Just Wondering

[Cactus Canyon]

2019 Force HD 37TS
When not using our coach, we keep it plugged into 110v 20a at our house. I’m always very careful to unplug it before turning on the generator so I can use the slides, A/C, etc.
But what if I forget, and start the generator while still plugged in? Will that damage anything?
Thanks.

[rcraighughes1]

Theoretically it shouldn’t

My dealer ready me riot act that I should make sure that never happens. If that surge fails and goes back into generator the whole thing is shot and would need replaced

[joet19711]

Originally Posted by rcraighughes1

Theoretically it shouldn’t

My dealer ready me riot act that I should make sure that never happens. If that surge fails and goes back into generator the whole thing is shot and would need replaced

Pretty sure that the default is always the generator even if plugged in to shore power. I have on occasion forgot to unplug and started the generator..

[Desert Boat]

The transfer switch will only allow one source to power the coach. The Model 40450 RVC in my 28ss prefers generator power, and will select that after a 30 second warm up if both are available.

There may be other reasons not to have both powered at once, but it is not unsafe to have both on.

[bclemens]

its not the end of the world, but weird things can happen if you do. I have had one latch to the gen side, when the gen was started when plugged in. Had to sort of reset everything to get it back to a proper transfer.

[Cactus Canyon]

Thanks very much! One less paranoia trigger, LOL.
By the way Brian, how does one sort of reset everything? Is it a big job?

[NavyLCDR]

There should be an interlock that keeps you from "mixing" generator power with shore power. It should be nearly impossible. If there is a catastrophic failure of the interlock, then there will likely be an electrical explosion due to mix matched A/C phases at the point where the generator output meets the shore power input. However, a failure of the system is 99% chance only going to result in a failure to switch from shore power to generator power and not connecting both sources to each other.

[TitanMike]

Originally Posted by NavyLCDR

There should be an interlock that keeps you from "mixing" generator power with shore power. It should be nearly impossible. If there is a catastrophic failure of the interlock, then there will likely be an electrical explosion due to mix matched A/C phases at the point where the generator output meets the shore power input. However, a failure of the system is 99% chance only going to result in a failure to switch from shore power to generator power and not connecting both sources to each other.

Most generator equipped RV's today have a transfer switch that handles this problem. When they fail it's usually no power at all from shore or generator.

Some simple installations have the best protection of all. Shore power is wired to an outlet in a compartment and generator power likewise to it's own outlet. A pigtail from the RV's power panel is then plugged into whichever power source you want. Since pigtail can't be plugged into both at same time no chance cross connecting.

[NavyLCDR]

Originally Posted by TitanMike

Most generator equipped RV's today have a transfer switch that handles this problem. When they fail it's usually no power at all from shore or generator.

I would have to disagree. Failure will usually result in the transfer switch being connected to shore power. Normally the transfer switch senses voltage from the generator and if it is present, it switches to the generator as power source. If there is not voltage sensed from the generator, the transfer switch reverts to the shore power connection - whether or not there is actually voltage present at the shore power connection. Assuming there is an ATS (automatic transfer switch) present, of course.

It is extremely unlikely that the transfer switch would fail such that there is no power available from either source or that both sources end up connected together.

[NXR]

Originally Posted by NavyLCDR

I would have to disagree. Failure will usually result in the transfer switch being connected to shore power. Normally the transfer switch senses voltage from the generator and if it is present, it switches to the generator as power source. If there is not voltage sensed from the generator, the transfer switch reverts to the shore power connection - whether or not there is actually voltage present at the shore power connection. Assuming there is an ATS (automatic transfer switch) present, of course.

It is extremely unlikely that the transfer switch would fail such that there is no power available from either source or that both sources end up connected together.

I believe our Progressive Dynamics transfer switch requires power from each source in order to connect that source. The default is "no power source connected".

The generator does have priority if both power sources are active.

Ray

[NavyLCDR]

Originally Posted by NXR

I believe our Progressive Dynamics transfer switch requires power from each source in order to connect that source. The default is "no power source connected".

The generator does have priority if both power sources are active.

Ray

It depends on the transfer switch, actually. Most 120v transfer switches such as the PD5100 have a single relay and will fail to shore power contacts closed. If the coil of the relay fails or the relay control circuit fails, the relay will move to the shore power contacts by a spring.



The PD5200 and 5300 series for 240v operations have 2 contactors, one on the shore power side and one on the generator side. The 2 contactors are interlocked so only one set can be closed at a time, and it does, in fact, require shore power to be present to close the shore power contactor. If either contactor fails, it fails open, so no power gets passed through that contactor.




I suppose most permanently installed RV generators are 240 volt, so TitanMike was right. Most generator transfer switches likely fail to no power state.

[NXR]

Originally Posted by NavyLCDR

I suppose most permanently installed RV generators are 240 volt, so TitanMike was right. Most generator transfer switches likely fail to no power state.

It's a bit of a nit to pick but it appears the Onan "50 amp" generator has two 120 VAC windings and does not actually produce 240 VAC. I don't have access to a good enough manual to say whether the two 120 VAC windings are 180 degrees out of phase and thus could even produce 240 VAC.

With our PD52 ATS there must be 120 VAC power to the connection that Progressive Dynamics designates as "HOT1" for the ATS control circuitry to work.

Interestingly, that implies that if one 120 VAC in a 50 amp pedestal dies but the other is present, we have a 50-50 chance as to whether the ATS will engage. We could either have half the RV powered up or not at all.

Ray

[bubbles]

Originally Posted by NXR

It's a bit of a nit to pick but it appears the Onan "50 amp" generator has two 120 VAC windings and does not actually produce 240 VAC. I don't have access to a good enough manual to say whether the two 120 VAC windings are 180 degrees out of phase and thus could even produce 240 VAC. Ray

Not 2 120Vac windings but a tap (splice) off the single phase output through 2 generator circuit breakers (30A/20A-30A/30A etc.). The Onan 5.5K generator is a single phase output generator as are probably all generators installed in our RV's.

As to the ATS; if it defaults to an input it would be the generator and the generator would have priority. If it does not default to an input the generator would still have priority. In other words if shore power is present and the generator is started the ATS will always switch to the generator input.

[bclemens]

Originally Posted by bclemens

its not the end of the world, but weird things can happen if you do. I have had one latch to the gen side, when the gen was started when plugged in. Had to sort of reset everything to get it back to a proper transfer.

I think when I had to correct it, it was not an exact science.

I cut the shore breaker, disconnected from shore power. Generator was off. I think I might have pressed down on the transfer connection a couple of times to make sure it was freed up (be very careful here and make sure there is NO power coming through). I think I powered on the gen for minute. Shut that down. Waited a minute or so and then plugged back into shower power, turned on the breaker. It all worked after that.

Might have all been placebo and we just needed to wait it out. It just would not switch back over to shore power on its own, until after I did those steps.

[NXR]

Originally Posted by bubbles;

Not 2 120Vac windings but a tap (splice) off the single phase output through 2 generator circuit breakers (30A/20A-30A/30A etc.). The Onan 5.5K generator is a single phase output generator as are probably all generators installed in our RV's.

Thanks for the clarification. I wish I could find a solid manual.

As to the ATS; if it defaults to an input it would be the generator and the generator would have priority.

I guess it depends on how you define "default". The few I looked at were set to shore power in the relaxed position so I would call that the "default".

Possibly their assumption is that most people would be on shore power far more than generator power so it makes no sense to power up the ATS contactor to connect shore power.

Agreed, when the generator fires up it energizes the ATS and switches the power source to the generator. That came in handy once during a particularly nasty thunderstorm. The power kept going on and off due to nearby lightning strikes so I just started the generator to reduce the power fluctuations until the storm passed.

Ray

[Cactus Canyon]

Like so many of these threads, each time I read it, I realize how ignorant I am of the complexity of our Dynamax.
Wondering where I can get a copy of Dynamax For Dummies.

[Desert Boat]

The Model 40450 RVC Automatic Transfer Switch in my 2021 28ss has separate relays for shore and generator. Since it is also a "power protection" device, it has to meet the requirements for voltage, ground, frequency, etc., before the shore connection will close. The surge protection is independent of the relay.

When generator power is available, it prefers the generator, after a 30 second delay for generator warm up.

My Onan 8.0 generator produces 120V, which is wired to both L1 and L2. L1 and L2 are tied together inside the generator, although they have separate 35 amp breakers.

On a 50amp shore connection you will see 240V between L1 and L2. On generator power, there is 0 volts between L1 and L2.

The available generator current (66 amps - 35 per leg) falls about 1/2 way between that available from 30 amp and 50 (=100 amp) shore power connections.

[bclemens]

Originally Posted by Cactus Canyon

Like so many of these threads, each time I read it, I realize how ignorant I am of the complexity of our Dynamax.
Wondering where I can get a copy of Dynamax For Dummies.

can be found here... https://www.forestriverforums.com/forums/f240/

[bubbles]

Originally Posted by NXR

I guess it depends on how you define "default". The few I looked at were set to shore power in the relaxed position so I would call that the "default".
Ray

My bad should have said defaults to shore input but generator has priority.

[CyberShanks]

Originally Posted by bclemens

can be found here... https://www.forestriverforums.com/forums/f240/

Wonder how many people followed the above link, like I just did. Funny thing is I ended up in the same exact place I was already at...


Jim