Wire got hot and popped fuse

TXtrucker
TXtrucker Solar Expert Posts: 28 ✭
in Solar Beginners Corner #1
Got my system put together today, but had a problem. I have a Flexmax 60 charge controller. The wire running from the charge controller to the batteries is 2awg and about 8 feet long. I have a 50 amp inline fuse between the controller and the batteries. The panels were sending about 18 amps to the controller when the fuse popped. The wire near the fuse was very warm. I have 6 145 watt panels wire 3 in series x 2 to the controller.

Do I need to use heavier wire or is the fuse not big enough? I will provide additional information if needed. Thanks
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  • willardj
    willardj Registered Users Posts: 15 ✭
    #2
    Re: Wire got hot and popped fuse

    1 ?. Why were you running a 50a fuse on a 60a cc? When your panels could put out as much 72.5a at 12v. You didn't say if your running a 12v or 24v system. Makes a difference.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #3
    Re: Wire got hot and popped fuse

    Yes, you probably need a larger fuse. Assuming this is a 12 volt battery bank.
    • 6x 145 watt panels * 1/12 volts = 72.5 amps maximum (very cold weather, perfect conditions, etc.)

    In practice, this is a 60 amp controller, so the wiring/fusing should be:
    • 60 amps * 1.25 NEC safety factor = 75 Amp minimum fuse/branch circuit (round up to next standard size)

    The 18 amps--where was that measured? (solar array, battery current?).

    Is this a 12 volt system?

    Check the fuse connections and wire ends are will connected/terminated/clean...

    With a MPPT charge controller, the current from the solar array may not be the same value as the current to the battery bank.

    The other possible problems--Miss wiring... Do you have loads sharing the wiring after the fuse (on the charge controller side) that could draw > 50 amps?

    And, if the controller was wired backwards--But I would assume the controller display would not even function--So, I do not think that was it.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Wire got hot and popped fuse

    No, this does not add up.

    If there were only 18 Amps going through 2 AWG wire and a 50 Amp fuse there is no way the wire would heat and/or the fuse would pop.
    720 Watts of panel could produce 60 Amps of current on a 12 Volt system under certain circumstances. That would exceed the 50 Amp fuse's capacity. For proper fuse rating, it should be an 80 Amp fuse on the line. 4 AWG wire would be more than sufficient to handle 60 Amps. But I have to wonder how you got 2 AWG connected to the controller as the terminals are only capable of handling 6 AWG (which would also be sufficient).
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  • TXtrucker
    TXtrucker Solar Expert Posts: 28 ✭
    #5
    Re: Wire got hot and popped fuse

    I am new to this stuff and still learning. Thats why I probably used the wrong size fuse. My battery bank is 4 6v wire 2 in series to give my 440ah 12v. The wire from the controller to the battery is aluminum. Would this be a possible problem? I will increase the size of the fuse and wire. My system is 12v.
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  • TXtrucker
    TXtrucker Solar Expert Posts: 28 ✭
    #6
    Re: Wire got hot and popped fuse

    I was wrong on the wire size. The wire from the controller to the batteries is 6 awg.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
    Re: Wire got hot and popped fuse

    Aluminium wire is a no-no. You need to use special connectors and corrosion inhibitor to make it work. Get some 6 AWG copper. Bad connections can cause all kinds of trouble: high resistance, arcing, fires ...
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
    Re: Wire got hot and popped fuse
    TXtrucker wrote: »
    I was wrong on the wire size. The wire from the controller to the batteries is 6 awg.


    Aluminium 6 AWG does not have as high current capacity as copper 6 AWG.
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  • TXtrucker
    TXtrucker Solar Expert Posts: 28 ✭
    #9
    Re: Wire got hot and popped fuse

    Thanks for the information. I will rewire the system this week with copper wire and get a bigger fuse
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  • TXtrucker
    TXtrucker Solar Expert Posts: 28 ✭
    #10
    Re: Wire got hot and popped fuse

    The wire from the charge controller to the batteries is 6 awg tinned marine battery cable and the wire from the batteries to the inverter is 2/0 awg tinned marine battery cable. Sounds like I will need to replace this wire with copper.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #11
    Re: Wire got hot and popped fuse
    TXtrucker wrote: »
    The wire from the charge controller to the batteries is 6 awg tinned marine battery cable and the wire from the batteries to the inverter is 2/0 awg tinned marine battery cable. Sounds like I will need to replace this wire with copper.

    Nope. "Tinned" is tinned copper. It's shiny silver like aluminium, but it's copper underneath the tin. :D
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  • TXtrucker
    TXtrucker Solar Expert Posts: 28 ✭
    #12
    Re: Wire got hot and popped fuse

    So if the wire is ok would the wrong sized fuse be the cause of the wire getting hot. To be specific the wire was hot about 1 foot on either side of the fuse.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #13
    Re: Wire got hot and popped fuse
    TXtrucker wrote: »
    So if the wire is ok would the wrong sized fuse be the cause of the wire getting hot. To be specific the wire was hot about 1 foot on either side of the fuse.

    Yes. Probably you were seeing close to peak current at some point. Trying to shove 60 Amps through a 50 Amp fuse will definitely cause some heating, which would spread down the wire. Normally a 50 Amp fuse should only have to handle 40 Amps continuous.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #14
    Re: Wire got hot and popped fuse

    I2R = Power -> heating... So either too high of current or too high of resistance. The fuse heats to blow, can heat wiring. Or poor wiring connections at the fuse can cause heating too.

    And, in some cases, for example using automotive fuse holders (especially installed in boxes) which are designed/built "poor enough", that they can over heat and fail/catch fire even when operated with "rated" loads.

    Still do not know the voltage of your battery bank--If 12 volts, then high "normal" current can be causing the problem... If 24 or 48 volts, then bad connections/wrong wiring/etc. may be the problem.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #15
    Re: Wire got hot and popped fuse
    BB. wrote: »
    Still do not know the voltage of your battery bank--If 12 volts, then high "normal" current can be causing the problem... If 24 or 48 volts, then bad connections/wrong wiring/etc. may be the problem.

    -Bill

    Uh, yes we do: 12 Volts, 440 Amp hours. Post #5. :D

    Bill is spot-on about cheap automotive fuse holders. Got to go for the good ones. They all look alike, but they don't all work alike!
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #16
    Re: Wire got hot and popped fuse

    Marc, you are, of course, correct... I even read that post. :blush:

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • TXtrucker
    TXtrucker Solar Expert Posts: 28 ✭
    #17
    Re: Wire got hot and popped fuse

    My battery bank is 12v. 4 6v batteries wired in series x 2
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #18
    Re: Wire got hot and popped fuse
    BB. wrote: »
    I2R = Power -> heating... So either too high of current or too high of resistance. The fuse heats to blow, can heat wiring. Or poor wiring connections at the fuse can cause heating too.

    -Bill

    Bad wiring connections between the wires and the fuse holder will heat the wires and will also heat the fuse enough to lower the current required to blow it.
    Bad connections between the fuse and the holder will cause the fuse to overheat and to a lesser extent heat the wires attached. The effect is similar to what you see when you plug an undersized extension cord into a possibly old high contact resistance outlet: the cord feels warmest at the point attached to the outlet, and maybe at the other end where the load cord is plugged into the extension. If the other end of the wire is cool, the problem is not that the wire is undersized.
    If you have a voltmeter, measure the voltage drop across the fuse holder under load.
    SMA SB 3000, old BP panels.
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  • TXtrucker
    TXtrucker Solar Expert Posts: 28 ✭
    #19
    Re: Wire got hot and popped fuse

    Update on my hot wire issue. I changed the fuse holder to a sturdy fuse block with a 60 amp fuse and that solved the hot wire problem. Everything is working properly.

    I looked at a chart about discharge rates and a 50% discharge would be around 12.06v. Does this sound right? I will be leaving my refrigerator and freezer plugged into the inverter tonight to see how far the batteries are discharged. I have 440ahr capacity and based on preliminary results I should be ok. Thanks for the help.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #20
    Re: Wire got hot and popped fuse

    The resting voltage is measured at ~77F and after several hours of "non-use" (no charging, no loads).

    Glad a new fuse holder fixed your "hot wire" problem.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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