Midinite Breaker wiring - Greatest power potential

Hairfarm
Hairfarm Solar Expert Posts: 225 ✭✭✭
in Off Grid Solar & Battery Systems #1
Greetings,

Been over a year since I last posted.

I bought a Midnite Big Baby box. Its purpose is to hold two breakers. The "input" breaker (63A) will be installed between my PV array and CC. The second "output" breaker (80A) will be installed between my CC and my battery bank. Like I said, both will be housed in the Big Baby box.

Midnite states that the "Positive (+) side of their DC breakers must go to the greatest power potential."

So can anyone advise if this is the correct way interpret this:

From my solar array the positive wire will go from the combiner box into the + of the 63 amp breaker then to the CC. Then from the CC, the positive wire will go into the negative side of 80A breaker and out the positive side on the way to the battery bank. That way each + is toward the greatest power potential.

Positive wire path: Array > into positive side of 63A breaker > out negative side of 63A breaker to CC > from CC into negative side of 80A breaker > out positive side of 80A breaker to battery bank.

Is this correct?

thanks!

Hairfarm
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Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: Midinite Breaker wiring - Greatest power potential

    The polarity for the 63 amp breaker between the array and the charge controller really does not matter. The solar array cannot output more than Isc-array (less than 63 amps?). You have the 80 amp breaker between the controller and the battery bank--So, technically, I guess I would point the positive connection of the 63 amp breaker towards the charge controller.

    For the 80 amp breaker, point the positive terminal towards the battery bank. The battery bank is normally the source of high current in a battery power system.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #3
    Re: Midinite Breaker wiring - Greatest power potential
    Hairfarm wrote: »
    Midnite states that the "Positive (+) side of their DC breakers must go to the greatest power potential."

    Well I guess in that case, the + side of mine would definitely have to be connected to my wife! :D
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #4
    Re: Midinite Breaker wiring - Greatest power potential
    BB. wrote: »
    The polarity for the 63 amp breaker between the array and the charge controller really does not matter. The solar array cannot output more than Isc-array (less than 63 amps?). You have the 80 amp breaker between the controller and the battery bank--So, technically, I guess I would point the positive connection of the 63 amp breaker towards the charge controller.

    I agree that the array should not be able to trip the 63 amp breaker. The breaker is really just a PV disconnect switch, so I would point its positive connection toward the array.

    Could the 63 amp breaker ever be required to break battery fault current? I think it would take a major CC fault AND a fault in the array wiring for that to happen.

    --vtMaps

    EDIT: btw, polarity does NOT matter on Midnite panel mount breakers. Polarity does matter on their din rail breakers.
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: Midinite Breaker wiring - Greatest power potential

    Note: there are such things as conventional wiring practices.

    You are looking at two different but inter-acting circuits here: one is the PV to charge controller, the other is the charge controller to batteries. In the former the power source is the PV array. In the latter we may think the power source is the charge controller, but that is only true when charging. Most of the time the power source, and all of the time the greater power source, is the batteries.

    Therefor for polarized breakers on an array (whose purpose is to protect against shorted panels) the '+' goes away from the panel it is protecting because if it shorts the power source will be the other panels.

    For a breaker between the array and charge controller the '+' goes towards the array even though there is no chance it will ever trip.

    For breaker between charge controller and battery the '+' goes towards the battery because the controller is not as likely to trip it as the battery (should the controller fault).
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #6
    Re: Midinite Breaker wiring - Greatest power potential
    Cariboocoot wrote: »
    Therefor for polarized breakers on an array (whose purpose is to protect against shorted panels) the '+' goes away from the panel it is protecting because if it shorts the power source will be the other panels.

    That makes total sense. To you and me, anyway. BUT midnite combiners all have their circuit breakers configured as string switches with the positive from the string going to the positive (line) terminal on the breaker. The negative (load) side of the breaker goes to the combiner bus.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
    Re: Midinite Breaker wiring - Greatest power potential
    vtmaps wrote: »
    That makes total sense. To you and me, anyway. BUT midnite combiners all have their circuit breakers configured as string switches with the positive from the string going to the positive (line) terminal on the breaker. The negative (load) side of the breaker goes to the combiner bus.

    --vtMaps

    Well, that's wrong.
    Sorry, but it is.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #8
    Re: Midinite Breaker wiring - Greatest power potential
    Cariboocoot wrote: »
    Well, that's wrong.
    Sorry, but it is.

    Are you saying I'm wrong about Midnite combiners, or are you saying Midnite is wrong to wire their breakers that way?

    before you answer, read this: http://midniteforum.com/index.php?topic=17.msg696#msg696
    and be sure to read down to Robin's response.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
    Re: Midinite Breaker wiring - Greatest power potential

    Robin is correct that it has no bearing on whether or not the breakers will trip.
    I'm saying it is wrong in that it does not follow wiring conventions as prescribed for directional breakers. I can understand why they did it too, as quite a number of people would be confused by the seemingly backward (but electrically correct) wiring. This includes inspectors who are notoriously dim-witted.

    The good news is that most anyone who uses these will never, ever find out if it makes a difference as failure of commercial panels is an almost unheard of situation.
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