General Boards > Technical Support
Patriot Charging System
Bob McCORMACK:
I am trying to get an understanding of how the Alternator/isolator system works on my '96 Patriot with a 3126 CAT. No one I have talked with seems to know. The Alternator (Leece Neville) is a special configuration for systems with a battery isolator. Hence it is special order and much more expensive. It features an extra small terminal on the regulator next to the "IGN" terminal.
I have a constant drain from the starter batteries through this extra terminal, grounding through the alternator. And the output from the alternator is barely 12 volts when running. What I can't find out is exactly what the wire to this extra terminal is supposed to do. Is it to sense battery voltage ? Should it have power to it when the ignition is off as it currently does ?
Since it drains the starting batteries if left attached I am assuming either something is failing to deactivate it when the ignition is off or a diode in the alternator has failed allowing grounding through the alternator.
Any one know how this system is supposed to work ?
Thanks Racer Bob
Bruce Benson:
Bob,
The alternator cannot see the chassis (starter) batteries because of the isolation circuit, thus the output of the alternator cannot be used to regulate voltage. The work around for this is to have a separate terminal on the alternator to sense the chassis batteries, thus then regulate the voltage of them.
Yes, it could be a problem within the alternator in which case you will need to take it into a alternator shop and have it repaired. You could attempt it yourself if you have the skill set. I would just remove it and take it in though.
Before you do that, check to be sure that the alternator is connected correctly. The sense wire to the chassis batteries should be connected to the small terminal closest to the positive output of the alternator. The small terminal closest to the large negative terminal should be connected to the ignition switch. The battery sense terminal should always be hot. The ignition terminal should be hot only when the key switch up front is on.
Here is a wiring diagram:
http://www.prestolite.com/images_alts/wiredia/pdf_web/2825LC_wiring.pdf
Your symptoms are very like those of an alternator that has the two small wires reversed, so have a look.
Bob McCORMACK:
Thanks Bruce. In this case none of the wires were ever touched so it is looking likely the alternator has developed a short. I have a new one coming since they are special order I decided it is worth having a new and spare unit no matter what. One question though. I just upgraded the house battery bank from 340 amp hour (4 12 volts) to 450 amp hour with 4 Trojan 105's. What about the possibility of that some how confusing things. Thought that doesn't explain the constant draw down of the starting batteries. Any thoughts ?
Bob
Bruce Benson:
Bob,
Unless you owned the coach since new and no work was ever done around the front of the engine you might still check the wires. As long as the coach is plugged in this low drain is not noticeable.
The changing of the house batteries would only make a difference in that it creates more load on the alternator. Heat caused by load is what makes them fail. Make sure that you do not start up with batteries low. Many coaches with more house amps than you have do fine with that alternator.
Rebuild costs at a local shop should be between $175 and $250. Turn around time is often the same day or less. Most shops have parts in stock for these alternators. The coach can be operated for many miles without the alternator installed if you give up the air-conditioning and run the gen set every so often.
Mine has failed three times (for no fault of the alternator) and I do not carry a spare nor plan to.
Richard And Babs Ames:
Something we found out the hard way about the battery charging system on our 1997 Patriot with the 3126B CAT engine was that the only charge the chassis batteries received was from the engine. The Onan genset starts and puts a drain on these batteries with no charge function and they died in 4 days.
We found out after Hurricane Charlie in 2004 and put 180 hours on it in 10 days. An Xantrex Echo Charger solved the problem. You may have a small solar panel that does help if parked and not using anything.
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