Shore power and generator

I was reading the manual on the Onan autostart, and in one mode it actually starts and runs daily for two hours, right before quiet time (preset) to recharge the batteries for the night. It would do this as a hot transfer in both directions between the inverter and generator and it is completely automatic. I wouldn't necessarily call that an emergency use only.

Not sure we'll ever be able to answer the question of whether is safe to 'live switch' Shore to Gen and Gen to Shore without having a discussion with the Engineers that designed the ATS 20/10/5/1 year(s) ago that happen to be in 'your' particular RV.

Reason is that it IS possible to design a system that detects when the AC is near zero, synchronizes the Genset output frequence with line frequency and then operates a Make-Before-Break solenoid so that both sources are at or near zero when the switch occurs. And do this in a matter of milliseconds to seconds. And the number of modern AutoStart gensets would indicate an economy of scale so RV manufacturers would probably opt for a 'Smart ATS' that can switch safely even if there's no built in autostart.

This didn't use to be a trivial circuit design, but now days, with all the specialized digital ICs available, it's probably pretty easy.

My old '94 Bounder, I researched the ATS and it's what you'd call 'dumb'. Basically, just a big relay.

In my '02 Winnie, there's some circuitry in the ATS box that makes the switchover so smooth, there's no 'telltale' of it, like I'd see in my old RV when the TV would flicker, the 120V desk lamp would flicker, or the computer monitor would glitch.

Naturally, out of habit I pretty much unload most of the circuits before starting or stopping the genset, even my new one, and if it's not inconvenient, I'll shut everything down, walk outside, and flip the 50A breaker on the post before starting the genset for it's monthly exercise. If it is inconvenient though, no qualms about unloading it from any heavy loads (MW, A/C, Furnace) and starting it up with some devices running. (Mainly my computer, water heater, refer, sometimes the TV).

Good luck to all!

On my Monaco the generator takes preference over the shore power. If I start the generator the transfer switch does not switch connections until the generator has gotten up to speed and is producing the correct power, per my EMS.
If my AC is on, the compressor shuts off as soon as the transfer switch changes from shore power to generator power, just like it shuts down with any power blip. For this reason I am not switching a heavy load. If the water heater was on electric, I might have a few more amps under load when it switches.
It takes about 2 minutes for the AC compressor to come back on after switching from shore power to generator power.
After several years, I have not had any problems from starting my generator while plugged in to shore power. I guess at some point in time I may have a problem, but I could say the same thing about any component on any RV.

I am another one who want to see where transfer switches are danger?
When even wood spoon can be dangerous, for years I have been camping having 2600W inverter/charger with built-in transfer switch.
Often plug into 20 or 15 amp shore power, at the moment when AC was starting, or I put oven at the same time, the shore voltage would drop and inverter would instantly switch to battery power. When the draw stabilized few seconds later it would switch back to shore power.
In drastic situation transfer switch could be switching more than 10 times per hour.
During 10 years of using it never had a problem with the animal.

MrWizard wrote:


its your RV your money.. take your chances, but don't try to rationalize it as being designed that way, because its not !

its an emg feature, NOT a weekly every time i camp and fell like it. . .

if i can't do with out either one for a few minutes, "pity me"

You can't bake your cake and eat it too.

Whether this feature is for emergency or everyday use doesn't alter the fact that it is designed that way.
It works, therefore it is designed to work as expected.

You can't have it both ways.
---------------
Progress isn't made by early risers. It is made by lazy men trying to find easier ways to do something. (Robert Heinlein)

auto generator start functions
only when shore power went OFF aka failed
and when dry camping and the batteries are low

in the first case no HOT loads are switched from shore power to generator arcing contacts, because the power went off, and tripped the auto start

in the second case there are NO AC loads on the generator except for the charge converter that comes on after the delay timer, it started because of low battery voltage

the first case is RARE

the second case is the main design use of auto generator start

the main reason most people don't want to unplug
is because they don't want to turn off the A/C or TV and reboot the sat box, or turn off the electric heaters etc.. for a few minutes

its TOO much inconvenience..

its your RV your money.. take your chances, but don't try to rationalize it as being designed that way, because its not !

its an emg feature, NOT a weekly every time i camp and fell like it feature

me i made it simple, my TV, PC, cell chargers etc. are always on the stand alone inverter
shore power, powers the stand alone converter, generator powers the converter, converter and solar keeps the batteries charged, batteries power the inverter

nothing except A/C or microwave get bothered by unplugging shore or turning off/starting generator

if i can't do with out either one for a few minutes, "pity me"

Mile High wrote:

wildmanbaker wrote:

Mile High wrote:
My gen has the autostart function, which allows the generator to start when shore power is lost, and it shuts off when shore power is restored, so at some point it's all designed to transfer with both supplies hot.

Oh NO! You are wrong. Just read the posts. Apparently not all transfer switches are made to NEC codes, and are dangerous. If you are worried about your electrical system, strip the breaker in the RV, start the generator, and close the breakers. No load on switching supplies and save yourself 2 trips to the power plug.

So you are saying don't trust the transfer switch at all, do it all manually? I guess I didn't read than in the posts.

I can't speak for everyones transfer switch, and I do know Iota had issues with the installers not using proper torque on terminals, but really, these are pretty simple systems. Just an overgrown triple throw knife switch held to shore power by a spring and generator power by an electric solenoid.

From my manual - it is obvious they expect any configuration of power at either source -

Automatic Transfer Switch Features
Unit will transfer to either shore power or
generator automatically when energized. In the
event both shore and generator powers are
available, generator power will dominate after a
30 second delay.

No, I was being sarcastic. Disconnects, transfer switches, and breakers are designed to operate at stated voltage and load, without damage.

In addition to the generator-shore power transfer, there is inverter-shore power transfer that occurs every time I hook up on mine, and both are hot.

I see that I searched the wrong parameters. Maybe MrWizard will show us the links to fried generators caused by failed transfer switches.
There are simply way too many coaches out there with auto-gen start as a factory option to believe that having this option available is a disastrous choice.
I do agree that turning off the loads before starting the generator is a good idea. However, if there is a power failure, most A/C compressors will not start until a few minutes have passed protecting the compressors and if the auto-start is set to kick in due to low battery voltage or high interior temperature the A/C is likely not running at the time so an overload situation is not going to be an issue in either case.

Nobody said ts is dangerous
What is dangerous is people routinely switching on the generator and ts with hot loads
This causes arcing, pitting and sticking of the contacts in the TS relay

Emergency switching, might happen occasionally or never, so the chance of cumulative damage to the contacts is almost eliminated

Being lazy for routine use and testing is what creates the danger

A Subject Search for transfer switch failure
Is not going to find much
The people who fried their generator
Came on here asking for generator help
Then find out why the generator fried when they started it while plugged into shore power
They find the melted burned stuck ts relay insides it's box , AFTER THE FACT,