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Author Topic: Transfer switches  (Read 4945 times)
Len Silva
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« on: August 02, 2007, 09:21:47 AM »

There are several threads here regarding generator transfer switches.  Rather than jump in them, I thought I might start a new discussion.

I was having some problems with my older Todd Engineering (now out of business) and started looking around.

It seems that there are two basic designs out there.  The less expensive units use two or three pole double throw contactors (relays) with a time delay.  Some (Iota ITS50R) use one two pole for the hot leads and another for the neutrals.

The second type, like mine and considerably more expensive use two three pole single throw mechanically interlocked contactors.  These are actually three phase reversing motor controllers (Allen Bradley Cat 505 or equivalent). One of these is the Esco ES350.

In my estimation, the second style is much preferred.  I think there is far less chance of a safety failure with this unit.  When mine gave me trouble, neither the generator or shore power would work.  That was because the mechanical interlock prevented it's operation.  All it needed was a good cleaning and all was well.

In the less expensive units it would be very possible for the hot leads to transfer but not the neutrals because the second relay failed or hung up.

The control circuit for the second style is a bit more complicated because it must apply control voltage to one contactor or the other rather than just a signal from the generator.

I don't have a question here, just throwing out what I have learned.

Len

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cody
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« Reply #1 on: August 02, 2007, 09:34:05 AM »

Our setup is very simple and was very inexpensive, we had an automatic transfer switch fail, we then went to a very simple but failsafe setup, we installed the line from the generator as a receptacle, when we unplug the shore power line, we plug it into the receptacle from the generator.  This way it's either shore power or generator power but never both.
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DavidInWilmNC
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« Reply #2 on: August 02, 2007, 09:50:44 AM »

I have an Iota switch, and it seems to work well.  Granted, I haven't used it much, but I did install an identical switch in a friends RV a few years back and it's worked great.  I believe there's some sort of interlock to preventone of the contactors from switching if the other doesn't.  I'll have to check the schematic, but it's not as simple of a design as I thought it would be.

The dual outlet method just doesn't cut it for me.  Sometimes, I'll run on inverter or generator while driving.  It depends on what I need to run, so I like to be able to start the generator and have everything switch over.  I still have the original OTR air, so I don't run the generator much... the inverter runs a few lights, stereo, and 'fridges while driving.  The other nice thing about an auto switch is when I only has access to 20 or 30 amp power.  Just fire up the generator and 30 seconds later, I have 50 amps of A/C available.  What might be superior to either of these is a manual transfer switch.  One that's designed to switch three legs (hot-hot-neutral) would work nicely.  Just pull the handle into the position for the desired power source. 

David
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Dreamscape
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« Reply #3 on: August 02, 2007, 10:20:52 AM »

Cody,
I like your idea. I currently have two 50 amp breakers, one for shore, one for generator. Just have to make sure to turn one off before the other. Your way is fail safe, and safer to boot! I like to keep this stuff KISS! Less to worry about or replace, that adds $$$ that I could spend on other needed items. Like finish the project!

Paul
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« Reply #4 on: August 02, 2007, 10:22:49 AM »

I use an Iota TS50R, but do not switch it when I have heavy loads like ACs or microwave running. I plan it so I'll have the transfer switch doing it's thing when the load is lightest.

Jay
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NCbob
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« Reply #5 on: August 02, 2007, 10:27:31 AM »

I'm with Cody on this topic...and for good reason.  For all the years I spent servicing Onan, and other brands, of automatic Transfer switches and paralleling equipment I can't help but feel that moving away from the old
KISS principle when it comes to buses is almost self defeating.

Basically this is my reasoning: Where in the world at midnite on a Saturday, in a driving thunderstorm, are you going to find someone who will troubleshoot and repair or furnish you with exactly the replacement you need for the one that just smoked?

It can all be avoided but running the generator output to a female receptacle to which you simply insert your shore cord.  From the shore cord on...everything you need is there...Main breakers and a load center for all the appliances.  What could be simpler?

Oh! But that might mean that you'd have to go outside in the rain if the campground power went off, start the generator and move the plug from the post to the generator outlet.  Too much trouble?
That's what they make umbrellas for!

NCbob
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« Reply #6 on: August 02, 2007, 10:30:09 AM »

NCbob, You said it much better than I! Hoorraahh!

Paul
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DavidInWilmNC
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« Reply #7 on: August 02, 2007, 10:40:29 AM »

Basically this is my reasoning: Where in the world at midnite on a Saturday, in a driving thunderstorm, are you going to find someone who will troubleshoot and repair or furnish you with exactly the replacement you need for the one that just smoked?

I can certainly appreciate the 'keep it simple' approach.  Being that I'm the one that installed my switch and panels, generator, and all the wiring, I'd be the one to troubleshoot and repair the switch.  Mine is very easy to get to.  Open a kitchen cabinet and it's right there.  I should probably buy another one (very cheap on eBay) for a spare, but it's no problem to simply bypass the switch.  In fact, it takes about 5 minutes.  Having said that, if I wasn't able or willing to trouble shoot and repair / replace components of this system, or if I just didn't know how to do so, I'd probably go with a manual switch or the two plugs method.  I don't see how one could go wrong with a switch like the one pictured below (but it would need to be able to switch the neutral; the one pictured won't).

David
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Len Silva
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« Reply #8 on: August 02, 2007, 11:06:50 AM »

NCbob and Cody,

I guess some of us just like to screw around with this stuff. You could make it more complicated/simple by doing both.  Set up cords and plugs wired through a transfer switch.  Automatic when you want it but simple to bypass if you have any problems Smiley.

Actually, the discussion I was hoping for is not whether or not to use transfers but rather the design of the various transfer switches out there.  I didn't even realize the differences until I did a little research looking for parts for mine.
There has been some discussion of welded contacts and other failures, some of which could be very dangerous.  I think the mechanically interlocked transfer is safer.
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Sam 4106
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« Reply #9 on: August 02, 2007, 02:30:24 PM »

Hi Len,
Thanks for the information about the different quality of transfer switches. I better understand what some of the other members were talking about.
My Magnetek ATS 100 transfer switch appears to have electrical interlock along with the mechanical interlock since there are auxillary contacts on both 3 pole contactors along with a small circuit board. Have you seen anything like that? My transfer switch has the UL symbol on it too. Are the cheaper ones UL listed? It seems like false economy to use a transfer switch that can backfeed your generator or make your shore cord live if a set of contacts weld themselves together. There are so many things to learn about our coaches and you just provided information to make them safer if people will learn from you.
Thanks Sam 4106
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« Reply #10 on: August 02, 2007, 08:22:09 PM »

i'm seeing transfer switches from ASCO around $900???  Briggs and stratton 100a for $600, triton for $1200 and guardian rts/ats 100 for $600.  any idea which brands are good/bad and what should a price be.  i want to power the whole bus with either the 12kw genset or shore power.  No battery bank right now, so no inverter/charger to worry about?  also, some seem to have an automatic switch that i assume you can override, which might be helpful if the camp shore power was deficient???

what do you think Len?
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« Reply #11 on: August 03, 2007, 06:40:12 AM »

also, some seem to have an automatic switch that i assume you can override, which might be helpful if the camp shore power was deficient???

Tom,
   We purchased our Iota 50 amp on Ebay.  It is wired so that the shoreline is primary. Anytime the generator is started it automatically switches to generator (after a time delay).  When the generator is turned off, it switches back to shoreline.  Jack
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« Reply #12 on: August 03, 2007, 06:53:30 AM »

Tom,a good 50amp transfer switch should cost you between 200 to 300  retail depending where you buy it i am sure you can find cheaper ones.just asking but why are you looking at 100 amp switches
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DavidInWilmNC
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« Reply #13 on: August 03, 2007, 08:03:01 AM »

Tom,
   We purchased our Iota 50 amp on Ebay.  It is wired so that the shoreline is primary. Anytime the generator is started it automatically switches to generator (after a time delay).  When the generator is turned off, it switches back to shoreline.  Jack

I've got the same transfer switch from the same 'place' (eBay).  I believe I paid around $60 or so for it.  I should buy another as a spare, as they're available for that price fairly often (as in currently).

David
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NCbob
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« Reply #14 on: August 03, 2007, 08:37:41 PM »

Actually, Len, while I'm not necessarily in favor of transfer switches, per se, my bus has a pair of old Honeywell contactors  that the P/O  installed with a 3 position switch which allows me to select the mode I wish to be in....center off...right (generator) or left (post power).

Designing a system which would involve either mechanical or electrical interlocks to avoid a paralleling situation with post power might be a bit more complex than what the average converter might wish to be involved.  Not that the information isn't out there and available...it just depends on how involved you wish to get into this phase of conversion.

Forgive me if I stepped on any toes with my comments.  In my situation I cringe every time I look at my relays and wonder how long it's actually going to take me to grab the bull by the horns and throw the whole mess out.

But as Fast Fred used to say...it's my way.

Bob
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