Problem running a lithium battery with built in BMS

S

Stumpalump

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Dec 30, 2024
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BMS stands for Battery Management System. A BMS is a circuit board built into lithium automotive cranking batteries. It does a few things like cuts off the battery when below freezing or when too hot. It regulates charge and cuts off when it gets drained to 25% charge. BMS also cuts off if the input voltage from the alternator if voltage happens to spike above 15.5 volts with a hard stop. Mine works as designed and averages about 14.7 V but on at least some cars like German go fast cars the voltage spikes to 16V plus for very short times. The battery stops accepting charge with a hard stop at 15.5V and that current with high voltage feeds the electrical system with a voltage spike. That blows headlights. These spikes are not a problem with AGM because they do not shut off and because lead acid batteries have about 1000 Farads of capacitance. I stopped using it for now because I have heard this problem also blows all sorts of electronics in vehicles besides just headlights. The techs at the two best suppliers of lithium, Dakota and Anti-Gravity both said to go back to AGM. They have heard of this problem. The AGM is 45 pounds heavier than lithium and in my go fast application that will not fly. No pun intended. How can I filter out the voltage above 15.5 volts so I do not get a hard BMS stop with the current and voltage spike that is wreaking havoc?
 
I have always heard that Li-ion batteries are not recommended for automotive use, for the same reasons you mentioned. The only people I have heard recommend Li-ion batteries for automotive use, are those that sell Li-ion batteries. They tend to downplay their disadvantages, resulting in the unfortunate consequences that many, such as yourself, suffer because of it.

If weight is that critical to you, find 45# elsewhere to strip out of your car, and put an AGM back in.
 
Very interesting.

Two AGM power sport batteries weigh nothing but should give 450 CCA. Walmart, $70 each.

Or might try an auto stereo stiffening capacitor, say 1 farad, and maybe even double that up if needed.
 
You could look into connecting a capacitor to the lithium battery. You shouldn't need 1000 farads. A 5 or 10 farad car audio capacitor might do the trick and they aren't very expensive.

Or, you could make your own lithium battery with LiFePo4 cells, and with no more protection than a cell balancing board. With high power cells, you can make a battery much smaller and lighter than an off the shelf lithium battery, and for a lower cost.

Sixteen A123 ANR26650M1B cells can provide 480 amps for 10 seconds, and would weigh in at only 1.2 kg. You can buy a 48-pack of these cells online (used) for $40. That's enough to make two or three car batteries. Energy capacity won't be great, and maybe there's a chance that your car might burn to the ground, but in a go-fast application those might be acceptable compromises.
 
Interesting, I have a lithium with BMS in two motorcycles (2014 KTM SDR w/ an antigravity restart and 2013 Yamaha FJR w/ the new optima) with no issues. I’ve heard of lithium with BMS not working well with vehicles with smart alternators but not from voltage spikes. I’ve heard concern of voltage spikes from the KTM dealer when I was in for service, but never an actual case. But I’m also not out there surveying owners so I’m not saying it hasn’t happened. I can see if you have a vehicle with a high output it being an issue; but that would be more the exception than the rule. I do keep my voltage output on my favorites on my dash just to keep an eye on things, but KTM which tends to be pretty particular on voltage variances has never been an issue with the antigravity.
 
The car is a 987.2 Porsche. Last of the good hydraulic steering and they shine because of weight and handling. Brail makes the only light AGM but the cranking amps and amp hours are low. They only make really small ones. Maybe I could stack two of them? I’ll check that out. I may go down to a group 48 but that adds 37 pounds of extra weight in a bad place that I’d like to avoid. Nobody seems to know why these cars spike to 16 volts even with a new Bosch alternator. I’d like to exhaust finding out why then fix that before buying a heavy battery.
 
The weakest part of any LiFEPo4 battery bank is the BMS. They're getting better but a few years ago guys with solar systems would replace them all the time. I have a 24v, 300 Ah system at home and luckily the BMS I put on it works wonders.

That said, your traditional flooded lead acid starter battery for the $$ and performance still can't be beat. You could make an argument for an AGM given the price and warranty, though.
 
Ferrari used the Optima red top 34R AGM in the Ferrari 430 Scuderia, as it was several pounds lighter than a group 48/H6 AGM they used in the regular F430. Ferrari shaved about 200lbs off the car by removing the carpet, leather, and using lots of carbon fiber...interior door panels, rear diffuser, engine bay panels, seats, steering wheel and a plexiglass rear window.

I went to a regular H6 AGM as I had three Optimas leak in a row. It was a good 9 or 10 lbs heavier than the Optima.

Sometimes the weight savings just ain't worth it...but I get trying to chase some weight savings.
 
Stumpalump said:
The car is a 987.2 Porsche. Last of the good hydraulic steering and they shine because of weight and handling. Brail makes the only light AGM but the cranking amps and amp hours are low. They only make really small ones. Maybe I could stack two of them? I’ll check that out. I may go down to a group 48 but that adds 37 pounds of extra weight in a bad place that I’d like to avoid. Nobody seems to know why these cars spike to 16 volts even with a new Bosch alternator. I’d like to exhaust finding out why then fix that before buying a heavy battery.
Click to expand...
I'm not an electrical engineer, but used to sell surgical lights years ago. Some of our customers had issues with voltage spikes and I recall we would have metal oxide varistors installed on the 24vt transformers to provide overvoltage protection to prevent the halogen bulbs from failing prematurely. I wonder if there is some way to do something similar to the lithium battery to protect it from transient voltage spikes?

Or maybe I am reading this wrong and it is not a 16vt spike but continuous voltage at 16vt for a period of time?
 
Last edited:
f355spider said:
I'm not an electrical engineer, but used to sell surgical lights years ago. Some of our customers had issues with voltage spikes and I recall we would have metal oxide varistors installed on the 24vt transformers to provide overvoltage protection to prevent the halogen bulbs from failing prematurely. I wonder if there is some way to do something similar to the lithium battery to protect it from transient voltage spikes?

Or maybe I am reading this wrong and it is not a 16vt spike but continuous voltage at 16vt for a period of time?
Click to expand...
I was told it is a spike. For how long I do not know. I think you are on to something but I have to have something that will handle the 150amps that the alternator puts out.
 
I guess it’s a little spendy.
IMG_7975.webp
 
give mechman alternators a call. they’re the name in aftermarket specialty alternators. i have a 370 amp from them with probably 100k miles on it and no telling how many idle hours running my sound system or 3k inverter. i can highly recommend idle my truck at 1500rpm and run my inverter hard until the cows come home.
 
I expect the regulator to converts the alternator output to a smooth DC, clean unwanted spikes.
Based on this, shouldn't the regulator be inspected?
 
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