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Old 05-07-2011, 12:09   #1
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Backfeed error: Xantrex w/ Koehler Generator

Our Koehler 6.5CZ has recently been repaired. Power is controlled through a Xantrex MS2000. The generator was started and ran without issues for about 30 minutes. The voltage on the Xantrex then increased to an unacceptable limit and the generator was shut down manually.

The Xantrex continues to work fine when using shore power. A transfer switch allows us to change from shore power to generator power.

The Xantrex was shut down and restarted. The Koehler generator was started and produced 120 V at 60 Hz. The Xantrex would not charge the batteries. A backfeed error occurred.

Please tell us of anything you can suggest to correct the issue.

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Old 06-07-2011, 04:15   #2
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Re: Backfeed error: Xantrex w/ Koehler Generator

Greetings and welcome aboard the CF, TravelingNanny.

Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"

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Old 09-07-2011, 02:27   #3
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Re: Backfeed error: Xantrex w/ Koehler Generator

Small gensets have notoriously poor output characteristics; voltage, waveform and frequency. The power into the MS2000 must be "qualified" in order to be passed through.
Unfortunately, the MS2000 has been discontinued so the manual is not available on line. There are, as memory serves, settings for max and min voltage and frequency that you can adjust to accept less than mains quality incoming power. Maneuvering
through the MS2000 menu system is very much like following Alice down the rabbit hole so take notes as you go, read carefully, and good luck!!

Charlie Johnson
JTB Marine Corporation
"The Devil is in the details and so is salvation."
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Old 09-07-2011, 16:51   #4
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Re: Backfeed error: Xantrex w/ Koehler Generator

It sounds like when the generator was repaired that it wasn't wired back up correctly. I don't know the details of the MS2000, but a backfeed error would suggest that the outputs of the MS2000 and the generator are connected together, which they should never be. The gen output (and shore power) should go to the MS2000 AC input. The loads are then connected to the MS2000 AC output, and anytime there is power on the input side it gets passed through to the loads and the charger runs.

I don't know the nature of the generator repair and whether this is plausible, but it's worth consideration. It would explain the symptoms that you describe.

Also keep in mind that there are lots of different bypass and selector switch possibilities that your boat could include as well which would complicate things further.
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