/diy/ - Do It Yourself

[Anonymous No.1599328]

sorry for asking stupid questions but fuck me

does the start or aux winding in a split phase motor still produce back emf even after the motor is at full speed and the centrifugal switch has kicked said winding out of the circuit?

every time i try to run and motor without it just heats up

whats the fucking deal, is it just coincidence and ive actually just had shorts in run windings causing the heat?

what the fucks the scoop

[Anonymous No.1599330]

>>1599328

every time i try to rawdog and split phase motor with just a run winding (no start winding) it just heats up*

[Anonymous No.1599333]

>>1599328
>does the start or aux winding in a split phase motor still produce back emf even after the motor is at full speed and the centrifugal switch has kicked said winding out of the circuit?

If the magnetic field is changing in a winding it will generate a back emf. If that winding is open circuited there will be no current flowing and thus no heat produced and no drag torque. If any coils in that winding have a closed path then current will flow, heat will be generated, and there will be drag torque as well that the regular winding has to overcome which will lead to additional heating.

[Anonymous No.1600489]

>>1599328
On a single capacitor motor, the aux winding is only used to create a rotating magnetic field when the motor is starting (before the centrifugal switch kicks out). With just the run winding in the circuit, you should be able to plug it in, start it by hand in either direction and it will run without drawing more amps or generating more heat than normal (once it's spinning).
On a dual capacitor motor, the aux winding is always in the circuit: When the motor is first turned on the aux winding is phase shifted by the capacitance of both start cap and run cap in parallel, once the motor gets up to speed and the centrifugal switch kicks the start cap out of the circuit, that same aux winding is still in the circuit but now its phase shifted by the capacitance value of the run cap only. (see pic) If you don't have a run cap, the motor will draw 1.5-2x the rated amps and will get hot that's how you know it went bad.

[Anonymous No.1601932]

>>1599333
The voltage between two points is actually charge concentration (electrons or holes, usually) at the end of the wires. To have a varying EMF, the charges must move => there must be current flowing through the windings

[Anonymous No.1602083]

>>1601932
Prove it in practice though. No meter allowed because current flow obviously.

[Anonymous No.1602250]

>>1600489

roger that but i'm talking specifically split phase motors.

no capacitors, just a start winding and an aux winding.

according to this thread, if i wanted to rewind an electric motor, i could theoretically remove all windings (start and run) and rewind only the run winding, leaving the start winding out entirely, and the motor would function perfectly fine, aside from having to give it a spin to get it started? it wont get hot?

[Anonymous No.1602419]

>>1602250
Does a motor produce back EMF?

Pertinent information: can the motor be used as a generator, i.e. can it also convert mechanical work into electrical work? In general for electric motors this is very yes. It's this ability to convert mechanical work into electricity that produces back EMF.

So in answer to your original question: yes.

[Anonymous No.1602429]

Instead of making a new thread, and since my question is about electric motors, I'll ask here.

I have a free to me table saw with a 13 amp (120 V) motor. The guy before me took out the switch and thermal protector and replaced it with a light switch.

I have a compatible 20 amp switch I am going to install and a bunch of thermal protectors to choose from.

If I understand correctly, a thermal protector should be 125% of the motor's amperage, yes? So could I get away with a TP rated for 15 Amps?

Sorry if this is a stupid question, but I cannot find the amperage of the original thermal protector (Ryobi BTS10 saw) on any specs pages, only links to replacements that don't show the specs. And being a poorfag, if I can use one of the ones I have, I'd rather do that than spend $12+ for an OEM TP.

[Anonymous No.1603663]

>>1602429
>So could I get away with a TP rated for 15 Amps?
Yes, that will be fine.
The TP switches and keyed switches they include with most table saws go bad after a few years. I however managed to have the plastic key escape from mine the last time I moved and just ended up replacing it with a 20 amp toggle switch.

[Anonymous No.1603847]

>>1603663
Thanks. I'll be wiring it back up after the paint dries and I reassemble it this weekend.

[Anonymous No.1603854]

>>1602429
How does the motor not have thermal protection built in? I have an old Craftsman and Delta saw and the stock switch on both is just a standard switch. The thermal protection is on the motor. Do they not both with that on modern tools?

[Anonymous No.1603860]

>>1603854
One the BTS10 (what I'm refurbing) the TP breaker is next to the power switch according to the schematics.

[Anonymous No.1603870]

>>1603854
its 50/50 with motors it seems. I wire up a lot of commercial exhaust fans and half the time its not built in and we have to get the thermal overload switches.. which has to suck for the customers because they dont automatically reset and being on a roof makes it hot so they always trip.