Author Topic: Transfer Relays  (Read 3445 times)

Fred Brooks

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Transfer Relays
« on: February 19, 2017, 10:49:20 PM »
    Greetings Guys,
  I thought we should re-visit this topic for the benefit of the newer owners of Beaver motorhomes or any luxury coach with a 50 amp shore cord.
   The reason I am bringing this up is because it is easy to hurt these devices if you are unaware of proper protocol when activating the Transfer Relay. As a luxury coach technician, I have changed more than 25 of these relays and the majority of them could have been prevented had the owner not abused them. Some of the newer transfer relays have built-in Surge Protectors and the cost can exceed $800.00 plus the labor to replace them.
    A transfer relay normally allows the power from the shore cord to pass thru it and go to the circuit breaker box inside the coach.
When the generator is started, it activates a 30 second delay relay and then activates the transfer relay. The transfer relay disconnects the shore cord input and connects the generator output to the coach circuit breaker box.
  Here is the issue, If you have any large loads currently turned on, you are transferring those high amperage loads thru the contactors of the relays. This over time burns and chars the surface of the contactors and causes them not to mate properly. This will give you a "buzzing noise" and eventually a failure.
   If you will  always turn off all large "loads" before plugging into shore power or starting your generator you will prevent the "sparks and burning" on the surface of the contactors.
    Hope this helps, Fred......Happy Trails
Fred & Cindy Brooks
2000 Marquis, Jasper
C-12 Wild Cat (U of A)
2014 Honda CRV
Proverbs 3: 5 & 6
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LaMonte Monnell

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Re: Transfer Relays
« Reply #1 on: February 20, 2017, 12:54:33 AM »
Thanks for the information Fred. After spending just shy of $3000 to get my Onan7500 Qd back in shape I don't need any more issues for a while.
Lamonte & Patti Monnell
2001 Beaver Contessa Naples DP 40' 2 slides
CAT 3126B
2021 Chevrolet Silverado Trail Boss

Weeki Wachee,Fl
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Joel Ashley

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Re: Transfer Relays
« Reply #2 on: February 20, 2017, 12:59:24 AM »
Thank you, Fred, for bringing this to new owners' attention again.  I might add that though the situation is unusual where one would have a heavy load already engaged when plugging in or starting the generator, it can happen. 

Arcing can occur for example if, when breaking camp, a portable heater had been left on.  I don't know that it would arc so much upon disconnect, but it likely would when you hook up or start the genset next time.  Perhaps a coffeemaker was on at last disconnect;  but some appliances may have circuits that don't auto restart motors or elements after a power loss - a switch must be deliberately reset.  I wouldn't worry much about a regular RV fridge that takes a while to auto-switch from gas to electric, but if you've converted to it, a residential one might pull some juice and cause arc burns upon a subsequent power-up.

One concern that comes to mind is a hydronic electric element switch, left on at the last parking spot, that might draw some juice and cause sparking at the transfer contacts upon again plugging in or powering the genset.  If the coach sat long after coming off the road, so that engine heat recycling had dissipated significantly from the hydronic unit, and the diesel burner was off, the element could conceivably move some juice across the contacts as they meet again.  That little switch can easily be forgotten when breaking camp.

It's just a good idea to make sure such things are off when breaking camp.  But where even the experienced among us can slip is when there's a sudden power outage in a park, and in our anxiousness to check it out we overlook shutting off the heater, hydronic element, residential fridge, or whatever might have been on at the time.

Joel
« Last Edit: February 20, 2017, 01:01:15 AM by Joel Ashley »
Joel and Lee Rae Ashley
Clackamas, Oregon
36.9 ft. 2006 Monterey Ventura IV, aka"Monty Rae"
C9 400HP Cat
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Lee Welbanks

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Re: Transfer Relays
« Reply #3 on: February 21, 2017, 04:00:54 AM »
I have always make it a practice when setting up at a new site with the gen running A/C units on to shut down everything including the gen before connecting to shoe power, once connected start all the A/C's and such back up. Joel is correct in make sure the electric side of teh Aqua Hot is off, this little baby pulls around 14 amps. Breaking camp turn everything off then disconnect from shore power, then start gen if needed.
A few minutes without the A/C running is much cheaper than replacing a transfer switch.
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LaMonte Monnell

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Re: Transfer Relays
« Reply #4 on: February 21, 2017, 04:35:08 AM »
Another thing to remember that is very important is not shutting the generator off after removing the load from it. Let it run for 10 minutes or more to cool it down before shutting it off.

I just had my 1000 hour service completed at Cummins Ocala. During that service the rotor was found with a section of magnets that came off. Upon further inspection the stator had several copper windings destroyed on it. They explained that Onan has had an issue with several of this era(2000-2004) 7500QD generators with rotor magnet issues due to the glue they used to install the magnets weakening over time. They now use an entirely different process for this and have no issues today.

The parts are not cheap, and add the labor in it is a costly bill! They told me it wasn't anything I had done wrong but one of those things......still less than a new generator.....
Lamonte & Patti Monnell
2001 Beaver Contessa Naples DP 40' 2 slides
CAT 3126B
2021 Chevrolet Silverado Trail Boss

Weeki Wachee,Fl