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Old 08-11-2017, 10:11 AM   #1
rickhz
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Transfer switch question

My trailer had a generator, but it had been removed by the time I had purchased the trailer used. I could see that they had cut the A/C line close to the generator and I thought that I just had to splice in a 30a cord to get it back up and running with an external generator. Come to find out they had cut the A/C line from both ends, removed the transfer switch, and installed a junction box in it's place.

The trailer itself is setup for 50amp service.

My question is, do I need a 50 amp switch, or just a 30 amp switch since I am only running a small generator?
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Old 08-11-2017, 12:03 PM   #2
JRTJH
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I've never thought along the lines of your question before, so I just looked at 5 or 6 transfer switch schematics online. ALL of them have line power flowing through the contacts to from the line voltage (50 amps) to the circuit breaker panel. So, should you install a 30 amp rated transfer switch, the first connection would be to a 50 amp power source. That's 20 amps over the rating of the switch.

Another way to look at it: You'll be routing 50 amps of power from the campground pedestal to the switch and from the switch to the circuit breaker panel in the trailer. When you activate the generator, you'll be routing a "smaller amperage" to the switch and from the switch to the circuit breaker panel. So, when on campground power you would be "overpowering" your transfer switch.

You need a transfer switch that matches the rating of ALL power that will be applied to it. What you'll be doing (if I understand your question correctly) is applying 50 amps of input power to the line leads, 30 amps to the generator leads and depending on the power source, providing either 50 amps or 30 amps to the circuit breaker panel. If you do that with a 30 amp transfer switch, when you're using shore power, you'll be sending 50 amps through that switch and probably overload it.

I don't think you can do that safely with a 30 amp transfer switch.
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Old 08-11-2017, 01:46 PM   #3
rickhz
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Thank you. You understood exactly what I needed to do.

I had a feeling the 50a would be the right switch. I just didn't want to spend the extra money if it wasn't necessary.
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Old 08-15-2017, 10:15 AM   #4
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It's always something...

I installed a TRC 40100 transfer switch this morning. Before installing the switch I tested my new Champion generator by plugging the 50a RV cable into an adapter and then into the 30a receptacle on the generator. Both my 15k and 13.5k A/C units started and ran fine like that (separately).

Now with the transfer switch in the circuit, the 15k A/C will no longer start. The relays chatter in the transfer switch. Will a cheap "hard start capacitor" fix this, or do I need to go with the more expensive Microair https://www.microair.net/collections...nt=30176048267 unit?
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Old 08-15-2017, 10:27 AM   #5
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I'd first look at the installation. Possibly the transfer switch contacts are corroded, misaligned or otherwise not making good contact??? If things worked before, they "should" work now. If they don't, chances are almost 100% that it's something you did or something you added to the system that caused the problem. My guess is either a wiring connection that isn't tight or a bad contact on the transfer switch. Remember, like our "infamous Chinese tires" that transfer switch almost certainly comes from the same place, just a different factory..... <sigh>
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Old 08-15-2017, 11:18 AM   #6
rickhz
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Lovely, a bad box hadn't crossed my mind.

What is different is that the generator's 25ft 30a cable is only 10 gauge.

When I first tested, I was running a 25ft 8 gauge 50a cable through a short adapter cable.
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Old 08-15-2017, 11:27 AM   #7
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Sounds like you are having voltage drop at the contactors in the transfer switch. I'm sure it would work fine with just the generator, but you are putting a load on the circuit causing voltage drop on the circuit and transfer switch. (Same power operating the transfer switch) One way to check is to put a volt meter on the circuit during "start-up" of the A/C. This will tell you how much voltage drop there is. Low voltage will cause contactors to chatter!
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Old 08-16-2017, 04:48 AM   #8
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Quote:
Originally Posted by MickLittle View Post
Sounds like you are having voltage drop at the contactors in the transfer switch. I'm sure it would work fine with just the generator, but you are putting a load on the circuit causing voltage drop on the circuit and transfer switch. (Same power operating the transfer switch) One way to check is to put a volt meter on the circuit during "start-up" of the A/C. This will tell you how much voltage drop there is. Low voltage will cause contactors to chatter!
Yep, that or there's enough of a surge with the AC to cause the contacts to chatter because the generator cant handle it well. I have the same issue with the contactors in my hardwired Progressive Ind EMS and my Yamaha. Doesn't happen with a Honda but the V1 Yamaha does not have enough surge capacity when running through the EMS.
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Old 08-21-2017, 04:50 PM   #9
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I have a mobile RV guy coming out to install a Microair on the 15k Wednesday. I'll give an update as to whether or not it solves the problem.
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Old 08-21-2017, 05:36 PM   #10
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I have a mobile RV guy coming out to install a Microair on the 15k Wednesday. I'll give an update as to whether or not it solves the problem.
I just installed one and my 15k AC starts from eco mode on both a 2000w Honda (expensive) and Kipor (cheap)
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Old 09-11-2017, 04:43 PM   #11
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Originally Posted by rickhz View Post

Now with the transfer switch in the circuit, the 15k A/C will no longer start. The relays chatter in the transfer switch. Will a cheap "hard start capacitor" fix this, or do I need to go with the more expensive Microair https://www.microair.net/collections...nt=30176048267 unit?
I had a similar problem. My automatic transfer switch had a low voltage sensor and it would kick out the relay when I turned on the AC. My generator is a Honda EU3000 and it struggles for a second before the engine speeds up. The transfer switch also had an irritating hum all the time.

I fixed my problems with a manual transfer switch. I am very happy with it.

Read about it here:

http://bobbystuff.com/rv/182/generat...ransfer-switch

Bobby
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