Advice on wiring schematic (24 panels, 2 charge controllers, one inverter)

Tmp4000 · June 2017

The following will be an air conditioning system, running off of a solar-derived electrical system. Each MidNite Classic 200 will be able to handle 12 panels (4x3 config). 24 panels total (each at 315W STC, 228W @ NOCT). This system will power a 900W air conditioner.

Is this wiring going in the right direction ? See below for my diagram. I am probably missing something...a disconnect or something, right ?

Any advice much appreciated.

Image: https://us.v-cdn.net/6024911/uploads/editor/1m/kvfz8qbzcsnb.png

BB. · June 2017

Each charge controller to battery connection should have a 100 Amp circuit breaker in the positive lead to protect against short circuits and to allow you to turn off each charge controller for service.

And you will want breakers between the battery bank and the AC inverter--To reduce chances of short circuits/overloads smoking your cables and to allow you to turn off the inverter for service.

Will you be grounding the DC battery bus to the ground rod? I assume the metal building will also be connected to the ground rod too.

If you have lightning in the area, you might want to consider installing surge suppressors of some sort +/- at the array, where the array goes into the power building, and on the AC mains output of the AC inverter.

https://www.solar-electric.com/midnite-solar-mnspd-300-dc-surge-protector.html
-solar-mnspd-300-ac-surge-protector.html

All wiring should run in parallel runs (+/-, Hot+Neutral, etc.). Do not make big loops or run +/= etc. wiring in loops as this can make for higher electromagnetic emissions and susceptibility to lightning.

-Bill

Tmp4000 · June 2017

Thank you very much @BB.

Questions:

I currently have a 15A, 300VDC breaker for the input array string (4 panel in series, with voltages from 160 - 185 VDC, including VOC)...is 300VDC the proper size or is 150VDC enough ? The reason why I chose 300VDC is because during the cooler temps the string will put out 4 *45V = 180VDC, which would be bigger than a 150VDC rated breaker.

At the Equator in the Pacific Ocean, we have recorded minimum temps of 24 Celsius...according to MidNite, this will raise the VOC of the array up to 180V...and then lower down to 160VDC - ish during normal NOCT

Does the Negative DC bus bar have to tied to Ground ??

Estragon · June 2017

AFAIK, using a breaker with a higher voltage rating than required is not a problem. Using a breaker with a higher amp rating than required for wire size is a problem.

The DC negative would normally be tied to ground. Some systems (eg telecom) are positive grounded, but negative ground is more common. The DC ground connection should be made in one place (only) and the bussbar is likely the most convenient place to do it.

BB. · June 2017

I had asked UL a very similar question.... I had (available) 48/60 VDC rated breakers and fuses... And technically, a 48 VDC battery bank runs upwards of 72 volts maximum (for a phone company/telecom system). Is a 48/60 VDC rated breaker correct for the application? The UL Engineer completely blew off the question about the max ratings (i.e., a 110 or 120 VAC rated circuit & fuses can have a high of 132 VAC).

UL and the UL Engineer has the full proprietary information from the Listing File (we "consumers" do not have access to this information). He was not at all interested in researching the question.

300 volt rated breaker is certainly the conservative choice.

-Bill

Tmp4000 · June 2017

So I will stick with my 300VDC breakers then...even though the array will max out around 180VDC

Here are my updated schematics...

And here is the Science Instrumentation using 3 Controllers, 36 panels:

Advice on wiring schematic (24 panels, 2 charge controllers, one inverter)

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