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Old 12-04-2020, 06:39 PM   #111
Volt_Ampere
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Default Re: 48volt club car limthium battery exploded

Most BMS do not provide enough balance current to do the job in a reasonable amount of time with the packs we use. I designed and built my own and I use a 1 amp balance current. This causes a fairly large voltage drop in the sense lines so I don't sense the voltage during the time that the balance current is on. I turn it off for a couple seconds to measure the cell voltages. I used power resistors and gave them plenty of air cooling space because at 1 amp they are dissipating 4W each. This is why most BMS do not balance at a very high current - they don't want to deal with the heat generated.
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Old 12-04-2020, 07:07 PM   #112
swb713
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Default Re: 48volt club car limthium battery exploded

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Originally Posted by Murby View Post
I agree.. big difference between an American product made in China and a Chinese product made in China.

The BMS units sold by most of these online retail shops are just cheap Chinese garbage that barely do what they're supposed to do.

I'm eventually going to swap my LA bats for lithium in my 2013 Precedent when they wear out.. and no way will I be using a Chinese BMS and having that thing charge in my garage.

My off grid system uses 25kWh worth of cells from a Chevy BOLT EV.. and I use a REC BMS. They are in my basement in a 14ga NEMA4x Hoffman enclosure. Might switch to Batrium or Orion when I do the cart.. will probably stick with REC since I'm so familiar with it now.

Here's a pic of the off grid unit.. When I got these cells, they were brand new, never cycled LG Chem. Going to wait for a deal like that to show up again for the golf cart.
A single stack of 14 is about the size of two loafs of bread with a capacity of about 6kWh. Two of them (65lb ea) could easily fit into the battery bay of my cart.. would probably give me 80 miles on a charge.. with the way I drive, I'd only have to charge the cart once a month.

People need to stop trusting Chinese stuff when failure has catastrophic consequences. It just isn't worth the gamble.

Either that, or switch to phosphate batteries.. when they go rogue, its basically just a smoke bomb.
Very nice and CLEAN work.
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Old 12-04-2020, 08:18 PM   #113
Murby
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Default Re: 48volt club car limthium battery exploded

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Originally Posted by Volt_Ampere View Post
Most BMS do not provide enough balance current to do the job in a reasonable amount of time with the packs we use. I designed and built my own and I use a 1 amp balance current. This causes a fairly large voltage drop in the sense lines so I don't sense the voltage during the time that the balance current is on. I turn it off for a couple seconds to measure the cell voltages. I used power resistors and gave them plenty of air cooling space because at 1 amp they are dissipating 4W each. This is why most BMS do not balance at a very high current - they don't want to deal with the heat generated.
When I put my pack together I had 2 of the 14 cell-packs that were 50mv below the other 12. When the REC was balancing, it was bleeding down 12packs at a time through those power resistors.. The BMS is designed to stop balancing when it hits 55degC.. and that's exactly what it did. hit 55, shut off for a while until it cooled down some, then went back to work.

Since it was a one time thing (new pack), I just put a computer muffin fan on it to blow air across the case to help it out.

I have my balancing settings pretty tight as I don't let any cell go beyond 10mv of the rest.

I find it impressive that you built your own.. Not sure I'd want to invest that kind of effort into it, but if I did, I would employ multiple redundant backups for safety.
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Old 12-04-2020, 08:21 PM   #114
Murby
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Default Re: 48volt club car limthium battery exploded

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Very nice and CLEAN work.
Thanks! Its amazing to watch it trick the Grid Tie solar inverters to make power off grid.
Charged it at 120 amps and the pack temperature went up just 2 degreesC. LOL.

I bought 70 of those cells.. wish I had bought 200. They're absolutely amazing.
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Old 12-13-2020, 12:57 PM   #115
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Default Re: 48volt club car limthium battery exploded

"Very nice and CLEAN work."

I second that, but you gotta cut those tails off of the wire holders-it's bugging my OCD
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Old 01-31-2021, 12:46 PM   #116
SoFLCart
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Smile Re: 48volt club car limthium battery exploded

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Originally Posted by simicrintz View Post
I second that, but you gotta cut those tails off of the wire holders-it's bugging my OCD
LOL!
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Old 04-13-2021, 12:31 AM   #117
Murby
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Default Re: 48volt club car limthium battery exploded

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Originally Posted by Volt_Ampere View Post
Most BMS do not provide enough balance current to do the job in a reasonable amount of time with the packs we use. I designed and built my own and I use a 1 amp balance current. This causes a fairly large voltage drop in the sense lines so I don't sense the voltage during the time that the balance current is on. I turn it off for a couple seconds to measure the cell voltages. I used power resistors and gave them plenty of air cooling space because at 1 amp they are dissipating 4W each. This is why most BMS do not balance at a very high current - they don't want to deal with the heat generated.
If they are limiting their balance currents so as to not deal with the heat, then they don't really know what they're doing..

I can't imagine a routine circumstance where more than two or three cells would have to be drained concurrently.. that's 4 to 12 watts to dissipate, which isn't much.. Some lithium ion LED flashlights dissipate that much energy.

My REC BMS has an internal temp sensor that stops balancing current if the unit gets too warm.. first time I hooked it up, I had 3 cells low so it actively drained the other 11.. and ya, it got warm and tripped its internal temp limit.. it just waits a few, cools down, and starts over again.

But that was upon initially hooking the system up, since then, I don't think I've ever seen it work on more than 1 cell at a time.

All I know is that these 100mA balance currents are a joke if trying to use them on a larger pack. From experience, I figure a BMS needs about 50mA per kWh of pack capacity. So if you have a 5kWh golf cart battery, you need about 250mA of balance current..
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Old 04-13-2021, 12:33 AM   #118
Murby
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Default Re: 48volt club car limthium battery exploded

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"Very nice and CLEAN work."

I second that, but you gotta cut those tails off of the wire holders-it's bugging my OCD

But if I do that, I'll have to tell my wife that my system is finished.. then I won't be able to add more capacity because she'll say "I thought you said you were done"...

For now, I just say "I have some more work to do on it but its working so we're good for now"

LOL
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Old 04-13-2021, 06:47 AM   #119
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Default Re: 48volt club car limthium battery exploded

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Originally Posted by Murby View Post
...

All I know is that these 100mA balance currents are a joke if trying to use them on a larger pack. From experience, I figure a BMS needs about 50mA per kWh of pack capacity. So if you have a 5kWh golf cart battery, you need about 250mA of balance current..
Well, I don't know what you consider a "larger pack" to be.

The ZEVA BMS advertises it's internal shunt balancing to be 120MH.

This BMS has worked fine on my 14 module Leaf pack for years now.
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Old 04-13-2021, 08:36 AM   #120
Volt_Ampere
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Default Re: 48volt club car limthium battery exploded

If you start with a pack in pretty good balance, then the lower balance current will do the job so it makes sense to manually balance a new pack before using the BMS for balance. Many BMS are not very large and they do not have the ability to dissipate much heat so balancing is very slow.
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