BIRD/BIM operation

[DogFather]

I think I have a general understanding of this device:

The alternator will charge the chassis batteries (its primary concern), if needed.
Then, if the coach batteries also need charging, it will charge them.

Question: Are the two battery groups ever in parallel during this charging process or does the alternator simply switch from one to the other. I'd think that they'd be charged independently, but have read differently.

Any advice, and especially references (can't find any), would be appreciated.

Thanks.

[bubbles]

They are paralled for charging.

[Trappfarmer]

So if the chassis batteries are flooded and the coach batteries are AGM they use the same charge profile? Doesn’t seem right.

[fonzie]

Here is one explanation:

https://battlebornbatteries.com/prod...ation-manager/

[caflorin]

I just replaced my BIM. From the year/model of you RV, I am guessing you have the same solid state BIM I installed. They don't make to older non solid state anymore. I also expect you have the -250 (225 AMP) as do I. I am attaching the literature which should answer your questions.

[DogFather]

Thanks for the replies.

Upon further research, I'm beginning to understand this better: under certain circumstances (varies with the BIM) the positives of the 2 batteries (or banks) will be temporarily connected for charging - thus, in parallel.

[bubbles]

Originally Posted by DogFather

Thanks for the replies.

Upon further research, I'm beginning to understand this better: under certain circumstances (varies with the BIM) the positives of the 2 batteries (or banks) will be temporarily connected for alternator (only) charging - thus, in parallel. I believe charging profiles would only apply to shore or solar charging - BIM not involved.

If connected to shore power the BIM will operate the same as for alternator charging except the coach batteries will have priority. Both coach and chassis batteries will be charged via BIM control when on shore power (charging source is the converter) just as they are when the ignition switch is on (charging source is alternator).

Open the PDF file from post 5 and read the first paragraph.
"Both batteries are charged if either is being charged. The coach
battery is charged while driving and the chassis battery
is charged while plugged into Shore Power at a
campground".

[DogFather]

Thanks, bubbles; I corrected my earlier post/misconception.

[Sunvalley ID RVer]

So I understand that the coach and chassis batteries are both being charged by the alternator while driving correct? While driving is there a coach power draw limit? My dealer said while driving and wanted air conditioning that I would need to start the generator.

Also on my dash of the 2021.5 Berk 34B I have an aux switch. The dealer said this ties the coach and chassis batteries together in case the chassis batteries needed help to start the diesel engine.

[Nightshifter]

On my 2019 XLT the coach batteries are charged while plugged into shore power from the inverter/charger. When the chassis batteries drop to 12.5v the BIM closes and ties the two systems together for 1 hour and then disconnects. It will check the chassis batteries periodically and charge them when needed. I was told this by the tech at Precision Plex.

[bubbles]

Originally Posted by Sunvalley ID RVer

So I understand that the coach and chassis batteries are both being charged by the alternator while driving correct? While driving is there a coach power draw limit? My dealer said while driving and wanted air conditioning that I would need to start the generator.

Also on my dash of the 2021.5 Berk 34B I have an aux switch. The dealer said this ties the coach and chassis batteries together in case the chassis batteries needed help to start the diesel engine.

The BIM is strictly involved with the 12Vdc side of the motorhome. The air conditioner is a 120Vac item and therefore, yes, you would need to run the generator for the air conditioner (unless your coach has an inverter than can handle it) and of course any other strictly AC voltage items. The only 12Vdc limiting is the battery condition/alternator/converter for those configurations where applicable. Yes, the aux start switch or whatever its nomenclature is in your coach is for what you were told.

[Trappfarmer]

Still need an answer to the different types of batteries (Flooded/AGM).

[caflorin]

Flooded and AGM. If you go to lithium, there is a different BIM also made by precision circuits. They are good at responding to queries.

[Lincman983]

The Li-Ion (Lithium Ion) batteries require a different battery isolation manager. It would have a green label

[Desert Boat]

Originally Posted by Trappfarmer

Still need an answer to the different types of batteries (Flooded/AGM).

Since the BIM does not connect continuously, the difference between AGM and Flooded does not matter. In normal operation, it only connects during bulk charging stage, so the differences in later stages don't matter.

From the Precision BIM flyer:

The BIM monitors the battery voltage of both the chassis and coach batteries over long periods of time. If it senses a charging voltage, it connects the two batteries together. If the charging system is drastically overburdened, the batteries will be isolated, however, if the BIM sees a long term charging of both batteries it will allow the batteries to remain connected and allow the charging system to do its job. Once the batteries have charged for one hour, the BIM will isolate the batteries to prevent overcharging, and will only reconnect the batteries for charging if one of the batteries drops to approximately 80% charge, and the other is being charged. The BIM does not guarantee 100% battery charge, but prevents harmful battery charge levels.

The difference between AGM/Flooded and Lithium DOES matter, which is why that uses a LiBIM.