I Flipped the Switch on my Over Paneled MN Classic & Array Upgrade Today

[MrM1]

Conclusion about Over Paneling a Midnite Solar Classic 150.

1. Over paneling is an excellent way to increase overall daily output. My average daily went from about 7-8 to over 12 kwh per day . On mostly sunny days in late Dec I am seeing 15.5 - 17 kwh per day. Before over paneling in early Dec on mostly sunny days it was 10-11 at most.
2. Over Paneling will not harm the Classic. With a 24v system it will simply clip at 94 amps or about 2600 watts.
3. But over paneling will cause the classic to be running at max out for a good majority of day.
4. This "running at max" creates heat. And the classic's FETs will exceed 90c, sometimes for hours.
5. The Classic is designed to start automatically limiting current above 90c FET temp to reduce heat
6. External fans only provide limited heat dispersion
7. The best way I have found to limit heat is to decrease the Classic's max output down from 94 (at 24v). It seems to be an almost 1:1 ratio of temp to amps for the first 5-8 amps of decrease
8. Running at 85 amps output the over paneled classic's FET temp dropped 10c with only 1 120mm external pc fan blowing on it. This still produces over 2300 watts from the array.

I'm still tweaking for a sweet spot of output to Temps , but will definitely NOT allow the classic to out put at max 94 amps due to heat.

 

[RobertGreen]

Best way to destroy high quality electronics, Run it at full max on a very hot day.

I don't remember the Midnite Classic having a duty cycle that you were supposed to adhere to. I would argue that if they can't operate under the conditions that they were engineered and rated for, then you don't HAVE high quality electronics.
edit: What I'm getting at here, is that if the device can't handle operating at nominal conditions, then they should derate it's specs

 

[MrM1]

My new array went online Dec 18. Array went from 2565w to 5136w and 104vdc

With a single classic 150 you can see from Dec 18 forward the increase. Dec 19-21 we were totally socked in, clouds and rain. Dec 22 was a full sun day and began a pattern of more typical weather thru today

Today's production with mostly sunny skies at 12:30pm is at 7.3 kwh so far

 

[MrM1]

I don't remember the Midnite Classic having a duty cycle that you were supposed to adhere to. I would argue that if they can't operate under the conditions that they were engineered and rated for, then you don't HAVE high quality electronics.
edit: What I'm getting at here, is that if the device can't handle operating at nominal conditions, then they should derate it's specs

I think it can do it. The cost would be a shortened life span. For a cheap controller that might mean a year or less. For a classic it might mean 5 years instead of 10

(all examples are best guesses)

 

[Tecnodave]

I think it can do it. The cost would be a shortened life span. For a cheap controller that might mean a year or less. For a classic it might mean 5 years instead of 10

(all examples are best guesses)

You have hit the nail right on the head....

 

[Wibla]

With all that solar, you don't need to torture the controller anyway, you're getting way more power overall

 

[MrM1]

I have a Growatt controller sitting here in a box. It's waiting to be installed on an off gird farm for my daughter, but install looks 2-3 months out. I have a mind to connect it to my second array just for giggles to see what happens.

 

[Wibla]

Do it! There's no better way to make sure it works properly, after all

 

[SpongeboB Sinewave]

The Classic will automatically drop the output current in increments of 5 amps when FETs get to over 90C so you were just on the edge of that happening.

The PCB temp is on the top control board but in-between the processor and auxiliary power supply so it is not ambient temperature.

Your WB Jr. temperature would be closer to ambient temperature.

Some electronics seems to run forever under very abusive conditions and some doesn't. Like people who smoke and are over 100 years old. I think you are OK here.

What would happen in summer though (over-paneled) is that when one array becomes enough, the Classic (or any MPPT) will current limit at, say, 96 amps and then it will get even more hotter because it has to do that 96 amps at a higher input voltage which means higher dissipation and then it may start derating. So, keep that in mind maybe when summer comes around, if that does happen, you may want to shed some of your winter solar extra clothing. I kind of like that analogy !

 

[MrM1]

What would happen in summer though (over-paneled) is that when one array becomes enough, the Classic (or any MPPT) will current limit at, say, 96 amps and then it will get even more hotter because it has to do that 96 amps at a higher input voltage which means higher dissipation and then it may start derating. So, keep that in mind maybe when summer comes around, if that does happen, you may want to shed some of your winter solar extra clothing. I kind of like that analogy !

Do the input volts get higher in summer?

Will using the output limit control (set to 85 amps as I have it now) still help?

I have 6 stings of 3 panels each. Each string has its on MN 15 amp DC breaker. I can turn off a string or 2 in the summer

 

[MrM1]

Do it! There's no better way to make sure it works properly, after all

OH I will...

And I'll probably buy a second classic before Summer

Problem is finding space for it and having to re invite my entire wiring set up. I would want to figure out how to add a wire trough, but then I'll have to extend both my inverter AC in and Out wires.

 

[SpongeboB Sinewave]

Do the input volts get higher in summer?

Will using the output limit control (set to 85 amps as I have it now) still help?

I have 6 stings of 3 panels each. Each string has its on MN 15 amp DC breaker. I can turn off a string or 2 in the summer

Well, actually the PV voltage should be lower in summer just because the panels would be hotter. This is what should happen in a normal, non over-powered array system.

What I meant there was that when you have plenty of sun on the array and it is overpowered like it is now, I would expect that you should get full power output (96 amps) much quicker. And since it would be over-powered at that time, the Classic would current limit its output to whatever it is set to, or, 96 amps. The way MPPT controllers current limit, or Vbattery voltage limit like in Absorb, is to raise the PV input voltage until the desired output current or voltage is reached. So, if the system is still connected as over-powered with PV when you have lots of sun, the PV input voltage will rise to keep the battery output current limited to 96 amps or whatever the setting is.


It can raise the input voltage up to open circuit..... Voc.... In which case there would be no output power from the PV at all. At least that voltage will not change with over-powered PV array. In fact, with hotter panels, that Voc should be lower than in the winter when the panels are colder. But over-powered PV while current limiting would mean the input voltage would be higher than its normal Vmp max power point voltage. The PV array might be capable of outputting say, 130 watts or something way over 96 amps, just as an example.

And Voc is where MPPT controllers start from in the first place before they drop that voltage down to increase the power output.

Pretty simple actually. Voc = no power. Vmp = max power out. Lowest voltage is equal to battery voltage which only happens when panels are shaded or hot or not high enough Vmp voltage for that battery voltage.

boB

 

[MrM1]

Well, actually the PV voltage should be lower in summer just because the panels would be hotter.

What I meant there was that when you have plenty of sun on the array and it is overpowered like it is now, I would expect that you should get full power output (96 amps) much quicker. And since it would be over-powered at that time, the Classic would current limit its output to whatever it is set to, or, 96 amps. The way MPPT controllers current limit, or Vbattery voltage limit like in Absorb, is to raise the PV input voltage until the desired output current or voltage is reached.

It can raise the input voltage up to open circuit..... Voc.... In which case there would be no output power from the PV at all.

And Voc is where MPPT controllers start from in the first place before they drop that voltage down to increase the power output.

Pretty simple actually. Voc = no power. Vmp = max power out. Lowest voltage is equal to battery voltage which only happens when panels are shaded or hot or not high enough Vmp voltage for that battery voltage.

boB

Thx. Educational

 

[MrM1]

Ok ... Today's upgrade seems to bring things down another 5-8°c. I added 3 120mm 1700 rpm Noctua pc fans. Dropped Temps from 76c to 69c when producing 2050w and 75 amps.

Only problem is, it seems the hottest side of the Classic is the opposite side of the fans. Can someone confirm the location of the FETs?

Mega Fan Upgrade

 

[SpongeboB Sinewave]

Interesting...

FETs are along the right side. Next to the inverter.

But they are on the bottom half. The internal turbo fan plastic might be inhibiting your external fan efforts ?

You could possibly unplug that turbo fan and take off the turbo fan cover that forces air from the turbo fan downward on the outside of the Classic pin fins on that right side.

 

[MrM1]

Interesting...

FETs are along the right side. Next to the inverter.

But they are on the bottom half. The internal turbo fan plastic might be inhibiting your external fan efforts ?

You could possibly unplug that turbo fan and take off the turbo fan cover that forces air from the turbo fan downward on the outside of the Classic pin fins on that right side.

I might try that, but I needto just wait and see how it does with a full day first . The Classic was already pretty hot when I turned the new external fans on. So it may have just been still dissipating heat.

And I think I have pretty much found a sweet spot for the class total out put amps. Setting it to about 87 amps seems to be the balance between production clipping and heat.

This should hold me until I can get a second classic

 

[Tecnodave]

Now you know why that I have 2 Classics....

 

[MrM1]

Now you know why that I have 2 Classics....

I knew, I just wasn't sure I needed one. I really didn't need the extra 2500w of panels, but when I read here that the classic could be over paneled, and I found a deal on some matching REC twin peak 2 290 panels to match-ish my existing array ... Well ... I couldn't resist. Go big or go home. Why add one string when you could add 3 more?

For me, getting a second classic is overkill. I could set the output limit to 80 amps, keep the heat really low and have more than enough. But who wants just "more than enough" when you can have so much surplus you've got to find ways to waste energy. ?

Now I'm even looking at my Schneider SW4024 and wondering, "why oh why did Schneider discontinue stacking?" Now I want to buy a second classic, add a third array to the back porch roof, buy a 3rd classic, rip out the SW and install 2 12kw Growatt's (or whatever) and run the whole house - 3 ton and 1 ton heat pump, water heater, dryer - all of it off grid! ?

Stupid Lifepo4 batteries. See the trouble they've caused? They're a curse I tell you! Life was simpler with led acids, more labor intensive but simpler.

 

[MrM1]

Do it! There's no better way to make sure it works properly, after all

Well ... I had every intention of trying it out for a while with the Growatt SC 4880-mpv SCC, but looking at the specs, this SCC has me a little concerned (being that it's not my SCC)

For 48v dc no problem
- up to 7000w array (3500w on each input)
- 250v voc
- 240v operating

BUT for 24 vdc systems
- max array 3500w (1750w each input). Even if I turned off one string I'm still at 2340w with 6 panels
- voc is 250 again
- BUT (according to the spec sheet - and I can't see how this isn't a typo) ... Operating volts is 60-100vdc. The 250v VOC model (according to the spec sheet) is the same as the 150v VOC model ?

With 290w panels in s3 my operating voltage is between 104 & 115. Too hi according to spec.

Would I damage it? Dunno. Dare I try just as an experiment to see what my array is capable of? ??

 

[Hedges]

View attachment 77821

Good to see this document. I had looked in the description of WBjr to see if it provided this function with Classic, but no mention.

According to this, only the classic WBjr connects to gets its output curtailed. But of course, with a battery shunt, current from multiple classics, other sources, and loads are all measured. Just curtailment is limited to the connected classic. System sizing would dictate whether curtailing one was sufficient.

This feature is useful to charge lead-acid at target current, while supporting much larger loads.
LiFePO4, too. @SpongeboB Sinewave : Ought to support a battery temperature/current curve, since lithium allowed charge current tapers off. But doesn't sound like that's in the firmware presently available.