A123 Fisker Karma Battery module - 7 cells with built in BMS

[Roil]

I have acquired a set out 15 of these A123 modules each of approx 1.3Kwh energy storage capacity, and consider using them as a replacement for my aging 12pcs 2V AGM battery each of 1100Ah.

I have 2 elements of concern regarding these batteries.

1) They lack one cell to simulate a proper 24V battery giving a practical voltage range from sub 20V up to 23.1V with charge Voltage at 25.2V. I believe my Tristar MPPT60 regulator can cope with that, the same goes for my Victron Multiplus 5000W inverter. Any comments from the experts on Solarpaneltalk?

2) Is there away to utilize the built in (on-board) BMS of the modules to secure cell balance and possible feed some CAN-bus info to my inverter and MPPT without going ballistic on cost and or design issues

Your views are highly appreciated

PS
For those of you who wonder why I have spent my money one these modules without sorting these issues first,,, do no be concerned - I haven't - current cost is 2 hours medium labour

[karrak]

I would think the big issue here is the BMS. It is probable that the battery BMS will balance the batteries autonomously but I wouldn't rely on this.

For safety and battery life I think it is critical to be able to monitor the individual cell voltages and preferably be able to shutdown the inverter or charge controller if any of the cell voltages go out of their safe operating range.

I had a quick look to see if anybody has reversed engineered the BMS but couldn't find anything. Unless you have the technical expertise or can find the information on how the BMS works and talks to the rest of the world I would look at disassembling the batteries and reconfigure the battery to ??p8S and install a new BMS that you can use to monitor the individual blocks of paralleled cells and shutdown the charge controller and inverter.

Simon
Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
BMS - Homemade Battery logger github.com/simat/BatteryMonitor/wiki
Latronics 4kW Inverter, homemade MPPT controller

[Mike90250]

Most "BMS" systems use a vampire bleeder board, usually rated at 1A or less, to attempt to bleed off excess charge of the first cell to reach FULL.

But if you have a 9A charger, and a 1A bleeder, you still have 8 amps going into the full battery. Will that be a problem?

[Roil]

Unless you have the technical expertise or can find the information on how the BMS works and talks to the rest of the world I would look at disassembling the batteries and reconfigure the battery to ??p8S and install a new BMS that you can use to monitor the individual blocks of paralleled cells and shutdown the charge controller and inverter.

Hi Simon

You are probably right - I have the full battery BMS harness probably including the BMS "central" if there anything like that.

This is a bit of a long term project so I should probably spend som time investigating

As for the 7 versus 8 cells I think it is a bit of a shame to destroy the nice and solid modules

[Roil]

Looks like someone has broken the CAN bus code for A123 battery with BMS

https://github.com/MITEVT/a123-arduino-can/blob/master/README.md

[Roil]

These nice A123 modules have been covering dust in my garage for years - But now suddenly there is a solution.

https://www.thunderstruck-ev.com/mcu.html - Thunderstruck has made a BMS solution that can talk to these A123 MBB's over CAN bus

First attempt is to build a "48V" battery pack out of 16 of my modules - Each of them consist of 7s3p 20Ah LiFePO4 (1,3Kwh).
The Volt will be low for a 48V pack (, but the Victron Multiplus can cope with that. Low 43v high 49v

[Heikki]

Roil, found your topic with Google. Not sure if you're still active here, but have you proceeded with your project?

[Roil]

Hei Heikki

Yes I have - I have now for more than a year successfully had the first pack operational with the BMS connected to my Victron Cerbo GX over digital inputs.
I use these to inform Cerbo GX about, High cell volt (one cell too high), pack volt high and temperature high. Not as advanced as a CAn bus connected pack but good enough.

I have currently started a project to have a second pack operational doubling my battery capasity. The second BMS will piggyback on the first.

[Heikki]

Good to hear you sorted it out. I'm building my setup also around Cerbo but with Tesla modules.

I was wondering if you have any extra Karma modules for sale? I'm trying to repair one Karma pack with a failed module.

[wandering bob]

Please help , new here and I can not figure out how to ask a question , how do I do that . Also , the question that I want to ask , I have a 200 amp lithium battery in my travel trailer and have acquired a new 100 amp lithium battery , can I parallel them like I can with a flooded battery ?

[Heikki]

There's a button for New Topic to create your own.

Screenshot_20250411_190416_Chrome.png

Answer to your question. No, you should never parallel lithium batteries if different capacity or type. Only parallel identical cells and always use a BMS to make sure you don't over-charge or discharge too much and balance the cells.

[Roil]

Hei Heikki

That could be, but I don't know yet.
The A123 modules came in many different size, what's your module buildup?

[Heikki]

This is module #5 from the pack - a normal 7s3p module.

[Roil]

Thats similar to mine, do you have a "dead" cell?

[Roil]

Are you using the original BMS board?