But now that I have it, I love it. The main advantage is that it does not
switch the circuits until the generator has produced stable power for 30
seconds or so. My cheap Generac generator is MUCH happier with that
feature.
Rick “leaving the dual AC question for others” Denney
--
'73 X-Glacier 230 "Jaws"
Northern Virginia
Offlist email: rick at rickdenney dot com
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 <gmc...@list.gmcnet.org> 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
If the relay switching time isn’t enough to handle the phase relationship,
oh well. It’s wise to shut off the air conditioner before switching between
two live loads.
The delay is there to let the engine on the genset stabilize before
imposing a load.
Rick “fulfilling a different requirement” Denney
On Wed, Sep 18, 2019 at 2:04 PM Johnny Bridges via Gmclist <
gmc...@list.gmcnet.org> wrote:
> We differ on a couple of points. What's the minimum disruption your A/C
> will recognize as a power drop? What's the minimum time for your source
> relay to pull in? If the second is lower than the first and if the two
> sources are out of phase, you'll take a breaker or fuse down. Realize,
> transfer
> is not a problem, in that you're leaving a dead source. Retransfer
> however can bite you since you're switching between two live sources and
> don't
> know the phase relationship between them.
> Back in The Day the gensets had 'parallelling' lights, simply lights
> connected across the A phase of both sources. Throw the switch when the
> lights
> go out. To automate this we hung a relay across the lights and let it
> inhibit the transfer switch motor when it was energized. This got the
> transfer
> to within 30 degrees or so of equal which didn't hurt anything. The
> option was/is a trip to the plant, usually in a storm.
>
--
'73 X-Glacier 230 "Jaws"
Northern Virginia
Offlist email: rick at rickdenney dot com