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Question on Fuse between battery and Solar Controller

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  • Question on Fuse between battery and Solar Controller

    I have been putting together a portable Solar Generator for home emergency use and camping purposes. I have 300w 24v 30a panel into a Tracer MPPT 30a solar controller, 3 large RV/Marine deep cycle batteries, and a 2000w Power Techon inverter in this portable setup. I see in the manual for the solar controller that it mentions a fuse between the positive battery cable and the solar controller (I am using an 8 gauge wire to connect), but gives no suggested fuse size. I want to order today a ANL fuse holder and a fuse, but not sure the size fuse I need. What do you all suggest? Thanks - Ken

  • #2
    A #8 AWG wire can handle 50 - 60 amps depending on the type of insulation and if it is in a conduit or free air. So you could use a 50 amp fuse but the Tracer is only rated at 30 amp output so it is doubtful that the #8 wire will see much more than that.

    What is the wire size between the battery and 2000 watt inverter?

    If your battery system is setup for 12 volts then that 2000 watt inverter can draw more than 165amps which would require wire sized around #2/0 and have at least a 150 amp fuse protecting it.

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    • KenRush
      KenRush commented
      Editing a comment
      SunEagle... thank you for the response and info. My inverter to battery is using 2awg cable and a 200 amp anl fuse. Ken

  • #3
    Ken

    The problem is that even using a #2 awg with insulation rated for 90C and run in free air it is only good for about 190 amps.

    Normally wire is rated at 75C which would give that #2 a 170 amp rating.

    So that 200 amp fuse will not protect that #2 wire if your 2000 watt inverter can draw more than 2000 watts.
    Last edited by SunEagle; 07-07-2016, 12:15 PM. Reason: added more info

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    • #4
      See diagram below for proper fuse location.

      With an 8 AWG copper conductor between the Controller and Battery you can use a fuse or breaker up to 80 amps using a 90 degree conductor insulation in Free Air. That DOES NOT MEAN you should use a 80 Amp OCPD, it just means that is the largest you can use in your application.

      In solar and many low voltage applications conductors are over sized to limit voltage drop which is exactly what you have done. A 30 amp circuit only requires a #14 AWG conductor in your application to meet minimum safety requirements set by NEC. The fuse is installed at the Battery Term Post, not the Controller. You want the OCPD to be as small as possible and still be operational. Very easy to figure out what you need.

      Does 30 amps ring a Bell? 300 watts into a 12 volt battery is 25 amps.

      What you should be more concerned with is what size fuse and wire you are using between the battery and Inverter. a 2000 watt Inverter on a 12 volt battery is just plain ignorant and dangerous. That is a 48 volt battery application, not 12 volts.
      Last edited by Sunking; 07-07-2016, 02:50 PM.
      MSEE, PE

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