Please help me understand this MPPT power up.

[Roswell Bob]

I am about to bring a good size 48v LiFePO4 array on line with new Midnite Classic 200 charge controllers. I have been using some Make Sky Blue controllers on my existing Lead Acid array. I have not had such good luck with these controllers. I get these big fat sparks when I connect them up and expect that they may be failing at this point....maybe.

I believe that these MPPT controllers are basically buck converters with some fancy control algorithms to find max power point.

I recall that the recommended way to hook up is to make connections to the battery first. This seems backwards to what I would expect. This is what I don't understand. I assume that there is a good amount of capacitance on the primary side of the controller which the PV array connects to. Connecting the (low impedance) battery array to the controller would cause a large current to flow through the reverse diode of the upper buck transistor to initially charge the input capacitance. This kinda scares me a little bit.

Is my analysis correct, and is this anything to worry about?

Thank you.

 

[TorC]

The SCC reads the battery voltage on wake up so it can automatically set initial charge parameters. That's why the order is what it is and is important. Without the battery it could read some wild stray voltage.

If you are worried about a spark, put a small wire through a resister across first. Charge up the SCC caps with that, then connect the big wire. Usually the inverter is where this can matter, however.

 

[WindWizard]

I am about to bring a good size 48v LiFePO4 array on line with new Midnite Classic 200 charge controllers. I have been using some Make Sky Blue controllers on my existing Lead Acid array. I have not had such good luck with these controllers. I get these big fat sparks when I connect them up and expect that they may be failing at this point....maybe.

I believe that these MPPT controllers are basically buck converters with some fancy control algorithms to find max power point.

I recall that the recommended way to hook up is to make connections to the battery first. This seems backwards to what I would expect. This is what I don't understand. I assume that there is a good amount of capacitance on the primary side of the controller which the PV array connects to. Connecting the (low impedance) battery array to the controller would cause a large current to flow through the reverse diode of the upper buck transistor to initially charge the input capacitance. This kinda scares me a little bit.

Is my analysis correct, and is this anything to worry about?

Thank you.

There have been any issues with my two Outback Mppt's. I have had them off numerous times. To bring them I turn on the battery breaker and wait for them to stabilize then turn on the solar panel breaker. I have never had any problems. There is not a large current that flows into the Mppt's.

 

[WYtreasure]

Do you have any disconnects which are approved for use "under load" between your battery and SCC?
Something like a safety switch or a circuit breaker.

I looked at the old manual and the recently revised manual. I do not see where a connection sequence is clearly stated in the instructions.
Hopefully I am missing something OR additional instructions came with your unit.

https://www.midnitesolar.com/pdfs/classic_manual_Rev_1933.pdf

https://www.midnitesolar.com/pdfs/Classic_Manual_Revision_22Jan2021_Final.pdf

 

[TorC]

It's not really a connection sequence, it's a power on sequence. For the reset, the sequence is exactly as I described. For power on when configured it's possible it will remember its configuration unless it sees something obviously wrong, in which case it may not matter what the power on sequence is.

 

[WYtreasure]

It's not really a connection sequence, it's a power on sequence. For the reset, the sequence is exactly as I described. For power on when configured it's possible it will remember its configuration unless it sees something obviously wrong, in which case it may not matter what the power on sequence is.

I guess you are correct. It just seems like the manual should either "state clearly" here is the sequence "or" that it does not matter. I could find no clear statement regarding connection or power on sequence. Snot the first time I have been confused today.