Inverter problem. Input voltage too high...


New member
Hi gang, I have a recurring problem that should be easy to solve, but corporate politics are making it ridiculous. I build custom vans for a non-profit organization. They are governed by committee, and a committee of people who know NOTHNG, yet think they know better than we do.
Short story- The Samlex SAM3000-12 inverters see 14.4v when the truck is running. This causes a GFCI receptacle to see too much ac voltage, and shut down.

Long story- Mercedes evidently made a change to the ‘19 Sprinter and added an internal Automatic Charge Relay/battery separator. These vans are the only ones with the issue. On the ‘18s, we installed a Blue Sea ACR, and didn’t have the problem.
Now... the GFCI in question does not function properly anyway due to the limitations of the modified sine wave inverter. It SHOULD just be replaced with a standard receptacle, yet some committee member decided hat not having a GFCI “will kill people”, and even with the explanation, corporate won’t hear it.
The end users are on our side, and just want a solution. They need the inverter to function with the truck running.

My thought is some form of voltage regulator?.?. Either on the 12v input, or the 120ac output. I find some tiny, cheap adjustable regulators, but this needs to be bulletproof. Failure is not an option. It also can NOT require any input or attention from the users. Set it and forget it...
It must be small to allow for mounting either inside the seatbase with the rest of the electrical components, or underhood if it’s on the 12v side.

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Engineer In Residence
Have you actually measured the voltage on the inverter output? A good inverter should have an output voltage spike due to a minor variance in input voltage.

The factory data sheet lists the following. 15VDC is the max input. Note that the output voltage range is plus 13%, or 130VAC (RMS). Check the datasheet for the GFCI. If possible change to a GFCI that can tolerate 130VAC. Also verify if the output voltage is actually getting that high.

Input Voltage Range 10.5 VDC to 15.0 (+/- 0.5) VDC
Output Voltage Wave Form Modified Sine Wave
Output Voltage 115 VAC Output Voltage Regulation +13% / - 0%
Output Frequency 60 Hz ± 5%


Well-known member
Good luck regulating 5000W (>415A) of surge current.. Your just going to have to convince your committee that the safest thing is to throw your inverter in the garbage because whatever you try to bolt onto it is going to be a bigger danger than just buying the proper gear... so they can have this inverter if they really want it, but its not going to work.. cuz, well.. it doesn't.


Engineer In Residence
I wonder if swapping to a different style of protection would be workable, ELCI maybe?


Engineer In Residence
Looking at the inverter spec sheet, the neutral is floating, so unless you are bonding it to ground at your distribution panel, or you have a transfer switch, the GFCI may not function properly.

Do these vehicles have a shore power connection?


Active member
If the GFCI is tripping with and input of 14.4VDC it would seem to be a warranty issue.

GFCI tests for leaking current. Increased voltage would cause a GFCI to trip if there was something funny with the GFCI or the wiring.

The committee member is right in some aspect.....if the AC output of the inverter is grounded internally to the case the GFCI should not be removed unless there is another GFCI in the circuit