I have an Electric Moose. It’s built on a small van shell in 2005 in Los Gatos by a company that went out of business soon after they built a small fleet for University California Santa Cruz. Has a 20k water cooled motor bolted to a manual transmission. Its light, fun, and perfect for a work/handyman business that I do on occasion.
Although it’s a running solid street legal vehicle I don’t /can’t get more than 10 miles out of it. It’s been charged and would hold its own but I can’t risk it dying on me so for the last 2 years I’ve put it on airbnb and get $50 a night during the summer months as we’re very close to the beach and some people just like the idea of a hippie style adventure.
So I’m not giving up on it’s 45 cell power house has but it’s never been able to charge right and thats why I’m here today. The basic facts about this problem;
45 liFePo4 100ah batteries, the blue ones.
If a full charge at 3.7 x 45 should achieve 166.5 v
A the full discharge of 2.9, 130.5 would be empty
Even when bottom balanced the batteries charge at different rates.
The maximum amount I’ve been able to get to is 151volts, when any of the batteries hit 3.7 the BMS will kick it off. Before I could only get to 146 but by draining the highest offenders I’ve gotten that extra 5 volts.
It seems that the same batteries will always be the first to fill up again unless I drain it down over night to the 3.2-3.4 range.
I’ve heard these batteries store most of there energy in that range.
I’ve played around with a few different ideas like active balancers/equalizers and they start to work but as I found the cheapest ones only come in 4s or 8s and you lose 1 as they must be cascading and at only 1.2 amps of transfer to balance 8 in sires at a range of 3.3 -3.7 can take days and then the cascading point always seem to be more affected by draining fast and lower then the next battery.
I tried the 17s version and it became an issue at the cascade and with the led that show whither it’s actually working they use energy and has drained the 17th battery bellow 2.9 filled the cascaded next one to 3.7 and cause the batteries down from it to be off in a linemen with it eg. 2.9, 3.0, 3.05, 3.07, …
They have new pricier 5a version’s that are my next option if I can’t figure out what else to do. The BMS controller requires a password to adjust as it charges at 7amps at the end which I think should be less. And some sites even say it can be overcharged to 4-4.2 without damaging it as long as it doesn’t sit at that level.
Is there a BMS that can charge individual cells
Am I cascading the wrong way.
Is the only way to truly bottom balance all of cells is to have them all parelled for a few days.
Should the BMS reduce the amount of charge as bank fills.
I’m going to try and add pictures but I thought I shouldn’t wait any longer as I can’t have anything in the van to work on the batteries and rental season is around the corner.
Thanks in advance for any ideas, or if you have any questions so I can clarify the issue for others.
I didn’t have time to study the (long) post.
I can tell you that it’s not practical to voltage balance lifepo4 batteries. The voltage has little to do with state of charge.
You can do it one of two ways.
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Bottom balance, as you have done. Charge until the lowest capacity battery is full. That’s it, you will not be able to use more amp hours than the smallest battery can provide.
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Top balance. Use shunt balance boards on the top. Again, you can only run battery down until the smallest battery is empty.
You can replace the weak cells, but it may not add much mileage. Or you get a larger battery.
Active balancers will never be happy on lifepo4. They will always be shifting charge around to no good end. IMO Cascading is a pita, and hasn’t worked well for me.
“Even when bottom balanced the batteries charge at different rates”
Not true. Cells in series will always have the same amount of ah added to each cell. Not counting self discharge losses as heat.
Trying to get more capacity from a string, than the weakest battery can provide, is a fools errand. IMO