How to Design a dimmer that don't depend on the load's resistance

Thread Starter

Bassem Faris

Joined Jun 22, 2022
3
Hi all
I have an angle grinder which have Maximum power of 950 watt
And my country provide 220 volt as voltage source
But it have one speed and i want to make a dimmer to control its speed.

I used this circuit but it provides at least 130 VAC
It make the machine rotate so fast
How can i make a dimmer to provide zero volt at least?

Note : i used big heat sink IMG20220623004544_BURST000_COVER.jpg
 

Ramussons

Joined May 3, 2013
1,274
Controlling a motor by voltage control is not a preferred option. At lower voltages, the motor may not have enough torque and it will stall.
A PWM driver will be a much better option if it is a DC motor.
A VFD drive will be fine for an AC motor.
 

LowQCab

Joined Nov 6, 2012
2,171
To make a Speed-Controller for an "AC-DC-Series-Wound-Motor" requires that
a Tachometer-Signal must be generated by the Motor for Feedback to a Controller.
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LowQCab

Joined Nov 6, 2012
2,171
There are many "Tool-Hacks" You can find on the Internet that quite often
use super-cheap and plentiful Angle-Grinders for a Power-Source.
But what many people don't realize is that, as a general-rule, they are either OFF or ON,
with lots of quirky-behavior and complaining anywhere in-between those 2 states of operation.

For an application that requires slow, smooth, controlled, application of Power,
they can be rather radical and uncontrollable, ( and very noisy ).

Smooth-Control, while retaining adequate Torque to actually do some work, requires RPM-Feedback.
Without RPM-Feedback, if You slow down the Motor, then apply a Load, it will just stall-out.
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MaxHeadRoom

Joined Jul 18, 2013
25,469
The feature of the series field/Universal motor is that it has the advantage of high torque down to low RPM, one reason why they were/are used as automotive starters.
The reason is that as the motor-load/current increases, this causes a correspondingly higher field current, hence higher torque.
In some instances, removing the load altogether can cause the motor to destruct due to over-speeding. They should always have some kind of residual load.
 
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Thread Starter

Bassem Faris

Joined Jun 22, 2022
3
Thanks all for your time ❤
I appreciate it
My variable resistor was made with bad quality
I replaced it with better one and it works now well
 
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