Motor question

The mains induction motor on my bandsaw exploded, with fire, yesterday - the magic smoke literally drove me from the room - and so the bandsaw needs a new motor.
The original motor was marked as follows:
1/3 HP 225W 240v 50 Hz 1450 rpm class E heat 60C 1998
I have a motor of similar size (from a £25 Aldi bench drill) which is marked:
500W / S2 - 30 mins 230v 50 Hz 1390 rpm Safety class 1 04 2004
Now I frequently cut rather large things with the saw, which can take longer than the 30 minutes the S2-30 min rating allows.
It will be derated to whatever the saw uses - the original motor didn't struggle, so presumably somewhere around 200 W - but will probably be used for an hour or so at a time.
Is it okay to use this motor in this way? Looking at eBay,the prices of new S1 motors are quite ferocious, so it would be good if it can be used.
Thanks,
-- Peter Fairbrother

Peter Fairbrother wrote:
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You will possibly find it will go the same way in time. S2 ratings will be the result of a number of parameters some of which will be cooling etc. You could try running the Aldi one for an hour or so and see how hot it gets off load. I can't imaging that sort of motor will have much design margin it. I reckon you would be better off with a used one of known make of the bay/freecycle/asking for one in this NG etc I don't think I have anything here at the moment but if it ever warms up, I'll go and have a look.
Bob

Bob Minchin wrote:
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Well I spent most of a day bodging the Aldi motor into place, and it doesn't seem to get too hot.
The bad news is, it goes the wrong way round :(
It's a single phase 4-pole capacitative start induction motor - is there an easy way to make it go round the other way?
Thanks,
-- Peter Fairbrother
I can't imaging that sort of motor will have much
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Peter Fairbrother wrote:
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Not always possible with cheaper motors. Just depends how they are wound. To be reversible, the starter winding must be isolated from the run windings as you have to reverse the relationship between the two windings. It is sometime possible to open up the motor and pick the connections apart if you know what you are doing.
Bob

Bob Minchin wrote:
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[..]
Well I thought as much, and I opened up the motor, and now I'm confused. I thought that capacitative start motors had a centrifugal switch, but this doesn't have one that I can see.
Could it be a capacitative-run motor? The capacitor is 12 uF, the motor plate power is 500 W.
Can't see anywhere obvious to pick the connections apart, but maybe I can just turn the entire stator+windings around?
Bob, thanks for your help, it's appreciated
-- Peter Fairbrother

On Mon, 13 Feb 2012 23:15:33 +0000, Peter Fairbrother
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Greetings Peter, It sounds like you have a permanent capacitor split phase motor. If this is the case then if you look at the power wires coming into the motor one should go to the motor windings and the other should connect to one motor winding AND one lead of the capacitor. Changing the power lead so that it connects to the other capacitor lead will cause the motor to reverse directions. The pemanent-capacitor split phase motor has two identical stator windings. The windings are connected together at one end and to one of the power leads. The other ends of the windings are bridged by the capacitor. By connecting the other power lead to one or the other capacitor lead you are powering one winding directly and the other winding through the capacitor. The capacitor provides the phase shift which determines which way the motor will turn. This type of motor will have lower starting torque than one with a centrifugal switch but will run smoother. This is why this type of motor is often used for bench grinders. Please let me know if this information was helpful. Cheers, Eric

snipped-for-privacy@whidbey.com wrote:
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Hi Eric,
Thanks for that - I didn't quite get your description, but it's one of those situations where a diagram is worth a zillion words, and having found a diagram on the 'net it all makes sense.
I did know there were such things as capacitative-running motors, aka permanent capacitor split phase motors etc, but thought they were only made in small sizes. Which is why I was surprised to find this motor was one.
I probably managed to find the wires to reconnect, but instead just turned the stator and windings round as it was easy to do. It's now working - yippee!
Thanks,
-- Peter Fairbrother

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On this side the term is Permanent-Split Capacitor. http://openbookproject.net/electricCircuits/AC/AC_13.html#xtocid714738
jsw

Peter Fairbrother wrote:
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Eric has answered from an electrical point of view - by the way the word is Capacitor/capacitive :-)
Manufacturers are avoiding centrifugal switches largely on the grounds of cost and getting away with PSP motors in application where slightly less starting torque is acceptable. One top of the range motor maker is now fitting electronic timers to their capacitor start motors to get best starting torque without the centrifugal switch.
Turning the stator end for end should work OK in theory; just check there are no polarising pins or similar fitted to prevent this from happening in manufacture.
I hope it lasts OK in the new application.
Bob

Bob Minchin wrote:
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My spellchecker allows both capacitive and capacitative... but not "spellchecker", hmmm.
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Makes sense - switches are not just expensive, they are unreliable. I didn't know they could make efficient psp motors though, and thought they stopped at maybe 100 W or so in size.
One top of the range motor maker is
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There is some sort of electronic doohickey in the leads to the capacitor, but I haven't investigated it.
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Turned round now and it's working, and thanks for the help. It's also very much quieter than the last motor, can hear the belt flap and the blade go round now.
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Me too - cut through 5 square inches of ally in about ten minutes, it got really quite hot, too hot to touch comfortably. Smelled a bit, but the motor hadn't been used for a while - smelt hot, not burned.
How hot can a motor get (and still work)?
-- Peter Fairbrother

On 14/02/2012 19:41, Peter Fairbrother wrote:
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It depends on the class of insulation Peter but that information I doubt very much is easily available. The cheaper a product is normally there is less info around. If there is a UL mark on it and a number then you may be able to find something from www.ul.com.
Regards,
Rob.

news.plus.net wrote:
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If you want to extend its life I would radically increase airflow with a decent fan with its own motor. Run this after the hot motor has been turned off until cool. The real answer is a correctly rated motor but you seem determined to ignore the signs. Bob

Bob Minchin wrote:
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You seem to be missing the situation a little - a correctly rated motor would cost about £85 which I haven't got handy, while using the present motor costs me nothing :)
-- Peter Fairbrother

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In my experience overloaded motors smell hot first. Could a metal chip have fallen in?
jsw

Jim Wilkins wrote:
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I don't really see how, but maybe.
I was in the next room when it started making graunchy sounds and vibrating. I lifted the saw from the work, but that made no difference, so I went to stop the saw - but before I could, BANG!
Checked the bearings, they seem OK. The inside parts of the windings are fried black tho'.
Can't remember any grossly overheated smell before the bang, and after the bang the burning smoke smell was so overpoweringly awful that I wouldn't have noticed one.
-- Peter F
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The Taiwanese motor on my 4" x 6" bandsaw occasionally makes a loud buzzing, growling racket on starting which may be from the centrifugal start winding switch not opening. My old Maytag washing machine made similar but less distressing sounds after I replaced the drive belt with one from the hardware store. They need the factory belt which slips to let the motor quickly jump to working speed while the heavy drum slowly accelerates.
If you find that the start switch failed, perhaps a spring broke, then the load rating wasn't the problem.
jsw

Peter Fairbrother wrote:
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Peter,
I had similar happen on my 4 x 6 when I was in the other room and the blade jammed in the cut, which it does sometimes on large aluminium sections if not lubricated often enough. It didn't smell good but not that strong so I removed the end to inspect and quickly put it back and ditched the motor outside destined for the tip. I have never smelled anything so foul and acrid, cutting through a dead snail or 2 in a box section that had been outside was a bit nauseating, but the motor inside was bad. I replaced it with a machinemart motor, PSC so the starting torque isn't as good requiring the blade be lifted, but other than that it works well. One thing is the machinemart motor has a snap on cover and I have knocked it and jammed the fan on occasions and have also had the fan come loose and the motor has gotten quite hot but it has never smelt hot and has done more work than the original by now.
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