Proxxon Mini Drill - Speed Control

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123mmm

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Hi, I have a Proxxon Micromot 50, which has only a on/off switch. I want to make a speed controller for this drill.
This mini drill needs to be powered using DC current, and a voltage between 12 and 18 Vdc. It has a power of 40W.
I know that there are on the market speed controllers, but I want to make my own.
I have a 24 Vac/2.5 A transformer with 12Vac center tapped secondary, which I want to use at this project.
I also have a 18 Vac/2 A transformer.

I know that there I need to use a rectifier, and thyristor.
Can you please recommend a schematic ?
 
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You will have much more low speed torque if you leave the AC side alone and buy/build a PWM speed controller to control the DC input power to the drill.
 
Ok. And I will need to use a stabilized power source for the pwm regulator and for the drill, or I can use the rectified and filtered dc ?
 
Rectified and filtered is generally fine, just don't exceed the PWM duty that would be more than the effective voltage of your motor (i.e. if your motor is rated at 12v and you are driving at 18v from your filtered supply, limit yourself to 75% duty cycle). You can buy PWM controllers for a couple of $ / £ from places like Banggood.com
 
You can connect something like this...

**broken link removed**

To something like this...

https://www.ebay.com/p/PWM-DC-Motor...-Controller-Switch/942293033?iid=263119717691

Trying to build your own DC power supply is a waste of time and a greater safety risk than buying a cheap Chinese wall adapter. The switch-mode power supply of these adapters are small, cheap, run reasonably cool and no significant noise when heavily loaded. Save your transformer for a small audio project that you will never build.
 

A Thyristor before the bridge is a rather crude way, there are plenty of 555 PWM designs out there if wishing to wind your own.
Also $2.50 on ebay.
DIY = http://www.discovercircuits.com/DJ-Circuits/simplepwm2.htm
Max.
 
I decided to build my own PWM controller and I found a 12V/5A SMPS.
The schematic is this: https://www.multisim.com/content/jcWPXBhUCutR4dmEitXfLg/high-frequency-pwm-with-ne555/open/
And I built the circuit on a breadboard.
But on the oscilloscope, it looks like the attached screenshots **broken link removed**
Why it does it look like this and not like the results from the simulation from the above link ?

Later Edit:
I managed to make the waveform better by adding 2.2uF capacitor and 100uF capacitor. I added the 2.2uF capacitor very very close to the power pins of 555. I also added a 100nF capacitor. But the waveform is still not looking as expected from the simulation.

Why the wave form does not look perfect ?

**broken link removed****broken link removed****broken link removed**
 
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All your attachments appear to be broken.
I've used a very similar circuit a few times with no problems, the 555 works well in may situations even not so good ones.
Do you have a 10nf to gorund on pin 5, some chips need it.
 
I also can't see your attachments but...

Circuits that you run on a simulator can appear perfect because they're using perfect models with perfect connections and no parasitic effects.

Circuits that are built on solderless breadboards are not perfect, and can suffer from stray capacitance, inductance and resistance that can make circuits misbehave.
 


I cannot see your attachments but I assume you are seeing a non-perfect square wave. It could be your power supply is sagging as the 2.5A load is quickly applied. Or it could be an inductive effect you are seeing as the PWM hits beach off cycle.

I hope you are not trying to drive your 2.5a load directly from a 555 timer.

Also, solderless breadboards are not intended to carry 2.5A so you may see some effects from that as well.
 
Sorry for the images. They appeared to be ok when I uploaded them.

I built another PWM, using an Arduino UNO, and I got the following screenshots:
The 1, 2 and 3rd are with the oscilloscope probe on the load ( I used as load a 27R/5W resistor), and the 4th one is from the Gate of the Mosfet ( I used an IRF630). I used a 100R gate resistor and a 10k pull down resistor.

The code is using the PWM.h library. I also used a potentiometer to "create" the square wave at the output.

Please have a look at the screenshots and please tell me if they are good or not.
 

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Most switch mode power supplies,or at least ones not made for motors don't like motors. The commutators and brushes of the motors put them into shutdown mode.
 
The waveforms look ok, you can see the lack of drive current to the gate, hence the rounded leading edge, and theres a little ringing, but it should still work Ok.
You'll need to make sure the 'duino is well decoupled or the noise from the motor will mess things up, also make sure the motor doesnt briefly pull so much current that the voltage drops & resets the 'duino.
 
I built the attached schematic and it looks like it is working good.
I am interested in attaching a snubber circuit to my schematic.
Can you please answer a few questions for me?
1. I saw on the internet different types of snubbers. Some of them are capacitor and resistor, others only capacitors, others zener diodes, etc. Which one should I use in this project ?
2. Where should I connect the snubber circuit ? In parallel with the load or in parallel with the mosfet (D to S) ?

Note: in my built schematic, R7 is missing.
 

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As far as I remember my proxxon dremel tool was powered by 12V AC and had the typical triac arrangement for speed control.
 
Mine is powered at 12Vdc. It is a proxxon micromot 50, the model without the speed controller.

I read somewere that the variable speed version needs unfiltered DC.
 
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The Rc method might not be so easy.
The C needs to be big enough to absorb the energy in the spikes and the R enough to damp it.
A method I've seen and used is to solder a 100n cap across the motor, then solder another 100nf to one motor terminal then to the motor case, and the same on the other terminal.
 
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