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1 hour ago, The Blind Wolf said:I probley won't need a balancer on these if I just build the cell banks and connect them and then charge, they should be ready to just go.
It's the slow death that gets batteries every single time...
It's the slow death that gets batteries every single time...
Huh? what you mean by that? These are brand new k26650 cells never used.
The slow drifting apart that the cells do over time...and before long, one (or more) are getting quite overcharged, and the slow death of the battery ensues.
Oh, you mean in a group of cells, there is always one that bites the dust before the others do. Might be because of a 1% diff in chem or, less resistance then all the others and causes the bank or group of cells in a pack go bad, then y ou have to take it all apart and figure out which one is the bad one.
No, just that a pack of Lithium batteries without balancers on them...will eventually drift apart. And die prematurely.
There have been people on Will Prowse's diysolar forum that decided they knew better and didn't need a balancing BMS because they didn't understand the implications and they paid the price too. The differences in the cells, even brand spanking new cells are not identical, will cause one cell pack to become fully charged before the others and that means it will hit the region of rapid voltage rise before the others do too, and that leads to inevitable over-voltage of the pack. Similar problems happen at the discharge end of the equation too with over-discharge.
Without a BMS to cut off charging, and preferably one that does balancing too, this is how it will play out.
Ah, now I understand, well, the dang prob is these Daily BMS the medical grade ones, sucks at balancing. I guess for now I can get 24 balancer for these 3.2 batts then in a week or two get14 more for the lythuim iron. I need the main batts to be ready more then these 18650 banks.
So as soon as they come in Sid I need 24 of them set for the 3.2 cells. When I log in to these that I've got sitting on a 24v floating solar charger, all the cells are at the same voltage from the bms balancing. I just wish two of the batts I got one a Battle Born and the other anytime wouldn't go to darn 15v, its making my built cells star around 13.38v and can't go any higher cause the other batt is at 15v. I guess I could try to run them both down at 12v level then hook back up as 24v.
There have been people on Will Prowse's diysolar forum that decided they knew better and didn't need a balancing BMS because they didn't understand the implications and they paid the price too. The differences in the cells, even brand spanking new cells are not identical, will cause one cell pack to become fully charged before the others and that means it will hit the region of rapid voltage rise before the others do too, and that leads to inevitable over-voltage of the pack. Similar problems happen at the discharge end of the equation too with over-discharge.
Even with a BMS, if it doesn't have balancing, the packs will run into trouble. I have twin LiPo cells that each have their own. After letting them sit for a week with 7 in parallel, they all showed the same Voltage, 4.300. Now after letting them sit for a month in series, this is what I get for a reading on each:
4.230, 4.240, 4.239, 4.240, 4.230, 4.235, 4.228 Now if a VOM only read to 2 digits, all would show 4.2. If 3 digits, then 4.23 to 4.40. It isn't until you get to 4 digits that you see what they really are at. Now without an active balancer, you'd have to put them all in parallel once a week or so to keep them in shape.
Yes and no. You can get away without balancing so long as the BMS does its job of stopping charging once one cell hits the maximum for its chemistry, and likewise for the minimum, but the penalty of not having cell balancing is that you top and tail the capacity of the overall battery with the limit being the 'worst' performing cell (pack) at either end of the SOC. Like hair care, it won't happen overnight, but it will happen.
Believe it or not but some early hybrid EVs didn't have cell balancing and would eventually end up with very very limited range after 3 years or so despite there not actually being a defective cell. Removing the battery and bringing each cell to full charged more or less restored the car to normal.
Still waiting on the shunt balancer order to arrive. Parts are coming from 4 different suppliers, 3 overseas and one domestic...so we'll see how fast things move along.
10 hours ago, Sid Genetry Solar said:Still waiting on the shunt balancer order to arrive. Parts are coming from 4 different suppliers, 3 overseas and one domestic...so we'll see how fast things move along.
Did you find a heat sink supplier?
Did you find a heat sink supplier?
Ha, no...haven't looked. So much to do as a one-man design team...
Partially assembled PCBs for the battery shunt balancers arrived today. Waiting for parts from 3 other suppliers to put this all together...
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That's 80 of the units in this photo. There's 400 that I have to solder the remaining parts on, program (after I write the updated firmware!) and then test. Then mail to Sean for sale.
Yeah, I got my work cut out for me 😉
*cough* I need 26 of them please. 14 of them set for 4.2 and 12 set for 3.65. wrap the one set together and the other set and send them to sean with a big note that they are mine. . . Hope soldering on the wire isn't going to be a pain.
Sid, wouldn't it save some money for you just to ship them out yourself instead of shipping them to Sean to ship out? Or is he coming down for another visit soon? 🙂