# leaf battery balancing



## rottie (Oct 8, 2015)

you want to balance to within 10mV of each other, ie. 4.2 nominal 4.19 min and 4.21 max.


----------



## Castiron (Dec 16, 2015)

Thanks, but 4.19-4.21 is 20 mV isn't it, which still isn't very much.


----------



## miscrms (Sep 25, 2013)

In operation in the Leaf, I believe a 10-20mV spread is typical with active balancing. Keep in mind there's only about 400mV difference in cell voltage over 80-90% of the SOC range, so they need to be pretty tight.


----------



## rottie (Oct 8, 2015)

ok, +/- 10mv is what I have used and recommended by Orion BMS system.
It is also why I wrote the values the way I did, to eliminate confusion.
You can balance tighter but then you get into possible race conditions.

Lithiums' do not have a wide working voltage range.


----------



## WolfTronix (Feb 8, 2016)

The Leaf BMS also balances all the time, since the balance resistors are only 430 ohms.

I measured it in this video with the balance resistor being commanded to be on and off:
http://youtu.be/E-hDNjh4qyc

Enjoy,
Wolf


----------



## minispeed (Jun 30, 2013)

Fur what it's worth my 2015 leaf is usually 9-13 MV difference when fully charged. It's been as low as 7 once andas high as 16 at least twice. I put a ton of millage on it, 40k km a year, quick charge it a lot, trickle charge it sometimes and L2 fully charge it every night. My cousins 2014 was 6 when I checked his battery but I've only checked it fully charged once, he drives his less rarely quick charges and never trickles.


----------



## Castiron (Dec 16, 2015)

Thanks, I'm putting together a couple sets for hunting buggies and the range was .11v on one set and .2v on the other, so I just put ea set in parallel for a week and took them off yesterday and they are all balanced exact.


----------



## Caps18 (Jun 8, 2008)

How balanced will these batteries remain over time if they are bottom balanced at 3.00V and then used without a BMS? Charging to 4.15V. Do the batteries self level between themselves at all?


----------



## Sunking (Aug 10, 2009)

Caps18 said:


> How balanced will these batteries remain over time if they are bottom balanced at 3.00V and then used without a BMS? Charging to 4.15V. Do the batteries self level between themselves at all?


I have a racing golf cart with Leaf Cells Bottom Balanced, and in service now for about 3 months. I do not use a BMS, just a cell level monitor that I rarely connect to eliminate parasitic drains. I took great care BB each cell to 2.6 volts exactly. I hooked them all up in parallel and, used a CellPro PowerLab 8 set for 10 amps, then 5 amps, and finished discharge at 1 amps and let it set for 24 hours. 

As of today, no measurable drift in 3 months. I am running 26S. I have the motor controller set to disconnect @ 93 volts, and CCCV @ 107 volts. I stay away from the knees at both ends of the charge/discharge curve.


----------



## Caps18 (Jun 8, 2008)

Wasn't it hard to drain these to 2.6V? Does it matter what lower voltage you take them down to?

Thanks for your response, I'm not quite to the installing and wiring of the battery part yet, but it will be coming up in the next few weeks.


----------



## Sunking (Aug 10, 2009)

Caps18 said:


> Wasn't it hard to drain these to 2.6V?


 Not at all. No harder than driving, flipping a switch, and wait. I started by connecting the cells in series, and drove the cart until the pack voltage reached 78 volts 3.0 vpc for the bulk discharge. Then connected them in parallel and used my CellPro to take them down 2.5. In all 1.5 days of work. 



Caps18 said:


> Does it matter what lower voltage you take them down to?


Yes, just as important if you top Balanced. On the Top you are balancing to 100% DOD and maximum capacity. However Capacity in each cell is not known, only what 100% SOC is. If you BB, you are referencing 0% SOC and 0 AH. So with BB you know where 0% SOC is and what the capacity of each cell is. Once you connect them in series completely discharged, and pump 60 AH in every cell has 60 AH. When you discharge say 50 AH, you discharge every cell 50 AH.

The difference is in charging, and selecting the right charge voltage via trial and error with a cell monitor. With BB the cell voltages are only equal at 0% capacity. When charged all the cell voltages are slightly different. For the initial charge you have to monitor every cell to find the weakest cell in the pack. The weakest cell when charged will be the highest voltage cell 
in the pack. So for that first charge you monitor every cell, and when the weakest cell reaches 4.2 volts, terminate charge and note charger voltage. Go out and drive, and repeat the process a few times to zero in on the charger pack voltage to make sure the weakest cell does not get over charged. 

To start, select the charge voltage to 4.1 vpc. Example in my 25S system is 106.6 volts. I ended up at 106 volts.


----------

