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What is going on with this cell?
#21
Ok. And I have seen that most of these probably do have high internal resistance too, just empirically though as seen in my OP. I took another one that was sitting full for a month just now and set it at a 2C discharge and it immediately drops to 3.0V. The good ones handle it well and stay at 3.2V.

Thanks everyone, I think I'm ready to approach BH about getting these replaced.

BTW, i know you can't tell who you are talking to through a forum. I'm actually a Electrical Engineer who specializes in embedded systems designs for robotics. I'm just cutting my teeth on battery chemistry physics on the side for fun and too learn. I'm only book smart, trying to get street smart on them. I'm actually disappointed in all the BMS options on the market and probably about to design my own.
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#22
(08-18-2020, 07:26 PM)madsci1016 Wrote: I'm only book smart, trying to get street smart on them. I'm actually disappointed in all the BMS options on the market and probably about to design my own.

We all get "street smart(er)" by learning & building :-)
re the BMS, take it you've seen the others being developed out there? eg Stuart Pitaway & this thread:
https://secondlifestorage.com/showthread.php?tid=8540
Be great to see something come together.
Cell monitor comms via a common isolated bus & "off board resistors" ie not surface mount seem key features I've felt missing!
Running off solar, DIY & electronics fan :-)
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#23
off board resistors is made by diy bms as an example and several others. With that said its actually cheaper with surface mount components nowadays Smile
NOTE! My links supplied in this message may be affiliated with Ebay and by clicking on them you agree on the terms.
YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 100kWh LiFePo4 | 20kWh 14s 18650 |  66*260W Poly | ABB S3 and S5 Trip breakers
Upcoming: 14S 18650~30kWh
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#24
(08-19-2020, 11:02 AM)daromer Wrote: off board resistors is made by diy bms as an example and several others. With that said its actually cheaper with surface mount components nowadays Smile

Yeah surface mount are cheaper but I'm worried about the thermal stress on the joints & other parts of having the main load resistor on the board itself. 
All kinds of factors in it I'm sure:
- surface mounted power dissipation is limited
- surface mount better with EV market (better with vibration, smaller)
- cheaper to make
- monitoring temp harder on external resistor
and more I haven't thought of too.
Running off solar, DIY & electronics fan :-)
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#25
Power disipation is the only thing but to be honest thats not an issue really. You have built in tempereture sensor and if properly done the board is stressreliefed. You can also glue on heatsink if you really need to.

But.. When you need that amount of balancing you have other issues like i tend to say Smile
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NOTE! My links supplied in this message may be affiliated with Ebay and by clicking on them you agree on the terms.
YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 100kWh LiFePo4 | 20kWh 14s 18650 |  66*260W Poly | ABB S3 and S5 Trip breakers
Upcoming: 14S 18650~30kWh
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#26
So i reached out to battery hookup and asked for replacements for the cells that show self discharge, and they are sending me replacements. SO moral of the story is battery hookup is awesome.
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