gfci and 120/12v converters

[greenkarson]

sorry if this is in the wrong section.  But after googling my problem i found every one has a different answer.  so here it is
    at a campsite with my (new to me) camper last summer the electric hook up was too far away to run my big heavy 30amp cord.  So i ran a smaller gauge cord to the standard 120v double plug.  But it would immediately trip the gfci in the plug. so after a frustrating weekend I cam home and plugged into the gfci plug at the house with a longer extension cord as well.  with the same results tripping the gfci
I didn't want to run anything heavy with the long cord just keep the battery's topped up and maybe a light or two.  so last year in frustration i cut the ground off the cord and every thing ran fine.
   So this week i decided to try to get to the bottome of it.  And here is what i came up with

test 1
i disconnected the 120/12v converter from the power supply and started with the 120v circuits.  Every thing ran fine never tripped the gfci.
test 2
removed all the 12v circuits from the output side of the converter powered up. gfi tripped immediately.
so i knew the gfci tripping had nothing to do with the circuits or plugs through out the trailer
test 3
removed the ground wires from the bus bar in the control panel and powered up with only the converter/charger (low battery) on and microwave display screen and a couple small lights on.  re connected all the grounds back to the buss bar with power on gfci still never tripped.  until i turned the converter breaker off the on again.
test 4
with everything wired up again slowly reset gfci push button  and it never tripped converter was on. so just to see what would happen i turned the micro wave on just to see if it could handle the surge. and sure enough the gfci tripped as soon as the microwave cut it. tried this several times with the same results

So I'm thinking that the gfci must be just tripping from the surge load and that the trailer has no actual wiring problems(i tested the extension cord first it was ok)

does this seem logical that a surge load like a converter and a micro wave at the same time with a long cord could trip a gfci?

thanks again

[vtpeaknik]

I don't know about your "converter", but my Iota DLS-55 (converts 120VAC to 12VDC at up to 55 amps) makes an impressive spark/pop-sound when you first plug it in to an AC outlet.  Seems that there is a huge inrush of current to capacitors in its circuit.  This is not an AC-transformer-based charger, rather an efficient switching-mode circuit, presumably the input part of the circuit is diodes and large filter caps to turn the AC into DC?

Perhaps you can set up a way to slow-start the "converter".  E.g., add a switch that disconnects it from the AC supply, but bypass that switch with a resistor chosen to limit the inrush current to just a few amps.  E.g., a 20-ohm resistor would limit it to 6 amps even if the converter side is a dead short.  Also would help if you can disconnect the load (battery) from the converter.  Then plug in with both switches off, after a few seconds turn AC side on, then DC side.  That way the resistor does not need to be huge (in power handling capability) since the converter will be running in "low idle" after the initial rush and until the load is connected.

Or, instead of a resistor, use a light bulb, e.g., a 100W incandescent bulb (for 120VAC) would limit the current to about 1 amp, but allow more than that in the first instant before it heats up.  Sure cheaper than a large resistor...

[OperaHouse]

I think you are possibly dealong with excessive capacitance to ground.  Almost all electronicdevices now have a small capacitor to ground.  Add a number of devices and that current will be enough to trip the GFI.  The long extension cord adds even more capacitance.  Cutting the ground and it working adds credence to this theory. 

[greenkarson]

thanks for the speedy replys!
operahouse if that was the case would'nt it pop the gfci as soon as every thing was turned on every time.  Even when i reset the gfci slowly?  in the last test the converter was running and the microwave was on just not in cook mode and it never tripped untill i hit the cook button putting on the large load.

[OperaHouse]

Amicrowave is not resistive load.  It adds considerable harmonic distortion to the line voltage with a long lead.  These harmonics are higher frequencies and add even higher currents through capacitance to ground.  This is just one of the possibilities I would look at

[GreatBallofFire]

 so last year in frustration i cut the ground off the cord and every thing ran fine.

Nothing is wrong, the ground fault is doing exactly what it is designed to do. The circuit senses the change relative to ground and reacts. Once you cut the ground off the cord, any difference relative to ground no longer mattered. As other posters have already mentioned, switching inverters often have some resistance or capacitance relative to their ground that the GFI probably doesn't like.

-Mark