Inverter + distance question

Hello all,

System is slowly coming together. I did switch from a 12V to a 24V system for a few reasons. I do have a question maybe someone can help with:

I need to run a small inverter (24VDC to 115VAC - 400 W to power my cable modem and wireless router) from the load center in the house. The load center is fed by 85 feet of 2 AWG wire from the garage. Calculated 15A draw at the load center for the inverter. Other than the obvious not exceeding the carry capacity of the wire within 5% loss, any other issues that may come up? Thanks.

Comments

  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Inverter + distance question

    What is the voltage to the CC from the PV? I assume this is the voltage you are sending to the CC then 24V to the battery...? or are you talking 120V?
     
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  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Inverter + distance question
    King-01 wrote: »
    Hello all,

    System is slowly coming together. I did switch from a 12V to a 24V system for a few reasons. I do have a question maybe someone can help with:

    I need to run a small inverter (24VDC to 115VAC - 400 W to power my cable modem and wireless router) from the load center in the house. The load center is fed by 85 feet of 2 AWG wire from the garage. Calculated 15A draw at the load center for the inverter. Other than the obvious not exceeding the carry capacity of the wire within 5% loss, any other issues that may come up? Thanks.

    The term "load center" implies a 120/240 VAC distribution. As such it is incongruous with "run a small inverter".

    85 feet of 2 AWG indicates a high current level, which is either indicative of low Voltage DC or an AC trunk line.

    15 Amp draw sounds like a standard 120 VAC circuit as 400 Watts on 24 VDC is going to be higher than that (about 17 Amps, not including low Voltage conditions or surge demand allowance).

    5% loss is probably more than you want anywhere in the system.

    Now if you are saying your 24 Volts will run 85 feet on 2 AWG and you estimate the maximum current to be 15 Amps then you would have less than 2% Voltage drop under those conditions.

    2 AWG copper will handle about 100 Amps maximum. At that level and 24 Volts expect 12% V-drop. At 120 Volts expect <3% V-drop.

    It all depends on Voltage, current, wire size, and length.
  • King-01King-01 Registered Users Posts: 28
    Re: Inverter + distance question

    Let me expand:

    Batteries in garage are at 26.8V DC.

    2 AWG wire runs 85 ft to a Square D QO load center and QO breakers (rated up to 48V DC). Inverter would be run off of a circuit breaker.

    Total amp draw through the 85 ft of 2 AWG is around 45A, keeping it at approx 5% loss.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Inverter + distance question
    King-01 wrote: »
    Let me expand:

    Batteries in garage are at 26.8V DC.

    2 AWG wire runs 85 ft to a Square D QO load center and QO breakers (rated up to 48V DC). Inverter would be run off of a circuit breaker.

    Total amp draw through the 85 ft of 2 AWG is around 45A, keeping it at approx 5% loss.

    Okay, that all makes sense and is quite correct by my calculations as well.

    So long as the battery or termination point of that 2 AWG is protected against over-current, all is well. Under heavy load (on the batteries, especially as they become more discharged) the inverter may 'see' Voltage low enough to cause it to shut down, depending on what its LVD is at.
  • King-01King-01 Registered Users Posts: 28
    Re: Inverter + distance question
    Okay, that all makes sense and is quite correct by my calculations as well.

    So long as the battery or termination point of that 2 AWG is protected against over-current, all is well. Under heavy load (on the batteries, especially as they become more discharged) the inverter may 'see' Voltage low enough to cause it to shut down, depending on what its LVD is at.

    Class T fuse where it leaves the garage, along with a battery disconnect. LVD not an issue, battery capacity is more than sufficient for both the garage system and house system to run at the same time for a while.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Inverter + distance question
    King-01 wrote: »
    Class T fuse where it leaves the garage, along with a battery disconnect. LVD not an issue, battery capacity is more than sufficient for both the garage system and house system to run at the same time for a while.

    Then all is good. :D
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: Inverter + distance question

    However the general case is that the inverter is located near the battery, then run AC the distance? Whats to stop you doing that?
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  • oil pan 4oil pan 4 Solar Expert Posts: 766 ✭✭✭✭
    Re: Inverter + distance question

    Why do people like running low voltage DC long distances?
    2 gauge wire is very expensive.
    That 85 amp 24 volt load could easily be handled by a length of far cheaper 12/2 gauge UF wire if inverted 120 volts AC or 14 gauge wire if inverted to 240 volts AC.

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  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Inverter + distance question

    I think a couple of you may have missed the fact that the LVDC wiring is already in place.
    Why, I don't know.
    Putting in additional wiring to run AC in from the garage is evidently not desirable in this case.

    But as a rule the longest runs should always be done at the highest Voltage.
  • oil pan 4oil pan 4 Solar Expert Posts: 766 ✭✭✭✭
    Re: Inverter + distance question

    Yeah I saw that it was already there.
    I just want to understand the fascination with long runs of low voltage DC.

    Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

    Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

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