120VAC to 120VDC Mixer Motor Conversion

Thread Starter

dredgeboater

Joined Feb 2, 2018
5
Hello All,

I have a Kitchenaid K5SS mixer. The label says 115 volts AC @ 60Hz, with a max wattage of 300.

From the looks of the motor, it is a series-wound universal type with replaceable brushes.

What I would like to do is to operate the motor with 120VDC as I believe the machine would run cooler, and provide more constant torque through all speed ranges.

I have a 400V 25amp bridge rectifier; is this conversion as simple as adding the rectifier to the circuitry? From research, if I were to add a capacitor after the rectifier, the output dc volts would read around 169-170, but is this necessary?

Also, would the variable speed control, which is presently a flyball governor acting against a moveable switch plate be able to be used with this setup, or would I need to replace with a potentiometer?

Thank you and am looking forward to your reply.
 

Thread Starter

dredgeboater

Joined Feb 2, 2018
5
Power schematic.JPG

From the above schematic, I was wanting to know if this motor would run 120VDC by adding in the bridge rectifier drawn in red and attached to the terminals depicted above.
I think this would work with the current speed control left alone and unrectified, and therefore not using a dc potentiometer.

What are your thoughts?
 

MaxHeadRoom

Joined Jul 18, 2013
19,145
It should work the way shown, whether it will run quieter and cooler is left to be seen.
If it has the flyball governor this offers a certain amount of automatic rpm control, are you intending to convert to potentiometer? If so the automatic rpm will be lost.
Max.
 

crutschow

Joined Mar 14, 2008
23,478
Your modification will provide rectified AC to the motor, not steady DC, so I don't know how much difference that will make in motor operation.
A large capacitor would smooth out the rectified AC but would also cause large peak currents in the control circuitry which could damage it.
 
Last edited:

MaxHeadRoom

Joined Jul 18, 2013
19,145
Universal motors operate in a run-away condition, they require some kind of feedback for rpm control, hence the fly-ball governor.
No need for a capacitor when using full wave DC .
Max.
 

Colin55

Joined Aug 27, 2015
519
"Universal motors operate in a run-away condition."
They RPM until the energy IN equals the energy for RPM. That's why the RPM is very high

It does not matter if the input is AC or through a bridge, the RPM will be the same as the energy IN will be the same.
You need a diode to reduce the energy IN and thus the RPM.

No-one has realised this.
 

MaxHeadRoom

Joined Jul 18, 2013
19,145
They operate in a so-called run away condition due to the ever weakening field, this is why DC motors used in industrial applications that have a wound field have field loss protection, shuts off the motor supply should the field fail.
Otherwise they have been known to accelerate to destruction, also why you should not run the old style automotive starter motors on the bench unloaded.
A diode or triac etc does not provide good regulation with a series motor, controllers that do, have some form of feedback device.
Max.
 

Thread Starter

dredgeboater

Joined Feb 2, 2018
5
Thank you all for your replies.

If it has the flyball governor this offers a certain amount of automatic rpm control, are you intending to convert to potentiometer? If so the automatic rpm will be lost.
Max.
Max, I am thinking I have several options.

1) Keep the flyball governor, and use the AC circuit for speed selection feeding rectified AC to the motor.
2) Remove the TRIAC, speed switch, flyball governor. Install a 1:1 isolation transformer to the main, come off of the isolation transformer to the bridge rectifier, wire a potentiometer in series to one leg of the rectified AC and use this for speed control.

3) The third option would be to put in a AC motor drive, but I do not know the values of resistance, voltage, and capacitance that I need to do this. I'm thinking that the motor drive converts AC to DC, and a potentiometer built in to the device controls the input voltage to the field and armature.

DB
 

Thread Starter

dredgeboater

Joined Feb 2, 2018
5
Your modification will provide rectified AC to the motor, not steady DC, so I don't know how much difference that will make in motor operation.
A large capacitor would smooth out the rectified AC but would also cause large peak currents in the control circuitry which could damage it.
Thank you for your reply.

Question - Since the rectifier is installed downstream from the TRIAC circuitry, and the capacitor installed after the rectifier, does peak current increase at the TRIAC?

DB
 

Thread Starter

dredgeboater

Joined Feb 2, 2018
5
"Universal motors operate in a run-away condition."
They RPM until the energy IN equals the energy for RPM. That's why the RPM is very high

It does not matter if the input is AC or through a bridge, the RPM will be the same as the energy IN will be the same.
You need a diode to reduce the energy IN and thus the RPM.

No-one has realised this.
Colin, from the circuitry in my mixer, the flyball governor works against the switch plate that operates contacts. As I understand it, the mixer at all speeds save "off" and "high" are regulated with the flyball governor and switch to provide 80v AC to the field and armature. When the governor senses too much rpm at a selected speed, it acts against the switch operating contacts that run off of the 40v AC leg of the TRIAC, slowing the motor down until the desired speed is attained. Then the flyball slacks off, opening the 40v AC leg and closes the 80v AC leg. When the speed selector is moved to a faster speed, switch plate moves away from the flyball, the flyball slacks off opening the 80v AC leg, and closes the 120v AC leg increasing motor rpm. The flyball will then move back toward the switch plate, opening the 120v AC leg and closing the 80v AC leg regulating rpm at the selected speed.

When the fastest speed is selected, the switch plate is moved away from the flyball where it cannot operate against the switch plate; this keeps the contact closed where 120v AC is fed to the armature and field.

Summarizing, the mixer uses electro-mechanical methods to control the energy and rpm.

Best,

DB
 
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