Chassis Battery not charging

[MooreUP]

I’m a newbie so sorry if I’m asking dumb questions. My 16 year old grandson stayed in the Vegas 4 nights while his parents were here a few weeks ago. It was on SP the whole time. A week or so after they left, I went to start it and the engine was totally dead. The house batteries had just enough left to open & close the slider. I can’t find anything my grandson may have left on, and when I put a multimeter between the negative terminal & cable, I got .57 milliamps with the transfer switch off, and .85 milliamps with it on. From what I’ve read, that seems marginal. I charged the chassis battery with my battery charger yesterday & started the engine. The battery shows 14.4 volts with the engine running, so the alternator is apparently OK.
Today, when on SP the coach batteries and B terminal of the BIM 160 are at 13.65 and the chassis battery and A terminal at 3.56. While plugged in, I can hear the converter, but it’s apparently not charging the chassis battery. The buss bar under the fridge shows 13.65
With the generator running, I get similar results; coach batteries & B terminal of BIM 160 at 13.55, chassis battery and A terminal 3.56.
So apparently the BIM is not switching between the batteries when the coach batteries are charged? Is there a fuse or relay that could be causing this?
I’ve searched this forum and have seen good advice, but I haven’t pinned it down so far. Thanks for any help or advice.

 

[16ACE27]

Yes, there's an inline fuse as seen in the attached information sheet:

https://forestriverinc.com/files/Co...s - Battery Isolation Manager Explanation.pdf

Does activating the emergency start switch close the contacts?

 

[MooreUP]

Yes, pushing the emergency start triggers the relay. And thanks for the BIM 160 information. That's helpful.

 

[16ACE27]

Yes, pushing the emergency start triggers the relay. And thanks for the BIM 160 information. That's helpful.

But does triggering the relay cause the A & B terminals to be at the correct (same) voltage?

You gotta figure out if you have a BAD BIM main contacts, bad BIM logic circuit, or bad BIM connections. Two out of 3 mean a new BIM is in your future.

 

[MooreUP]

This morning, after being on SP all night, the A (chassis) terminal was 12.5 & the B at 11.86. When holding the emergency start switch, the A was 12.32 & he B was 12.38. After SP disconnected, A was 11.87, B was 12.5. After 20 minutes, A was 11.97, B at 12.5. Starting the engine then, with it running both were at 14.39. So both A & B are charging with engine running, but not when on SP. Seems the BIM is working correctly? Does this point to my converter as my problem? Again, thanks for any help.

 

[16ACE27]

B - House was dead with SP connected: Status of battery disconnect and 50 amp DC battery breaker?

How long did you hold the ESS for? The Chassis battery went from 12.5 to 11.87 - essentially dead.

At the same tine the house went from 11.87 to 12.5. How?

Did you mix up what was A and what was B?

 

[MooreUP]

My apologies! The first sentence should have read: A was 11.86, B was 12.5. The rest of the statements are correct. Thanks for your patience.

 

[MooreUP]

Still working on figuring this thing out. All the switches & relays seem to be doing what they're supposed to. I did check the water level in the chassis battery and it was below the top of the plates—coach batteries were fine. I'm trying different situations & logging readings for a few days. If I learn more, I'll follow up. Thanks again for advice & help; I'm definitely on a learning curve here.

 

[16ACE27]

Still working on figuring this thing out. All the switches & relays seem to be doing what they're supposed to. I did check the water level in the chassis battery and it was below the top of the plates—coach batteries were fine. I'm trying different situations & logging readings for a few days. If I learn more, I'll follow up. Thanks again for advice & help; I'm definitely on a learning curve here.

Your chassis battery is probably toast. Take it to your local auto parts store and have it tested.

 

[MooreUP]

So I pulled the chassis battery, which was new in 2023 & took to the Auto Parts store, where he tested it with two different devices & it was fine both times. I reinstalled it & we're going on a little 3 day trip today, so we'll see how it does. I'm thinking I've been chasing a nonexistent problem, but we'll see. My grandson definitely ran everything down somehow, but perhaps, being new to this I just didn't understand how it all functioned together. Anyway, thanks to your help and some research, I know a lot more about the unit than I did. Thanks again.