Single phase motor controller.

I know this is a very rudimentary question, but here goes anyway.
I've got some small machine tools that I would like to put motor controllers
on. I'm not sure that's the correct phrase though. Perhaps just a "mag switch".
The larger motor is a 1/4 HP, General Electric, single phase, 115V, 5.2A, 1725 RPM, general purpose motor. I suppose you would typically find it in furnace to run a fan. I would also like to be able to reverse the motor.
The smaller motor is about 1/6 HP with similar specs as the last one.
I'd be surprised if I needed 10k operations. I just like the idea of the control not having a memory. I don't need overload protection. The motor has automatic thermal protection and of course the circuit is on a breaker.
This is not in an industrial atmosphere. It's for hobby use.
So, do I really need a relay capable of interrupting 3-6x the FLC? I was hoping of simply wiring a relay who's contacts were rated for 10 or 15A.
Thanks for any thoughts.
Regards,
Robin
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1) Is the motor(s) you want to reverse one that can be, some are not?
2) Motor starters are rated for the motor size and also come in reversing models. See / call your local GE supply or other electrical supply outlet or the GE Industrial Systems web page. A GE is not a requirement though and they many makes will work.
3) Also check the NEC and local codes.

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Robin,
Any 10 to 15 A relay will do fine. The worst that will happen is that the contacts will either weld or burn out. Then you replace the thing. Reversing is a different matter. With a three phase motor this is very easy -- just flip two of the leads. It's a bit more difficult with single phase motors. Strictly speaking, a single phase motor has no 'direction' and can't start because it doesn't know which way to turn. A second phase, shifted in time with the regular one, is created by adding a capacitor into the circuit. That is the little cylindrical can mounted on top of the motor. A small, internal speed switch switches the capacitor on until the motor is up to speed. I'm not sure of the exact arrangement but definitely it is not meant for user access. Reversing motors can be bought but are not commonplace. Perhaps some appliances have them.
Walter.

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phase,
into
definitely
not
Walter,
My motor doesn't have a visible capacitor on the outside of the motor.
I looked at the terminals on the motor. There are only two plus ground. I will have to open it up. From what I've seen of other motors, the two terminals are in fact wired to both coils. If I bring both coil terminations out, I should be able to reverse the motor..?
I looked on GE's website. My motor isn't a current model. However, I'm pretty sure I found one with the identical specs and it's ECCW so I can rewire it for reverse. If their "extra info" server would just work, this wouldn't be so tough...
I want to be able to reverse as this has specific applications in machine tools (typically while threading).
Thanks for the answer Walter, mindspringnews as well.
Regards,
Robin
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Robin S. wrote:

Yes you should.
In general (and Walter has a hell of a lot more experience with this, so I don't know why in hell _I'm_ answering) a single-phase induction motor will have two coils, one of which is arranged electrically to be out of phase with the other. One will be the "main" or "run" winding, and the other (the out of phase one) will be the "start" winding. The phase shift will either be done with a capacitor (very common), a high resistance winding or a resistor (both rare, but used in way-older motors because caps are beastly things). In most motors the start winding will cut out above a certain motor speed -- you can often hear the click when this cuts in or out.
At any rate, if you have access to all four terminals (main winding and starter winding) you should be able to reverse the rotation by reversing the polarity of either winding with respect to the other -- this makes the starting magnetic field rotate in the opposite direction, so your motor starts in reverse. Bringing your start winding out to a DPDT contacter (or plain ol' switch) will allow you to reverse it's polarity.
If your motor has an obvious access plate, and if there are four terminals behind it that the two power wires connect to, and especially if there are some more-or-less cryptic markings that indicate motor direction & hookup relationships then your motor was made to be manually reversed if not externally reversed, and you just need to bring out the appropriate wires (and figure out what they are). If not, then you have to figure out where the windings are and all that folderol, and I wish you luck.
You may want to check out rec.crafts.metalworking. I have ceased to subscribe until after the presidential election, whereupon I'm hoping that the off-topic flame wars will have subsided to a tolerable level. None the less there are a lot of very astute people on that list, many of whom will have direct experience with what you are trying to do.
--

Tim Wescott
Wescott Design Services
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I'll just use a toggle switch. I don't plan on switching direction under power (or at least not on purpose).

That's exactly what I was planning on doing. Excellent.

That's a good idea. I've been posting to r.c.m. for over 5 years now (roughly) and it is certainly an excellent resource. I thought I'd come here and get it straight from the horses mouth (just in case the engineers saw something wrong with my idea.)
I ended up buying a 20A 120V Omron relay surplus this afternoon. The one thing is that it has a 100VAC coil. Should I put a resistor in series to reduce the voltage?
Thanks for the comments.
Regards,
Robin
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Robin S. wrote:

Or a 12V indicator light -- assuming it has the same current rating.
That way, when the lathe stops working you'll know the light's burnt out :).
Depending on your relay a resistor may not be necessary, but you're talking about up to 44% more power dissipation, so it's probably a good idea to put it in.
--

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That's a rather odd rating. A resistor will work but remember that the relay is a very inductive load. The only simple way to find the right value is to put a meter in series and try out different values.
How about finding some components in old, junk appliances like automatic washers, have motors, relays, etc.
Walter.

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There is a second reason why a motor might have two windings and four leads. It has nothing to do with direction. Some motors are built to be 120 / 240 VAC selectable by having two sets of windings brought out to four terminals. Series is 240, parallel is 120. There are generally four posts with two slider bars that can be put into two different positions. If this is what you see, it is NOT a bidirectional motor.
A friend of mine once bought a radial arm saw very cheap because "it doesn't work". It didn't have any torque and kept cutting out on overheat. My friend figured there was a defective over heat cut-out and spent some time trying to find a new one. Then he noticed the motor was pinned for 240 VAC. It took all of five seconds and he had a perfectly good saw for a fraction of the price.
Walter.

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There are many reasons why there maybe 2 windings, besides all those mentioned till now, there are also multiple speed motors w/ dual windings. Here, for example you might switch between starting on a 6 or 8 pole winding and running on a 4 or 2 pole winding. The centrifugal switches are used to do both applications of starting and speed switching.
A capacitor can be used for starting direction, but there are also RUN capacitor types. I worked at GE motors for many years and there are a lot of variations done for different reasons.
Robin S. needs to be sure what his motor is and that it is an ECCW ( Ether Counterclock or Clock Wise ) type that he thinks it is. He should contact GE w/ the motor model #. Get a wiring diagram from them or a different motor if needed.
Dennis

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I had a similar experience with a pump motor to a swimming pool. I still can't think of why it was wired for 240 volts.
Michael

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A worth while review / overview. Several linked pages.
http://www.tpub.com/content/neets/14177/css/14177_86.htm

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Herman Family wrote:

Mines wired for 240. But then it's wired to 240. Makes perfect sense to me. :-)
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Walter Driedger wrote:

So where do they put the start winding in such a setup? Do they just use one that will work at 120V but not burn up at 240, and only switch the main one around, or do they use two separate start windings, one for each main?
--

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On Sun, 30 May 2004 14:54:00 -0400, the renowned "Robin S."

Robin: Try to get ahold of a surplus contactor rated 15-30A rather than a relay. Try Princess Auto, Above All or what's left of Active Surplus.
Best regards, Spehro Pefhany
--
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snipped-for-privacy@interlog.com Info for manufacturers: http://www.trexon.com
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Spehro,
I never thought to look at Princess Auto. Active is truly a shadow of its former self. I asked about contactors but had to explain they were like higher power relays.. Not very reassuring.
There is a Princess Auto out where I work, as I understand (Steels and Airport road). I'm not sure exactly where it is but I'll have to look them up.
Thanks for the suggestion.
Regards,
Robin
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On Sun, 30 May 2004 20:57:06 -0400, the renowned "Robin S."

Their big new store is on the West side of Dixie, north of Courtney Park Drive (which, in turn, is north of the 401). Surplus is in the back left section.
Sayal on Matheson, West of Dixie should have them too, but price is probably higher.
Best regards, Spehro Pefhany
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snipped-for-privacy@interlog.com Info for manufacturers: http://www.trexon.com
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Excellent I'll try and go tomorrow.
Thanks again Spehro.
Regards,
Robin
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