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Thread: Connecting Generator and Inverter

  1. #1

    Default Connecting Generator and Inverter

    Ok, we have a 2300 Watt Gasoline Generator, I also have solar which runs off my inverter.

    We have a thick gauge extension cord wired to the mobile home, we than have the male end of that extension cord to plug either into the generator or inverter (depending on what we have running).

    I've built a "Y" with 1 female that plugs into the extension cord wired to house, and 2 males (1 for generator, other for inverter).

    I know that if the generator is running it will not only feed power to the house extension cord, but also feed up through the "Y" back into the inverter (which cant be good).

    So, I wired in a 20AMP light switch between the "Y" section going up to the inverter to shut power off going into the inverter when we have the generator running, that way AC current isnt feeding back up into the inverter outlets.

    Even after wiring the switch it will still show 10-15VAC coming through the other side of the switch which is going into the inverter.

    Is it safe to plug this extension cord and keep it in the inverter if the inverter is off and that light switch is off, even if it still shows 10-15VAC?

    Is it normal to still show small voltage even with a switch off?

    What can I do to safely have both plugged in at all times?, as it is very inconvenient having to switch between the two when we want to run a high powered item (ex: vacuum, fridge, microwave, ac)

    Thank You.

  2. #2

    Default Re: Connecting Generator and Inverter

    What is your inverter? There are many which have AC IN ability to allow them to charge batteries while passing AC loads through to generator or grid power.

    If not, you need to completely disconnect the inverter when running the generator and vice-versa. RV's used to have manual On-Off-On switches for just this purpose. Now they use automatic transfer switches such as this:

    http://store.solar-electric.com/ioitauactrsw.html

    Without knowing the details of your system, it sounds like a bit of voltage is 'leaking' through the neutral wire. In any case, this isn't good: both 'Hot' and 'Neutral' AC lines need to be completely disconnected from one AC source when using another.
    1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

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

  3. #3

    Default Re: Connecting Generator and Inverter

    It is a Pure Sine wave inverter (off brand), 1200W Continuous. Nothing fancy.

    I was thinking the same thing, maybe something is leaking through the neutral.

  4. #4

    Default Re: Connecting Generator and Inverter

    To get a better idea of what's going on, disconnect the inverter and turn it off. There should be no voltage reading across any of its AC out. Run the generator: with the switch off, the part of your 'Y' cable that goes to the inverter should also read zero volts across any combination of the terminals that would connect to the inverter. If there is still some voltage reading or if it only shows up when the cable is connected (but switch off) then there is probably a bad neutral to ground connection or a bad Earth ground. There should be only one neutral-ground connection, and it's usually at the breaker box. Strange and not at all good things can happen if the gen has another neutral-ground or additional Earth ground.

    Again, it's hard to be specific without knowing the actual over-all set up.
    1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

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

  5. #5
    Join Date
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    Default Re: Connecting Generator and Inverter

    If your DVM is very high input impedance you may pick up some reading just by the capacitance coupling within the switch.

    If you put a light load, like a night light on the inactive plug you will likely see the voltage drop to zero.

    Also I assume the inverter you are using is a small H-bridge output type. Both neutral and hot are floating with respect to ground. There is usually a capacitor (about 0.1 uF) from each of the two prongs to the ground terminal of the plug. You need to use a DPDT switch for your A-B switch to avoid having some 'live current' from the neutral line from the small cap to ground. It is just the current through the 0.1 uF cap but it will still give you a 'tickle' if you are standing on earth ground or in contact with anything electrically grounded.

    If your generator is an inverter/generator, at that wattage, it is same floating H-bridge output.
    Last edited by RCinFLA; August 22nd, 2009 at 19:49 PDT.

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