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Re: [GMCnet] Auto transfer switch [message #348084 is a reply to message #348079] Wed, 18 September 2019 09:19 Go to previous messageGo to previous message
powwerjon is currently offline  powwerjon   United States
Messages: 849
Registered: March 2013
Karma:
Senior Member
I don’t agree your comments on Transfer switches and RV AC units.

I have had transfer switches on all three of the coaches that I own or have owned. I installed 2 myself and one was already installed on the stretch coach. The transfer switches only have the time delay when they go from shore power to generator power. The 30 second delay is to allow the generator to come up to speed. There is no delay when switching from back to shore power. When I shut my generator off the switch to shore power is almost instantaneous, the power will have a small blip. If your generator is running and your shore power comes back the generator still powers the coach, it doesn’t switch back to shore power.

Now lets discuss AC units. All RV AC units have a time delay relay, typically a 2 minute delay. This is to allow the pressures to equalize in the freon side of the system so the compressor does not start under load and possibly cause the AC breaker to open. It has nothing to do with the transfer switch. If by chance you have a power blip at your campsite and the power just goes off and then back on then the AC unit will not start cooling until the time delay relay times out, only the fan runs. Now if you turn on the AC unit the compressor will start or if you have the AC in Heat ( if it has a heat strip ) or just in FAN mode, it will start with no time delay.

In a sense the transfer switch and AC time delay relay work together to help both the generator and AC unit.

As alway comments are welcome.

J.R. Wright
GMC Great Laker MHC
GMCGL Tech Editor
GMC Eastern States Charter Member
GMCMI
78 GMC Buskirk 29.5’ Stretch
75 GMC Avion (Under Reconstruction)
Michigan

> On Sep 18, 2019, at 9:03 AM, Johnny Bridges via Gmclist wrote:
>
> The 30 second (overkill) delay in some of the auto transfer switches is a low cost way to keep from having the AC essentially look at itself until the
> magnetic field in transformers and/or motors dies down. If the peak waveform of one source sees the peak of the other it may cause enough current to
> drop a breaker or open a fuse. (In high power setups it certainly will). It probably isn't necessary in the GMC unless the A/C is running and
> doesn't reset the compressor timer. Half a second is plenty. If you have a simple relay and the A/C breaker pops when you swap, that's why. Ask me
> how I know thism :)
>
> --johnny


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