talked about sulfate forming on the surface of the battery's plates during discharge, and the sulfate also forms as a result of self-discharge. Sulfate also forms quickly if the electrolyte level is allowed to drop to the point that the plates are exposed. If this sulfate is allowed to remain on the plates, the crystals will grow larger and harden till they become impossible to remove through charging. Therefore, the amount of available surface area for the chemical reaction will be permanently reduced. This condition is known as "sulfation," and it permanently reduces the battery's capacity. A 60 amp hour battery may start performing like a 40 amp hour (or smaller) battery, losing voltage rapidly under load and failing to maintain sufficient voltage during cranking to operate the vehicle’s ignition system. This last condition is evident when the engine refuses to fire until you remove your finger from the start switch. When you release the starter, the battery voltage instantly jumps back up to a sufficient level. Since the engine is still turning briefly, the now energized ignition will fire the spark plugs. In the next installment, we'll see exactly why increased internal resistance due to sulfation causes less power to be delivered to the starter.
Deep discharging is another battery killer. Each time the battery is deeply discharged, some of the active material drops off of the plates and falls to the bottom of the battery case. Naturally, this leaves less of the stuff to conduct the chemical reaction. If enough of this material accumulates in the bottom of the case, it'll short the plates together and kill the battery.
Overcharging is an insidious killer; its effects often aren't apparent to the innocent purchaser of the ten-dollar trickle charger who leaves it hooked to the battery for extended periods. A trickle charger charges at a constant rate regardless of the battery state of charge. If that rate is more than the battery's natural absorption rate at full charge, the electrolyte will begin to break down and boil away. Many a bike rider has stored a bike all winter on a trickle charger only to find the battery virtually empty in the spring. Also, since charging tends to oxidize the positive plates, continued overcharging can corrode the plates or connectors till they weaken and break.
Undercharging is a condition that exists on many vehicles. Your voltage regulator is set to maintain your system voltage at around 14 to 14.4 volts. If you're one of those folks who drives a lot with your voltmeter showing only 13.5 volts because you're burning more lights than Farmer’s Christmas display, you should be aware that that voltage is sufficient to maintain a charged battery but insufficient to fully recharge a depleted one. Remember, we said that gassing occurs when all or most of the lead sulfate has been converted back to lead and lead dioxide. The voltage at which this normally occurs, known as the gassing voltage, is normally just above 14 volts. If your system voltage never gets that high, and if you don't ever compensate by hooking up to a charger at home, the sulfate will begin to accumulate and harden just as plaque does in your mouth. Consider a thorough occasional charging to be like a good job of flossing and brushing your teeth. If you practice poor dental hygiene, you can go to the dentist, and have them blast and scrape at the yucky stuff. When your battery reaches that stage, it's curtains!
14. What Type Of Charger, And Why
Your alternator and a standard automotive taper charger have a lot in common; they seek to maintain a constant voltage. Here's the problem with trying to quickly charge a deeply discharged battery with either one. Remember, we discussed how a heavy current draw would make a battery appear dead. Then, as the acid diffused through the cells, the concentration at the plates' surface would increase and cause the battery to spring back to life.
In similar fashion, the voltage of a battery during charge increases due to the acid concentration that occurs at the plates' surface. If the charge rate is significant, the voltage will rise rapidly. The taper charger or vehicle voltage regulator will taper the charge rate drastically as the voltage rises above 13.5, but is the battery state of charge commensurate with the voltage? No! Once again, it takes time for the acid to diffuse throughout the cells. Although the voltage may be high, the electrolyte in the outer reaches of the cells is still weak, and the battery may be at a much lower state of charge than the voltage would indicate. Only after charging for an extended period at the reduced current will the full capacity be reached. This is the reason you must not judge a battery's state of charge by measuring voltage while charging. Test it only after allowing the battery to sit for at least an hour. The voltage will reduce and stabilize as the acid diffuses throughout the cells.
Within the past several years, several companies have developed chargers that can charge a depleted battery quickly, and then hold the battery at a voltage that will neither cause it to gas nor allow it to self-discharge. These are sometimes referred to as "smart chargers" or multi-stage chargers. Here's how they work.
We said that a battery could accept a much higher rate of charge when it's partially depleted than when it's near full charge. These multi-stage chargers take advantage of that fact by beginning the charge in a constant current, or "bulk charge" mode. Typically, they provide a charge rate of between 650 milliamps and 1.5 amps, depending on make and model. This bulk charge is held constant (or should be) till the battery voltage reaches 13.5 volts, thus allowing the battery to absorb a larger amount of charge in a short time and without damage. The charger then switches to a constant voltage or "absorption" charge. The idea here is to allow the battery to absorb the final 15 percent of its charge at its natural absorption rate to prevent undue gassing or heating. Finally, these chargers switch to a "float" mode in which the battery voltage is held at a level sufficient to keep it from discharging but insufficient to cause overcharging. The various companies disagree generally on what this float voltage should be, but it's usually between 13.2 and 13.4 volts. Actually, the float voltage should be temperature compensated between 13.1 volts at 90 degrees Fahrenheit to 13.9 volts at 50 degrees. Most of the very expensive high power multi-stage chargers for use on larger RV batteries are temperature compensated, but none of the motorcycle units are to my knowledge; they use a compromise float setting
15. GEL BATTERIES vs AGM BATTERIES
AGM (absorbed glass mat) is a special design glass mat, designed to wick the battery electrolyte between the battery plates. AGM batteries contain only enough liquid to keep the mat wet with the electrolyte and if the battery is broken no free liquid is available to leak out.
Gel Cell batteries contain a silica type gel that the battery electrolyte is suspended in, this thick paste like material allows electrons to flow between plates but will not leak from the battery if the case is broken.
More often than not AGM Batteries are mistakenly identified as Gel Cell Batteries. Both batteries have similar traits; such as being non-spillable, deep cycle, may be mounted in any position, low self discharge, safe for use in limited ventilation areas, and may be transported via Air or Ground safely without special handling, but are still subject to our dangerous goods provisions.
AGM Batteries outsell Gel Cell by at least 100 to 1. AGM is preferred when a high burst of amps may be required. In most cases recharge can be accomplished by using a good quality standard battery charger or engine alternator. The life expectancy; measured as cycle life or years, remains excellent in most AGM batteries if the batteries are not discharged more than 60% between recharge.
Gel Cell Batteries are typically a bit more costly and do not offer the same power capacity as do the same physical size AGM battery. The Gel Cell excels in slow discharge rates and slightly higher ambient operating temperatures. One big issue with Gel Batteries that must be addressed is the CHARGE PROFILE. Gel Cell Batteries must be recharged correctly or the battery will suffer premature failure. The battery charger being used to recharge the battery(s) must be designed or adjustable for Gel Cell Batteries. If you are using an alternator to recharge a true Gel Cell a special regulator must be installed.
Gel Cell batteries contain a silica type gel that the battery electrolyte is suspended in, this thick paste like material allows electrons to flow between plates but will not leak from the battery if the case is broken.
More often than not AGM Batteries are mistakenly identified as Gel Cell Batteries. Both batteries have similar traits; such as being non-spillable, deep cycle, may be mounted in any position, low self discharge, safe for use in limited ventilation areas, and may be transported via Air or Ground safely without special handling, but are still subject to our dangerous goods provisions.
AGM Batteries outsell Gel Cell by at least 100 to 1. AGM is preferred when a high burst of amps may be required. In most cases recharge can be accomplished by using a good quality standard battery charger or engine alternator. The life expectancy; measured as cycle life or years, remains excellent in most AGM batteries if the batteries are not discharged more than 60% between recharge.
Gel Cell Batteries are typically a bit more costly and do not offer the same power capacity as do the same physical size AGM battery. The Gel Cell excels in slow discharge rates and slightly higher ambient operating temperatures. One big issue with Gel Batteries that must be addressed is the CHARGE PROFILE. Gel Cell Batteries must be recharged correctly or the battery will suffer premature failure. The battery charger being used to recharge the battery(s) must be designed or adjustable for Gel Cell Batteries. If you are using an alternator to recharge a true Gel Cell a special regulator must be installed.
16. Battery Standards Ratings -What the... ??
Battery Standards/Ratings usually refer to the country of origin for that battery and/or a specific battery type that is unique in style.
To convert CCA, a SAE (Society of Automotive Engineers) standard, to an EN, IEC, DIN or JIS standard, please refer to the following table.
In Europe, the EN, IKC, Italian CEI, and German DIN standards are used. In Asia, the Japanese JIS standard is used.
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