Lithium Golf Cart Fire

[chelmuth]

Here's a screen shot of the charger that I was using.

[scottyb]

Their opening ad line is kind of ironic

That charger far exceeds the maximum recommended charging voltage of your batteries.

Charger rating
INPUT 100-240 volts, 50/60HZ. OUTPUT: 57.6 volts, 15.0 amps

Your NMC battery spec is below.

It is still not clear if your batteries actually had over voltage protection on the BMS. I see they are selling GEN 2 batteries now.

Reputable battery manufacturers publish the actual voltage that shuts down the batteries. Nowhere can I find that number for your batteries.


Did your batteries have this warning sticker?

How about your original charger?

[Volt_Ampere]

That charger was totally wrong for your batteries - but I'm still concerned that the BMS did not do it's job and terminate charging before any cells were overcharged!!!

[WalterM6]

The fire described here was caused by a BMS failure. Even if the charge voltage was too high, the BMS should have intervened and stopped charging

.

Here's another thought on the BMS not doing its job. When the BMS detects that the battery max voltage has been exceeded it will shut down until the battery drops below a certain level. Which is pretty quick. The delay before it is able to start again is 2 seconds. So the BMS will continuously be cycling on and off every 2 seconds. Maybe after a few hours of this something finally gives out. Perhaps a longer time delay between the time it shuts off and is able to restart again may have avoided this problem.
Just to be clear I'm talking about Chinese BMS's like Daly and JBD. Not some $500 BMS.

[Pat911]

Originally Posted by 1sharphook

It is still not clear if your batteries actually had over voltage protection on the BMS.

Over (and under) voltage protection are basic functions of the BMS and every one should have it. There is no excuse for a BMS to not have this protection.

As Volt_Ampare said, that is definitely the wrong charger, but the BMS should have prevented over charging and hence the fire.

This highlights another problem with the mis-information when it comes to lithium. Many end users think that all lithium batteries are the same, and the only spec they need to worry about is the capacity (Ah rating) and that all 48v chargers are the same, except for current output and quality. The Big Battery BDGR battery cannot be charged with off the shelf “standard 48v” lithium chargers, which put out around 58v. They need a special, non standard 50.4v maximum charger.

[Pat911]

Originally Posted by WalterM6

.

Here's another thought on the BMS not doing its job. When the BMS detects that the battery max voltage has been exceeded it will shut down until the battery drops below a certain level. Which is pretty quick. The delay before it is able to start again is 2 seconds. So the BMS will continuously be cycling on and off every 2 seconds. Maybe after a few hours of this something finally gives out. Perhaps a longer time delay between the time it shuts off and is able to restart again may have avoided this problem. 30 minutes if possible.

Just to be clear I'm talking about Chinese BMS's like Daly and JBD. Not some $500 BMS .

Hi Walter,

I thought about this scenario but electronics can handle cycling every 2 seconds. If there were a relay doing the switching then the contacts may have welded themselves together, but not electronics. They can fail to a short but it’s normally caused by exceeding current limits, not switching.

There should also be a deadband in the BMS, I know my “cheap Chinese JBD” has this function. This enables setting the trip voltage at say 4.2v per cell and the trip release voltage at say 4.15v per cell. That would stop the cycling you mention.

The $500 BMS you mention would not be any better than the Chinese ones, where do you think it comes from? A BMS is only as good as the settings programmed into it and what we have here may be a case where incorrect parameters have been programmed.

Originally Posted by Pat911

The fire described here was caused by a BMS failure.

Originally Posted by Pat911

Over (and under) voltage protection are basic functions of the BMS and every one should have it.

I'll wait patiently for your evidence his batteries actually had over voltage protection.

Any chance you can provide a user manual or specification sheet to support your BMS failure claim?

Can you educate us on the differences between big battery gen 1 and gen 2 batteries?

[Pat911]

Originally Posted by 1sharphook

I'll wait patiently for your evidence his batteries actually had over voltage protection.

Any chance you can provide a user manual or specification sheet to support your BMS failure claim?

Can you educate us on the differences between big battery gen 1 and gen 2 batteries?

1. Any Lithium battery that is for sale to the general public or is for use in consumer products should (must) have a BMS that protects the cells. If it does not, then the manufacturer is opening themselves up to very costly lawsuits as their products are unsafe to use. I don't have conclusive proof, but I very much doubt that Big Battery would have released a battery without even the most basic BMS protection. If they did then they have no business manufacturing batteries.

2. I cannot supply a user manual or specification for the BMS used as I have no idea which BMS is being used. At no point did I claim that I did. Without examining the failed BMS, which would now be a pile of ashes, no one can conclusively determine the cause of the BMS failure. My SPECULATION of what caused the BMS failure comes from over 35 years experience in the electronics industry and holding an Electronics Engineering Degree AND from what would be expected from even the most basic BMS being used. I also have extensive knowledge of lithium batteries, their dangers and how to use them safely.

3. No, not conclusively, I don't work for Big Battery. But once again, from my knowledge and experience, I can SPECULATE that the Gen 2 might have different cells, and/or BMS. The changes might be due to a number of reasons such as component availability, continuous improvement, cost saving measures....the list goes on.

Hopefully I've answered your questions to your satisfaction

[chelmuth]

Yes they had that sticker, I had the gen2 batteries.
Also I’ll be talking with the engineers from BB this afternoon.