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Reversing (non reversing) Motor

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GrizzlyJoe

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Hi guys. Tnx for letting me ask a dumb question here. I'm retired from electronics all my life but this is a theory question. My brother bought a 3 H.P. -240 ac motor from Grizzly.com to run a bandsaw with. He bought the first one he came to that had the right shaft size. When he got home he immediately welded on a different base (which would void any warranty) and then he wired it up only to find it ran the wrong direction. The grizzly model number is H5387 and only had two wires exiting motor. The book says it is non-reversing. I'm thinking that is because there is no block inside with all the wires terminating on it, most of all others made by same company will reverse. Detective work has led me to find out that it is a Capacitor start-Capacitor run motor with the start switch only cutting out the start capacitor and leaving in the run capacitor (parallel run cap with start cap & switch). QUESTION: If I physically swap connections from start & run circuitry by inverting connections - will it reverse rotation ? I would have to open up wire terminations to do this and can, but I want to be sure it will reverse. Otherwise for him it will be cutting up his band saw and sticking the motor out the side.....Tnx to all for your help.
Joe
 
If you can disconnect the capacitors, the motor won't start. However, it will run in either direction.

Taking care not to loose your fingers on the bandsaw, you might be able to use it by turning on and flicking / shoving it in the right direction.

That does depend on how much friction there is, as there will be very little motor torque at low speeds. Obviously you won't have any real load when starting.

If you can get to them, reverse either winding and leave the capacitor connected, it will run in reverse.
 

QUESTION: If I physically swap connections from start & run circuitry by inverting connections - will it reverse rotation ?


No, that would just put the start cap on the run winding,
and the run cap on the start winding.

You have to reverse one of the windings.
Not both.

I dont think there is any reason why it would object to running
the other way.
Best of luck with it,
John :)
 
john1 said:
You have to reverse one of the windings. Not both.

That's correct. Normally the main winding is the one to choose, and leave the aux winding alone.

(The main winding sports the starting capacitor, which is usually removed from service after startup by a built-in centrifugal switch [but you said differently; it had its own start switch?]. The aux winding sports the run cap 100% of the time.)

Without knowing exactly what motor you have, this is my best advise.

FYI,
Corey
 
Update on Reversing AC Motor

Hi Again Everyone. Tnx for the replys to my post but since posting I have run across this small picture that might make it a little clearer for everyone.
I want to cut the Aux winding loose from L1, cut the capacitors loose from L2 and then flop everything upside down and rewire. My question is and still remains, will this start the motor in reverse direction. The phase shift will be changed across the stator due to the L C network being upside down? Thanks for your help.
 

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Hi Nigel and tnx again. It's not that I haven't paid any attention to your replys - I have and do agree with you on the solution but to explain why I haven't yet done that, look here at the attached photo. It's a new motor ($260.00) with NO terminal board with wire terminations on it. If I smoke it, my brother would not be too happy. I would have to cut open butt splices, tie strings and pull wires from varnish, I've been down that road before and it's a rough one to trave. Anyhow, I'm reluctant to do that. I think I'll suggest he buy the right motor or stick it out the other side of his bandsaw, Hi. 73's and tnx again.
Joe
 

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I can see one big capacitor in your photo. Where is the other one?

I see what you mean about modifying that motor, but you might be able to cut the wires and use connector blocks while leaving the splices alone. If you label the wires, use connector blocks and is doesn't work, you can just go back to what it is now.

Have you tried no capacitor and starting by hand?
 
Update on Reversing AC Motor

Hello Diver300 - Tnx for the reply. The second Cap is hanging from motor at top right of motor (still in Black covering). I have not tried spinning the motor as to reassemble it all includes putting the switch, Mechanical Fan and end plates all back together. Still hoping for something easier. Thanks again
Best Regards
Joe:)
 
Is it possible to use gears to reverse it?

A couple of cogs would do the job.
 
Hi Joe.
I agree with those who suggest that you swap the connections to either the start winding or the running winding,but if the saw is belt driven and there is enough space to twist (cross) the belt between the drive pulley and the driven pulley it will cause the driven pulley to run in the opposite direction.


Regards
JMcG
 
GrizzlyJoe said:
I want to cut the Aux winding loose from L1, cut the capacitors loose from L2 and then flop everything upside down and rewire. My question is and still remains, will this start the motor in reverse direction.

Howdy again,

If you remove the three connections you mention, and then flop *everything* upside down, you're back where you started. But if you remove the three connections you mention, and then flop L1 and L2 with accompanying main winding upside down only, then you're okay. (Communicating is so wonderful.)

But, the right thing to do here is to just swap the wires to the main winding (two disconnections vs. three). That's what you want to do, and leave everything else alone, and the motor will rotate in the opposite direction.

(Also, according to the diagram you supplied, the start capacitor is simply added to the run cap at start time, then pulled out. It's making the phase shift bigger for a short time to get it to start. This is a variation of the PSC motor [permanent split capacitor], called a two capacitor start/one capacitor run motor.)

Corey
 
I can see how difficult it will be to disconnect the windings. Is there any chance that you could assemble the motor with the body reversed, but the end plates and the rotor the present way round? You might even be able to tap the stator assembly out of the casing and fit it the other way round.

Thinking of obscure solutions, the capacitor advances the phase of the current to the start winding. You need to delay that current and the motor will run backwards.

Two methods occour to me. One is to replace the capacitors with inductors, but sourcing them would be difficult. A totally untried suggestion is to replace the capacitor with a lamp dimmer. They work by delaying the turn-on point of the voltage to the lamp, so one of those might delay the current in the starting winding, which would give you reverse torque.
 
Last edited:
The End of Story

Hello again everyone and thanks for all the input, it was appreciated. I finally bit the bullet and tore everything apart and numbered all the loose ends, then drew up a motor schematic so I would know where everything went. After seeing all of the wiring for this 220 volt motor and the connections, I went ahead and flipped the starting circuits and rewired everything. Used plenty of heat shrink and lots of wire ties (tie wraps?). Crossed my fingers and fired it up - no smoke and it was running in Reverse now. I have to admit that I took plenty of time and triple checked everything. Once again I would like to thank all who volunteered help. I have attached a schematic if anyone would care to see it. Tnx & 73's Joe
 

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GrizzlyJoe said:
Crossed my fingers and fired it up - no smoke and it was running in Reverse now. Once again I would like to thank all who volunteered help.

Cool man,
Corey

P.S. Sounds like your brother owes you big time...
 
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