Fuse Block (Bluesea) odd question.

Wanderman
Wanderman Solar Expert Posts: 180 ✭✭✭
in Solar Beginners Corner #1
I have 6 panels. Wired in sets of two (parallel) theh home runned into three separate fuses on a fuse block with common outputs. On the "wires from the panels side each fuse reads the normal around 17 volts. on the common side (after the fuse) I am down to 13.8-ish

Is that weird. I've never noticed it....any idea if it's important or means something???

Thanks,

Rick
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Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,641 admin
    #2
    Basically 3.2 volt drop across each fuse?

    Just measure voltage drop across each fuse.

    3 volt drop x 20 amps (examples} = 60 Watt loss of power (which is 20 Watts of heating for each fuse). This does not sound right (too much loss.... That much heat could popa fuse).

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Wanderman
    Wanderman Solar Expert Posts: 180 ✭✭✭
    #3
    Thanks for responding BB!!!

    I Knew it was weird. The fuses do heat up quite a bit, but I used what I believed to be an appropriate rating.. 15 amp fuses the wire is way bigger, but the panels should only develop 12 amps or so (in pairs) max... What am I missing here??

    Rick
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #4
    Generally, in cases like this, the clips on the fuse holder are not making good contact, which makes heat, which weakens the spring clips, which makes poor contact......
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,641 admin
    #5
    Generally, 15 amp fuses for "typical" solar panels seems to be the "correct" size.

    Are you placing two panels in parallel to one fuse? Or one fuse per string (of one or more panels in series).

    If the fuses are getting hot, also check for clean (no corrosion/dirt/etc.) on contacts and wiring, check wiring screws are torqued correctly, and that cables/metal around fuses does not look browned (overheated).

    While 12 amps on a 15 amp fuse is OK for in terms of NEC, and my basica suggestion (80% of 15 amp rating is 12 amps)--Anytime you have significant heating in the distribution/branch wiring, there is usually something not right.

    The type of fuse and fuse holder can also affect operations too... For example, typical automotive fuse holders--I would stay away from them. They seem to be highly variable and have been known to overheat and even fail (nearly catching wiring insulation on fire) at way less than rated capacity (poor connection to fuse blades?):

    https://www.littelfuse.com/products/fuses/automotive-passenger-car/blade-fuses.aspx



    Note that the blade fuses could be fine, but the fuse holders have the conduction/heating issues... Just don't know from my keyboard.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,641 admin
    #6
    I should add... If you are getting 12 amps at Vmp/Imp for the panel (string), I would check and see if the series fuse rating is actually 20 amps, and not 15 amps.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Wanderman
    Wanderman Solar Expert Posts: 180 ✭✭✭
    #7
    Here is a photo of the setup. It's low light levels now, but I am getting a significant voltage drop when checking at the positive terminal of the fuse block. Testing through the fuse (when disconnected from block) gives me correct readings.

    When I use a jumper #8 wire between the panel wire and the positive terminal of the block, I STILL see the drop.

    Huh?


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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,113 ✭✭✭✭✭
    #8
    BB. said:
    I should add... If you are getting 12 amps at Vmp/Imp for the panel (string), I would check and see if the series fuse rating is actually 20 amps, and not 15 amps.

    -Bill
      Note, OP says he is paralleling two panels into a single fuse then combining the 3 doubled panels. There are no series wired "Strings"

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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #9

    To be honest I'm not surprised there are issues with voltage drop associated with those fuses, thet really aren't designed to sustain high current for long periods of time, it is rather a distribution to feed small intermittent loads. As there are three spare holders, two fuses in parallel for each circuit could help, but remember the fuses would have to be half the amperage for instance, a 20A circuit would need two 10A fuses in parallel. Naturally a better solution would be to use more robust fuses or DC circuit breakers.
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  • Wanderman
    Wanderman Solar Expert Posts: 180 ✭✭✭
    #10
    What I do not understand is when I test ON the fuse itself, I see correct voltage (with it disconnected from the Bus) When connected to the positive bus (with or without the fuse) I see the drop. Why!?
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #11
    When testing on the fuse, are you testing under load (ie with significant current flowing)? Voltage drop can be much different under load vs the tiny current from a multimeter.
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  • Wanderman
    Wanderman Solar Expert Posts: 180 ✭✭✭
    #12
    No load, just the flow from the panel. Fuse is disconnected from the bus. When connected the only load is the tristar mppt45
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #13
    For there to be voltage drop there has to be current flow,  regarding charge controller, is it connected to a battery?  
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
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  • Wanderman
    Wanderman Solar Expert Posts: 180 ✭✭✭
    #14
    Yes. This is a fully operational system. Battery was charged and had a supplemental charger attached. 
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #15
    Having things connected will produce results that may seem confusing, to test voltage drop across the fuse the controller should be charging at a high current, the higher the current the higher the volt drop, Ohm's Law V= I × R, 
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
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  • tabbycat
    tabbycat Solar Expert Posts: 55 ✭✭✭
    #16
    Remove two of the  strings from the block and check the voltage  drop with the third string attached to each fuse holder. That should isolate the problem fuse holder. If there is no difference then replace the block with one with a higher total current rating i. e. greater than  the  sum  total output of the panels..
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