Forum Discussion

Kayteg1's avatar
Kayteg1
Explorer II
Apr 22, 2016

? for electric/electronic experts.

I have camper with build in converter that also has 120V breakers on it.
Recently I added electric element for water heater and hard wire it to AC breaker. The switch on the wall has small light that comes on when heater is on.
I also added 1750W inverter, that is directly hook up to the battery and I just plug coffee maker or microwave to it when I need it.
Today just for the sake of it, I tried to to run AC off my 1750 inverter. I pulled main camper cable and plug it into inverter with converter breaker off. AC did not start, hesitating for few seconds before inverter went to overload, but what I noticed, the control light on heater element was on.
I flipped all 120V breakers off and the light was still on, regardless if the switch was on or off.
So somehow the inverter power with shore cord on it back-feed to the switch.
I know those control lights can run on big margin of voltage and I think that with my mechanical education I am pretty good in electrics, but that keeps me scratching my head with no idea.
So one more time - 120V on shore cable coming from inverter, with all 120 breakers off feeds somehow via ground and neutral wires to keep the switch control light on.
What da heck?
  • grizzzman's avatar
    grizzzman
    Explorer
    Apr 22, 2016
    How is the switch wired? as an example mine runs on 12 volts (the switch) and triggers a relay to apply power. 2 You CAN NOT run your A/C with such a small inverter and if you could you would need a LARGE battery bank to maintain it.

    Good Luck!
  • Kayteg1's avatar
    Kayteg1
    Explorer II
    Apr 22, 2016
    Switch light is wired between ground and the element hot wire.
    No 12v used in this set.
    I am thinking the inverter send some kind of ghost voltage via neutral wire and that backfeeds to the light via the heater.
    Not real life problem as I will not use that kind of configuration, but having light coming on when switch is off sure makes your hair standing.
  • Chris_Bryant's avatar
    Chris_Bryant
    Explorer II
    Apr 22, 2016
    Sounds like a floating neutral. You might measure 60 volts between neutral and ground, and 60 volts between hot and ground.
  • Kayteg1's avatar
    Kayteg1
    Explorer II
    Apr 22, 2016
    Chris Bryant wrote:
    Sounds like a floating neutral. You might measure 60 volts between neutral and ground, and 60 volts between hot and ground.


    English Please :)
  • time2roll's avatar
    time2roll
    Nomad
    Apr 22, 2016
    Kayteg1 wrote:
    Chris Bryant wrote:
    Sounds like a floating neutral. You might measure 60 volts between neutral and ground, and 60 volts between hot and ground.


    English Please :)
    Go ahead and measure the voltages and post them up.

    BTW please also post the brand and model number of the inverter.
  • Kayteg1's avatar
    Kayteg1
    Explorer II
    Apr 22, 2016
    MotoMaster Eliminator inverter.
    I measured 102V between hot and neutral (is that becouse of square wave?)
    and 9V between ground and each prong.
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Apr 22, 2016
    Good Lord!
    Do you lash a ten year old because he cannot run when burdened with a sack of portland cement? "Hey Dewey! Shake the jar and see if they fight"

    102 volts. Check your battery connections because it is something you can do for free. You ain't gonna like hearing the truth. Mix up a big martini and relax.

    MSW uses stepped waveform. It has a peak but it is somewhere in the RMS vicinity, County? State? Hemisphere?

    Your inverter is perverted. It hates you.

    Load it with a 1,500 watt heater. Wear a mask and gloves. Put the local recycle center on "auto-dial". Right after "Fire Department"

    Seriously. Treat the device as being damaged. Protect yourself when testing. This is no joke. If your meter is any good, the inverter is history.
  • time2roll's avatar
    time2roll
    Nomad
    Apr 22, 2016
    Considering what you have... I think all is working as designed even if a bit funky.

    I believe that inverter is designed to operate separate appliances plugged directly into it.
    Not designed to drive a subpanel (RV).
  • DrewE's avatar
    DrewE
    Explorer II
    Apr 22, 2016
    The low reading could very well be due to the non-sine waveform. Most cheaper multimeters, and some not so inexpensive ones, do not show accurate RMS values for non-sinusoidal AC waveforms. Typically they are actually responding to either the peak or the average voltage with the output scaled to show an RMS voltage for a sine wave input. (I think the average responding meters are more common.)

    Particularly if the glow is rather faint, your guess of the pilot light responding to voltage from the neutral (which is floating on your inverter) is reasonable, especially if the light is a neon light. The pilot should be wired between the switched hot and the neutral, rather than the switched hot and ground; the safety ground should not be used as a current carrying conductor in an AC circuit, even for an itsy-bitsy pilot light. Fixing it would also cure the phantom illumination, assuming that's what the cause is.
  • Kayteg1's avatar
    Kayteg1
    Explorer II
    Apr 22, 2016
    MEXICOWANDERER wrote:


    Load it with a 1,500 watt heater. Wear a mask and gloves. Put the local recycle center on "auto-dial". Right after "Fire Department"

    .


    That's a miss. I did what you said and the heater works just fine, although operating from single battery low voltage warning come on.
    In strange way the 102V no load come up to 110V under the load.
    The inverter operates the panel as well, just will not start up AC.
    So with all the suggested tests, I can see that the 9V inverter sends between ground and neutral is what was turning the switch light on.
    Anybody having different idea, let me know?
    EDIT Drew typed at the same time I was typing above and sounds like we come to the same conclusions. He beat me to it. ;)
    Thanks guys.
    This is heater wiring. It might not be clear, but Camco is using ground for control light.

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