Windings and Relays and Centrifugal Switches

[bajaespuma]

Oh my!

 

This is a serious request for a serious lesson on these components, what they do and how they work. I've girled-up to the point that I will admit that I have no clue and I'd ask the gear-heads in this organization to explain all of this. If there are posts from the past that do this I'd appreciate y'all directing me, us, to them.

 

[akronman]

past post

while this isn't an explanation, it's a link to a repair of one style centrifugal switch I have on an early 50's Hamilton dryer with a Delco motor, and the same switch showed up on a 62 GM Frigidaire dryer.

One question I have on capacitors----do they store up power to start the motor at maybe 120% of power, to get it going, or do they hold back some amount of power and start the motor at maybe 80% so as not to jolt a non-moving motor with too much at the beginning? I' ve never known.

Centrifugal switches kick in once the motor is nearing top speed, and on a dryer then turn on the heat so the dryer won't start unsafe heating if the motor/blower/airflow isn't working. I believe they simutaneously switch from the "start windings" on the motor to the "run windings" but that's where the motor profesionals' answers will ge good to read.
Most washer motors I've seen have a different type of centrifugal switch with only one operation, moving the power from start to run, nothing to do with an extra circuit for heat or anything, of course.

Hopefully I haven't muddled the question, and I'll enjoy the pros answers.

http://www.automaticwasher.org/cgi-bin/TD/TD-VIEWTHREAD.cgi?41652

 

[arbilab]

Wish a semester of electric shop was mandatory in school, surrounded by it as we are.

Centrif switch turns start winding off. Run winding is on any time motor is powered. In dryers a separate switch triggered by the same weights turns on heat. In certain Maytag washers centrif switch also switches run winding to low speed (if selected) once it's running.

Why two windings or more? Their poles are offset so as to make the magnetic field appear to rotate and thus drag the rotor with them. Different numbers of poles will produce different speeds. Why turn the start winding off? Back to that 'appearance of rotation'. The start winding operates at relatively high current so its poles get magnetized sooner than the run poles.

Capacitor is another way of making the field appear to rotate. It shifts the voltage and current peak of the start winding to make that winding lead the run winding. Many configurations are possible. AC compressors for example, have 2 run windings with a capacitor in series with one. These are called capacitor-run and do not have centrif switches. What you have to stick outside the motor to make it work depends on how it's designed internally. And why there are so many component arrangements and not just one.

Certain GE washers use a start relay performing the same function as centrif switch by measuring current which drops once the motor is moving. I'm sure you've seen lights dim when a motor starts then go bright again. Motors use max current at dead stop. That's why they tend to smoke and trip if they don't succeed in starting.

There's more to it, like CEMF, counter electromotive force. And how 'induction' works in the first place. But those aren't "necessary" to understand the component functions.

 

[whirlaway]

Added Punch!

Capacitors give the motor an extra jolt to start the motor to keep it from lugging,or starting a heavy load.Like a compressor on an ac unit,sometimes when they shut down they maybe in the middle of a compression stroke adding an extra load on the motor and the capacitor gives it the extra boost to get it going with out damaging the motor.I have a 1910 Hoover junior vacuum,its starts and then you hear a click once it reaches a certain rpm a clutch kicks in and the fan and beater bar starts so not to overload the motor,it has a huge motor on it but it has such a slow take-off,the later ones were smaller and more powerful and did need the switch. Bobby

 

[whirlaway]

Error

In my last sentence The newer motors did not need the clutch!

 

[akronman]

Thanks

To arbilab and Whirlaway---------you've explained in a way I can get near understanding, a huge improvement over before.
Thanks

 

[arbilab]

I spoze the way motors work most concerns motor designers. It only becomes a bother for "us" when they DON'T work.