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Thread: Blown battery fuse question

  1. #11

    Default Re: Blown battery fuse question

    Quote Originally Posted by Steve961 View Post
    When I fixed the short and replaced the fuse everything worked just fine. The funny thing is it did take a bit to figure out the fuse was blown. Since my panels were producing power the inverter kept working and continued to power 2-3 LED lights I had on in the cabin. It's only when I tried to turn on my 45 watt Vornado fan that the SureSine stopped working.
    Okay, you just described a flaw in the wiring. The charge controller should go directly to the battery through the controller fuse. The inverter should come off the battery through the inverter fuse. You don't want a situation where the charge controller goes to the inverter and then to the battery. It will work electrically, but it makes it hard to figure things out when something goes wrong/doesn't work right.
    1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

    Ohm's Law: Amps = Volts / Ohms
    Power Formula: Watts = Volts * Amps

  2. #12

    Default Re: Blown battery fuse question

    Quote Originally Posted by Cariboocoot View Post
    Okay, you just described a flaw in the wiring. The charge controller should go directly to the battery through the controller fuse. The inverter should come off the battery through the inverter fuse. You don't want a situation where the charge controller goes to the inverter and then to the battery. It will work electrically, but it makes it hard to figure things out when something goes wrong/doesn't work right.
    I see your point, but that's why I had a 60 amp circuit breaker dedicated to just the inverter. I also have separate dedicated fuses for each charge controller. The 80 amp terminal battery fuse was meant as a last ditch fail safe for the battery. I truly thought the 60 amp circuit breaker would trip before the 80 amp battery fuse blew. I could remove the 80 amp battery fuse which would then do what you want, but I wouldn't be comfortable with it. I would also need to have two battery switches rather than the single one I have now.

    Thanks.

    Steve

  3. #13

    Default Re: Blown battery fuse question

    60 Amps @ 12 Volts = 720 Watts. That will never trip on a 300 Watt inverter.

    As a rule, breakers will take longer to trip in an over-current condition than fuses will.
    1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

    Ohm's Law: Amps = Volts / Ohms
    Power Formula: Watts = Volts * Amps

  4. #14

    Default Re: Blown battery fuse question

    Quote Originally Posted by Cariboocoot View Post
    60 Amps @ 12 Volts = 720 Watts. That will never trip on a 300 Watt inverter.

    As a rule, breakers will take longer to trip in an over-current condition than fuses will.
    I tried to size the breaker for the surge capacity of the inverter, which is 600 watts. I had researched this site before getting my breaker and it seems 60 amps is not out of line. I can certainly install a smaller breaker as I can't use more than 300 watts at a time anyways. Could I also install a 100 amp fuse at the battery to create a greater differential between the breaker and fuse? I currently have 6 gauge wire feeding the inverter and DC panel.

  5. #15

    Default Re: Blown battery fuse question

    Using the surge rating for sizing breakers is often a mistake. The problem being the inverter can't maintain the surge rating for as long as it takes to actually trip the breaker anyway. Following the NEC derating rule then results in a breaker that provides no protection because the inverter will probably fry before over-current is maintained long enough to trigger the breaker.

    Morningstar actually recommends a 100 Amp fuse on these! They also suggest a 3 Amp on the output which is pretty much a wasted effort too.

    Were it me I would rely on the fact the inverter is never going to be fully loaded, much less overloaded, and size it for nominal Voltage (not minimal Voltage) @ maximum continuous output, or 300/12 = 25 Amps, and "size up" from there to a 30 Amp breaker. That will be sufficient in most cases. A lot of this has to do with interpretation and application and someone is going to say I'm wrong because my plan doesn't follow the minimum Voltage/maximum power rule plus NEC derating. Okay, I've already said it doesn't so don't tell me it doesn't.

    Oh, and don't scrimp on the wires! They should always be as large as you can fit in the terminals; the fuse/breaker needs to be the weakest point in the circuit. 6 AWG should handle 60 Amps.

    Your battery fuse did what it was supposed to do: popped when the current got too high and kept the wires from frying. If you go up to 100 Amp you're pushing the max current limit of the 6 AWG.

    I can't see your battery switch clearly. Is it ON/OFF or 1/2/BOTH type?
    1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

    Ohm's Law: Amps = Volts / Ohms
    Power Formula: Watts = Volts * Amps

  6. #16

    Default Re: Blown battery fuse question

    Quote Originally Posted by Cariboocoot View Post
    I can't see your battery switch clearly. Is it ON/OFF or 1/2/BOTH type?
    It's a 1/2/Both type, and it's set to 1.

  7. #17

    Default Re: Blown battery fuse question

    Quote Originally Posted by Steve961 View Post
    It's a 1/2/Both type, and it's set to 1.
    Well then, could you wire it so there is the 80 Amp fuse on the battery feeding the center of the switch, then have #1 go through the appropriate size fuse/breaker to the charge controller and #2 through the appropriate size fuse/breaker to the inverter? That way in OFF nothing is connected, in #1 the controller is hooked up, in #2 the inverter is hooked up, and BOTH would be normal operations.

    Possible?
    1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

    Ohm's Law: Amps = Volts / Ohms
    Power Formula: Watts = Volts * Amps

  8. #18

    Default Re: Blown battery fuse question

    Quote Originally Posted by Cariboocoot View Post
    Well then, could you wire it so there is the 80 Amp fuse on the battery feeding the center of the switch, then have #1 go through the appropriate size fuse/breaker to the charge controller and #2 through the appropriate size fuse/breaker to the inverter? That way in OFF nothing is connected, in #1 the controller is hooked up, in #2 the inverter is hooked up, and BOTH would be normal operations.

    Possible?
    In looking at the battery switch wiring diagram, I think it would behave exactly as it is now. I'll probably just switch out my 60 amp breaker for a 30 or 40 amp version - that would be the easiest thing to do.

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