DIY Speed Controller for Power Tools

[Mazay]

Simple and Cheap Voltage Regulator for Power Tools: angle grinder, drill machine, bench grinder etc.

[mdhatter3]

Where did you buy the speed control from ? I would be interested in building this.
Thanks

[Inner]

Where did you buy the speed control from ? I would be interested in building this.
Thanks

Buy AC 220V 2000W SCR Voltage Regulator:
- Aliexpress - https://ali.ski/p6jLL
- Amazon - https://amzn.to/3I28jnT

[sawtooth1953]

Simple and Cheap Voltage Regulator for Power Tools: angle grinder, drill machine, bench grinder etc.

Thank you for showing the simple build for this handy gadget. But please tell us what we need to make one like it.
What are the characteristics of the "simple and cheap voltage regulator"? Is it just an incandescent light dimmer?
Which one did you use?

[BuffaloJohn]

That's a triac controller... plenty of circuits online showing this simple circuit...

Traces on the PCB look a bit small for a 25A rating

[Frank S]

That's a triac controller... plenty of circuits online showing this simple circuit...

Traces on the PCB look a bit small for a 25A rating

A couple years ago I bought a 25 amp rated triac just like that one but for 120v . and you are correct the traces on the PCB are grossly inadequate plus the lower you set the knob limiting the voltage the lower the working current will be supplied to the tool On some things it doesn't matter but others the load has to be drastically reduced to prevent Majic smoke from leaking out of either the tool or the controller

[BuffaloJohn]

Knowing where to find useful information is often the challenge one faces to solve a problem.

This post is about a DIY Speed Controller which uses a triac to do a simple Pulse Width Modulation (which for a triac is really acting as a chopper circuit on the input sine wave of line voltage). When looking at the product itself, it shows the back side of the PCB and you can see the traces pretty well. Having some experience making boards, I looked at the board and thought the traces looked awfully small.

Here is the product:

https://www.amazon.com/HiLetgo-Contr.../dp/B00LODGP2E

The back of the board is image 4 and the width of the board where the connector is found is 35mm (according to image 3)

So - how wide should the traces on the PCB be?

The answer is that it can be calculated and you need to know the current, the thickness of the copper (either in oz/ft^2 or in mils or mm), the temperature rise that is acceptable on the trace.

Note: You don't need to know the voltage of the circuit - that would be used to calculate the spacing between traces, and not the individual trace width.

Here is a pretty good tool to calculate the trace width:

https://www.digikey.com/en/resources...cb-trace-width

Lets look at this product that looked questionable...

It says the maximum current is 25A.
We will assume 1oz copper as that is what the board looks like from the image.
It says the temperature operating range is -20C to 40C. From this we can infer that the maximum temperature rise would be 30C (most components are rated to 70C and if the PCB traces are near the components have a lot of current flowing (that 25A rating) they are heaters and 70-40=30C.

If we plug the info into the tool, we get a trace width (it is an external layer) of 574 mil which is 0.574in or 14.6mm

Looking at image 4, there are 4 through hole pins on the 35mm edge and if there was zero clearance between traces, this trace width would be 35/4mm = 8.75 mm - quite a bit lower than 14.6mm.

How much lower might the 8.75mm be since we can't have 0mm spacing between traces? We need to know the minimum spacing. That requires a different calculator and I used the first one that came up on a search for pcb trace spacing voltage.

Here we need to know the voltage which is 220V AC so that means the peak voltage is 220 * sqrt(2) = 311V which gives a spacing (we see solder mask on the traces, so we can use the "coated" of 0.8mm. I would guess from the image, there is at least an 0.8mm spacing, so that is good.

So - given a board width of 35mm, four traces and four spaces, the trace width could only be 7.95mm ((35 - (4*0.8))/4) which is a little over half of the calculated trace width. Interestingly, if we rerun the trace width calculator, we can get to 7.9mm with a 16A current...

Based on what we have learned, it is unlikely this product can actually handle a 25A load. Maybe the triac is rated to that, but the board can't handle it.

Even with the 16A limit - you would probably require active cooling to keep the product from letting the smoke out...

[DIYer]

Thanks Mazay! We've added your Power Tool Speed Controller to our Electrical category,
as well as to your builder page: Mazay's Homemade Tools. Your receipt:

Power Tool Speed Controller by Mazay

tags: controller

[nova_robotics]

Great idea. It would be an awesome addition to a ton of different tools. Except for the bench grinder at the end. Do NOT use this on an induction motor.

[NeiljohnUK]

I remember building a simple diac/triac controller from components back in the 70's, stall current was always the issue, always better to run at full power/sine wave and reduce speed with gearing if you are loading the motor.