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Vintage465's avatar
Vintage465
Nomad
Jun 18, 2019

Gathering parts to refine my solar

I have a new combiner box to gather up my three 150w panels. Prolly going parallel to start with. In my current set up of two 150w panels in parallel there is no fusing before the controller or between the controller and the batteries. Reading a document by Renogy regarding fusing they recommend one at the combiner box and between the controller and the batteries. Makes sense to me. The fusing size doesn't really seem difficult to figure out.
My question is:
1. Having this nice sized wire then throwing in a fuse really sizes down the wire size for the distance of the fuse. Yes it's only an inch but it is about 25% the size that the 8ga. conductor is that will be carrying the voltage and amps to the controller.
2. Will using a circuit breaker remove the "choke down" of the fuse?
3. Or is this like seriously not something to be concerned with?

Thoughts?
  • BFL13's avatar
    BFL13
    Explorer II
    Jun 18, 2019
    Your panels can put out approx. 30 amps, and #8 can handle about 50 amps. You fuse to protect the wire, so maybe a 40amp fuse.

    The 40 amp fuse will not "choke" 30 amps. #8 should be also good for RV size lengths at 30 amps.
  • pianotuna's avatar
    pianotuna
    Nomad III
    Jun 18, 2019
    Hi,

    Or do not fuse at all. A switch would perhaps be more useful. Just make sure it is DC rated.
  • Vintage465's avatar
    Vintage465
    Nomad
    Jun 18, 2019
    pianotuna wrote:
    Hi,

    Or do not fuse at all. A switch would perhaps be more useful. Just make sure it is DC rated.


    When you say switch, are you referring to a circuit breaker? A straight up switch won't protect anything...........right?
  • Vintage465's avatar
    Vintage465
    Nomad
    Jun 18, 2019
    BFL13 wrote:
    Your panels can put out approx. 30 amps, and #8 can handle about 50 amps. You fuse to protect the wire, so maybe a 40amp fuse.

    The 40 amp fuse will not "choke" 30 amps. #8 should be also good for RV size lengths at 30 amps.


    Great! Thanks,
  • BFL13's avatar
    BFL13
    Explorer II
    Jun 18, 2019
    You should fuse the wire from controller to battery. No need to fuse between panels and combiner or from combiner to controller with the three 150s in parallel. (It can be different with them in series, "depending") This guide has it all--worth a study.

    http://www.cooperindustries.com/content/dam/public/bussmann/Electrical/Resources/technical-literature/bus-ele-an-10191-pv-app-guide.pdf

    However some controllers like Morningstar don't like it when they are connected to the array but not to a battery. So to make sure that does not happen, you install a switch (that you can get at--so near the controller, not on the roof) between combiner and controller.

    When swapping out your battery you use the switch first and last After re-installing the battery you let the controller see what voltage the battery is at--as required for a "12/24" controller, then re-connect to the array.
  • ppine's avatar
    ppine
    Explorer II
    Jun 18, 2019
    The smart thing to do is fuse both runs. From the batteries to the controller use a resetable 40 amp fuse block. It will not "choke" your current at all. From the s panels, use an in line fuse that connects with wc4s. Don't give it a second thought.
  • pianotuna's avatar
    pianotuna
    Nomad III
    Jun 19, 2019
    There are good reasons to have a switch, and no good reasons to have a fuse or breaker between the panels and the controller.

    Vintage465 wrote:
    pianotuna wrote:
    Hi,

    Or do not fuse at all. A switch would perhaps be more useful. Just make sure it is DC rated.


    When you say switch, are you referring to a circuit breaker? A straight up switch won't protect anything...........right?

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