Current limits and undocumented feature OCP?

[Sweet Taterman]

I've performed some testing to verify function of the user settable current limits and also to verify operation at full output. For this testing I used a rather stiff input source in the ~20-24V range while charging into a 12V battery bank.  The CC is in SOLAR mode with LoMax ON. I took a rather cautious approach with the test procedure since the input source is stiff. To this end, I used fusing on the input side with fast TC curves. I would change out the fusing as I upped the settable input current limit keeping the fusing not too far above the setpoint. I started at 12A fusing and finally worked my way up to 110A. I also precharged the CC input caps with a current limited source before closing in the main supply. If/when this CC is placed in service it may be somewhat "over paneled" a bit beyond the 130% suggested limit in the MN sizing tool. I therefore am interested that the CC handles this in the expected manner which for me would be to limit at unit maximum or user set limit [if lower], end of story. Observed behavior has raised several questions.
Starting on the low end with the input current limit set at 10A it will eventually clear a 12A fuse. This makes me wonder if the periodic sweeps to determine MPP ignore the user set input current limit or go some engineered amount above it. What is the intended operation here?
At the other end of the testing with the output limit set at 95A [1A below the units maximum for the tested in/out voltages per MN published curves] and the input set at 75A limit which is sufficient to drive the output to maximum I observed the following. The display showed ~95A out, the yellow LED illuminated, and the MNGP lower right occasionally flashed AMP LIMIT. All this is as expected. Now the undocumented part. The MNGP lower right flashed OCP [no mention of this in manual but from context I interpret as Over Current Protection] and the output current dropped to neighborhood of 40A or so where it held for a short while and then increased in a stepwise fashion to ~95A where it would hold a short while and then repeat the pattern. At no point did the FET temp per the MNGP exceed 52C. I was too slow witted at the time to think to measure whether this cycle matched the sweep interval for MPP but my sense is that it did not and was occurring more frequently. I just checked this morning and the MPP sweep interval is set to 3 min which must be the default as I never had adjusted this. What's going on here. I was hoping that in an "over paneled" scenario I could expect full output at times of high insolation but the above observations suggest maybe not.
MNGP FW 1042, Classic FW 1181 SN5767

[Westbranch]

ST, there is a post here about Over-voltage, IIRC the CC will shutdown until the OV drops below its (CC)  limit 150/200/250.  Don't remember if OC is mentioned in it.

[boB]

Sweet Taterman,

You are correct that OCP means Over Current Protection.   That will happen with very high peak currents.

If you want to use the power supply to test it, especially a stiff supply like you are using, may I suggest that
you change the mode to Hydro and use the Manual MPP V mode instead of Solar.  Solar mode, as you have
found, is too fast for a power supply.  It will also rarely find the correct MPP V.  It is really meant for
a real PV array.  i.e. Something without filter caps and their internal current limits, etc.

At first, try setting they MPP V just under your power supplies' Voc.  Make sure, of course, that the
minimum input V is below that point, maybe somewhere just above battery voltage.

Then, the Classic should slowly ramp down from the Voc of your power supply and just current
limit at your 95 amps output.

Then, if you want to try and adjust the input voltage for different power output, from the main
status menu, press the Soft-Left key to lower the input voltage or the Soft-Right key to
raise the input voltage.   (upper left and upper right keys on the MNGP)

As for the sweep interval time on the Solar mode, 3 minutes is the default time
but that is a "must sweep" time interval.  There are times, in Solar mode, that the
Classic may sweep before that time interval.

The Manual MPP V mode in Hydro will pretty much sit where you tell it to.

Also, in almost every mode (not wind though), from the main status menu,
pressing the ENTER button will force the Classic to do a sweep.  Hydro mode
as well.   With manual MPP V Hydro mode, I think doing that will try to force the
input voltage to go to the manual set point voltage if it was higher.

A real stiff supply (low  source impedance, high current), can sometimes overload
the Classic at voltage that are very close to the Voc voltage and are sometimes
hard to regulate there.   20 volts input and 12 volts output should be pretty easy
though as they are close together and there is fairly high PWM resolution for the
Classic to finely adjust that input voltage for those conditions.

boB

[Sweet Taterman]

boB: Thanks for the detailed reply!