The company I work for uses MPPT 150/70 SCC to charge a bank of lithium batteries.
As part of the installation process, our test engineer connects the SCC to the battery bank, and then connects an external power supply (in constant current mode) to the PV input of the SCC to simulate solar panels and test the charging system and pre-charge the batteries since we have to put everything together at night (I won’t go into details as to why).
During a long test, I noticed that the output of our power supply was swinging wildly around the setpoint. We removed the supply from the PV input and connected to the batteries to charge directly. The power supply still oscillated around the setpoint and finally died.
My thought is that perhaps the control loop in the power supply was chasing the control loop for the MPPT and it got into an oscillation and self-destructed. Does this make sense?
If that is likely, then my thought is that we should disable MPPT when attempting such a test. Which tracker mode would be best? From what I see in the manual, there are three modes, Off, Constant I/V, MPPT on.
Its an mppt - its trying to track the input… Loading and unloading it. So yeah overall not a great plan.
The mppt sometimes even shorts its input most power supplies don’t handle that either.
Test it with a solar panel at the workshop before taking it to site. At least they can handle it.
I’d never run the power supply in constant current mode but in constant voltage mode (with overcurrent protection).
And configure the MPPT so it never pulls more power than the power supply can deliver.
That never caused any issues here and if I’m not mistaken someone from Victron told me it shouldn’t cause issues on the MPPT either.
What do you think about disabling MPPT just for test?
Which mode would be best?
You could max current/charge limit the MPPT. That pretty much it as suggested by Bart.
The suggestion is based on how a solar panel works. It will only ever have a certain max voltage and current. (And the panel has a max current and voltage as you know)
Still not entirely sure how it is a great test though? Sure as a bench or troubleshooting rma test. But for install prep?
And it doesn’t help at all with actual solar array comissioning?
We have to pre-charge the batteries, and I can charge them faster at 80V/25A through the SCC then I can at 57V/25A directly to the batteries (our supply is limited to 25A).