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Old 06-27-2011, 02:05 PM   #1
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Automatic Transfer Switches-Caution

After speaking with the technical support staff of Iota Engineering and Parallax Power Supply the consensus is that we may be using our transfer switches incorrectly. Neither manufacturer recommends switching while under load as contact pitting will occur resulting in loss of switch life. Their 50 amp. rating is for normal current carrying capability not switching current. They each recommend turning off all inside load before switching power sources. However when pressed they did say that switching 5 or 6 amps will probably not cause a problem. Inductive loads are the worst load type to cause contact damage. The normal operating current of the motors coupled with the inductive inrush currents can cause contact bounce resulting in even more loss of contact/switch life and early failure.


The switch is normally wired so the generator has priority. When the switch senses power from the generator the switch's control board takes 120 volts from the black wire from the generator where it is converted to 110 volts DC and is applied to the relays as control power to close the contacts. Before the contacts are closed however, the control board goes thru a timing sequence to allow the generator to get up to speed before it's asked to carry load. If the generator is running when connected to shore power the generator will continue to supply power to the coach until it is shut off. At that point control power will be lost and the contact will immediately switch to shore power. This is where the most damage is possible to the contacts especially if a motor load is running in the coach. Since AC power is sinusoidal if the power cycle is on the increase at the time the generator was shut down and the incoming shore power is also increasing the voltages will combine and a high voltage will be fed into the coach in the form of a spike. Hopefully, surge protection will dissipate it to ground with no effect.


So what can we do to prevent transfer switch damage. Before we start our generators we should turn off all motor loads such as air conditions and fans and reduce the total load to about 5 6 amps. Once the generator is started and available for load servicing the power configuration in the coach can return to normal.


Typically we run our generators while on the road to power the air conditioners so when we arrive at our site the generator is normally running while we hook up. Before turning on the 50 amp breakers at the power pedestal, turn off all air conditioning load and turn off the generator. Then turn on the breaker.


This should help eliminate problems associated with transfer switches and extend its service life saving us inconvenience and money.
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Old 06-27-2011, 02:20 PM   #2
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Thanks for the headsup

Not really off subject, well maybe a little. I have been wondering about running the generator when driving to run AC. The load center and transfer switch on the MH delays connection of the generator for 10 seconds after starting but the generator manual says to let it run for two minutes before adding a load. Here is the problem, if I start out in the morning not needing AC and later in the day want to run the generator and AC, should I already have the thermostat set so that as soon (10 seconds) as the generator comes on line the AC will start or should I stop and wait 1 or 2 minutes then turn on the AC? The thermostat is some 20 feet behind the driver's seat.
I realize that the second choice would be best for the system but does that make the extra stop worth it?
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Old 06-27-2011, 02:26 PM   #3
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Great info... thanks RJay!

I guess it's another case of "just because we can... doesn't mean we should."

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Old 06-27-2011, 03:36 PM   #4
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Hi Bill,


The 10 second delay before the switch closes is to allow the generator to stabilize after start. I believe the 1 to 2 minutes the manual requires is for warm up. If I'm not mistaken there is always a delay after you turn on the thermostat to when the air conditioners comes on. So you would be able to turn on your thermostat before you leave and just turn on the generator when you need the air and you wouldn't have to stop. The objective is you don't want to switch the A/C load or loads over 5-6 amps.
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Old 06-27-2011, 04:13 PM   #5
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Hi Bill,


The 10 second delay before the switch closes is to allow the generator to stabilize after start. I believe the 1 to 2 minutes the manual requires is for warm up. If I'm not mistaken there is always a delay after you turn on the thermostat to when the air conditioners comes on. So you would be able to turn on your thermostat before you leave and just turn on the generator when you need the air and you wouldn't have to stop. The objective is you don't want to switch the A/C load or loads over 5-6 amps.
Thanks,

I ran 100 miles home from Tampa last week by myself and the dash air obviously didn't quite do the job.(97 degrees outside). In the future I'll do as you suggested. It was one of those things where I convinced myself that home was "just around the corner" and I really wouldn't sweat to death before I got there.
You've got to love Florida in the summer.
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Old 06-27-2011, 04:33 PM   #6
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As someone who is presently in Texas I feel your pain. Even a couple of hours at that temp is not fun!
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Old 06-27-2011, 09:00 PM   #7
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One thing I forgot to mention in my original post is Iota is no longer producing their switch. They said the depressed RV market and other suppliers undercutting their price caused them to get out of the RV market.
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Old 06-27-2011, 09:03 PM   #8
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I have seen Iota switches for sale. How long have they been out of the business?
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Old 06-27-2011, 09:11 PM   #9
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Originally Posted by Peddler View Post
if I start out in the morning not needing AC and later in the day want to run the generator and AC, should I already have the thermostat set so that as soon (10 seconds) as the generator comes on line the AC will start or should I stop and wait 1 or 2 minutes then turn on the AC? The thermostat is some 20 feet behind the driver's seat.
Isn't that what Cruise Control is for?
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Old 06-27-2011, 09:14 PM   #10
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I have seen Iota switches for sale. How long have they been out of the business?
They are still in business. I stopped in at IOTA Engineering at their plant in Tucson. I was looking to buy a transfer switch. They did not have any and there was no immediate plan to re-tool and manufacture a new batch. Security seemed abnormally high; made me wonder if they have a secret military contract that is keeping them busy.
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Old 06-27-2011, 09:31 PM   #11
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Thanks for the headsup

Not really off subject, well maybe a little. I have been wondering about running the generator when driving to run AC. The load center and transfer switch on the MH delays connection of the generator for 10 seconds after starting but the generator manual says to let it run for two minutes before adding a load. Here is the problem, if I start out in the morning not needing AC and later in the day want to run the generator and AC, should I already have the thermostat set so that as soon (10 seconds) as the generator comes on line the AC will start or should I stop and wait 1 or 2 minutes then turn on the AC? The thermostat is some 20 feet behind the driver's seat.
I realize that the second choice would be best for the system but does that make the extra stop worth it?

The Newmar products have a 90 second delay from AC power on before the compressor powers up, I would expect recent vintage Winnebago products to do something simular. If it does not appear in your manual, try it at home. Turn your breakers off, turn the thermostat to cool, throw the breakers on, and then time how long before the air conditioner comes on. Should be the same time for the generator power.
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Old 06-27-2011, 09:44 PM   #12
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I have seen Iota switches for sale. How long have they been out of the business?
When I spoke with them today they said they were no longer making them. They probably still have some in stock? They are not going our of business they just stopped making the transfer switch.
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Old 06-28-2011, 08:12 AM   #13
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The Newmar products have a 90 second delay from AC power on before the compressor powers up, I would expect recent vintage Winnebago products to do something simular. If it does not appear in your manual, try it at home. Turn your breakers off, turn the thermostat to cool, throw the breakers on, and then time how long before the air conditioner comes on. Should be the same time for the generator power.
According to my Iota manual for the switch it states there is a 20-30 second delay before the switch is connected to the generator. I know there is a delay after the thermostat is turned on to when the air conditioner comes on but I couldn't find it in the Comfort Control manual. I'm sure someone out there knows.
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Old 06-28-2011, 09:31 AM   #14
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I think the "Wait 2 minutes before applying load" is a bit... Over cautious.

But as noted, the 30 seconds the ATS waits (normally it's about that long) plus the time delay before the compressor kicks in.. Should cover it.

I don't like firing up the generator with big loads already on line.. but to be honest, there is no inductive "kick" when the switch closes.. Only when it opens. So you should now SWITCH under load, but turn is ok.
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