Angle grinders & power tools in general

Go To Last Post
16 posts / 0 new
Author
Message
#1
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Anyone have any idea how the insides of power tools like angle grinders work?

I've googled and understand that they have motor brushes which suggests some kind of brushed motor. Any idea how the speed control works? Is it something like PWM?

Just interested as at 2kW (pretty standard angle grinder power) I'd have thought it'd be difficult to limit output in a handheld device without losing lots of power in heat.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Some of the angle grinders are pretty primitive, with a rheostat for "speed" (really power) control.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I was not aware that you had variable speed angle grinders. They are normally fast or stop.

When they are at permanent stop, you buy a new one.

David.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

There definitely are variable speed angle grinders. After more searching I think they might use some kind of dimmer circuit with triac, but I'm not sure.

And a rheostat, as in a resistor?? Wow!

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Power file: is that what you're looking for ?

The black (and decker) on the left is 26 years old and recently died: it has been a wonderfull tool abd did lots of dirty and hard work.
The orange one is the new version, with filter in the exhaust and variable speed. Triac based I think.

Attachment(s): 

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tricia, and Ulyana. You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

grinders any many power tolls use a type of AC motor that i know as a Special Motor, not sure what the correct name for them is. they are usually 2 pole motors and control the speed by "chopping" the AC signal. that means the top part of the sinusoid is cut out and there is no power going to the motor for a very short period of time until the sine wave goes back below that point again. not sure if newer power tools use this use this method, I know that certain power tools i have owned in the past used something like this.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

That's interesting!

So we are using a modified sine wave inverter (dc/ac converter) in our product. This involves a pulse wave approximation to a mains sine wave. Does this mean that products incorporating speed control are unlikely to work with this kind of inverter? (Because the zero crossing points are kind of messed up) See attached picture

Attachment(s): 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

most likely! It will upset light dimmers as well as well as dimmable electronic ELV ballasts (transformers). One way to be sure - try it!

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I've used angle grinders of all sizes for decades and never seen one with variable speed.

Scattered showers my arse -- Noah, 2348BC.
Rob Gray, old fart, nature photographer, embedded hardware/software designer, and serial motorhome builder, www.robgray.com

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Quote:
The black (and decker) on the left is 26 years old and recently died: it has been a wonderfull tool abd did lots of dirty and hard work.

Couldn't agree more. I have one of those (looks like exactly the same model!) in the tool department in the summer house. Still worked last time I had a need for it. Not needed very often, but sometimes it's priceless!

As of January 15, 2018, Site fix-up work has begun! Now do your part and report any bugs or deficiencies here

No guarantees, but if we don't report problems they won't get much of  a chance to be fixed! Details/discussions at link given just above.

 

"Some questions have no answers."[C Baird] "There comes a point where the spoon-feeding has to stop and the independent thinking has to start." [C Lawson] "There are always ways to disagree, without being disagreeable."[E Weddington] "Words represent concepts. Use the wrong words, communicate the wrong concept." [J Morin] "Persistence only goes so far if you set yourself up for failure." [Kartman]

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Yep will have to just test.

For the naysayers, there appear to be plenty of variable speed angle grinders:
http://www.halfords.com/webapp/w...

http://www.toolstop.co.uk/index....

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

A little belgium company sells kits for this kind of stuff:
http://www.velleman.eu/distribut...

I believe it's similar to al light dimmer (Phase control) but modified a bit to handle the inductive load.

Complete schematics and assembly instructions:
http://www.velleman.eu/downloads/0/assembly/assembly_manual_k2636_rev2.pdf

I have taken several of these motors apart and they were all wound as series motors.
http://en.wikipedia.org/wiki/Bru...

These motors have more in common with DC motors than with AC motors.
Just think of it as a DC motor, but instead of the (permanent) magnet of a (small) dc motor the stator is replaced with an electromagnet. When the aplied voltage changes polarity then also the voltage of the stator changes polarity.
And if both the electromagnetic fields of the rotor and stator are changed at the same the net result is a force (rotation) in the same direction.

Direction is reversed by a 2 pole switch which reverses the current through the rotor while direction of the current through the stator stays the same. (Doesn't mean they can ALL be reversed this way).

I'm pretty sure these motors also run on DC. But you'll probably have to limit the voltage because DC is not "held back" by the self induction of the motor windings.

A few weeks ago I saw a "motor speed control" made by a servo motor which pushes the button in of a standard electric hand drill on http://hackaday.com

EUR50 for a 700W electric motor is:
"good value vor you money..."

Another tip for free:
If you can find an old washing machine (clothes) somewhere...
In those white boxes you can usually find a similar motor with speed control
(350 - 20.000 RPM) and speed feedback with an encoder.

Doing magic with a USD 7 Logic Analyser: https://www.avrfreaks.net/comment/2421756#comment-2421756

Bunch of old projects with AVR's: http://www.hoevendesign.com

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

In English they are called Universal Motors. Wikipedia has a paragraph on their characteristics.
http://en.wikipedia.org/wiki/Electric_motor#Universal_motors
I was not aware that the integral fan often serves as an intentional load to keep it from overspeeding.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Well, I've heared those stories about "exploding" motors from excessive RPM at no load.

So I took apart an old vacuum cleaner and removed all "unnecassarry parts" from the axle and put it in a 2mm thick steel container before powering it up.
I even oiled the bearings a bit.

I was very dissapointed but according to the noise it made it didn't even run at a much higher rpm than it was designed for.
On second thought... I should have tried DC, that might have helped a bit.

Results may vary :-)

Doing magic with a USD 7 Logic Analyser: https://www.avrfreaks.net/comment/2421756#comment-2421756

Bunch of old projects with AVR's: http://www.hoevendesign.com

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hmm, recently just saw a drill that had a multiple-tapped coil. with the speed control permitting the current to flow to either one of those taps.

That sounds like a workable but cheap way to do without a triac.