MegaCell Charger Workflow & reliability

I

ivan123

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Jul 4, 2022
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Hi All,

After starting my powerwall project a 2 months ago, i replaced my cheap Xtar tester for a MegaCell Charger.
With the MCC i already tested around 800 cells, and decided yesterday to retest the cells i tested before with the Xtar.

Now, i noticed that the measured capacity with the MegaCell charger is mutch lower than i tested with the xtar.

I decided to change the default workflow to:
LVC Recovery
Charging (not in original workflow)
Rest 5 min (not in original workflow)
Mcap test
Rest 5 min
Low cap test

The Mcap test will charge the battery as well as the first charge task in the workflow.

My assumption was that one charge job will fully charge the cells, but during the second charge (in the Mcap test job) there is a lot of charging capacity left, for some cells over 300mAh.
The capacity result between the original workflow and the custom workflow is really noticeable.

This all leaves me with a few questions:
1. How reliable are the MCC results?
2. What is the best workflow, to get reliable results without losing to much time (sure, I can do 4 cycles, but it will cost me a day per cell, maybe there are other options).

If you have a MCC: Show your workflow :)

Thanks!
 
Last edited:
Do you have proper IR tester with AC method? Like YR1035+ or so.
Maybe those cells have too high AC IR?

Try to test your workflow with know good cell with low IR.
Mcap itself is should be enough.
Note MCC - is correct term, MCT - will be a puzzle for MegaCell Charger owners.
 
Oleksii said:
Do you have proper IR tester with AC method? Like YR1035+ or so.
Maybe those cells have too high AC IR?

Try to test your workflow with know good cell with low IR.
Mcap itself is should be enough.
Note MCC - is correct term, MCT - will be a puzzle for MegaCell Charger owners.
Click to expand...
Thanks, i changed my post :)

i don't have a IR tester ATM, if i see different results in 1 or 2 cells, thats ok and possible.
For now, i have tested 15 (samsung) cells, and all cells have huge differences in testing.
Most of the cells have a IR of 0.1 - 0.15 (according to the MCC software)
 
Do not trust IR measured by MCC, it's just a reference thing, cannot be compared with AC method. Well, that's a long story ...

Load all 16 slots and do just single Mcap test (even without MCM (MegaCell Monitor) - software), just using hardware button. Write down resulted capacity, repeat Mcap a few times to be sure what actual capacity on the those cells.
Then compare with Xtar.

Normally you would want to calibrate MCC current per slot, which is possible up to +-10mA in settings.
 
Ok, i noticed some settings where wrong, changed them and got now a much more reliable test.

1. The Max charging voltage on my charger was set to low for some reason. Can't remember changing this, i set it now to 4.24 volts like in the video here:
View: https://youtu.be/f4Hq_jkCnpU?t=157

After charging the voltage drops just a little, but the cells are good. I tested a few times using the "double charge" workflow, but only in rare case the MCC was able to put in maybe 10-15mAh.

2. I also looked at the minimum voltage, and set it to the cut-off voltage that is on the datasheet of the manufacturer.
I assume the manufacturer will also check the capacity between max volt and cut-off voltage, not just between max volt and 3 volt?
 
No sense to use "double charge". It's a known thing that after charge cutoff cell voltage drops a little, during 5-10 minutes.
If give it to rested longer time (a few days) the cell may accepts additional portion of mAmps, but that does not make sense.
Use the same approach to test capacity. I recommend to 1st make self discharge test during a 1+ month, then perform capacity test.
This way all cells start from the same SoC, which should provide more consistent results.
 
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