Help understanding Chassis Battery / BIM Issue

[MoHoGo]

2017 Anthem - We have been on shore pwr a couple of days. Last night I noticed on the VT that the chassis battery voltage was down to 11.8 volts, but the VT indicated both charges were working.

Did the following.


1) Turned the breaker for shore pwr on/off - No Change
2) Started the coach and the chassis batteries went from 11.7 to 13.8.
3) Shut the coach off and the chassis battery voltage started to drop again while connected to shore power - 12.4, 12.3, 12.1 etc.
4) Turned shore power breaker off and started the Gen Set, after change over delay the chassis batteries showed 13.8 volts.
5) Turned gen off and shore power back on and chassis batteries dropped to 12.4, 12.1 etc.
6) Did this sequence a second time and then with shore power on and gen off the chassis batteries are reading 13.8 volts on shore power so I am assuming they are charging again.

While everything now appears to be working, I am trying to understand what the issue may have been. Exploring a bit more I looked at the BIM relay and found at the bottom of the relay the light gage wires that I assume are the pick coil were loose enough that I could move the spade / ring lugs. Now I am wondering if the charge voltage was not getting to the batteries?

Not sure how the BIM factors into the charging circuit so any further info would be appreciated. Also, if auto gen is on and the chassis battery voltage drops does that trigger the gen to start or is auto gen only for the house batteries?

Again thanks for any additional info on how this all works.

[LWBAZ]

Jim, based on the symptoms you outlined my guess is that your Battery Isolation Manager (BIM) wasn’t working.

When you’re connected to shore power or running your generator, the BIM should connect the chassis battery bank to the house battery bank. Not continuously, but long enough/often enough to keep your chassis batteries charged up.

Conversely, when you’re dry camping (no shore power) and aren’t running your generator, the BIM should isolate the chassis battery bank from the house battery bank so your chassis batteries don’t discharge along with your house batteries.

Since your chassis batteries were dropping in voltage while connected to shore power, that suggests your BIM was not doing what it’s supposed to do. The loose wires you found (and presumably tightened up) could have been the cause, or it could be that your BIM is failing.

Yes, they do fail. Ours went bad, but the issue we experienced was the opposite of the problem you described. In our case, the BIM stuck in the on position so our chassis battery bank was continuously connected to our house battery bank. Not a big issue when connected to shore power or running the generator, but once we went dry camping I noticed our chassis batteries were being drawn down in unison with our house batteries. Not good! I contacted Entegra, they sent a new BIM, I installed it, and all was well.

In your case, I’d monitor the situation. If the problem doesn’t occur again, you can safely assume the loose wires on the BIM were the problem. If the problem comes back, you’ll probably need a new BIM.

Good luck and keep us posted on what you find.

[MoHoGo]

Thanks Larry, I am assuming that was the issue. We are keeping an eye on it now. Also, thanks for the explanation on the BIM...was not really sure of its' function.

[Victory Blue]

I’ve had Entegra CS looking into a similar problem for a couple of months. CS did not have me look at the BIM.

On shore power my Vegatouch display shows the chassis battery voltage drops from about 13.1 to about 12.3 V when I turn on all of the interior lights; of course the chassis batteries shouldn’t be affected by the interior lights. A meter on the batteries shows the actual voltage to be over 13, so the VT is getting the chassis voltage readings from the wrong place. I haven’t been aggressive with CS because in my case it appears to be a bad reading, rather than a real problem.

Have you checked your actual chassis battery voltage when the VT is showing close to 12V?

Edit: now that I have read Larry’s post I will ask CS if I’d could have a BIM problem. Thanks, Larry.

[LWBAZ]

Originally Posted by MoHoGo

Also, if auto gen is on and the chassis battery voltage drops does that trigger the gen to start or is auto gen only for the house batteries?

Forgot to answer this question in my previous post. That auto generator start functionality is triggered by one of two things, depending on what you've enabled:

1. The house (not chassis) batteries fall below the threshold voltage you've specified for a given period of time.

2. The thermostat functionality that controls the roof AC/heat pump units calls for one or more of the rooftop units to fire up.

Bottom line, the voltage of the chassis batteries doesn't trigger auto generator starting.

[twinboat]

You never mentioned the house battery voltage ( or I missed it ).

The house battery needs to be above 13.3 volts before the BIM will connect the chassis battery. Maybe your float voltage is a tad low.

[MoHoGo]

Originally Posted by LWBAZ

Forgot to answer this question in my previous post. That auto generator start functionality is triggered by one of two things, depending on what you've enabled:

1. The house (not chassis) batteries fall below the threshold voltage you've specified for a given period of time.

2. The thermostat functionality that controls the roof AC/heat pump units calls for one or more of the rooftop units to fire up.

Bottom line, the voltage of the chassis batteries doesn't trigger auto generator starting.

Thanks for the clarification...that is what I was wondering.

[MoHoGo]

Originally Posted by Victory Blue

I’ve had Entegra CS looking into a similar problem for a couple of months. CS did not have me look at the BIM.

On shore power my Vegatouch display shows the chassis battery voltage drops from about 13.1 to about 12.3 V when I turn on all of the interior lights; of course the chassis batteries shouldn’t be affected by the interior lights. A meter on the batteries shows the actual voltage to be over 13, so the VT is getting the chassis voltage readings from the wrong place. I haven’t been aggressive with CS because in my case it appears to be a bad reading, rather than a real problem.

Have you checked your actual chassis battery voltage when the VT is showing close to 12V?

Edit: now that I have read Larry’s post I will ask CS if I’d could have a BIM problem. Thanks, Larry.

Bill, yes I did and the chassis battery voltage at the battery was the same as the VT reading. Thanks...

[MoHoGo]

Originally Posted by twinboat

You never mentioned the house battery voltage ( or I missed it ).

The house battery needs to be above 13.3 volts before the BIM will connect the chassis battery. Maybe your float voltage is a tad low.

Twinboat, very interesting. I didn't mention the house voltage and don't remember the reading now. I just went to the VT panel and don't see a setting for float voltage or any way to adjust, am I missing something? Also, would you happen to know what the voltage reading is to energize the BIM relay and where that voltage comes from? BTW, the VT is set for the AGM2 charging profile.

[TurboDaveTX]

I had an electrical ghost this week. Starter turned over more slowly than usual Wednesday but started. Working on A/C issue. Friday AM service said the chassis battery would not start but jumped it from coach batteries. I was standing in front of the coach and all of a sudden the headlights and clearance lights came on. Stayed on a couple of minutes then went off. About 10 minutes later as I was leaving, the lights came on again and went off in about two minutes. No one in the coach. Replaced both chassis batteries and the lights stopped coming on by itself. Owned a coach since 1972 and have never seen this before. Bought coach new 7/2015 so batteries were probably close to 5 years old. I thought we had a ghost!

[twinboat]

Originally Posted by MoHoGo

Twinboat, very interesting. I didn't mention the house voltage and don't remember the reading now. I just went to the VT panel and don't see a setting for float voltage or any way to adjust, am I missing something? Also, would you happen to know what the voltage reading is to energize the BIM relay and where that voltage comes from? BTW, the VT is set for the AGM2 charging profile.

In your case, the connect voltage will come from both the house bank and the chassis battery.

The house bank needs to be at, what BIM says, a charging voltage ( A bit vague ) and your chassis battery at 80% capacity.

Most float voltages are 13.4 volts so that should be over the BIMs trigger voltage.

[MoHoGo]

Originally Posted by twinboat

In your case, the connect voltage will come from both the house bank and the chassis battery.

The house bank needs to be at, what BIM says, a charging voltage ( A bit vague ) and your chassis battery at 80% capacity.

Most float voltages are 13.4 volts so that should be over the BIMs trigger voltage.

Now you have me wondering, this morning my chassis batteries are 12.3 and house batteries 12.8. Charger 1 & 2 indicate they are in the float stage. Should the float voltage reading be higher?

BTW, found out that the two terminals I found a bit loose on the BIM were the loop from the battery boost switch so that was not the original issue.

[Victory Blue]

Originally Posted by MoHoGo

Now you have me wondering, this morning my chassis batteries are 12.3 and house batteries 12.8. Charger 1 & 2 indicate they are in the float stage. Should the float voltage reading be higher?

BTW, found out that the two terminals I found a bit loose on the BIM were the loop from the battery boost switch so that was not the original issue.

Jim,

Our issues still sound eerily similar. When you're watching the VT with all of the interior lights on does the chassis battery voltage change when you turn the lights off?

[MoHoGo]

Originally Posted by Victory Blue

Jim,

Our issues still sound eerily similar. When you're watching the VT with all of the interior lights on does the chassis battery voltage change when you turn the lights off?

Chassis changes from 12.3 to 12.2 and House from 12.9 to 12.6. Bill, what does the VT read for your Float Voltages? Let me know

BTW, someone else posted the following link on troubleshooting the BIM. Wanted to pass it along. http://www.precisioncircuitsinc.com/...e-Shooting.pdf

Travelling today so I won't be able to contact Entegra C/S, but feel that I need to follow up on this and I thought I would start with them. But getting good info is always the luck of the draw. May try Mike O or PJ if all else fails.