Can't get desk top computer to work with inverter?

captlee
captlee Registered Users Posts: 3
in Solar Beginners Corner #1
I am running a 50 ft romex 12 volt wire to the inverter for my desk top computer and monitor but tries to start but wont?
what can I do to fix this problem? Thanks:confused:
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #2
    Re: Can't get desk top computer to work with inverter?
    captlee wrote: »
    I am running a 50 ft romex 12 volt wire to the inverter for my desk top computer and monitor but tries to start but wont?
    what can I do to fix this problem? Thanks:confused:
    Sketchy Information, but put the Inverter 3-4 foot from your batteries with the proper size DC wire connecting the two. Then run the AC wire to the computer.
    .
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #3
    Re: Can't get desk top computer to work with inverter?

    What BC04 said... It sounds like your DC cabling is not cable of bringing the needed current to the AC inverter. For example:

    300 watts * 1/0.85 inverter efficiency * 1/10.5 volts inverter cutoff = 33.6 amps @ 12 volts DC
    33.6 amps * 1.25 NEC derating = 42 amp branch circuit+breaker/fuse

    Using the NEC (national electric code), you would need >~8 awg cable to carry that amount of current safely.

    12 AWG cable carrying 33.6 amps 50 feet, using a generic voltage drop calculator, will have ~6.4 volts drop at the DC input to the AC inverter.

    Of course, if you are not using a 12 volt battery bank, the calculations will be different, and the voltage drop will be less.

    In general, with power systems, the AC inverter and Battery bank should be located very close to each other using heavy cabling (sized for the DC current) and use a fuse/circuit breaker to protect against short circuits. The "long wire runs" would then be sent out at the higher 120 (or 230) VAC circuits. Sending low voltage/high current DC is difficult and would use a very large diameter copper cable to keep voltage drops manageable.

    Welcome to off grid solar power design... These "gotcha's" are every where. We suggest that you tell us your loads/power needs, and we walk through a paper design (or three) before buying the hardware to make sure all is done correctly/safely first.

    -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: Can't get desk top computer to work with inverter?

    Welcome to the forum.

    Desktop computer & monitor = 200 Watts. 200 Watts on 12 VDC = 16 Amps (not including inverter consumption or conversion loss). V-drop on 12 gauge across 50 feet with those specs: 2.6 Volts or 21%. By the time the power gets from the battery to the inverter the Voltage isn't high enough and the inverter won't run.

    Solution: shorter distance or larger wire. I'd suggest the shorter distance, as with the example above you'd be running at least 2 AWG to keep the Voltage above LVD on the inverter. 50 feet of that would be quite expensive.
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  • captlee
    captlee Registered Users Posts: 3
    #5
    Re: Can't get desk top computer to work with inverter?

    Well Thanks to all of you fine folks out there I now know what to do thanks again:O) this thread is done.
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