diode, for a motor controller circuit for a manual mill

Thread Starter

JJthe3rd

Joined Oct 9, 2020
10
Hello,

I'm working on a motor controller circuit for a manual mill. This circuit uses an on-off momentary switch to feed the motor, a right-left-off switch to select the direction of rotation, and a potentiometer to select the motor speed.

There is one component in particular that I am unable to identify. It looks like a rectifier diode that has a gate control, but I don't know how to verify this assumption.

Here is the wiring schematic:
WiringSchematic.jpg
This is the component I would like to identify:
1602276307855.png
Here is a picture of the physical component:
1602276378794.png

Any help would be greatly appreciated.
Thank you,
Jason
 
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MrChips

Joined Oct 2, 2009
23,958
It is not a diode. The general term is a thyristor. Specifically, they have different names, SCR (silicon controlled rectifier), diac, triac, quadracs, used in different situations and depending on how it is fabricated. It is the essential controlling device used in AC light dimmers and motor speed controllers.

(Presumably your switch function is LEFT-OFF-RIGHT, not right-left-off.)
 

Thread Starter

JJthe3rd

Joined Oct 9, 2020
10
It is not a diode. The general term is a thyristor. Specifically, they have different names, SCR (silicon controlled rectifier), diac, triac, quadracs, used in different situations and depending on how it is fabricated. It is the essential controlling device used in AC light dimmers and motor speed controllers.

(Presumably your switch function is LEFT-OFF-RIGHT, not right-left-off.)
Thank you for the clarification! You are correct that the switch is Left-off-Right.

I have access to a sine wave generator and an O-scope and some other equipment. How would you recommend testing this component?
 

MrChips

Joined Oct 2, 2009
23,958
You can test this with a house light bulb, a resistor, and connection to AC mains.

However, if you have never worked with AC mains before I would recommend that you get assistance from someone who has more knowledge and experience working with AC mains.
 

MaxHeadRoom

Joined Jul 18, 2013
23,381
You have a wound shunt field motor, I would have thought that they would have cleaned up the rectified DC a little?
What is that N/C contact in the field circuit.
The easiest way to test is with a low voltage (~6v transformer) to Triac in series with a lamp, use a 100ohm jumper from the Gate (shorter terminal) to the Anode.
Lamp should light, turn off when the resistor removed.
Also check the diode in the gate.
Max.
 
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Thread Starter

JJthe3rd

Joined Oct 9, 2020
10
You have a wound shunt field motor, I would have thought that they would have cleaned up the rectified DC a little?
What is that N/C contact in the field circuit.
The easiest way to test is with a low voltage (~6v transformer) to Triac in series with a lamp, use a 100ohm jumper from the Gate (shorter terminal) to the Anode.
Lamp should light, turn off when the resistor removed.
Also check the diode in the gate.
Max.
My knowledge is very limited and this circuit is rather old so it probably isn't the best setup. How would you clean up the rectified DC?
I don't know what the normally closed contact represents but I think it is something inside the motor housing.

Thank you for your advice!
 

MaxHeadRoom

Joined Jul 18, 2013
23,381
What was the original symptom? Not working at all?
The motor looks like it needs a little maintenance, have you checked the brushes for length/wear and the condition of the Comm?
Max.
 

Thread Starter

JJthe3rd

Joined Oct 9, 2020
10
What was the original symptom? Not working at all?
The motor looks like it needs a little maintenance, have you checked the brushes for length/wear and the condition of the Comm?
Max.
Yes. The circuit board got old and shorted something. There were burn marks on the board from an arc and the motor did not run. I have replaced the motor brushes. When you mention checking the Comm, do you mean making sure the wires are in good shape?

After testing the SRC it seems that it is not performing how I would expect it to. I'm thinking about replacing the whole circuit and using a MOSFET for motor control. Do you have any thoughts on making that work?
 

MaxHeadRoom

Joined Jul 18, 2013
23,381
The COMM is the commutator, the copper bars that the brushes seat on.
If using a Mosfet, that would imply DC.
If proceeding using AC, look at the Fairchild app notes AN-3006 & AN-3003.
Max.
 

Thread Starter

JJthe3rd

Joined Oct 9, 2020
10
The COMM is the commutator, the copper bars that the brushes seat on.
If using a Mosfet, that would imply DC.
If proceeding using AC, look at the Fairchild app notes AN-3006 & AN-3003.
Max.
I have a rather surface-level understanding so this may not be reasonable, but I'm assuming that the motor I have must use AC rather than DC. Thus using a MOSFET would not be feasible for this application.

Also, it looks like AN-3006 is being used as a motor speed controller so I can look into that more.
 

Bernard

Joined Aug 7, 2008
5,788
Your other post is closed so what is old is new again. To control motor with a MOSFET you could use a full wave rectifier giving unidirectional pulses.
I once , about 2004, used a strange dimming circuit using rectified AC by selecting the number of pulses allowed out of 10 pulses using a 8 position
piano switch. It is still working today.
 

Thread Starter

JJthe3rd

Joined Oct 9, 2020
10

MaxHeadRoom

Joined Jul 18, 2013
23,381
They are two different items, for a Universal motor, the 1st item would be OK, and although the KBIC controller is also a dedicated DC controller, it is not the choice for a Universal motor.
A shunt-Universal motor is a misnomer, a Universal motor is a Series Field motor, NOT shunt wound field.
Max.
 

Thread Starter

JJthe3rd

Joined Oct 9, 2020
10
They are two different items, for a Universal motor, the 1st item would be OK, and although the KBIC controller is also a dedicated DC controller, it is not the choice for a Universal motor.
A shunt-Universal motor is a misnomer, a Universal motor is a Series Field motor, NOT shunt wound field.
Max.
Do you know if the Rockler motor controller would work with this application since I'm using a universal type motor?

Motor information plate:
MotorCase.jpg
 
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