120v inverter to generator inlet

docwisdom
docwisdom Registered Users Posts: 2
in Off Grid Solar & Battery Systems #1
Good afternoon.

My first post here. Just have an interesting request.

I have a tankless water heater that is natural gas with an electric start. I already have a 240v 4 wire generator inlet on the side of the house with a mechanical interlock.
My question is if I would be able to safely wire the 120v output from an inverter into the generator inlet and power the electric control portion of the water heater and a few lights around the house.
I read this post http://forum.solar-electric.com/showthread.php?11423-Inverter-s-AC-OUT-to-Generator-Inlet-Box and understand the extra load the neutral would be taking. My plan would be to have all circuits off in the house except the water heater and any one or two lighting/plug circuits I may need on-demand.

I would be ok going with a transformer solution as well if anyone knows of any in the $150 or less range. I am only planning on having a 1500-2000 watt inverter running off two marine deep cycle batteries.

Thanks
· Share on Twitter

Comments

  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #2
    Re: 120v inverter to generator inlet
    docwisdom wrote: »
    Good afternoon.

    My first post here. Just have an interesting request.

    I have a tankless water heater that is natural gas with an electric start. I already have a 240v 4 wire generator inlet on the side of the house with a mechanical interlock.
    My question is if I would be able to safely wire the 120v output from an inverter into the generator inlet and power the electric control portion of the water heater and a few lights around the house.
    I read this post http://forum.solar-electric.com/showthread.php?11423-Inverter-s-AC-OUT-to-Generator-Inlet-Box and understand the extra load the neutral would be taking. My plan would be to have all circuits off in the house except the water heater and any one or two lighting/plug circuits I may need on-demand.

    I would be ok going with a transformer solution as well if anyone knows of any in the $150 or less range. I am only planning on having a 1500-2000 watt inverter running off two marine deep cycle batteries.

    Thanks

    Interesting, but not unusual. :-)

    If you have an off-grid inverter which produces a pure sine wave output (furnace controls, etc are notoriously unhappy with Modified Square Wave) and could either get by with feeding just one of the two 120 volt busses in your breaker panel (all of the circuits you need would have to be on the correct bus) or you supply a 120 to 240-with-center-tap transformer or autotransformer component, it should work just fine.

    If you want to try to use an MSW inverter, you also need to be very careful to check whether its AC output is 120 volts to ground or 60 volts to ground on both the hot and neutral wires. If the latter, connecting it to your generator inlet can smoke the inverter if your transfer switch does not disconnect the ground to neutral bond that is part of your existing main panel.
    SMA SB 3000, old BP panels.
    · Share on Twitter
  • docwisdom
    docwisdom Registered Users Posts: 2
    #3
    Re: 120v inverter to generator inlet

    Thanks very much for your reply. Do you have any examples of the transformers you mention? (brands, models?) I did a google search but came up with a lot of different results and am not sure exactly what I am looking for so couldn't decipher it.
    I have not purchased an inverter yet, so I will follow your recommendations for features to look out for.
    I am using an interlock, not a transfer switch.

    Thanks again.
    · Share on Twitter
  • ChrisOlson
    ChrisOlson Banned Posts: 1,807 ✭✭
    #4
    Re: 120v inverter to generator inlet
    docwisdom wrote: »
    Thanks very much for your reply. Do you have any examples of the transformers you mention? (brands, models?)

    If you want a high quality transformer that comes in its own enclosure and is fan cooled, you can get an Outback PSX-240

    Attachment not found.

    The PSX-240 weighs about 50 lbs or so and they usually cost $400-500.
    --
    Chris
    · Share on Twitter
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #5
    Re: 120v inverter to generator inlet

    Unless you have some 240 volt loads you need to power from the inverter, then there is no need for a transformer at all. Just jumper the two "hot" inputs to the generator inlet on the side of the house and feed the same 120 volts from the inverter in on BOTH hot inputs, and the "neutral" from the inverter, in on the neutral line of the same inlet. This will work fine for your 120 volts in house loads. You can make the jumper in the connector from the inverter that plugs into the house generator inlet on the side of the house, so when you unplug the inverter from the house, everything is back to normal. A lot simpler, cheaper and less drag on the inverter, since it doesn't need to power a transformer. Some may warn of overloading the neutral lines in the house, but if your inverter is limited to 1500 to 1800 watts, that's not a concern.
    · Share on Twitter

Categories