Transfer Switch

[raywaller]

I have a 42 ft, all electric 2005 Travel Supreme Mid Engine coach. My question is "how are the two Magnum inverters connected to the transfer switch that is between the inverters  and shore power or auxiliary generator"?  The inverter that provides power to my microwave has checked good, so the Magnum rep and I now think the problem of "varying" voltage is coming from the transfer switch.

[kaypsmith]

The nature of this is a little confusing, please bear with me on trying to give an answer. Assuming that there is a transfer switch between shore power/generator and the inverters, it would be much like a transfer switch between generator and shore power, it would look for 120 volts from either source and stay switched to which ever is present unless in the case of a regular switch, the generator when is cranked the switch will move to generator power, usually with a delay. Burnt points on a transfer could possibly cause fluctuating power but usually just fail. In the case of a transfer switch between shore/generator and inverter, that switch is usually built into the inverter itself. It will be helpful to know the model number of your Magnum inverters to give a better answer. Also will be helpful to know when the fluctuation occurs, when on shore power, generator, or inverter. Faulty neutral connections can be very annoying and should always be checked for tightness to assure that is not where the problem lies, if you are uncomfortable working with electricity, please have someone that does this type work for a living, check all electrical connections in the coach. If this problem has just started, plug into another CG source to see if the problem goes away.

[wildebill308]

1 hour ago, raywaller said:

I have a 42 ft, all electric 2005 Travel Supreme Mid Engine coach. My question is "how are the two Magnum inverters connected to the transfer switch that is between the inverters  and shore power or auxiliary generator"?  The inverter that provides power to my microwave has checked good, so the Magnum rep and I now think the problem of "varying" voltage is coming from the transfer switch.

I would say the first thing you need to know/prove is the power at the pedestal correct. 

Bill

[raywaller]

The Magnum ME-2012 modified sine wave  inverters (2) came with my 2005 TS-ME coach and have worked fine for years.  It was only after a trip I took and stayed at a Government run travel facility outside Austin TX, and a KOA south of Wichita KS, that my problem started.  The microwave started making strange noises (different from normal), so I thought it was going bad (since it was an original unit).  I keep my coach connected to 50 AMP shore power in my barn, but the microwave problem exists on generator or shore power.  I found the voltage jumping and varying when the microwave runs, but only if it is plugged into outlets supported by one of the inverters; the voltage does not change if the microwave is plugged into outlets supported by the other inverter.  I sent the suspected inverter to a Magnum certified service center, but they said it checks out fine. Since the transfer switch is a common denominator for the shore and generator power sources, I thought I should better understand how it works.  Are the inverters on separate cables from the distribution side of the switch, or are they both on one cable (both inverters being connected in parallel to their incoming ac power). If parallel, then both inverters should be acting the same.  But if there are independent cables from the transfer switch to the inverters, then the transfer switch must have internal contacts/circuitry that might be causing problems for only one of the inverters. Since Travel Supreme is out of business, and I don't have wiring diagrams in the documentation that came with the coach, I decided I better reach out to FMCA members for help on how multiple inverters are normally wired.  All advice/suggestions would be appreciated.   

[kaypsmith]

With your added information, on a 50 amp service, the power incoming to the coach it the pedestal is properly wired, power is 240 volts, 120 volts powered from L1, and 120 volts powered from L2. Yes a 50 amp transfer switch also incorporates L1 and L2 also. Inside the transfer switch there is two sets of contact switches, one from shore power, the other from the generator power. Both sets of contact switches have two contacts one for L1 and the other from L2. Next question for you is does this also happen when running on the generator? If so, then next place to check is the main circuit breaker panel inside the coach, you could have a loose connection there, this has happened to me in the past, turned out to be a faulty breaker. If the problem does go away while on the generator, then I would concur that the problem probably lies within the transfer switch. I looked up your inverter model #ME2012 up, and the transfer of 120 volts input to 120 inverted 120 volts is within the inverter. Best test for the internal transfer switch is to bypass the inverter with the same circuit that the inverter is on, straight to your microwave to see if the problem goes away. Also are the inverters both on the same, or separate battery banks, and have you load tested those batteries?

[richard5933]

Have you pulled the outlet itself? Are the wires going to the outlet properly tightened? Ground well connected?

I'm in agreement that it sounds like you've got a loose connection or ground somewhere.

If the problem was with the transfer switch then the problem should exist on all the outlets fed by that transfer switch. If the problem is the microwave, then it should exist no matter which outlet you're using. Sounds like the outlet itself it the problem, which would mean either the receptacle, the wiring, or the breaker. Could also be the feed connection that brings inverter power to the breaker panel.

My first step would be to shut off all power, open the panel covers, and make certain that every connection is tight and that there are no signs of shorted/arcing wiring.