REGUARDING FUSE SIZE

aci2468

I AM USING 2  24 V DC (VMPP - 30.8) P V PANELS EACH 250 WATTS IN SERIES, GOING TO A PCM60X CHARGE CONT. WHAT SIZE CIRCUIT BREAKER SHOULD I BE USING

Raj174

Welcome acl2468, The panel amps, ISC, is multiplied by 1.56 and the result is rounded to the next breaker size. Example - ISC=8.09x1.56=12.62, round up to 15, which is the next breaker size up. 

aci2468

Thank you,  i really appreciate it.

vtmaps

Raj174 said:

Welcome acl2468, The panel amps, ISC, is multiplied by 1.56 and the result is rounded to the next breaker size. Example - ISC=8.09x1.56=12.62, round up to 15, which is the next breaker size up. 

Not always true... depends on the fuse or breaker. 

There may be two multiplications by 1.25, in other words, that 1.56 multiplier is 1.25 X 1.25 = 1.56. 

You always use one 125% multiplier, but the second multiplier depends on the type of fuse or circuit breaker.

Fuses and breakers have different types of ratings... some are designed to blow/trip when they carry their rated current, others are designed to carry their rated current without blowing/tripping.

If your fuse/breaker is designed to carry its rated current without blowing/tripping, then you only use 1 multiplier.  The second multiplier is for fuses/breakers that blow/trip at their rated load. 

Now, having said all that, why do you want a fuse between your panels and your charge controller?  There is no need for one.  Whatever fuse or breaker you put in there will be sized so that there will never be enough current from your panels to blow/trip it.  I recommend that you put a DC circuit breaker between your panels and your charge controller.  The breaker serves as a switch and it is very convenient to have a switch... most charge controllers must be powered up by connecting the battery before connecting the PV, and they must be powered down by disconnecting the PV before the battery.  Therefore it is very convenient to have a breaker/switch.

VERY IMPORTANT:  Whereas the breaker between your panels and your charge controller is more for convenience than safety, the breaker between your controller and your battery is absolutely necessary for safety. 

--vtMaps

aci2468

Sorry i did mean dc breaker, so i am still relying on your suggestion of using the 15 amp dc breaker by Midnite Solar at this point.
Thanks for the detailed info.  Have a Great year.

Raj174

That would be correct, and Midnite Solar is the brand I use too. Glad to help