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Author Topic: Transfer switches  (Read 4915 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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« 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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« 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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« 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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« 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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« 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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« 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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« 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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« Reply #15 on: August 03, 2007, 08:59:38 PM »

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

when i looked up auto transfer switches on ebay, iota never came up. 

100 amp is what i was looking for because the generator has 2 50amp breakers and the main bus panel has 100amp.  i realize the shore is 50amp max, but if the generator could put out over that, should'nt i be looking for 100amp???

so i just put in a bid on an iota 50A.  now to replacing
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Tom
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« Reply #16 on: August 04, 2007, 05:40:25 AM »

When we bought our bus the PO had a mechanical transfer switch in the middle bay and it was set up for 30 amp shore power. There was another switch in the coach that transfered power to whichever AC we wanted to use, as we can't run both of them on 30 amp shore power; but, the generator was set up to run both ACs. The PO warned us about connecting shore power while the genny was running. He said it would burn up the genny & that he had done it once already.

Rather than attempting to rewire what was there, I opted to upgrade to 50 amp shore power. I removed all the PO wiring and installed two normally open,100 amp, 3 phase contactors with 120V coils. The outputs from both are tied together and connected to the input of my Square-D 100 amp electrical panel. The input from contactor 1 goes to the output of the generator (2 hots & neutral). The input of contactor 2 goes to shore power. I ran some 14/4 stranded wire to the control panel in the bus to a double pole, double throw switch (ON-OFF-ON). One side of the switch controls the shore contactor & the other side controls the generator contactor, therefore, there is no way to have both on at once. Also, I picked up control voltage for the input side of each contactor so if there is no power present, the contactor cannot be engaged. This system is simple, foolproof, & replacement parts are readily available.

It has worked flawlessly so far.

TOM
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Len Silva
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« Reply #17 on: August 04, 2007, 06:39:24 AM »

Tom,

I think you are on the right track using three pole contactors.  The ones I was refering to are three phase reversing contactors which are mechanically interlocked.  Here's one: http://cgi.ebay.com/ALLEN-BRADLEY-SIZE-TWO-REVERSING-STARTER_W0QQitemZ150146649078QQcmdZViewItem?hash=item150146649078

Len
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Dallas
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« Reply #18 on: August 04, 2007, 06:44:19 AM »

Tom,
I like your idea, and since I plan on adding 50A capability to our old bus, is there a way you can post a wiring diagram of your setup?

I'm not real smart when it comes to electricity.... I still haven't figured out how to get the broken light bulb base out of the lamp without getting zapped! Cheesy
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« Reply #19 on: August 04, 2007, 08:00:33 AM »

I still haven't figured out how to get the broken light bulb base out of the lamp without getting zapped! Cheesy

Dallas,

Stick a raw potato in the socket, and it'll spin the broken base right out!

Jay
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niles500
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« Reply #20 on: August 04, 2007, 08:03:44 AM »

UNPLUG it!
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- Niles
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« Reply #21 on: August 04, 2007, 08:25:33 AM »

Dallas,

I think part of the problem is you do not understand the true nature of "light bulbs".  They don't really emit light, they suck in dark..   This is easily proven.  Shake  new light bulb and you hear nothing, because it has not had a chance to fill with darkness yet.  But if you shake a bulb that no longer works you can usually hear the darkness rattling around inside.

Now if you break the bulb, since the darkness has been pulled inside the bulb it is changed and when it escapes you can't see it.  So, to change the bulb with out getting zapped, turn the reverse polarity switch (which some mistakenly believe is an on/off switch) to the "no longer sucking dark" mode and you should be able to remove the bulb without incident. 

Frank

PS: Remember the ultimate answer is 42
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Dallas
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« Reply #22 on: August 04, 2007, 09:00:23 AM »

Dallas,

I think part of the problem is you do not understand the true nature of "light bulbs".  They don't really emit light, they suck in dark..   This is easily proven.  Shake  new light bulb and you hear nothing, because it has not had a chance to fill with darkness yet.  But if you shake a bulb that no longer works you can usually hear the darkness rattling around inside.

Now if you break the bulb, since the darkness has been pulled inside the bulb it is changed and when it escapes you can't see it.  So, to change the bulb with out getting zapped, turn the reverse polarity switch (which some mistakenly believe is an on/off switch) to the "no longer sucking dark" mode and you should be able to remove the bulb without incident. 

Frank

PS: Remember the ultimate answer is 42

But, Frank...

Doesn't that mean I have to reconfigure the Dilithium Crystals to interface the flux capacitors?

And ...
87 SaftLiner...

When I tried the potato it didn't spin, all I got was a cooked potato!

Niles....

I unplugged the potato, but I still got zapped!
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« Reply #23 on: August 04, 2007, 09:06:00 AM »

How many(*) eyes that tater got?  Maybe one of you needs glasses


* Answer: 42
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« Reply #24 on: August 04, 2007, 10:16:39 AM »

thanks Dallas! 

After some of the comments i made and the questions i've posted about cables, connectors and transfer switches, i was feeling like the most ignorant person on this board.  Grin


after reading your post to dennis about his ground issue on another topic, i'm retracting the above comment.  i am back to being the most ignorant on the board.  Embarrassed  Sad
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Tom
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« Reply #25 on: August 04, 2007, 10:24:16 AM »

You guys are unbelievable!!!!!  Grin Grin Grin Grin Grin Grin

I thought I was confused   Huh Huh BEFORE I joined this board but I was wrong!!

I was just mistaken.... Now I am confused!   Huh Huh Huh

Len, I am not sure but is that type of arrangement used to reverse rotation on 3 phase motors? You could still use it in your application though...... I think!?

Dallas: I can probably post a diagram if you are not in a big hurry. I am looking for a copy of Visio  at a reasonable price unless anyone else has any suggestions for diagramming on a computer.
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Len Silva
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« Reply #26 on: August 04, 2007, 10:50:24 AM »

Len, I am not sure but is that type of arrangement used to reverse rotation on 3 phase motors? You could still use it in your application though...... I think!?

Yes, that's exactly what it is.  Expensive new ($200+) but quite reasonable as used or surplus.

They are basically two - three pole, single throw, normally open contactors with a mechanical interlock.
Len
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« Reply #27 on: August 04, 2007, 11:49:42 AM »

You guys are unbelievable!!!!!  Grin Grin Grin Grin Grin Grin

I thought I was confused   Huh Huh BEFORE I joined this board but I was wrong!!

I was just mistaken.... Now I am confused!   Huh Huh Huh

Len, I am not sure but is that type of arrangement used to reverse rotation on 3 phase motors? You could still use it in your application though...... I think!?

Dallas: I can probably post a diagram if you are not in a big hurry. I am looking for a copy of Visio  at a reasonable price unless anyone else has any suggestions for diagramming on a computer.


Tom,

Check out Google Sketchup and see if that will do what you want. Google gives a light version of it away free, but if you want I have a full version of Sketchup 5 I could make available to anyone who would like it.

http://www.sketchup.com/

Dallas
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« Reply #28 on: August 05, 2007, 09:45:07 AM »

Contactors generally have at least one set, and mostly several sets of auxiliary control contacts. I typically use one set of control contacts that are open when the contactor is energized to prevent another contactor or relay or other device from energizing. I really like to use two sets of control contacts. One set normally open and one set normally closed. 100% positive safety control.
Richard
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« Reply #29 on: September 07, 2007, 03:02:55 PM »

Sorry fellas, I'm going to resurrect this thread because Cody started a new one and the answers are here.

Richard and I have spent years working on Automatic Transfer switches and much more complicated equipment...but I believe he'll agree with me...the KISS principle still works all the time.

Contactors, whether manually switched or automatically switched have only one potential for me...when I most need it ...it'll fail and I don't have spare part and/or power!

Take my situation. I have a 50A shore cord (adaptable of course to 30A or 15A depending on what's available) and a 12.5 KW Generator which delivers 50A @ 240VAC. Wow!  A no Brainer!

I have one circuit breaker panel which handles all the 50A 240VAC power I want in the bus.  The main breaker is 50A.  So, why not feed the generator output into a 50A/240VAC receptacle wherein I can simply plug in my shore cord and feed my main panel?

DONE!  FINISHED!  VOILA!

It don't get any easier than that guys!

NCbob
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« Reply #30 on: September 07, 2007, 03:14:08 PM »

OK, I stand corrected.  Jackie, the 'light of my life', the 'Thorn in my side'  Wink, my partner, my helpmate mentioned, "Honey, some of these guys have inverters they depend on to take care of the AC load."

(We were in the generator business for over 30 years and she's not near as green as she's grassy lookin').

OK, maybe I'm and old f--t but as my Dad used to say, "The cow's need milking at 6 in the morning and 6 at night...pay attention there might be a test later".

That means, watch your batteries and if you get in trouble...you are "in control"!  You can start your generator (because it has a separate battery) and go on with your life!

I still endorse the KISS principle (besides it keeps SWWNBD off my butt)!

Bob
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« Reply #31 on: September 07, 2007, 05:37:50 PM »

I want to apologize to Dallas and the others to whom I promised to put a diagram of my setup on the board. I tried Sketchup & just don't have the time to learn it. I have a buddy who is going to let me used his machine with visio but I have not had time to get over there & do it.

All I can say is I'm sorry & I have not forgotten.

TOM
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