Load testing Headway LifePo4 batteries

[Juiced]

Here is a load tester we created for about 25$ to ensure we had good cells for our conversion.

Accurate? - Good enough to see if we had good / questionable / dud cells.
Scientific? - Mr Wizard approved!
Marketable? - Naaaaaaaaa

Meter - Already had.
2- 55W, 12V Fog lamps - 14$
Digital Timer - 8$
Fuse/holder - 3$
Switch - Leftovers


All cells were charged with the single cell unit and left to sit overnight after being disconnected from the charger .

First we used 4 new exercised cells for a benchmark. All tested to the same voltage 3.25V after ten minutes on the load.

The test started with a meter check to ensure all cells were at least 3.33 V.
4 were not. (DOA)

To ensure a good connection, the batteries were bolted in, not just slid into place.

If a cell went below the 3.25 mark at the ten minute mark they were moved to the retest area.
The ones that were from 3.20 to 3.24 were re-charged and tested again.
We had several "really new" cells that were not exercised so a few charges were needed to wake them up. All 5 that fell into that category tested good later .

We had three that metered good (over 3.33 V), but as soon as they were
put on a load....DIED!!!
That alone was worth the price of the testing equipment. Imagine if they were put into the box?





Fun stuff!!



Crazy Ed

[frodus]

nice work! As long as you can load it and the battery doesn't go "kaput", I think I need to get something like this put together.....

[Juiced]

Thanks, It was nice to put a battery in, hit the switch and timer, then do other things in the room....

Took 4 evenings to do all of them.




Ed

[frodus]

I'll have to get my current meter soon, and a good load. Did you bolt them all down each time?

[Juiced]

Yes, they were all bolted down.

I did wise up after a few and switched over to a wing nut/ bolt deal.

Much easier/quicker!

[frodus]

I might just build something with huge clips on them, most of mine will have screws on them anyway.

Need to get some large 100W+ resistors (I want to slam these to at least 3-4C).

[Juiced]

OUCH!!!!!

I stand here.....way over here....

[frodus]

Ok, Might need to get some solid state DC relays or some large FET's to turn the thing on.

[teddillard]

So this begs the question... why are these cells needing testing like this?

I mean, I understand the short answer, because some are bad, but why are they shipped bad? They're not tested in QC, or is there something about the shipping and handling that makes them fail?

I'm assuming you can get them replaced or refunded?

And did you get anything done today other than all these AWESOME posts? Seriously... great stuff, Ed!

[frodus]

Its hard sometimes to test fully, you really need to charge/discharge the cells to see if they discharge and charge correctly and actually deliver current. Some batteries can show Full voltage, but as soon as you load them, the voltage drops.


EVC stands behind and will replace bad cells if BMS was used.