Motor Speed Controller

[123mmm]

Hello, I have an 125 mm angle grinder with 720 W AC motor and soft start (attached pdf document). I want to build a speed controller for this angle grinder. I tested a simple triac dimmer (from the attached jpg schematic) but it doesn't work normally, because it is making a strange buzzing noise.
Is there any solution of making a speed (RPM) controller for this grinder, without removing the integrated soft start circuit ?

 

[Pommie]

Why would you still need the soft start when you can slowly increase the speed with the controller?

Mike.

 

[123mmm]

I can't remove it, because it is inside the case of the grinder ...
If I will try to remove it, then I should remove the entire module which contains the on/off switch ...

 

[Nigel Goodwin]

I can't remove it, because it is inside the case of the grinder ...
If I will try to remove it, then I should remove the entire module which contains the on/off switch ...

I would imagine the soft-start is essentially just a triac speed controller, so you can't add another external one.

 

[123mmm]

I found that the part number for the module which contains the switch and the soft start circuit is SWITCH DPX-2110-R 9553NB.
Do you know if this module can be opened to remove the soft start circuit, and add the external soft start and motor speed controller ?

 

[123mmm]

I finally opened the angle grinder and I removed the soft start circuit.
Does anybody know a schematic which has soft start and speed control into the same module ?

 

[Nigel Goodwin]

I finally opened the angle grinder and I removed the soft start circuit.
Does anybody know a schematic which has soft start and speed control into the same module ?

A speed-controller is soft-start - just pull the trigger slowly- although generally you can't make them fast start even if you pull it fast.

 

[ChrisP58]

I finally opened the angle grinder and I removed the soft start circuit.
Does anybody know a schematic which has soft start and speed control into the same module ?

What parts did you take out to remove the soft start function?
Can you post the schematic of the complete circuit in the grinder? You'll probably need to reverse engineer it.