Lithium Ion BMS question

[10rmotor]

I mentioned in another thread on racing batteries that I had made my own liPo4 battery using four fairly large cells for my P2 car with a suzuki GSXR1000. Someone asked if I had a bms on it, which I don't. In looking at the various flavors of BMS systems, it seems that the BMS is somewhat of a fuse between the battery and load. For the most part that doesn't bother me, but I question running the starter current through the BMS since that can be fairly high. Is it possible to just run starter current through the positive and negative of the battery, bypassing the BMS, and run everything else (ECU, fuel pump, data) and alternator charge through the BMS?

[BLS]

I mentioned in another thread on racing batteries that I had made my own liPo4 battery using four fairly large cells for my P2 car with a suzuki GSXR1000. Someone asked if I had a bms on it, which I don't. In looking at the various flavors of BMS systems, it seems that the BMS is somewhat of a fuse between the battery and load. For the most part that doesn't bother me, but I question running the starter current through the BMS since that can be fairly high. Is it possible to just run starter current through the positive and negative of the battery, bypassing the BMS, and run everything else (ECU, fuel pump, data) and alternator charge through the BMS?

BMS is Battery Management System. The good ones prevent the battery from charging when the temperature is below 32F as it will destroy the cells. It prevents discharge below a certain voltage / charge% to prevent damage and shortened battery life. It is quite a bit more than a fuse as it is a "smart" system. Without it you need to prevent those conditions.

[Rick Kirchner]

All those expensive commercial Lithium batteries have a BMS inside, which is one of the reasons they are so expensive. Here's looking at you $200 Milwaukee tool batteries....

I think you can get them for drone applications. Big multi-rotors might approach the kind of current we experience on starts.

[10rmotor]

Yup, after consulting with someone who knows a few details about lifepo4 batteries and discussing possible wiring options I've come to the conclusion that a small one that might be marginal for starter loads but perfect for running the car after starting, and monitoring charge current isn't the way to go and I just need to get a BMS with enough capacity for the starter as well. The main problem with bypassing the BMS for starter current was it necessitated a way to isolate the ground for the starter. So yeah, when all is said and done, to do it right a BMS is needed that is big enough for starter current, which is around 70 bucks which more than doubles the price (and adds weight, dangit!).

[BLS]

Yup, after consulting with someone who knows a few details about lifepo4 batteries and discussing possible wiring options I've come to the conclusion that a small one that might be marginal for starter loads but perfect for running the car after starting, and monitoring charge current isn't the way to go and I just need to get a BMS with enough capacity for the starter as well. The main problem with bypassing the BMS for starter current was it necessitated a way to isolate the ground for the starter. So yeah, when all is said and done, to do it right a BMS is needed that is big enough for starter current, which is around 70 bucks which more than doubles the price (and adds weight, dangit!).

Personally, I think you are making this more difficult than needed. A battery of the type you need is available for around $200 and weighing as little as 1.5 pounds. Just my opinion. This one has no BMS, requiring that you manage certain things - 1) don't charge it below 32F, and do not let it discharge below the minimum voltage. Get the correct charger that will balance the cells:
https://antigravitybatteries.com/pro...l-case/ag-801/
https://antigravitybatteries.com/pro...-case/ag-1201/

They are used in total loss race cars, charging between sessions as needed.

[10rmotor]

Personally, I think you are making this more difficult than needed. A battery of the type you need is available for around $200 and weighing as little as 1.5 pounds. Just my opinion. This one has no BMS, requiring that you manage certain things - 1) don't charge it below 32F, and do not let it discharge below the minimum voltage. Get the correct charger that will balance the cells:
https://antigravitybatteries.com/pro...l-case/ag-801/
https://antigravitybatteries.com/pro...-case/ag-1201/

They are used in total loss race cars, charging between sessions as needed.

Oh I know I'm making it more difficult. When I first started the project I just wanted to see if I could do it, so the cost wasn't really an issue. Later on when I put more thought into the long term usage of these batteries a BMS that monitored the charge current from the alternator seemed like a good thing to do. It isn't being used in a total loss system so charging between sessions isn't an issue. Charging during a session is the concern, and temps below 32 aren't a problem either.

[BLS]

Oh I know I'm making it more difficult. When I first started the project I just wanted to see if I could do it, so the cost wasn't really an issue. Later on when I put more thought into the long term usage of these batteries a BMS that monitored the charge current from the alternator seemed like a good thing to do. It isn't being used in a total loss system so charging between sessions isn't an issue. Charging during a session is the concern, and temps below 32 aren't a problem either.

Understood. Charging is generally current limited and there should be specs on the cells you purchased. The reason these small light batteries are sold without a BMS is to keep the cost down for something that is not as useful when used in competition where you can keep up with it.

[10rmotor]

Understood. Charging is generally current limited and there should be specs on the cells you purchased. The reason these small light batteries are sold without a BMS is to keep the cost down for something that is not as useful when used in competition where you can keep up with it.

If I knew more about and trusted the suzuki charging system more I might not be as worried, but the possibility of a runaway meltdown on these cells is a real issue. I may still go the easy route and get an antigravity battery or other motorsport type battery that is more convenient and tested than my homebrew setup. We will see.

[BLS]

I've only used them in a total loss system, no alternator, so I have no experience with that. I don't think it's a big problem but you might check out the other offerings meant to replace stock battery's and designed to work with the OEM charging system.

For example, just picking a Suzuki Katana with 1100cc motor, I get the following:
https://antigravitybatteries.com/pro...m/atx12-ah-rs/

$250, 2.5 pounds with a BMS for protection and built in jump starter

[10rmotor]

I've only used them in a total loss system, no alternator, so I have no experience with that. I don't think it's a big problem but you might check out the other offerings meant to replace stock battery's and designed to work with the OEM charging system.

For example, just picking a Suzuki Katana with 1100cc motor, I get the following:
https://antigravitybatteries.com/pro...m/atx12-ah-rs/

$250, 2.5 pounds with a BMS for protection and built in jump starter

I think if I was running a total loss system I wouldn't even bother with a BMS at all, and I would just use a balance charger between sessions. I'm not terribly worried about the jump start function and its more CCA than I need there are smaller/cheaper/lighter ones available so I'm probably gonna go that route. Thanks for the link!

[Joules5]

Personally, I think you are making this more difficult than needed. A battery of the type you need is available for around $200 and weighing as little as 1.5 pounds. Just my opinion. This one has no BMS, requiring that you manage certain things - 1) don't charge it below 32F, and do not let it discharge below the minimum voltage. Get the correct charger that will balance the cells:
https://antigravitybatteries.com/pro...l-case/ag-801/
https://antigravitybatteries.com/pro...-case/ag-1201/

They are used in total loss race cars, charging between sessions as needed.

I tried the Antigravity solution; it left me stranded after 3 race weekends, failed to 8V output, not taking a charge and I had to run to an AutoZone to pick up an AGM. The Li-ion are simply not yet at a point they will withstand the rigors of racing in my experience.

[BLS]

I tried the Antigravity solution; it left me stranded after 3 race weekends, failed to 8V output, not taking a charge and I had to run to an AutoZone to pick up an AGM. The Li-ion are simply not yet at a point they will withstand the rigors of racing in my experience.

What were you using it in? Total loss or charging? Which antigravity? If you use the non BMS version then you must keep it properly charged, not let it drop below the minimum voltage, and not charge it below 32F. Or you kill it.
Did you use a charger that balances the cells and provides the proper current and battery profile?

Quite a few people run these successfully. OTOH, if you don't need the weight loss, no real need.