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Author Topic: Transfer Switch  (Read 1489 times)
AndyG
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« on: March 25, 2013, 07:46:25 PM »

I decided to exercise the generator on the Freightliner today.  The engine started fine and ran normally but I was not getting power into the coach.  Never had any problems before.  I checked breakers and fuses and all was OK.  I decided to stop the generator and plug into shore power.  Everything worked and the transfer switch made its usual humming noise.  I tried the generator again and everything worked as it should.  Something was "sticking" in the transfer switch.  Is there any type of periodic maintenance that should be done to automatic transfer switches?  Part of the reason that I bought this rig is the ability to use the generator for backup power for my house.  If the power went out today I would have been left out in the cold.
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belfert
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« Reply #1 on: March 25, 2013, 07:57:47 PM »

Are you sure the generator is supplying power to the transfer switch?  I had the same problem and thought it was the transfer switch too.  I finally figured out the generator wasn't putting out power when this happened.  The problem only happened every 2nd or 3rd start.  It turned out my brushes were bad and I had to replace them.
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Brian Elfert - 1995 Dina Viaggio 1000 Series 60/B500 - 75% done but usable - Minneapolis, MN
AndyG
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« Reply #2 on: March 25, 2013, 08:01:52 PM »

I'm not sure of anything.  The generator did work fine the second time that I tried it.  Ths was after connecting to shore power then unplugging it.
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muldoonman
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« Reply #3 on: March 26, 2013, 05:57:18 AM »

What kind of generator? Having same problem on my 15 kw Kubota gen set with 187 hours on it. Justin Griffith off the board here has it and gen is only putting out 45 volts at transfer switch. Had problem before a couple months back and it was main breaker tripped. Gonna pull out today and check board. The way mine is mounted,  have to pull (slide) all the way out to reach gen on back on Kubota. Shore Power side works fine so transfer switch is working. Will let you know what it is on mine. Could be the same problem.

glen
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AndyG
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« Reply #4 on: March 26, 2013, 07:45:09 AM »

I have a 7KW Power Tech (PTS) diesel generator.  The automatic transfer switch is separate from the generator and I don't know the brand or model of it right now.  I suspect that the trouble was in the transfer switch but I'm not sure.  The second time I ran it everything works fine. 
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Lin
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« Reply #5 on: March 26, 2013, 08:59:48 AM »

I would think it would be useful to know what powers the transfer switch.  For example, you say that when you plugged into shore power the transfer switch had its usual hum.  That would seem to indicate that the transfer switch is powered by the shore line, meaning that that it defaults to the generator when there is not shore power and only comes into play when there is.  If that is the case, the failure would not have anything to do with the generator output, but more likely something with the switch itself or wiring.  The point is that knowing what powers the switch will make diagnosing the problem easier.
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Sam 4106
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« Reply #6 on: March 26, 2013, 10:30:31 AM »

Lin,

The typical RV transfer switch has the generator as the primary. For instance, if the shore power is 20 amp, and you want to use more power, you can start the generator to provide it, without disconnecting the shore power. However, a transfer switch has two contactors that both require power to activate. The shore power side activates immediately, but the generator side has a time delay, to allow the generator to get up to speed, before it activates. Usually about 30 seconds. When neither shore nor generator are providing power both contactors are open, so if you have an inverter in the system no power can back feed through the transfer switch. The hum, that Andy referred to, is from the electromagnet that engages the contactor. I hope this helps you to understand how a transfer switch works.

Good luck, Sam
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Lin
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« Reply #7 on: March 26, 2013, 11:25:13 AM »

Sam, I only use the transfer switch to go between the inverter and live power sources.  I switch from the generator to shore by moving a plug.  When there is no live sources (gen or shore) the transfer switch gets no power and therefore is in the default position, which allows the bus to be powered by the inverter.  However, if either of the live power sources are brought online, the transfer switch is activated and switches.  That is the only time that there could be any hum or similar in the switch.  If there is no AC source, the switch is just unpowered. When an AC source is activated, there is a delay before it transfers over, but that has nothing to do with whether it is shore or gen; they're both the same to the switch.  I suppose that the switch you are referring to is different than what I have.
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gus
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« Reply #8 on: March 26, 2013, 12:20:38 PM »

My system is the same as Lin's, a simple plug - no switches of any kind to fail. Of course this has its disadvantages in rain!
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AndyG
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« Reply #9 on: March 26, 2013, 12:34:23 PM »

My unit does not have an inverter.  The automatic transfer switch changes between the generator and shore power.  I suspect that the switch did not work properly and I'm curious if there is any preventative maintenance which should be done. 
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robertglines1
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« Reply #10 on: March 26, 2013, 12:44:38 PM »

Contacts are probably sealed unit. If not clean contacts with electrical contact cleaner. By the way have extra 30amp(new )transfer switch on shelf if you need it. Dad.   Bob
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Bob@Judy  98 XLE prevost with 3 slides --Home done---last one! SW INdiana
Sam 4106
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« Reply #11 on: March 26, 2013, 12:48:28 PM »

AndyG,

The only preventive maintenance I know of is to check the connections. You may have a loose wire connection that is only making contact intermittently. I had some loose connections in my transfer switch, so I know it can happen. It would be good to check the connections in the generator and circuit breaker panels, too. Please let us know when you solve the problem.

Good luck, Sam
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justin25taylor
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« Reply #12 on: March 26, 2013, 04:52:04 PM »

Andy,
The advice you have gotten is about all the maintenance you can do. Sam's advice should be followed. Those connections can sure get loose. That was Glen's problem (Muldoonman). We will get to his issue in a second.

What I would do is pop the cover off the transfer switch and see if it has one relay or two. Some of the less expensive transfer switches have only one relay. They usually default to the generator as was stated above. 

If you have a voltmeter and are not afraid to use it, check the leads coming into the transfer switch from the generator and see if you have voltage. If you do, the coil in the contactor/relay is not working properly, or is burned up. If you do not have any power from genset, check the breaker on the genset. If that does not get you going, let us know so we can help you troubleshoot the generator.

For those who are interested in Glen's problem, here it goes:

He brought me the coach and said the generator would not produce power.

I checked power at transfer switch and had about 60 volts from L-1 to N or L-2 to N, but nothing across L-1/L-2. I went ahead and flashed the field knowing it most likely was a bad regulator. Flashing did nothing.
I started to prepare the generator to come out. While doing so, I remembered not long ago, he had a no power issue and the main breaker was tripped on the generator. I decided I had better pull the cover off of the breaker enclosure on the genset before I went any farther. When I opened it up, I found burned wires, melted plastic and just a general mess.

The problem turned out to be one of the neutral wires had burned through the terminal block inside the breaker box. The breaker was hanging by the wires in the bottom and the top was held on by magic.
Upon really looking at the connections in the box, everything was loose. I showed glen, we bought a new enclosure/breaker and problem was solved.

He also has a small load imbalance between L-1 and L-2. This can cause generator failure as well as make the neutral carry too much current. I will juggle some loads around tomorrow and see if I can't get things a little closer. All the loads in his coach are 120 volt, and with the amenities that coach has, it needs all 50 amps. If he did not want to keep the option of powering his home from the coach, I would recommend he let me reconfigure the genset to 120 volt only.

Sorry for the novel above. Maybe someday I should start a blog or something...... Wink

Good Luck!
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AndyG
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« Reply #13 on: March 26, 2013, 06:59:12 PM »

Thanks to everyone fore their tips.  I ran the genset again today and it is still working fine.  After I move the toter away from the steam engine far enough to get the bay door open I will check the connections to the switch. 
Justin's post reminded me of a project that I did last spring.  The genset was set up for 120V only and I wanted to intstall a 240V plug for backup power to the house.  This unit has 2 legs at 120V.  The manufacturer had simply put a jumper wire between the two circuit breakers in the genset control box to balance the load.  To get 240V out you usually remove the jumper wire.  I did it a little differently.  I put a heavy duty toggle switch in the jumper wire.  For normal 120V operation in the coach the toggle switch stays in the on postion which mimmicks the original jumper wire.  For 240V I move the toggle to the off position which mimmicks removal of the jumper wire.  This idea may help Justin & Glen with their load balancing problem.
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justin25taylor
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« Reply #14 on: March 26, 2013, 08:17:26 PM »

Glad it's working Andy.
Excellent idea on the switch!!
Thanks.
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