What Kind of Switch is This?

[eclorian]

This is related to another thread I posted, but the nature of the question is different.

This is a governor switch in parallel with a resistor. The coils for the motor are in series with that part of the circuit. Based on this video I found, it looks like the switch opens and closes at a certain frequency which changes based on how close the contact points get. Is that correct? Does the use of AC current make that work somehow? I'm trying to figure out the stress on the parallel resistor at lower speeds.

Sorry if this is in the wrong thread, I couldn't figure out where it should go.

 

[rjenkinsgb]

It looks like a kind of small centrifugal governor; "flyweights" that move out against a spring, so the faster the motor turns the more the weights moves out.

The weight mechanism pushes a bearing that in turn moves the contact.

 

[eclorian]

It looks like a kind of small centrifugal governor; "flyweights" that move out against a spring, so the faster the motor turns the more the weights moves out.

The weight mechanism pushes a bearing that in turn moves the contact.

Based on the one I have in pieces on my kitchen table that actually makes a lot of sense.

So how does the speed control work, is it opening and closing at a frequency?

 

[rjenkinsgb]

This looks rather like it, possibly an earlier version?

US3660741A - Governor controlled food mixer - Google Patents

A lightweight, hand operated food mixer having a speed control which includes a mechanical governor for controlling the motor to any preselected speed. The speed control includes a manually operable cam and a switch which are mounted on a frame above the worm drive to the beater spindles. The...

patents.google.com

 

[rjenkinsgb]

The contact moves outward in proportion to the motor speed, due to the weight mechanism.
Every time the motor exceeds the set speed the contact opens until it slows down again enough for the contact to close and restore power.

It's not related to AC (other than that meaning less contact arcing) and the frequency or duty cycle will depend on the motor load - the more load and the faster it slows down, the shorter the breaks will be until the load gets to the point it never reaches the set speed and the contacts never open.

 

[eclorian]

This looks rather like it, possibly an earlier version?

US3660741A - Governor controlled food mixer - Google Patents

A lightweight, hand operated food mixer having a speed control which includes a mechanical governor for controlling the motor to any preselected speed. The speed control includes a manually operable cam and a switch which are mounted on a frame above the worm drive to the beater spindles. The...

patents.google.com

Ohh that's awesome, I need to learn how to look up patents.

 

[eclorian]

The contact moves outward in proportion to the motor speed, due to the weight mechanism.
Every time the motor exceeds the set speed the contact opens until it slows down again enough for the contact to close and restore power.

Ok, circuit analysis question. Is there any way to determine the potential current going through the parallel resistor at a given speed without actually putting an ammeter in there? Maybe by measuring the inductance of the motor? Really I'm just looking for maximum potential wattage at the slowest speed.

 

[rjenkinsgb]

I'd guess that the maximum dissipation in the resistor will occur when the motor is fairly heavily loaded on a low speed setting, so the contact duty cycle is somewhere around 50%

At light load the contact will be open more of the time, but the motor will not be drawing so much current as when under load.

As the load gets very high, the contact will be closed most of the time so not so much dissipation in the resistor.

It's very much guesswork; at low speed the motor back EMF will be low, so the current higher than when running at full speed; but the motor will accelerate back to speed in a shorter time due to the higher current.

The resistor may be acting as a snubber as much as anything; resistors were often used as snubbers to limit inducive spikes & protect contacts from arcing, going back a few decades.

If a contact controlling an inductive load simply switches open, the voltage spike induced can be massive - eg. easily in excess of 500V from a a common relay coil on 12V.
A resistor can allow the current to continue without such an extreme voltage increase.

 

[eclorian]

The resistor may be acting as a snubber as much as anything; resistors were often used as snubbers to limit inducive spikes & protect contacts from arcing, going back a few decades.

Thank you so much for all your help and for the information. I'm barely finishing up my two year degree, so learning about these things and how they work is not only fascinating, but hopefully useful in the future.

And, of course, helpful in rebuilding this mixer for my grandmother.

 

[MaxHeadRoom78]

The motors fitted are of the Universal (AC/DC) type, As in the other forum, if it is a Sunbeam mixer, it is just a simple cam fitted to the knob on the end of the mixer for speed control.

 

[Biker48]

It is the same theory of motor control on a Kenwood mixer. They have been using that system for years. They are electronic today rather than mechanical control, The system uses a cam which changes the distance between the motor and PCB which is influenced by the spring pressure (hope that makes sense).Look up the Kenwood chef mixer design for an explanation of the theory. This is a link to one article: https://www.instructables.com/Kenwood-Chef-A902-A904-AC-Motor-Speed-Control-Modu/