Big alternators (John De Armond)

From: John De Armond Subject: The Power Quest Continues Date: Sat, 15 Jan 2000 03:28:41 EST Newsgroups: rec.outdoors.rv-travel A few weeks ago I posted about my quest to equip my Itasca Class C motorhome with enough engine alternator and inverter to run all normal 120 volt loads except the air conditioner without having to run the generator. Specifically, the microwave and coffee maker. My desire is to be able to achieve continuous operation with the engine running while not dipping into the house batteries. I intend to have two alternators on the engine - one for the engine and cranking battery and a totally separate system for the house batteries and the inverter. A standard cross-connect relay will remain installed so that the systems can be cross-coupled if one alternator fails. My last post had to do with making the decision between 12 volt and 24 volt systems. I wanted the 24 volt version but alas, there simply isn't enough room for a 24 volt alternator in the engine bay. Indeed, space is going to be the single biggest problem. To run a 1500+ watt inverter, I need about 200 amps of generating capacity. A quick search of the net pops up products from places like Ample Power but at very steep prices, sometimes approaching $1000. Too rich for my blood. Besides, the engineer in me said "do it yourself". Another potential source was the vendors of high output alternators sold to the kids who like to make their cars go BOOM BOOM with big stereos. Alas, an examination of several of these alternators revealed that they are little more than slightly reworked regular alternators. In other words, low duty cycle and/or short life at the higher output. It appears that they spent more time on the chrome plating than they did on re-engineering the alternator. I talked to a local ambulance company owner and inquired as to who equipped their ambulances with high capacity alternators. He pointed me to Red Hot Battery Service here in Cleveland. Dudley, the owner, builds the special, high capacity alternators. He uses the large frame semi truck alternators and rebuilds them to make 200+ amps as a 1 wire unit (self-exciting). The price was great too, at $265. Brought a bad unit home to check for clearances. Damn! Itasca built the body of the MH so tightly around the engine that I would have to cut away and rebuild part of the bracketry that supports the body on the frame. Doable, but very time consuming. Back to Red Hot. We decided to take a look at late model large car and SUV alternators. The alternators have grown with the increasing power demand in late model cars. Our eyes settled on a Delco alternator for a late model Cadillac. This alternator is rated for 145 amps. Dudley told me that he was sure that when converted for one wire operation, it should be capable of near 200 amps. The best part is the price for a new (not rebuilt) unit is going to be under $150. Normally this alternator comes with a serpentine belt pulley. Dudley knows how to convert it to a V-belt drive which I must have. The nice thing about this alternator is that if one isn't enough, it is small enough that another can be mounted alongside it. OK, so the alternator is on order and will be here middle of the week. I have a bad core unit to use to begin fabricating the mounting brackets. I'll keep the list informed on how this goes. Assuming everything works OK, I'll post part numbers and Dudley's phone number. It looks like I can get the power generation side of this system done for under $200. Diodes I'll initially use the internal diode bridge in the alternator but I intend to fit the alternator with larger external diodes later. I've had great success in doing this in the past. This gets the diode heat away from the alternator, the engine heat away from the diodes and lets me use rugged high voltage stud rectifiers instead of the crappy little chip rectifiers the OEMs use. More on that later. Voltage regulator The specialty deep discharge battery charging voltage regulators such as the ones made by Ample Power (http://www.amplepower.com/) and Cruising Equipment (http://www.cruisingequip.com/ - note: these pricks charge for tech support!) are computer-controlled and will very rapidly recharge large house batteries. They implement the 3 stage charging cycle and monitor battery temperature to prevent overcharging. They are also quite expensive. They are primarily aimed at the offshore marine market where it is desirable to recharge the house battery with only a short engine run time each day. I'm going to initially use a simple internal regulator. The regulator that Dudley uses can be strapped to one of several voltages to match the application. Then I'm going to study the build-or-buy decision on the smart regulator. I kinda have the urge to do another embedded microprocessor project so I have a hunch I'll be building my regulator, particularly since I want to do some things that neither of these commercial ones do. Inverter. I'm going to order the Statpower ProSine pure sine wave inverter, probably the 1800 watt unit. I've had very good luck with this brand in the past and I just can't justify the price difference between the Statpower and the Heart and other high priced units, especially since I won't need high power shore power battery charging. I'm going the sine wave route because I'm tired of trying to suppers the hash that pseudo-sine inverters generate. Really screws up AM and ham radio. The pure sine inverter is a bit less efficient but since my main use is to run it from the alternator, that doesn't matter much. I'll keep the group apprised of what is happening. This is going to be fun! And it gives me the excuse I needed to order a new MIG welder (the Miller 250X kicks butt!) yesterday. :-) I'll probably end up with a writeup and some pictures on the web site when I'm finished. John