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Old 04-11-2020, 08:53 AM   #91
fstop
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Default Re: 48volt club car limthium battery exploded

Agreed - BMS is critical.

But do the BMS units commonly used prevent a failing cell from denigrating?

I was under the impression that the BMS would attempt to "steer" voltage to or away from cells as appropriate during charge or discharge, but in the event you have a cell(s) begin to fail and go low, and the cart is unattended, I'm not sure what the BMS could do about it? I'm not sure what caused this particular fire exactly (or that the owner knows), but I'm speaking generally.

Obviously if you are reading the display on your BMS (if it has one) daily, and / or checking things with a VOM daily you could likely stay ahead of an issue. But if you have other things going on besides checking voltages on the golf cart daily, this is where I think the danger lurks.

Then you must rely on the BMS - if that doesn't stop the problem (or alert you to it so you can stop it), then hopefully there is an effective enclosure around the pack that will. If that doesn't do it - well, hopefully the home has smoke / heat detectors and there is nobody home when it happens. Better yet, the cart happens to be outside somewhere.

Let's hope it doesn't happen to anyone - but knowing what CAN happen is certainly sobering.

Hopefully solid-state batteries will get here a little sooner than predicted, and make this type of thing less of an issue (or a non-issue).
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Old 04-11-2020, 12:11 PM   #92
DaveTM
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Default Re: 48volt club car limthium battery exploded

Quote:
Originally Posted by fstop View Post
Agreed - BMS is critical.

But do the BMS units commonly used prevent a failing cell from denigrating?

I was under the impression that the BMS would attempt to "steer" voltage to or away from cells as appropriate during charge or discharge, but in the event you have a cell(s) begin to fail and go low, and the cart is unattended, I'm not sure what the BMS could do about it? I'm not sure what caused this particular fire exactly (or that the owner knows), but I'm speaking generally.

Obviously if you are reading the display on your BMS (if it has one) daily, and / or checking things with a VOM daily you could likely stay ahead of an issue. But if you have other things going on besides checking voltages on the golf cart daily, this is where I think the danger lurks.

Then you must rely on the BMS - if that doesn't stop the problem (or alert you to it so you can stop it), then hopefully there is an effective enclosure around the pack that will. If that doesn't do it - well, hopefully the home has smoke / heat detectors and there is nobody home when it happens. Better yet, the cart happens to be outside somewhere.

Let's hope it doesn't happen to anyone - but knowing what CAN happen is certainly sobering.

Hopefully solid-state batteries will get here a little sooner than predicted, and make this type of thing less of an issue (or a non-issue).
Before anyone attempts to do a lithium install from the Leaf batteries, or any "secondary use" battery they need to educate themselves on how the systems they set up....or should set up operate.

The short story on my setup is the BMS balances the cells once charging is completed....and the BMS will prevent an overcharge should the battery charger goes nutz and keeps trying to charge the pack. Remember, chargers are only looking at the entire pack voltage. Not individual cell voltages. That's the job of the BMS.

The BMS (if properly set up) will cause the power drain on the batteries to STOP if either a given pack voltage is reached, or an individual cell voltage (minimum on both) is reached. Should that happen the user needs to be aware to begin charging immediately. If the unit is far away from a cord....then tow it back to a charging place. BTW, the "backup" of my BMS is the settings on my controller. If the BMS doesn't shut down the power from the pack going below a give Voltage, then the Controller is set to do that. On mine, the controller is set for 1-V lower than the BMS. Again....a backup should the BMS fail

Now, if the batteries for some given reason, get undercharged to the point where the unit won't run (no BMS or the BMS and the backup both failed) because the power drain on the batteries falls to no voltage.....or if the charging goes to a point where the voltage goes above the 4.2V per cell and are obviously over charged, then the owner of the units needs to be aware that the batteries are now trash.

IF the user somehow revives the pack and continues to use it......there is a high probability the lithium batteries will go into thermal runaway (FIRE) during a charging.

If you don't understand this......then stick to FLA's.

MHO
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Old 04-12-2020, 01:55 PM   #93
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Default Re: 48volt club car limthium battery exploded

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Originally Posted by DaveTM View Post
If you don't understand this......then stick to FLA's.

MHO
Very well said. There's a lot to understand regarding Lithium, esp if you are going to DIY with cells of potentially unknown origin. Be careful!
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Old 06-04-2020, 10:11 PM   #94
WalterM6
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Default Re: 48volt club car limthium battery exploded

After rereading this post, I see that it was entirely the owners fault for not setting up his BMS properly. It appears he had a BMS, but it wasn't tied into his cart to disable it in case of a fault. This should also be a lesson for those people who want to run w/o a BMS. The only think I did not see mentioned in the post is that you need to test your system. Just do not assume that your LV & HV cutoffs are going to work. You need to test them. Set your parameters in the software low enough or high enough so that it will simulate a failure. This was completely avoidable.
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Old 08-03-2020, 08:02 AM   #95
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Default Re: 48volt club car limthium battery exploded

I just want to say thank you to all who contributed to this thread - and to Jerald for posting about his experience. I'm glad that nothing else was destroyed and no one was hurt.

This is a wake up call that could not have come at a better time for me. I recently acquired a lithium system and installed it on my CC DS. The initial performance is amazing but it came with this "contraption" called a "BMS".

Lol.

I asked what it was for (I knew very little when I got it) and the person I got the kit from simply said, "It's extra protection, but you don't really need it."

Yeah, right. I "don't really need my house either", I guess.

This thread has obviously saved me from catastrophe due to bad advice. BMS installation is a MUST.

And I will also take that good advice regarding programming my Alltrax LV to a volt below the BMS voltage.

THANK YOU EVERYONE!
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Old 08-03-2020, 08:55 AM   #96
Sergio
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Default Re: 48volt club car limthium battery exploded

It definitely pays to do some learning on the technologies involved with Lithium packs and also understand the difference between opinions and facts.

A quick clarification:
The Alltrax "High Voltage" setting should be below the BMS HV cutoff.

The Alltrax "Low Voltage" setting should be above the BMS LV cutoff.

The goal is not to allow the Controller to trigger either of those events on a cell so the BMS only needs to shutdown on an emergency.
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Old 08-03-2020, 11:59 AM   #97
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Default Re: 48volt club car limthium battery exploded

Quote:
Originally Posted by Sergio View Post
It definitely pays to do some learning on the technologies involved with Lithium packs and also understand the difference between opinions and facts.

A quick clarification:
The Alltrax "High Voltage" setting should be below the BMS HV cutoff.

The Alltrax "Low Voltage" setting should be above the BMS LV cutoff.

The goal is not to allow the Controller to trigger either of those events on a cell so the BMS only needs to shutdown on an emergency.
Wait....unless my brain is into la-la-land again....which occurs often after age 60.....don't you have the above back-a$$wards?

I thought the Controller HV settings should be just a tad above the BMS HV cutoff, and the Controller LV settings just a tad below the BMS LV cutoff.

That way should the BMS "fail" ....then in just a little bit more either way, the controller will shut it down.
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Old 08-03-2020, 12:23 PM   #98
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Default Re: 48volt club car limthium battery exploded

The way I posted is the correct way to set it up.

The reason is that the Alltrax controller actively "Prevents" either setting from being exceeded.

If for example you get into a situation where the batteries can not deliver the required discharge current, the Controller will actively reduce the current to prevent the voltage from falling below the "Low Setting".

If Controller "Low Setting" setting was lower than the BMS LV setting, then it would trigger the BMS LV emergency shutdown and You would need to reset the BMS to get it going again.

The BMS shutdown should be considered like a last line of defense, just a like a fuse and not something that is needed during normal operation.
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Old 08-03-2020, 01:17 PM   #99
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Default Re: 48volt club car limthium battery exploded

Quote:
Originally Posted by Sergio View Post
It definitely pays to do some learning on the technologies involved with Lithium packs and also understand the difference between opinions and facts.

A quick clarification:
The Alltrax "High Voltage" setting should be below the BMS HV cutoff.

The Alltrax "Low Voltage" setting should be above the BMS LV cutoff.

The goal is not to allow the Controller to trigger either of those events on a cell so the BMS only needs to shutdown on an emergency.
Interesting. So if I am reading this correctly, you are saying that the Alltrax is intelligent enough that if you are in a LV scenario, it will then start limiting how much current it will source (draw) from the battery pack so that it will not pull the voltage any lower than this threshold.

By doing that, you should (theoretically) never actually trip the BMS LV setting.

If that is correct, then what is the logic for setting the HV trigger point of the Alltrax lower than the BMS? In a charging state, isn't the Alltrax irrelevant? Or is this the case for regen carts (which I don't have)?
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Old 08-03-2020, 01:35 PM   #100
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Default Re: 48volt club car limthium battery exploded

Correct, the Alltrax XCT Controller (can't remember if the SR does that as well) reduces the current during discharge in order to prevent the pack voltage from getting lower than the "Under Voltage" setting.

The "Over Voltage" setting is only for Sepex carts (XCT) as the Controller can easily generate enough current during Regenerative brake to raise the pack voltage above the Lithium cell maximum voltage".

The thing to keep in mind is that the Controller only sees the "Pack" and not individual "Cells" so it is entirely possible as Cells age, get out of balance or develop more internal resistance that a single Cell may get to an LV condition while the entire pack is still above the Controller setting.

The cell level monitoring is the reason a BMS is essential for safety.
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