Couple questions about 12V circuit breaker

Plowman
Plowman Solar Expert Posts: 203 ✭✭✭✭✭
in Off Grid Solar & Battery Systems #1
I have a couple Littelfuse 12V circuit breakers, bought at a local auto parts store for ~$6/ea.

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I've been using one of these 40-amp breakers as my main battery bank circuit protection for a couple months, it's installed between the positive battery terminal and a bus bar. I was planning on also using them in my charge controller and inverter circuits.

I rarely see these breakers mentioned. NAWS carries similar breakers (Bussmann Type 3). Any potential problems with using them for 24/7 service?

The ones I have are Type 1 (auto reset). Not my first choice, but that's what the auto store sells. Any potential problems with using Type 1?
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Comments

  • ILFE
    ILFE Solar Expert Posts: 364 ✭✭
    #2
    Re: Couple questions about 12V circuit breaker

    I think, the only issue you will have is, if you have a problem, the breaker will just keep resetting itself over and over, until it fails? I have never used Type I, so I am not really sure what will happen.

    Of course, using a type I breaker will be a heck of a lot better than not having any circuit protection.

    Why not find some place like ELectrical Depot and order your breakers from there? There may be cheaper places to deal with online. I just like doing business with the guy because he is dependable.


    EDIT: I completely missed your part about the Bussman breakers. I think they would be fine. Bussman is an old name in fuses and circuit protection.
    Paul
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #3
    Re: Couple questions about 12V circuit breaker
    ILFE wrote: »
    I think, the only issue you will have is, if you have a problem, the breaker will just keep resetting itself over and over, until it fails? I have never used Type I, so I am not really sure what will happen.

    Of course, using a type I breaker will be a heck of a lot better than not having any circuit protection.
    If the problem is a low to moderate overload, I could see the stress on the breaker opening to be relatively small.
    You are absolutely correct that the Type I breaker will reset on its own once the thermal element cools.
    If the overload is really large (e.g. short circuit in the wiring) the current that the breaker interrupts will be correspondingly large and the breaker is sure to be damaged quickly.
    In automotive applications a 10A Type I breaker will most likely be found on a branch circuit that is series protected by a main fuse or fusible link the serves most or all of the fuse panel. In that case you would not likely have a problem with the breaker cycling because the fuse would have blown too.
    In automotive applications, somebody is going to notice the breaker cycling and it is hoped that they will take corrective action. For an unattended system, the Type I seems like a really bad idea.

    There are also Type II self-resetting breakers. In those, there is an internal resistor which draws current and keeps the thermal element hot once the breaker has tripped. Sort of like the heat anticipator resistor in a heating thermostat. To reset a Type II you do not need to access the breaker, but you do have to turn off power to the circuit long enough for the breaker to cool and reset.
    SMA SB 3000, old BP panels.
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  • Plowman
    Plowman Solar Expert Posts: 203 ✭✭✭✭✭
    #4
    Re: Couple questions about 12V circuit breaker
    inetdog wrote: »
    If the problem is a low to moderate overload, I could see the stress on the breaker opening to be relatively small.
    You are absolutely correct that the Type I breaker will reset on its own once the thermal element cools.
    If the overload is really large (e.g. short circuit in the wiring) the current that the breaker interrupts will be correspondingly large and the breaker is sure to be damaged quickly.
    In automotive applications a 10A Type I breaker will most likely be found on a branch circuit that is series protected by a main fuse or fusible link the serves most or all of the fuse panel. In that case you would not likely have a problem with the breaker cycling because the fuse would have blown too.
    In automotive applications, somebody is going to notice the breaker cycling and it is hoped that they will take corrective action. For an unattended system, the Type I seems like a really bad idea.

    There are also Type II self-resetting breakers. In those, there is an internal resistor which draws current and keeps the thermal element hot once the breaker has tripped. Sort of like the heat anticipator resistor in a heating thermostat. To reset a Type II you do not need to access the breaker, but you do have to turn off power to the circuit long enough for the breaker to cool and reset.
    I would notice a tripped breaker within a few hours at most, I get all my electricity from this system. But maybe a few hours is too long?

    I didn't know the role of heat in how these breakers operate, that's interesting.

    My main concern is a shorted battery bank. Which makes me think I should not use one of these Type 1s as my main battery bank circuit protection. I bought a 63 amp Midnite breaker intending to use it between the battery bank and bus bars, but I found out too late that #6 is the biggest wire it will accept. I'm using #4.

    If I'm understanding you right, I could use a Type 3 for the battery bank, which will stay tripped if the battery bank short circuits. Type 1 should then be OK for the inverter and charge controller circuits.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #5
    Re: Couple questions about 12V circuit breaker
    Plowman wrote: »
    If I'm understanding you right, I could use a Type 3 for the battery bank, which will stay tripped if the battery bank short circuits. Type 1 should then be OK for the inverter and charge controller circuits.
    Yes, although I would try to avoid them for inverter and CC too just on general principles.

    And for wiring to the breaker terminals, the standard solution to the problem is to use a butt connector (properly crimped) to tail a few inches of #6 onto the ends of your #4 or larger wires.
    The shade tree mechanic approach of just clipping off a few strands is NOT recommended.
    You can also find crimp type "ferrules" which neck a #4 crimp connector down to a pin which will then fit into the #6 lug.

    Please avoid cheap Harbor Fright mechanical or hydraulic crimpers. If you do not want to buy or borrow the right tool you can often get the connections made up for you at your local welding supply operation (not local welder.)
    SMA SB 3000, old BP panels.
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  • ILFE
    ILFE Solar Expert Posts: 364 ✭✭
    #6
    Re: Couple questions about 12V circuit breaker
    inetdog wrote: »
    Yes, although I would try to avoid them for inverter and CC too just on general principles.

    I agree. When I began ordering circuit protection for my first solar installation, I decided to go with Type III - 50a rated breakers. I wired them as close to the battery (positive) terminal as possible. They have been in operation since January. If you think you may be away for any length of time, definitely go with Type III only.

    Attachment not found.



    As far as a crimper for terminals, I placed an order with Wind-Sun a few months back. I had them throw a Hammer Crimp Tool in the order. So far, it can't be beaten, certainly not with a hand crimper of any kind. The only draw back is, the spring loaded lock pin will not hold the ram in the up position. Not a major problem to work around, though.

    It will crimp sizes from #16 awg to 4/0 gauge wire / cable. That covers everything I will ever need it for.

    Attachment not found.
    Paul
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