DPDT ac/dc switch

JoeyInCali said:
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Unique's ac motor with Minarik controller is somehow reversible.:confused:
http://www.distel.co.uk/DC_MOT_CON1.htm
I dunno if that helps.
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Joey, what makes you think that it uses an A/C motor? It looks like a universal motor but I can't be sure.

Dick
 
rhncue said:
Joey, what makes you think that it uses an A/C motor? It looks like a universal motor but I can't be sure.

Dick
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It is a DC motor. Probably has braking on its circuit board to allow it to reverse instantly without blowing out the motor. I saw Brian throw one in reverse while running forward and it turned right around and went the other way. I did this to a Sherline motor and controller once and had no problem at first. So, I decided to do it several times and what I found out with the Sherline was that it was damaging the motor little by little and after a few dozen times burned it out. I used the Sherline motor on some of my early Mid Size Cue Smith lathes and I quit because the motor was not continuous duty. It would shut itself down after about 1/2 hour of shaft cleaning type of work. After cooling off for a few minutes it would work again. So I searched high and low and found a continuous duty 3/4 HP DC motor for the Mid Size and have used it ever since. I don't have instant reversing on it, but I also don't have many problems either.
 
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rhncue said:
Joey, what makes you think that it uses an A/C motor? It looks like a universal motor but I can't be sure.

Dick
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The controller is supposed to be for 115 vac.
Me's bad.
 
rhncue said:
I doubt very seriously if the Hightower machines use a reversible A/C motor. A/C reversible variable speed motors are very expensive and must come to a complete stop before the reversing switch can be thrown.
Dick
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My Grizzly lathe has a reversible AC motor on it and the whole thing cost $1800 delivered new a few years ago.
You can throw the lever into the other direction while the motor is running but it will just keep on running in the same direction.
Like you said it must come to a sop to reverse direction.
 
WilleeCue said:
My Grizzly lathe has a reversible AC motor on it and the whole thing cost $1800 delivered new a few years ago.
You can throw the lever into the other direction while the motor is running but it will just keep on running in the same direction.
Like you said it must come to a sop to reverse direction.
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That's a charactoristic of induction motors, which are a type of AC motor. The direction the motor STARTS rotating can be controlled, but the same method will not reverse a running induction motor. Note that this application uses a DRUM SWITCH , and not a simple DPDT toggle switch. Go to books.google.com and search on DRUM SWITCH, the section of the Alerich/Keljik book explains it fairly well, and the book includes other good information on motors.

When you reverse a DC or universal motor (or a synchronous motor for that mater) their can be very large current surges that heat up the wires more than normal and can burn through the insulation, ultimately letting the smoke out. Anecdotally, most will have seen the lights dim when a large motor is started. Reversing a motor is a bit like staring one, except that it is not just starting, it first must stop the reverse rotation and THEN start the motor. This will dim the lights much more than just starting the thing. Little motors like the ones in question may not dim lights, but the effect is still there.

Dave

PS to Chris, thanks for the story about burning out Sherline motors, you answered the question "yes, but how many times ?" I suggested earlier with "a couple dozen".
 
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