split phase AC motor - help

Folks,

I bought a motor on the weekend... AC (240VAC) which has a tag saying it's "split phase" wound. therre is no starting capacitor, but there is an audible click on shut down (after spinning down) so i suspect there is a starter switch inside somewhere.

My questiosn are, can this be reversed?, how? I opened the terminal panel, and found two screw terminals with external power and two internal wires applied. I am having problems getting much further itnothe motor since the alloy frame has frozen most of the steel or brass bolts/plugs.

Thanks, Des

Reply to
Des Bromilow
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This is a centrifigual switch which turns off the start winding, it is usually mounted on the fan end of the main shaft.

You have to locate the two wires that run to the start winding, usually at the centrifigual swithch, and reverse them. Leave all the other connections the same. This energises the start winding in the opposite polarity to the main winding, and it will run backwards. The main winding doesn't care which way it runs, it just goes in what ever direction it is started in.

We reversed the rotation on a split phase phase drill press in our shop when we were apprentices, it was fun watching the unsuspecting tradesman try to drill a hole with the drill bit running backwards, took him quite a while to figure it out!

If all else fails, try baking it an oven, not too hot, the alloy will expand more that the steel and they might come out easier, dry out any moisture in the windings while you are at it.

regards,

John

Reply to
john johnson

"john johnson" wrote: You have to locate the two wires that run to the start winding, usually at the centrifigual swithch, and reverse them (clip) ^^^^^^^^^^^^ Since there is no starting capacitor, according to the OP, what produces the phase shift for the starting windings? I am not doubting you--I am puzzled.

Reply to
Leo Lichtman

Leo sez: "> Since there is no starting capacitor, according to the OP, what produces the

On this type of motor the start winding provides necessary phase shift without a capacitor. The start winding is situated on the armature, offset from the main winding, in position to generate a properly shifted auxiliary field for starting. Many lower HP induction motors are this type. Design-wise, if the start cap is eliminated it uncomplicates things to some extent. A probable trade off is that heavier wire is required for the aux winding and more space in the armature slots to accommodate that wire. I am guessing the centrifugal start switch can be made of lighter material without the capacitor starting surge.

Bob Swinney

Reply to
Robert Swinney

It's not clear to me from the description that the motor isn't a repulsion induction start type. It will be apparent to him when he goes to rig it for reversing. :)

Jim

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Reply to
jim rozen

In both capacitor start and split phase motors the start winding mainly occupies the mostly vacant stator slots 90 electrical degrees away from the main winding. In a 2pole machine 90 electrical degrees corresponds to 90 mechanical degrees, 45 mechanical degrees for a 4 pole machine.

In all cases, to generate maximum starting torque, the starting winding current should lead (orlag) the main winding current by a substantial amount - preferably 90 deg.

In a capacitor start motor the presence of the capacitor results in a large leading phase shift so the starting torque is good and low start winding heating makes the motor reasonably tolerant of frequent starts.

In a split phase motor, to reduce cost, the capacitor is omitted and the start winding is wound with fewer turns of relatively thin wire. The fewer turns and thin wire means that the starting winding has a lower inductance and higher resistance than the main winding. This difference in L/R ratio between the two windings results in enough phase difference to generate usable starting torque.

The possible phase difference without a capacitor is fairly small and, because of the thin wire, self heating is high. This means that the starting torque is reduced and the motor is less tolerant of frequent starts.

Jim

Reply to
pentagrid

Greetings Jim, I have known, for many years, the physical characteristics of both capacitor start and split phase motors. I knew the capacitor shifted the phase to get the motor started. Also I knew that in a split phase the start winding would get hot and burn up if not switched off. I di not know how it shifted the phase> I always assumed it was because the start winding was in quadrature to the run winding. But I guess it still needs to be out of phase too. And making it with fewer, thinner windings does just that. So I learned something new today thanks to you. Cool! Cheers, Eric R Snow, Who doesn't know it all yet

Reply to
Eric R Snow

I've read that the primary purpose for a start capacitor on a repulsion induction motor was to increase starting torque. In applications where I've added start caps to several motors that needed to start under load, they were able to start reliably and had no other problems.

WB .................

Reply to
Wild Bill

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