Testing an Automatic Transfer Switch

[Yarome]

I haven't looked at or tried to adjust the time delay in my ATS, but its has something like a 15 second delay BEFORE it toggles to Generator AFTER it starts. I figure that allows a brief warm up time and for the RPM and frequency to stabilize and settle in before it switches.

 

I'm heading south soon, wish you would be in Florida instead of out west some winter so we could chit chat. Some year I may do the Quartzsite thing.

 

They generally aren't adjustable. More than likely it's not your ATS that's causing the delay.. although it might be a part of it.. but more likely your genny isn't passin da gas until it's fully spun up and the regulator is settled in.

 

No kiddin! I seem to remember you owe me a 1.5 amp feeding for my ice maker.

 

Any time you folks want to mosey over... you know me... I'm always kickin around somewhere's in the TX or NM hills come winter.

Edited October 6, 2016 by Yarome

[ms60ocb]

While I don't have a lot of experience with RV generators that have an auto start function, those which I have examined the auto start only happened if the battery voltage dropped due to battery discharge. I have not seen one that had an auto start function as a back-up to shore power. If you have, I'd be interested to know who makes it and anything else that you know about it.

As I looked at my Auto Generator Start control (Magnum ME-AGS-N) Coupled with the Magnum Inverter/Charger there are many options. The sales person told me that the Generator can start on loss of source. Reading my Manual says yes buttttttttttttttt only if programed to run daily for a specified time, like in the boonies. With that setting and you normally had AC power to the Inverter /Charger the the generator would be locked out, but if the AC power was lost during that specified time to auto-run the generator would start on Dead line/Dead Bus condition.

I do not have a Temperature monitor on my Generator Start as I did not select that option.

I have used my Generator on the average of 1.5 hours per month but the two reasons I purchased the generator was having a hot lunch on the road and being cool. When two A/C are required particularly when only 30 Amp service is available in the heat of the day.

Clay

2016 MS 38PS3

[Lou Schneider]

I saw a Break-Before-Make transfer switch fail with it's contacts welded in opposite positions, connecting the generator and shore power together.

 

It was on a radio station remote van with a 6 Kw generator that could run the broadcast equipment and the air conditioner. It was set up at an RV show, sharing a temporary, daisy-chained 20 amp power feed with about a half dozen other display RVs.

 

They had just started a 3 hour broadcast, and the technician in charge of the van decided he wanted to run the air conditioner When he turned it on the compressor load pulled the shore power voltage low enough to make the transfer switch relay chatter on and off. He quickly turned off the air conditioner, then during a program break started the generator without first unplugging from the shore power. The equipment in the van was backed up by an on-board UPS, so there was no reason not to unplug from the shore power first, he just forgot.

 

The show management wasn't happy when the shore power feed blew it's breaker with a large bang while smoke poured out of the converters in the other RVs sharing the feed. We wound up paying for those. The on-board UPS exhausted it's batteries about an hour later so we also lost over half of the scheduled program.

 

When the van got back to the shop, I opened the transfer panel and found the shore power relay welded shut. So was the generator power relay. No mechanical interlock between them, just the control circuit logic to keep them from both energizing at the same time. The chattering shore power relay welded itself shut when the tech tried to start the air conditioner on shore power, then when the generator relay pulled in, it's power backfed down the shore power line and the surge welded the generator contacts shut. Only the 20 amp breaker at the start of the daisy-chained power feed kept the generator from self-destructing.

 

The onboard UPS protected the equipment inside the van, the other RVs sharing the circuit weren't that lucky.

Edited October 8, 2016 by Lou Schneider

[oldjohnt]

GREAT STORY LOU, thanks for posting. I envisioned a say two pole transfer switch where the two were MECHANICALLY (electrically isolated of course) tied together like done on a two pole circuit breaker so its NOT possible for one to be in one location and the other a different location, if one toggles over the other has to follow, they're joined IE THEY ARE MECHANICALLY JOINED AT THE HIP. I never designed one but if I did that would be my method. My example is an X pole DOUBLE THROW (Genset or Utility) NOT any sort of multiple switches or contactors whereby one might get welded in one location and the other still be allowed to toggle to another.

 

Oh well

 

John T

[blrdck]

As the original poster I have learned a lot about the whole subject. My TS is quite old and as far as I know works properly, i.e. if the generator is started, I have power. If the generator is not running and I plug into shore power, I have power. I did not know that the TS is designed to default to the generator. I was concerned about what would happen if the rig was plugged into 120 volt shore power and the generator was started. It seemed to me that if the TS was not working properly there would be 120 volts coming in from two sources which I thought could fry everything in the rig. Apparently this would only happen if the contacts had been welded together because of a large load. Thanks.

[Kirk W]

I was concerned about what would happen if the rig was plugged into 120 volt shore power and the generator was started. It seemed to me that if the TS was not working properly there would be 120 volts coming in from two sources which I thought could fry everything in the rig. Apparently this would only happen if the contacts had been welded together because of a large load. Thanks.

While your concern is highly improbable due to the way the ATS is designed, I hesitate to say impossible. In your ATS there is one set of movable contacts that has a connection to the output side which supplies the loads inside of the RV. The movable contacts sit connected to the shore power side if there is no power applied to the coil of the solenoid and they contact the generator side when power is applied to that coil because the coil is also connected to the generator's output. If you were to remove the cover it looks similar to this picture, although there are several different versions, this is a simple one.

In this type the RV load is connected to the terminals on the left of the picture. Shore power connects to those on the far right which are closed with no power to the solenoid. The second from the right connections are for the generator supply. This is a very simple version but it does show the way things work to disconnect one supply before the other is applied. I have seen an ATS which has two separate sets of contacts for the two supplies with a single solenoid that was mechanically connected to both so that it opens one as it closes the other and there may be other designs as well, but all are intended to operate in the way that this one does.

[oldjohnt]

GREAT PICTURE AND POST Kirk, a picture is worth a thousand words. To add just a bit, If alls working correct and there are no stuck close contacts, the RV panel left OUTPUT of TS can ONLY be connected to one right side INPUT or the other (Genny or Utility). A problem would be if one contact toggles while the other one does NOT (cuz its stuck) . In some multiple contact devices and two pole circuit breakers etc., the two are mechanically tied together, such that its impossible for one to toggle but not the other IE if one is stuck closed the other cant go ahead and switch. Such a design (mechanically tied contacts) would be one solution to the hazard you spoke of. NOTE I'm NOT saying how your or other TS's may or may NOT be designed and built, or if its 30 or 50 amp, or if it has or does not have tied contacts, or how many contacts you have, I haven't seen all of them lol The unit in the picture does NOT appear to have tied contacts, its probably cheaper to build that way, RV makers have been known to utilize "cheaper" methods, and such is the type you may well have WHICH COULD END UP WITH ONE STUCK CONTACT WHILE THE OTHER SWITCHED, and that's baddddddddddddddd.

 

FWIW I AGREE WITH KIRK, ITS IMPROBABLE BUT NOT IMPOSSIBLE. As I noted before I learned to NEVER SAY NEVER

 

John T

Edited October 11, 2016 by oldjohnt

[Dutch_12078]

In case it might help the discussion, here's the schematic for a Parallax ATS50 ATS. Note that they use a two relay time delayed setup with both mechanical and electrical interlocking.