Wiring

97TJ · February 2012

I have drawn up a crude wiring diagram for my small off grid cabin solar system. It was suggested that I post it here for comments. I have most of my components but need to order breakers from our sponsor and would welcome comments. Wire sizing will be determined using the voltage drop calculator.

waynefromnscanada · February 2012

Re: Wiring

Hey, couple of things hit me at first glance. Nothing serious, but should be considered.
1) the controller rated @ 45 amps, could at times be faced with over current. I would suggest a 60 amp charger which would also allow for possible future PV expansion.
2) all negative battery connections should be at one point only. Same for all positive connections, all at one terminal, and at the opposite corner from the neg. connections.
One more thing - - how long is the run between panels and controller? It COULD be more productive to wire the panels in series for higher voltage, and use an MPPT controller. What is the voltage rating of your panels?
I'm sure others will also have suggestions, which is good. As my Grandfather used to say, two heads are better than one - - even if one of them IS a goats head!

westbranch · February 2012

Re: Wiring

Hi, at first glance it looks like when you are on battery you will also be charging the batteries, I don't think this is what you want to do.
HTH

97TJ · February 2012

Re: Wiring

The run between the panels and the controller is about 25'. Maybe less if I shift them a little further east. That might mean taking a tree down which I don't really want to do. The Power distribution panel is wired so as to not allow the power inverter as a source of power when the generator is running.

niel · February 2012

Re: Wiring

i do see you have the battery connections cross connected so i am not sure how wayne saw otherwise? for clarification the one + and - lead coming from the battery bank may just be on short heavy wires to the bus bars where the multiple connections can tie together.

the point of going with a larger mppt controller could hold validity, as was stated, if you expand later and many do. this you know best though.

the point of placing the pvs in series is a good one. this affords one optional breaker then, but the breaker may still serve as a disconnect for the pvs to controller connection. the higher voltage will also allow smaller wire to be used as opposed to when all where paralleled. you can play with a v drop calculator to see what those differences are and i have a link to one i helped to develop in my signature line. you may also need to bump the value of the fuse to 20a due to nec rules if i'm remembering them right.

also on the breaker subject you may not need 150a for the inverter's breaker unless the inverter specified it. my 1000w inverter uses a 125a breaker and 1000w/10.5v (worst case the batteries should ever go, but that is until 100% dod or dead) = 95.24a.

SolaRevolution · February 2012

Re: Wiring

You should definately not plug the 35 amp charger into an outlet fed from your 30 amp distribution panel.

In my opinion it's usually good practice to have a dedicated generator output AC panel to serve loads which should not be connected to the battery system, or at least a way to plug things directly into your generator.

It may be that you can always remember to disconnect the charger when running off of the batteries but this is a perfect case for Murphy's law: "If something can go wrong, it will."

It could be as simple as forgetting to manually switch between your sources. It would be a horrible result for your batteries sake.

niel · February 2012

Re: Wiring

good point solarevolution as one wouldn't want to chase one's tail so to speak. it may help to know what 30a power distribution panel he is using or if it has a provision to hardwire an outlet for charging only from the generator input side of the switch. to tap the output side of the switch as is more likely the case with a general ac outlet allows either source of ac to operate the charger and you don't want that for the charger.

97TJ · February 2012

Re: Wiring

Thank you for all of the input. As far as the charger, maybe I should rewire the generator output to a junction box first and tap into that for a 20 amp outlet. I'll recheck the recommendation for the power inverter breaker also.

97TJ · March 2012

Re: Wiring

niel wrote: »

you may also need to bump the value of the fuse to 20a due to nec rules if i'm remembering them right.

125% of the 11.55 isc (from panel info) is 14.43 amps. So is using a 15 amp breaker just a little to close for comfort so to speak?

niel · March 2012

Re: Wiring

it's been awhile for me, but i believe the nec states another 25% buffer on top of that for pvs, but having it trip sooner by going just the initial 25% and rounding up to the nearest commercial value to me is not a hazard or a detriment. worst case is it just may prematurely trip under some rare circumstances.

97TJ · March 2012

Re: Wiring

Got it. Thanks. I appreciate your help and everyone's on this forum. Now I need to place a small order with our forum sponsor.

SolaRevolution · March 2012

Re: Wiring

The PV output circuit ampacity rating is higher than "normal" circuit ratings because PV can receive more sunlight than the standard test conditions used for rating modules (1000 Watts/sq meter) for prolonged periods. The best example I know is direct sun plus the reflection from snow (or water) hitting panels set at a high winter tilt angle.

"Normal" electrical circuits need to be rated for 125% of the continuous load.
PV circuits need the normal 125% plus another 125% for periods of higher insolation.
NEC 690.8

125% x 125% = 156%
So, PV circuits need to be rated for at least 156% of the Isc rating.

Wiring

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