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Old 06-06-16, 04:43 PM   #10
Journeyman EcoRenovator
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Join Date: Jun 2011
Location: a field somewhere
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BMS musings:

After some initial research: Building my own BMS is probably a bit out of my time/capability ranges. Buying one does get pricey. So right now I'm leaning towards the basic cell monitoring with the option to turn on cell balancing. From what I've read, cell balancers gone bad kill more battery packs then packs left alone.

Some relatively inexpensive made in china offerings. Can anyone check my math/understanding. My brain is a bit fuddled lately. Lot going on besides the new battery fun.

Problem: What amp BMS do I need?

Given: 48v.

Max. of 2400 watts draw. Surge power for 10 secs or less. And usually a max of 1500-2000 sustained for more than a minute or two (vacuuming and the fridge starts and runs).

6 battery packs providing power.

So if I take: 48v with 2500w I have 50 amps draw.
Then I divide by 6 packs. And I end up with 8 amps draw.

If I consider expanding my system to two inverters. That might go 20 amps tops?

This is important as the BMS get more expensive per amperage.


I haven't had the time to check the cell levels yet. Right now they look good as all the packs basically add up to 3.84/cell. Which might indicate that the cells are fairly well balanced.

Fun photos from the unload:

Here's the pack in the back. Of my truck.

The Eagle has landed

It was a bit tricky. The biggest battery was at the wrong end. I could slide the pallet in the bed but the tractor couldn't lift it. Finally, after three or four adjustments to the forks and then running the revs to the line. I got it up an inch. and very. very. very. slowly and carefully backed up. Heading for the shed.

Lithium pack is out

The tractor really can't support the weight and the pack begins to drop. It's a race to see if I can get to the tractor-run-in before it droops to the ground.

Huzzah. Al pays for himself again. Always good to have a buddy who can lift 500 lbs with his two iron arms.

After a good battle with the cover. The important part. Testing voltages.

Testing 1-2-3

As always. There's a bit more info at the blog.


Any body else with ideas re: BMS. Yes, No? Huh?
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