[Richard]

I thought about what Gordon said. Do you have a DC clamp on ammeter? If so I would measure the current out of the alternator when the mystery is happening. One of two things is happening. The alternator is not putting out voltage during the mystery, OR as Gordon says there is a heavy load dragging the alternator down. Putting an ammeter on the positive line out of the alternator would answer this question.

[rheavn]

The current when the genset is running & inverter charger ON is zero.

The current when genset is running & inverter charger OFF is 27. 

When the inverter charger is turned off the check alt light goes out immediately and the VMS battery voltage returns to 14V.

Follow up question:  In the summer I run with the genset running so I can run a/cs.  If I shut off the inverter charger am I right in thinking that the alternator will charge both batt banks when running? Or is there some other problem that needs to be corrected?

[Richard]

A ha!

As disconcerting as the warning light is, you do not really have a problem. As guessed earlier, when the charger sees a power interruption, it goes automatically into the charge mode. Depending on how the charger is setup, the first stage could be as high as 14.4 volts. As the charger is charging the house batteries at 14.4 volts, the echo charger sees that the house battery voltage is higher than the chassis battery voltage, so it sends amperage/voltage to the chassis batteries. The trickle charger is working exactly as it should. The only problem is that now the chassis batteries are at a voltage slightly higher than what the alternator regulator thinks they should be. So, the alternator regulator does what it is supposed to do, and it doesn't excite the alternator to produce any current.

I think that as soon as the house batteries finish their charge cycle, then the situation will correct itself. If it annoys you, then you can turn the charger off,

If you want to double confirm that this is what is happening, then with the coach plugged into shore power, crank the engine. You should not get the warning light. Unplug the coach from the pedestal. Wait 30 seconds, and plug it back in. If the power interupption idea is the true culprit, the charger will go into charge mode when the coach is plugged back in, and you will get the warning light.

As far as turning off the inverter charger in the summer, and letting the alternator charge the house batteries, I am NOT a fan of charging the house batteries with the alternator. One, on some Newells with the triangular belt setup, it is a recipe for burning up an alternator/AC belt. Two, in my opinion, it is rough on the alternator to charge the house bank even if they are AGM. When I installed the lithium, setup I removed the isolator. I can use the merge switch and charge the house bank manually if I chose, but I would only do that in an emergency.

[rheavn]

Thank you so much to Richard, Gordon and all the other contributors.  I asked the same question of Newell and they told me that the ONLY thing that could cause this issue was bad batteries---no other ideas!

The odd part of this issue is that no one else has expressed that they have this same issue when they are driving & start the genset.

[Richard]

My guess was based upon having seen this exact behavior on Coach 390 when I owned it.

[bestgenman]

Thank you for the kind words Steve.  The only other issue could be tied to the batteries.  Before I switched to Lithium, I did a load test on each 8D AGM.  The regular carbon pile load testers would not stand up to the duration.  This was overcome by a Rube Goldberg tester of an old inverter and AC loads.  The results were interesting, four of the six were in decent shape but two were nearly dead at the end of the test.  I was using the LVCO ( low voltage cutout) feature of the inverter and timing the run.

The results were surprising.  Just wondering if you could have the same battery conditions and could it be tied to the problem?  I’m assuming this is a fairly new problem and not something you have been encountering since the batteries were new.

Still grinding this in my feeble brain.

[rheavn]

I replace my batteries, both house & chassis every five years and have avoided battery issues with this maintenance schedule.

The "Check alt" light started about 2 years ago.  After Newell told me batteries were the only thing that could cause this to occur, I had the batteries load tested and they tested good.  Since then I have replaced all the batteries, on schedule, and nothing changed.  I have also changed my merge switch which I do on a 2 yr schedule.

"I am NOT a fan of charging the house batteries with the alternator."

If you are driving without the genset on, isn't the alternator charging both battery banks?  I thought this is what the battery isolator allows. 

I do understand that the triangle belt setup is not the best.  I have run air ducting to the rear of the alternator to increase cooling and I don't start out without the batteries being in float mode prior to starting the engine.  I have also put a 3 13/16" pulley on the alternator--came with a 3 1/4" pulley.  This has eliminated belt squeal.

I get this "strange issue" when I am driving and Suzy starts the genset prior to stopping.  Now I understand why.

Thanks again to all for your info & patience with someone who has a lot to learn on electricity.

[Richard]

If you are driving without the genset on, isn't the alternator charging both battery banks? I thought this is what the battery isolator allows.

That is exactly what the isolator does, almost all mohos today have that setup. If an owner is diligent about house battery charge, and knows not to try to recharge a deeply discharged house bank with the alternator, then no harm no foul. The problem arises in two situations. One the house bank is depleted because the coach has boondocked and the owner having been told the engine will charge the house batteries, cranks up and drives away. This will KILL your alternator eventually, unless you have one of the oil cooled 50DN jobs. The second is the conversion to lithium for the house bank. The lithiums will accept amperage at an insane rate resulting in dead alternator.

There is no criticism of what you are doing. I put my opinion out there because there are many others reading the thread, and they may not have the experience and diligence that you do.

What inverter and control panel do you have? We may be able to tweak some of the charge settings to keep this from happening.

[rheavn]

I have the Xantrex 2500 and their control panel. I keep threatening to upgrade to the Magnum or Outback setup.

[folivier]

Steve, I have the Xantrex Prosine 2500 in my Foretravel and was able to find an ACS control panel for it which gives easier programming and more features. I'm pleased with it and have 3 Battleborn LiFePO4 batteries that I'm using with it.
No plans to change it out until it quits working.
Which monitor panel do you have with it? The one with just lights or the ACS with digital display? The ACS allows you to make many more adjustments.