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Old 01-09-2021, 04:34 PM   #1
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Brand: Thor Motor Coach
Model: Axis 24.1
State: Connecticut
Posts: 206
THOR #20289
Precision Circuits BIM

I am pretty sure that my new Axis to be delivered in a few weeks comes with a Precision Circuits BIM. See https://precisioncircuitsinc.com/pro...ion-manager-2/. I believe it is installed in the engine compartment on the driver's side. These suppositions were posted by a recent Axis owner so I expect they are correct.

The PC BIM is a bidirectional device. You can read about it by clicking the link in the upper right of the URL above.

I would like to use it to pass through solar charging current from the coach battery to the chassis battery to keep them both fully charged. That current will be fairly low as I plan to have only one 100 watt panel installed. And in the winter the max current I expect is 5A or so.

So, presumably the PC BIM has a solenoid that pulls in to connect the two batteries when the appropriate voltage levels are reached. Is it a latching relay type? In other words when it pulls in does the coil current stay on all of the time (non latching) or does it drop to zero until it gets a signal to unlatch (latching).

The answer is important because if it is pulling current all of the time (at least several amps if it a non latching type) it won't charge the chassis batteries very well.

David
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Old 01-09-2021, 11:06 PM   #2
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Brand: Thor Motor Coach
Model: Aria 3901
State: Idaho
Posts: 476
THOR #9660
Quote:
Originally Posted by DavidEM View Post
I am pretty sure that my new Axis to be delivered in a few weeks comes with a Precision Circuits BIM. See https://precisioncircuitsinc.com/pro...ion-manager-2/. I believe it is installed in the engine compartment on the driver's side. These suppositions were posted by a recent Axis owner so I expect they are correct.

The PC BIM is a bidirectional device. You can read about it by clicking the link in the upper right of the URL above.

I would like to use it to pass through solar charging current from the coach battery to the chassis battery to keep them both fully charged. That current will be fairly low as I plan to have only one 100 watt panel installed. And in the winter the max current I expect is 5A or so.

So, presumably the PC BIM has a solenoid that pulls in to connect the two batteries when the appropriate voltage levels are reached. Is it a latching relay type? In other words when it pulls in does the coil current stay on all of the time (non latching) or does it drop to zero until it gets a signal to unlatch (latching).

The answer is important because if it is pulling current all of the time (at least several amps if it a non latching type) it won't charge the chassis batteries very well.

David
As I understand it there is no "coil" as it is a solid state unit. According to Precision Circuits there is no draw when the unit is open or closed. I am attaching the link for the PDF from the company.

I do know that in our Aria, the solar system (100 watts) from the factory runs through the BIM. I am now running 400 through it to charge both sets of batteries.

http://www.precisioncircuitsinc.com/...ger-Rev7-1.pdf
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Old 01-09-2021, 11:42 PM   #3
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Brand: Thor Motor Coach
Model: ACE 27.1
State: Florida
Posts: 5,372
THOR #7035
That is my understanding as well: the BIM is solid state and only "consumes" gate current to open/close the main connection.
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Old 01-10-2021, 01:01 AM   #4
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Brand: Thor Motor Coach
Model: 2020 Magnitude SV34
State: Florida
Posts: 1,517
THOR #12751
Precision Circuits BIM

I think you are missing the point of the BIM.

When on shore, generator or solar power, the BIM monitors the chassis battery voltage. When the chassis battery drops to ~12.6v, the relay engages and the chassis batteries are charged whike the house batteries are being charged.

When the engine is running, the BIM will enage to allow the alternator to charge the house batteries when they drop to ~12.6v.

If you install your solar controller to chage your house batteries, the BIM will determine when to allow the chassis battery to be charged when solar power (or any other power source is available for that marter) to charge the house batteries.

There are two BIM models.... a 160A and a 225A model for stabdard batteries. My Magnitude had the BIM160. I have two flexible 160W solar panels installed and it kept my house and chassis batteries charged while my coach sat at the Thor Service Center for the better part of two months.
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Old 01-10-2021, 02:16 PM   #5
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Brand: Thor Motor Coach
Model: Axis 24.1
State: Connecticut
Posts: 206
THOR #20289
Thanks for the Precision Circuits reference document guys. I missed this critical statement before: " The BIM remains in the ON or OFF State, without coil power"

Notice it says "coil power" which seems to imply a latching relay is used. Also I have a hard time seeing a solid state switch working at 160 or 225 amps with no triggering power draw.

So the PC BIM should work fine for charging both coach and chassis batteries while solar is hooked up to the coach batteries. FWIW if I install LiPO batteries I will swap it out for PC's "L" version. That version cycles on and off to prevent overtaxing the chassis alternator. Anyone used it for this purpose?

David
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