Automatic Transfer Switch? Explain please

[sandy43]

Was reading some post by "geo" about the Automatic Transfer Switch and this Iota thing. Is this something to do with generators? I've explored all parts of my Alpine and I don't have anything like that. Have no idea what an Iota is or an Automatic Transfer Switch. Is this something from the factory to make your RV generator ready? Am I missing something, please explain. Thanks

[f6bits]

Wikipedia has some info:
http://en.wikipedia.org/wiki/Transfer_switch

It’s a handy device that uses three power sources, I believe. Shore power, Generator Power, and Batteries/Inverter. Should you lose shore power, the ATS will use inverter power from the batteries until your generator can take over. When shore power returns, it’ll switch back.

At least that’s how I think it works. Dunno how much is part of the generator prep package.

[Festus2]

Sandy -
If you Google Automatic Transfer Switch or Iota Automatic Transfer Switch you will be able to get an idea of what it does and what it looks like. Basically, it senses the presence of another available power source, such as a generator for example, and automatically transfers or switches shore power to generator power.

[geo]

Sandy43 -

To expand a bit on what Festus2 posted, which is correct:

An Automatic Transfer Switch (ATS) is part of a "Generator Prep Package" whether installed in manufacturing or post-sales. All the ATS units I have seen have two power inputs and do not interact with the converter/inverter. The power leads are supplied by either the shore power or the generator. (Sorry, a little science has to come in here.). The power we used is an alternating current. Think of it as the electricity flows back and forth, kind of like a water wave hitting the shore. Here in North America, our electricity alternates some 60 times per second. Now to introduce two different sources of electricity together, one has to assure that this alternating cycle is exactly matched, or one of the power sources will be literally "fried"! The price, size, and sophistication of less expensive generators do not allow the necessary monitoring and adjusting equipment to match these two sources of alternating current. It is better to separate these two alternating sources and never "let them meet".

So, enter the ATS. This is a unit usually rated at 120VAC, 30 amp or 240VAC, 50 amp (the latter being 50 amp per hot lead). One input to the ATS is shore power, the campground hook up. The other input is the generator-supplied power. These inputs are connected to their own input switches and the output of these switches are tied together and go to the RV circuit breaker/fuse box. Inside the ATS is a little monitoring circuit that controls the solenoids (electro-magnets) that open and close those switches. When the generator is not running, the shore power switch is closed to allow power to the RV. But when the generator is running, that ATS monitor senses the generator current. First, the switch for the shore power is opened for a certain time (around 45 seconds sometime). Then the generator switch is closed to supply power. When the generator is shut down, the ATS generator switch is opened, and a few seconds later, the shore power switch is closed.

So, you see, the ATS keeps the shore power and the generator power completely separate and never allows the differing alternating currents to "see each other".

But when something goes bad with the ATS, the results are usually very bad. Fire, 8 gauge wires that heat up and melt, etc. So keeping the ATS dry, keeping the switch contacts clean, and keeping the lug screws at the proper torque are things an RVer needs to do.

Let me know if this helps.

Ron

[f6bits]

Geo, thanks for the detailed info. I could have sworn that an ATS had three inputs. Now that I’ve read about more about it, I see that one should expect a gap in power during the transfer.

[geo]

Scott -

You are exactly correct. During the transfer, there is either a quick "drop" or a period of delay. This transfer delay can possibly be a problem. Usually appliances such as microwaves will shut off during a power drop and not restart when the power is returned. But AC units are not usually "geared" for that type of response. A quick power drop and connect can be termed a "power surge". So the key here that the ATS manufacturer must gauge is how long to allow the power to be dropped so as not to possibly harm connected power users.

If one is planning on a switch to/from shore power and generator power, I would recommend shutting down the AC and any other "power users" during the switch. So, if I am running the AC (a different thread here on the Forum) while travelling, I will shut the AC off, manually shut down the generator, plug in the shore power, and power everything back up. Yes, I know I am overriding the ATS, but it just makes me feel better keeping the shore power and generator power apart.

I do think that it is interesting that most ATS units have a longer shore power to generator drop than vice versa. I suppose this is to allow the generator to come up to full speed and power.

As many Forum members have noted, one should have a quality surge protector between the RV and shore power. I had one of the nice Surge Guard units but was thinking about a mounted surge protector inside the RV basement. When the Iota ATS recall was announced, that was the tipping point. I got the TRC Surge Guard ATS 40250 with the remote monitoring unit. This combines both the ATS function and the surge protection formerly handled by the outside inline protector. And I could not be happier! The remote monitor is great! One can see what the input power is "doing", and can also see how many amps are being used from each of the 50 amp "power legs". Yes, I guess I did ditch the recall replacement, but I am certainly happier with the replacement I installed.

Ron

[sandy43]

Thanks guys for the info. I now understand the ATS system, at least I think I do. As said before, I don't have these things and probably never will. I do have a 3000 Honda generator, but hardly ever carry it with me.

Now the big question, couldn't I just plug the shore power plug (30 amp cord) into the generator and have sufficient power for minor things? Is this a problem to my RV? I live in Hurricane country and I might need to do this at some point. Thanks

[K&Gs3400RL]

Yes you can run a few things in the trailer when plugged into the generator, to keep from draining your batteries. I think the Honda 3000 will run the Microwave and the Air conditioner (but not at the same time.)

[rgwilliams69]

I have an on-board Onan 6500 but carry a Honda 3000 with me also to use when I only want to run one air (much more fuel efficient and a little quieter). The Honda easily runs the rear or front air, and will run the microwave, etc. but of course not at the same time as the previous poster noted. We do a lot of race tracks and when we set up the generator starts up and never turns off until the weekend is over. Honda has a winner in the 3000 and it matches up great with the Alpine (we have a 2011 3640).