Wanting to modify Cerbo Gx to JK BMS CAN interface

Modifications
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1

Hello All.

I run a bit of an unusual setup. Off grid. I have been running FLA for many years, and have recently built a lithium battery from 2x 16s BMW Battery packs, controlled by a JK BMS.

The system is currently running stand alone, as the CAN interface has been giving me lots of trouble. I have a contactor to disconnect the LA battery from the system at a set voltage. Both the LA battery, and the lithuim battery each have there own dedicated charging systems. Disconnecting the LA, then allows the lithium to charge to its desired higher voltage.

My issue is: Once any cell in the Lithium has discharged to the cutoff, the BMS shuts off the discharge, and outputs Low Voltage through CAN. This output then shuts down my system. In reality, I already have the FLA attached to the system, as the voltage has dropped below the specified value, and can easily run on that, with the BMS having shut down the lithuim.

It runs fine under standalone, other than not actually being able to set the voltage high enough to fully charge the BMW packs, which is why im here.

I would like the added protection, and benefit of actually having the BMS tell the charger what to do..

Is there anybody who has had experience modifying the CAN Driver, to eliminate the Low battery from the chain.

The only other option I would have is to run a controller in between, and “Block” the low battery signals.

Once I get this sorted, I will then also be able to properly charge the packs, and hopefully also resolve some of the cells going under-voltage before the others. I also keep a regular eye on the battery, through the Jk App, to ensure everything is as it should be, and try and catch problems before they become too large.

Any thoughts will be appreciated. But please don’t just remind me how this is not recommended. If I end up destroying my lithium, its fully on me..

2

The BMS switching off due to low voltage should be your last line of defense, not your first. Before your system reaches that point your inverters should have switched off already.

By using the Venus OS large you can use nodered, which enables you to use virtual devices, for example a virtual battery, which can then be fed whatever real information you want. Heres an example of a BMS combiner done in nodered (please note i have not tested the flow myself)

Virtual BMS - Node-RED - Victron Community

3

Thankyou for that. Will look down that line.

Yes agree the BMS, shouldn’t be the only source to protect the battery, and will likely add another contactor controlled by the BMS for the battery in the future. As mentioned, the FLA battery has the ability to discharge slightly lower than the lithium, so am just looking to isolate the problem from the chain, and not shut down the inverter. As we 100% rely on this system for all out power, with no grid connect at all.

Thanks again