When combining charge controllers, do thier panel Watts need to be balanced?

[Silver_Is_Money]

In a thread on this forum a member determined that for my house and the 250 Watt panels I have access to, ideally I would need a total of 28 of them. If I go with 2 x Midnight Solar Classic 200 charge controllers, and I wish to utilize panels in 7 strings of 4 in series (to achieve the total of 28 panels), this would require that 4 strings (16 panels) be wired to the first charge controller, and that 3 strings (12 panels) be wired to the second charge controller. Is this possible, or do both charge controllers when used with a single battery bank have to see the exact same panel load as to the number of strings?

[inetdog]

In a thread on this forum a member determined that for my house and the 250 Watt panels I have access to, ideally I would need a total of 28 of them. If I go with 2 x Midnight Solar Classic 200 charge controllers, and I wish to utilize panels in 7 strings of 4 in series (to achieve the total of 28 panels), this would require that 4 strings (16 panels) be wired to the first charge controller, and that 3 strings (12 panels) be wired to the second charge controller. Is this possible, or do both charge controllers when used with a single battery bank have to see the exact same panel load as to the number of strings?

The Classics will work just fine, for the most part, when set up completely independently, with the caveat that the total power available from the two sets of panels should not exceed the power which will produce the maximum charging current (~C/8 for FLA) when the batteries are charging in Bulk stage.
But you can easily link the two Classics together in a master/slave (Follow Me) mode that will let them coordinate the current that they deliver. Especially if you include the WhizBangJr. battery current shunt into the system.

[Silver_Is_Money]

I just ran the numbers on the Midnight Solar Classic Sizing Tool website and the summed charging amps of the two combined charge controllers (one with 16 panels and one with 12) calculate out to C/9.053 for my chosen battery bank. Is that far enough off from the ideal C/8 that the batteries I'm considering should be abandoned and batteries of a bit lower amp hour rating should replace them?

[Mike90250]

C/9.053 for my chosen battery bank

Sounds good, between 8-15 is a number to strive for. The Classics have a controllable setting for output amps, and that can be used to throttle them back if needed.

Classic 200's. Do you really need the 200V version ? You do loose some efficiency with the higher voltage down conversion. Have you run the calculations for lower voltage/ larger wire and use the classic 150 ?

[Silver_Is_Money]

Sounds good, between 8-15 is a number to strive for. The Classics have a controllable setting for output amps, and that can be used to throttle them back if needed.

Classic 200's. Do you really need the 200V version ? You do loose some efficiency with the higher voltage down conversion. Have you run the calculations for lower voltage/ larger wire and use the classic 150 ?

Mike, I thought I needed the Classic 200's in order to achieve strings with 4 panels in series. Open Circuit voltage is 36.9.

VOC at -30 degrees C = 176.8 volts, which well exceeds the 150 volt rating of the Classic 150 (unless HyperVOC kicks in, which occurs at +20 degrees C).

[inetdog]

Mike, I thought I needed the Classic 200's in order to achieve strings with 4 panels in series. Open Circuit voltage is 36.9.

VOC at -30 degrees C = 176.8 volts, which well exceeds the 150 volt rating of the Classic 150 (unless HyperVOC kicks in, which occurs at +20 degrees C).

HyperVOC kicks in, as you call it, when the string voltage rises above 150V, not at a particular temperature. And it only protects the CC up to the limit of 150 plus the battery voltage. I do not see any indication of what your battery voltage is, except indirectly in terms of what voltage would be required for 16 panels to be within the current range of the CC. But if your battery bank is 48V, then HyperVOC would protect the CC up to 198V.
However, as long as Voc was above 150 the CC would not operate to produce any power.
You could simply use strings of three panels instead and only use 27 of your 28 panels. Or configure one CC to operate with 3 panel strings (18 panels) and the other with two panel strings?

[Silver_Is_Money]

I'm totally confused regarding the deficiency of the Classic 200 vs. the Classic 150 for this application. Specifically what would drive me to desire the 150 over the 200?

[Mike90250]

I'm totally confused regarding the deficiency of the Classic 200 vs. the Classic 150 for this application. Specifically what would drive me to desire the 150 over the 200?

My classic has VOC array of about 180VDC Normally runs at 130V PM. But it's a hot sucker, downconverting 130V to 60V into my charger, that's better than 2:1 reduction. The fans run all the time If I used 3 PV strings of 3 panels, instead of the 2 strings of 5, I could have used the classic 150, which handles more power at lower voltage. But I had a long wire run and chose small wire, and running my MPPT quite hot, instead of going to the next larger conduit, and larger wire in it.

So my suggestion based on experience, is that if you can use larger wire and less PV in series, pay for the wire and one more slot in the combiner and run the system cooler.

[Silver_Is_Money]

My classic has VOC array of about 180VDC Normally runs at 130V PM. But it's a hot sucker, downconverting 130V to 60V into my charger, that's better than 2:1 reduction. The fans run all the time If I used 3 PV strings of 3 panels, instead of the 2 strings of 5, I could have used the classic 150, which handles more power at lower voltage. But I had a long wire run and chose small wire, and running my MPPT quite hot, instead of going to the next larger conduit, and larger wire in it.

So my suggestion based on experience, is that if you can use larger wire and less PV in series, pay for the wire and one more slot in the combiner and run the system cooler.

Got it! Less in series, more parallel strings, and go with the Classic 150 for a cooler operating (but more expensive) system.

[inetdog]

So my suggestion based on experience, is that if you can use larger wire and less PV in series, pay for the wire and one more slot in the combiner and run the system cooler.

The CC will, in addition to running cooler, also be (no surprise) more efficient in converting panel power to battery charging power with a lower ratio of input voltage to output voltage.
Unless you have a very long run of DC wiring, that will probably override any savings in copper that going with series and smaller wire may give you.

GTIs, on the other hand, do very well with voltages up to a few times the peak utility AC voltage.