• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Soft starter and variable speed control for AC motor

123mmm

Member
Hi. I just found and built the attached schematic. It is a soft starter and a speed controller for AC motors. I checked the circuit and it worked with 70W/230V light bulb and then with a 720W angle grinder.
For making the soft starter working, I needed to make it start in the same time with the grinder, so I connected a new 3x1.5mmp cable from the grinder's switch to the circuit. Please find attached the connection schematic.
I would like to ask a few questions about this circuit:
1. Does the connection of the motor is correct ? I have 2 wires going from the switch to the stator windings, then from the stator windings 2 wires are going to the brushes. Is there any better solution for connecting the motor ?
2. Does the connection of the switch is correct (B1 on the schematic) ?
3. In order to turn off the circuit, does it needs to be disconnected from both wires (live and neutral) or it is Ok to disconnect only one of the wires ?
4. When I first opened the angle grinder's case, I found an 0.22uF/275V capacitor. I would like to know if this capacitor is still needed there ? If yes, then how can I connect it to the motor ?
 

Attachments

Last edited:

MaxHeadRoom78

Well-Known Member
Apparently it is a Universal motor, if 120v NA you only need to switch one conductor (Live), the field should remain in series with the armature, normally a simple triac or SCR following a bridge (for DC control) is all you normally need.
Max
 

123mmm

Member
If I do not use the soft starter, then the motor starts suddenly when button pressed and it shakes my hand... this is why I am using this circuit...
 

Latest threads

EE World Online Articles

Loading
Top