# 20A 12V Load for lithium battery cycling tests - Car Battery + DC power supply with diode?

Ok I have searched, can't find anything.

I have a high capacity lithium ion battery testing rig, and I have some iCharger 406 units that are doing the testing for me. That side works awesome, and I can charge/discharge the lithium ion 3.7V battery at up to 70A.

These lithium ion cells are from EVs - 55Ah - very high capacity.

These units are able to both charge the lithium ion cell from source, plus regeneratively discharge the lithium ion cell back to the supply (at about 80% overall efficiency). Maximum current draw from 12V source during charging is about 27A.

My problem is that if I use a lead-acid source battery (12V car) then after 3 or 4 cycles the source battery is depleted due to the losses in regeneration.

I'm thinking of putting both a 12V battery plus a 12V computer DC power supply in parallel, using a diode on the power supply. I know that the computer power supply works fine on its own with this setup.

So:

DC12V --->|-+--iCharger---LiIon
Batt  ------/


I understand that this is oversimplifying, but the idea being that the battery would have a higher voltage than the power supply for the majority of the time, and thus be primarily discharged until about 11.3V (12V - forward voltage drop of diode on the +12V DC power supply), at which point the power supply would pretty much be supplying the majority of the power.

• What is an iCharger? Add a link to its datasheet into your question. Also provide the complete output specifications of your 12V power supply...not just the output voltage. – Elliot Alderson Feb 18 at 18:41
• Hi Elliot. The iCharger in this case is is somewhat irrelevant. Basically we can look at it as something that either sinks 27A or sources 20A depending on the battery voltage. The power supply provides a fixed 12V up to 50A. – Sean Graham Feb 20 at 23:49
• progressiverc.com/icharger-406duo.html – Sean Graham Feb 20 at 23:54