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Unread 04-25-2015, 08:26 AM   #1
Getting Wild
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Default Nissan Leaf Balancing

I decided to do a Nissan Leaf conversion. I am contemplating the BMS top balance vs the bottom balance and wondering if there is a third option. What about top balancing the cells by individually charging them? I have a hobby charger for lithium batterys which has 3 options: LiIo 3.6v, LiPo 3.7v, and LiFe 3.3v. I am wondering if I could use one of those settings to charge each cell to full charge and get the same results as a bottom balance?

Secondly, I have read as many Leaf conversion threads as I can find. Truly a wealth of information. Thank you to all who took the time to document the process. Now that a bit of time has elapsed since those builds, would you do anything differently if starting over?
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Unread 04-25-2015, 08:59 AM   #2
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Default Re: Nissan Leaf Balancing

Any balancing is only temporary. You need a BMS that keeps your cells in balance and protects EVERY cell from over / under charge. This is the key to long Lithium battery life.
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Unread 04-25-2015, 09:02 PM   #3
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Default Re: Nissan Leaf Balancing

Unfortunately, your hobby charger would have to be able to charge the Leaf cells to about 4.1 Volts. Nominal voltage for the cells is 3.8V. Also remember that each of the 2P sections is 60-66aH. Your charger would need to be capable of charging at a fairly high amperage to fill em up.

I used a mini-bms on my 84V pack and am doing the same on my 72V pack. These will eventually top balance my packs. On the other hand Sportscoupe and others just bottom balance the packs with no bms. I'm sure both methods will work, but I like the added security of neither overcharging nor over discharging my pack.
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Unread 04-25-2015, 09:11 PM   #4
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Default Re: Nissan Leaf Balancing

No BMS won't work for very long. (Unless you manually balance frequently)
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Unread 04-25-2015, 10:12 PM   #5
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Default Re: Nissan Leaf Balancing

Quote:
Originally Posted by ronncat View Post
Unfortunately, your hobby charger would have to be able to charge the Leaf cells to about 4.1 Volts. Nominal voltage for the cells is 3.8V. Also remember that each of the 2P sections is 60-66aH. Your charger would need to be capable of charging at a fairly high amperage to fill em up.

I used a mini-bms on my 84V pack and am doing the same on my 72V pack. These will eventually top balance my packs. On the other hand Sportscoupe and others just bottom balance the packs with no bms. I'm sure both methods will work, but I like the added security of neither overcharging nor over discharging my pack.
I did not consider the ah, only the volts. My thoughts were that even if I did not reach full charge, as long as each cell was charged to the same level, they would be balanced the same way a bottom balance would. No question the BMS on my LifePo pack has kept me safe. Saving a few dollars by going without is tempting.

Roncat, you mentioned in a previous post that you had some problems with the BMS install on the ezgo. No hesitation in getting another as opposed to bottom balance?
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Unread 04-25-2015, 11:24 PM   #6
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Default Re: Nissan Leaf Balancing

Quote:
Originally Posted by Oneunder View Post
I did not consider the ah, only the volts. My thoughts were that even if I did not reach full charge, as long as each cell was charged to the same level, they would be balanced the same way a bottom balance would. No question the BMS on my LifePo pack has kept me safe. Saving a few dollars by going without is tempting.

Roncat, you mentioned in a previous post that you had some problems with the BMS install on the ezgo. No hesitation in getting another as opposed to bottom balance?
The problem was my fault

Just make sure to not short the cell modules to pack voltage and you will be fine. Take it from me… a little electrical tape on the unhooked connections is worth its weight in gold
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Unread 04-26-2015, 07:23 AM   #7
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Default Re: Nissan Leaf Balancing

http://www.diyelectriccar.com/forums...bms-53768.html

http://www.diyelectriccar.com/forums...ing-85458.html

There are plenty more if you want to drive yourself crazy reading. It's just a golf cart....
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Unread 04-26-2015, 08:11 AM   #8
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Default Re: Nissan Leaf Balancing

SC,
Thanks for the links. Lots of good information above my pay grade. Did you get the ah meter from Lightobjects? If so, how do you like it?

You posted a diagram of individual cell monitoring device. Did you make these or purchase them?
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Unread 04-26-2015, 09:59 AM   #9
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Default Re: Nissan Leaf Balancing

Quote:
Originally Posted by Oneunder View Post
SC,
Thanks for the links. Lots of good information above my pay grade. Did you get the ah meter from Lightobjects? If so, how do you like it?

You posted a diagram of individual cell monitoring device. Did you make these or purchase them?
I too am a simple man and those EV guys will argue top balance vs bottom balance all day long. It's like which is better, Ford or Chevy.

I didn't use Lightobjects Ah meter.

I also didn't post an individual cell monitoring device, I posted a cell balance warning device. It's not available as a "kit", you have to make it yourself. It consists of a few LED's and a couple resisters.

The purpose is to instantly let you know if a cell goes high of low. It is highly accurate depending on the resister value used. It does not tell you which cell went high of low though. That didn't worry me, I liked the fact it was always monitoring the pack and was under $10.

Link here:
http://www.evdl.org/pages/battbridge.html
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Unread 04-26-2015, 12:52 PM   #10
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Default Re: Nissan Leaf Balancing

Quote:
Originally Posted by Volt_Ampere View Post
No BMS won't work for very long. (Unless you manually balance frequently)
BMS we use is designed to "shunt" power from cells that fill up first, allowing all the cells to "catch-up" at the end of the charge cycle. Basically balancing the pack everytime. Only problem i have had with balance was on a cell whose BMS board had failed to control overvoltage (cell was reduced capacity & replaced). Our current bms has the ability to disable the cart if voltage goes too low, and shut down charger if any cell goes too high. We do bring them in for checkups (check terminals, Bms operation, and charger).
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