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.

[Edward Buker]

Bob,
As discussed before, there are current loads coming off the chassis batteries, mostly I believe they are computer/electronics related to the Cat motor. There are others like radio electronics that hold memory settings etc. Without something like a Xantrex echo charger you only have the main engine to charge these batteries when the engine is running. All the time it is not running, it is discharging the batteries at some rate. I know that you have been speculating that the alternator is shorted and drawing down the chassis batteries. If you have a meter that will measure 10 amps DC you could put that meter in series with the sensing leads on the alternator and see what the current draw is in a static mode. You could also lift the chassis battery plus leads and put the meter in series with that and see what the static current draw to the whole coach is. That would tell you if the alternator is doing the bulk of the discharging. Have everything turned off that draws current while you take these measurements (lights, etc).

The main charger only charges the house batteries as others have mentioned. If you have a continuous duty solenoid for the emergency start switch you could put another switch in its place, that is not a momentary type, and use that system to tie the house and chassis batteries all together. That would then tie the chassis batteries to the house charging system. I did this in my last coach and would tie them all together for about 8 hours a week for charging. That worked but you had to remember to couple and decouple these systems on some schedule.

You mentioned that the house batteries were measured to be 9.5V. I indicated that this is a fully discharged state. When you had the engine running they came up to 12V. That indicates that you have charging taking place and that the alternator has raised the battery voltage by 2.5V. Without knowing the current at that voltage you do not know if the alternator is doing its job or not. If it is 12V and 165 amps it is doing its job. I have seen this condition before, that the alternator cannot put out enough current to raise the voltage to 14V given the severe load of the batteries in the discharged state. They will come up in time but battery and charging measurements need to be taken with light to moderate loads on the alternator, with batteries that are not severely discharged, if you are going to go by voltage measurements as your charging systems measure of health.

I'm not convinced the alternator is bad. If you fully charge the batteries using an external charger to 12.6V when the charger is disconnected for a half hour or so, and then run the engine you should measure 13.8V to 14V on the chassis battery. If not, then I would pull the alternator and have it checked.  In the end you will need an echocharger or some method of keeping the chassis batteries charged while the coach sits. The loads are just too significant for the chassis batteries to handle, for any significant time duration has been my experience. Hope this helps.

Regards Ed

[Bob McCORMACK]

Let me make this a little clearer.   There is no issue with the house batteries.  With everything off, there is a 9.5 volt drain on the starting batteries.  I get this by putting the meter between the positive post and the cable.  Next I took the voltage at the "sensing" wire by disconnecting it and running the meter from it to the chassis.  Same voltage as the starting batteries, as would be expected.  The batteries have no problem taking and holding charge and pass a draw down test just fine.

I next put the meter between the "sensing" wire and the terminal on the regulator/alternator.  I then get the same 9.5 volt reading.  Clearly something, most likely a diode, in the regulator/alternator is allowing a limited amount of current to pass through it to the ground and thereby completing the loop.  

Add to this the fact that when running, the max output from the alternator is 12.06 and everything seems to point to the alternator/regulator.

The shops here (SF Bay Area) do not carry the special regulator with the extra terminal so it has to be ordered from the factory.  They were out of parts and awaiting a shipment this week.  The alternator isn't the issue, the regulator is the special part.   Unfortunately I have to be able to move the rig at a moments notice so I can't have it down for more the the time to replace the alternator.  The belt drives just about everything else so I can't run it without the alternator in place.

By the way, I have had the rig since October and it never had a problem until recently.  Up tell then it always had good charge no matter how long it sat.  The charging system worked fine until now.

Great to get so much help.

Racer Bob

[Edward Buker]

Bob,

My understanding is that you lifted the lead off of the positive chassis battery terminal and measured the voltage between that lead and the battery terminal at 9.5V. If that is correct what you measured is the difference between the positve battery terminal which I assume is at 12.6V (if fully charged) and the voltage sittng on the cable coming back from the coach which is probably some capacitive residual. The 9.5V measurement means that the chassis positive battery cable is sitting at around 3V when disconnected. Those measurements do not provide any meaningful information regarding the current draw from the battery when just sitting, or the health of the alternator/isolator charging current and voltage reaching the battery when running. I believe you have recognized a real problem with your coaches electrical system but the meaning of your measurements have not shed the light on the problem that is needed.

We have been really trying to help here but sometimes the best advice one can give is to decide when the individual asking for input could better be served by getting some additional help to trouble shoot the system. It may be time to bring someone with an electrical troubleshooting background on board to take a hard look at this. Just a suggestion for you to consider given these problems can be complex at times.

Hope this helps.

Regards Ed

[Bob McCORMACK]

Well here is some additional info.   The starting batteries held 12.7 all week when not connected.  When I connect them up I get a .2 amp draw which goes away when the "sensing" wire is disconnected from the alternator.

Started the motor and saw the same .2 amp draw.   Voltage at the batteries dropped to and held a constant 12.45 while running.  Same at the isolator terminal which is supplied by the alternator.   Once motor was stopped, batteries returned to 12.7 volts after about 5 minutes.  

All this has no effect on the house batteries.   I have a new alternator coming and will install since it is clear the alternator is not making power.   In the mean time I noted the battery reading and left them connected over night.  I will see what they read tomorrow.    I have now enough information to understand how the isolator is involved with things so I can now eliminate it from the equation.  Seems clear, alternator doesn't put out.

When I get the new one installed I will post the results.

Thanks All

Racer Bob

[Edward Buker]

Bob,

Very good. That set of measurements and your conclusion match well. The voltage you started with indicated a fully charged battery and the voltage dropping once started indicated no positive current flow from the alternator and the ouput voltage was not in the expected charging range of 13.8 to 14.4V. The 200 milliamp current draw of the sense lead would consume one amphour every 5 hours. A single group 31 battery has about 105 amp hours. A 40% discharge level would take about 200 hours or 9 days. If you had two of these batteries in parallel for the chassis that would take 18 days to reach the 40% discharge level. 40% discharge is a good point to recharge for battery longevity. When you get the new alternator you can check the sense lead in the static mode and see if that current draw is normal for that regulator design and you will have your discharge rate and how long the coach can sit before charging understood. The rest of the coach apparently does not draw any significant current with the ignition off. Again, good job.

Regards Ed

[Bob McCORMACK]

[size=14][/size]New Alternator installed, problem solved.  Pretty easy job on the Patriot with side radiator.

Racer Bob

[Edward Buker]

Bob,

Congratuations on your fix. It always feels good when you solve the problem yourself and have the motorhome back in shape for travel.

One suggestion. You might measure the chassis battery voltage once every day or two (assuming you are starting at 12.6V) without running the engine and see what the voltage drop rate is while the coach is sitting. I would look to initiate charge when the voltage dropped below 12.3V. Starting batteries do not like deep discharge cycles. Knowing that duration and setting some charge schedule that fits your particular discharge rate will give you less battery trouble over time. Again, good job.

Regards Ed