Breaker sizing

SwampYankee

Off grid 12V
PV array is four 250W panels (1000W) total coming into a MS combiner box
Each panel is on a 15A breaker
Combiner output wire is 6 gauge
Charge Controller is a Midnite Classic 150

Panel specs:
Maximum Power Point Voltage Vmpp
30.7 V
Maximum Power Point Current Impp
8.15 A
Open Circuit Voltage Voc
37.7 V
Short Circuit Current Isc
8.72 A
Module Efficiency (%)
15.4%

My question is what size breaker between the combiner box and the charge controller in reference to volts. I was told 50A is what I need but what voltage breaker should I be looking for? If my math is correct I am at 150V combined.

Something I just thought of.....The Classic 150 has an operating voltage of 150V if Im correct so with my current config am I over in total volts from my array anyway?? Maybe the Classic 200 rated at 200volts would be more fitting. Totally lost on this!

Thanks
Swamp

Cariboocoot

Re: Breaker sizing

You do not need any breaker between the combiner box and charge controller. It won't do anything but act as a disconnect. If you do use one as such it needs to be able to handle the combined current of all parallel panel connections. With the Isc @ 8.72 for four in parallel this would technically be (8.72 * 4) 34.88 Amps. As usual the derating needs to be done in case of high insolation so that's * 1.56 and round up, which works out to a 60 Amp breaker.

Remember it is not going to be over-current protection, just a disconnect. Voltage doesn't really enter in to it either, so long as the breaker can handle the Voc of the array. At <40 Volts that should not be a problem for a Square D QO and certainly not for a MidNite 150 Volt breaker.

SwampYankee

Re: Breaker sizing

Thank you thats what I wanted to know.
After more research I found that when the PV is wired in parallel voltage doesn't add it stays the same so when it comes to volt input for using the Classic 150 I am well within the limits inputting a max of 37.7, is this correct?

Thank You!

Vic

Re: Breaker sizing

Swamp,

Since you are using a Combiner, that implies that all of your PVs are in parallel. This means that (as Coot mentioned) the input voltage to the Classic is just the Voc value of a single PV module.

You really should have a disconnect on the PV cable from the Combiner, near the Classic. Using a circuit breaker as the disconnect is standard practice. You will want this disconnect, to switch off the PV voltage into the Classic when you do FirmWare updates, if nothing else.

If you use the MidNite line of DC breakers, using a NEC Safety Factor of 1.25 is adequate, as these DC breakers are rated to carry the Rated current continuously, although using 1.56 as the factor is not an issue, as this breaker is really just a disconnect.

Often the MN (and Outback) breakers are very inexpensive, and since you will need a breaker on the output of the Classic, it is often convenient to place an input breaker in the same box as this output breaker.

Good Luck with the new system. Vic

SwampYankee

Re: Breaker sizing

Thank you both you have cleared it all up! Love this forum. I am using a breaker between the combiner and Classic and I have placed all my breakers in one box, inverter x 2, water pump, combiner to CC, and CC to batteries. I also added a DC batt switch from Blue Sea which cuts all power to the camp. I call lit the "Wife Switch".

Thank you gentlemen!