Automated Discharger for Large AH Cells

SolarForU2

New Member
Joined
May 15, 2021
Messages
15
Location
NZ
I'm looking for something to discharge Lifepo4 battery cells at a constant current down to a predefined cell cut-off voltage. I don't need to measure power out, just bring them down to a fixed value.

I have been using a CellPro PowerLab 8, for smaller batteries, but its pretty hopeless on these larger 400 AH battery cells and I have a lot to do.

Spec is discharge individually at 30-50 amps down to a set 2.9v, then taper off discharge current to approx an amp @2.9v; at that point cell is virtually fully discharged.

If anyone has seen something to do this, please post a link.

Cheers
Mike
 

RCinFLA

Photon Sorcerer
Joined
Jun 21, 2020
Messages
1,779
You can put multiple 20 amp load testers in parallel with same set cutoff voltage and discharge currents to achieve higher net discharge current.
 

SolarForU2

New Member
Joined
May 15, 2021
Messages
15
Location
NZ
Thanks, looked at those, also similar items on AliExpress; I wouldn't believe they would run continuously for > 10hrs at 20 amps, spec's on these sort of items are fantasy and perhaps 1/2 the rated value at best. Sorry I wouldn't trust them on any expensive batteries.
 

Sabre36

Solar Addict
Joined
Dec 13, 2019
Messages
106
There are plenty of options but none are inexpensive.For heavier loads we use Array electronic DC loads (3721A). we also have quite a few WMR CBA testers (CBA IV Pro, CBA V-Pro etc. with amplifiers.)
 
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SolarForU2

New Member
Joined
May 15, 2021
Messages
15
Location
NZ
Think I might design and build my own using a simple buck converter, to load up the battery under test with any current between 0 and 50 amps, set by a 10 turn panel mounted pot.
Same for the battery voltage end set point, use a similar pot to present a reference voltage to the cpu; cpu will have a 4-wire differential voltage sense connection to the battery terminals to exclude voltage drops in the high current wires.

Something like this, block dia.
Discharger.PNG

Building it this way allows connection to different battery cells without having to alter the load resistor too much. The cpu can lower the current as the battery gets down to its end point.

I will get 7 of those 100W 0.33R aluminum shell resistors and place them in parallel bolted to a sheet of alloy with a small fan.

About to send some pcbs away, so will make up a design for this in the next week or so.


Cheers
Mike
 
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