Community Forums

richguess · 08-31-2022, 08:43 AM

I have 2 92 AH AGM coach batteries and one 92Ah AGM Chassis battery. Solar charges the coach batteries when in storage, without problems. Although probably unnecessary, I disconnect my chassis battery when stored. My RV (Thor ACE 27.2) has a BIM160.

The electric step is powered by the chassis battery. Yesterday, when I took the RV to storage and disconnected the chassis battery, the electric step still worked, as did my chassis powered cigarette lighter socket. I assume that the power was being provided by the coach batteries via the BIM. This certainly isn’t always the case, as usually the step doesn’t retract when the chassis battery is disconnected. The batteries were fully charged, the coach had been running and the are pretty new. I’ve been suspicious my BIM wasn’t working properly in the past. Is this a normal operation for the BIM? How can I test the BIM to see if it’s working properly? BTW, the battery power switch in the RV was off.

153stars · 09-02-2022, 04:46 PM

My step also seems to work no mater if chassis is off but switch by door on. Switch other position steps stay where the are unless power up chassis.

twinboat · 09-02-2022, 05:04 PM

The BIM will stay latched until the battery voltage drops down to 12 .6 volts, so your house batteries, that charge at 13.4 volts, are still in the circuit after shutting down.

If you wait or turn something on connected to the house batteries, it should un-latch and you'll have no power on the chassis side

richguess · 09-02-2022, 10:30 PM

Excellent. In your first sentence, did you mean chassis or coach? That stop @ 12.6V?

richguess · 09-02-2022, 11:26 PM

Só, if it’s latched (I assume that means the 2 sets of batteries are connected) the house batteries provide the power to the chassis battery, until they become dangerously low. Then they unlatch.

twinboat · 09-03-2022, 12:50 AM

Quote:

Originally Posted by richguess

Só, if it’s latched (I assume that means the 2 sets of batteries are connected) the house batteries provide the power to the chassis battery, until they become dangerously low. Then they unlatch.

12.6 or 12.7 volts is the standing voltage of a full charged 12 volt battery.

Not sure what's dangerous about that.

richguess · 09-03-2022, 08:02 AM

No, I’m just trying to understand the system. I thought the BIM’s function was to provide a connection between the chassis and coach batteries, that allows one to charge the other when voltages drop. If the chassis battery’s voltage drops, for example, the BIM then allows for the coach batteries to provide current to it. But, it will not allow the coach batteries to go below a certain voltage, and allow the chassis battery to deplete the coach batteries.

With the chassis negative disconnected, I’m assuming the coach batteries then take on the function of the chassis battery, via the BIM. My coach batteries are connected to my solar panels, and hence here in sunny CÁ are usually close to 100% charged (on my shunt based battery monitor.). So, even with my chassis battery’s negative disconnected, the RV still starts, the step works, etc. This is the normal functioning?

richguess · 09-03-2022, 08:16 AM

Addendum to above: so, I’m assuming that by disconnecting the chassis battery’s negative cable, the BIM thinks the chassis battery is below 12.6V. It sends current into the system, and hence powers whatever the chassis battery would have. In this sense, there’s not much point in disconnecting the chassis battery’s cable.

DavidEM · 09-03-2022, 08:20 AM

Quote:

Originally Posted by richguess

Addendum to above: so, I’m assuming that by disconnecting the chassis battery’s negative cable, the BIM thinks the chassis battery is below 12.6V. It sends current into the system, and hence powers whatever the chassis battery would have. In this sense, there’s not much point in disconnecting the chassis battery’s cable.

Correct, but only if your BIM was wired properly and Thor doesn't seem to know how to wire them. Connect the chassis' DC system to the Battery A terminal and the coach's to Battery B.

Look at the bottom of the attached pdf for the BIM 160.

David

twinboat · 09-03-2022, 09:53 AM

Quote:

Originally Posted by richguess

Addendum to above: so, I’m assuming that by disconnecting the chassis battery’s negative cable, the BIM thinks the chassis battery is below 12.6V. It sends current into the system, and hence powers whatever the chassis battery would have. In this sense, there’s not much point in disconnecting the chassis battery’s cable.

The better plan is to leave it connected and let your solar keep all of the batteries maintained. That's what a properly operating BIM does.

richguess · 09-03-2022, 07:09 PM

I have previously corrected (reversed) the BIM wiring, as indeed the chassis and coach hookups were reversed. Per twinboat, I will reconnect the chassis negative and leave it on when parked. In addition to my 200w of solar, I run the genset under load for 45 minutes monthly, so that should take care of everything. Thanks for everybody’s help.

Rich