Safe to use CC to Limit Amps?

[Vic]

Situation here is two Classic 150 on two identical separate arrays.  Having trouble finding a way to use both CCs just now,  until Networking CCs and/or EA is implemented.

Usually this is not an issue,  but at times,  as this is still a construction site,  having the charge  capabilities of both arrays would be helpful.

It has been said that certain other CCs should not be run on a large single array,  trusting the CC to limit cuttents at/below the max rated or temp derated output current.  I had wondered about bussing both arrays together,  feeding a sincle Cl 150,  and set the Max current to about 70 A or something similar,  trusting that the single classic on a 5.88 Kw STC array will be able to take care of itself.  This high rate charge would probably not be excessively long in duration.   At mid-day today,  the pair of CCs can do about 90 amps combined.

The ambiant in the power room is around 23 degrees C in the afternoon ... NO A/C yet.

Thanks,  Vic

[boB]

Well, I say give it a try.  We won't void your warranty....   Just let us know how it goes.

Actually, we have a very large array at work now so I ~should~ be able to overload a
Classic pretty well.  I suppose we could REALLY try it and connect up to a 12V battery
but then we have to find a good 12V load.  We're wired for 48V in the lab right at
the moment.

boB

[Vic]

OK,  boB,

Will not try this test.  It is always bad to hurt things,  unless in the R&D Lab.   Was just obsessing a bit.  There will be several days,  soon,  when we will place largish demands on the system,  and there will be no one available to manage recharge  -- the system can take it,  and at worst will catch up on recharge in a couple of days.

If time is available,  will again look at trying to get the two CCs to exit Asorb gracefully without using EA. (I could not figure out what was going on,  'cause EA had not been implemented).  Most days,  a single array and CC handle things very well.

TU again,  Vic

[boB]

I remember, when working on the early MX60 design using a bench supply, the current limit being
semi slow and seeing many seconds of 140 amp output.  Didn't hurt anything but certainly makes
you take notice !   If the controller is pretty much cold at the time, you can really overload them
big time for a while.  The thing to do is to be able to have the controller run for a long time
and not get too hot, which would either break it or reduce its life if done for too long and
too hot.

boB

[Kent0]

boB,

I would also like to know what happens if you push a Classic to current limiting for extended times, say three or four hours with an array that's 50% to 100% oversized. Current limiting should reduce the duty cycle of the switching transistors and increase the rms current through the switching transistors, just as a high ratio between input and output voltage does. That would be a stressful circumstance. If the Classic is truly protecting itself, it should reduce the output current (even lower than the current limit setting) as much as necessary to operate safely.

[boB]

boB,

I would also like to know what happens if you push a Classic to current limiting for extended times, say three or four hours with an array that's 50% to 100% oversized. Current limiting should reduce the duty cycle of the switching transistors and increase the rms current through the switching transistors, just as a high ratio between input and output voltage does. That would be a stressful circumstance. If the Classic is truly protecting itself, it should reduce the output current (even lower than the current limit setting) as much as necessary to operate safely.

Hi Kent.

The Classic will reduce its current limit with increasing FET  temperature above a certain point.  It does this in 5 Amp increments.
If the first 5 amp drop in current limit doesn't reduce the temperature, it will do it again.

So, you will see the lower left yellow(ish) Clip LED on the MNGP come on when current limit is active.

Then, as temperature drops, it will release this sliding current limit back to its original setting.

That's the idea anyway and it works pretty well here.  The Classic, as all UL1741 listed controllers are tested
to full power against temperature limits until temperature stabilization and then subjected to some other
nasty things.

It should take full power 24 hours a day but we all know that's not always good for long life.

For Solar, it will usually get a chance to "rest" for the night !  I know that works good for me.

boB