Power tool speed controller (brushed motor) - Page 1
Forum section: electronics / projects

author: nukie
author_rank: Frequent Contributor
timestamp: September 19, 2012, 04:49:03 am
content: Hi all,I have a very fierce Bosch angle grinder. Whenever I turn it on the vibration at full speed(depending on attachment) would give me hand and arm massage. The noise is terrible, birds will fly off instantly, earplugs is required. I have been researching for a speed controller or should I say wattage limiter. I searched around, and the local magazine has published two models. They are too expensive, for the price I could buy another angle grinder and have some loose change.I found this today and if anyone good with AC power please help me out. I looked into SCR because they are cheap and simple to work with. If I implement the circuit in the first patent, what are the things that I should be aware of? I am going to house the circuit in a plastic box along with all the sockets and switches.http://www.google.com/patents/US5714861http://www.google.com/patents/US4153863In the second link there are interesting patents regarding speed controllers.I want a low power angle grinder so I can cut softer material such as aluminium with more precision. Please don't tell me mains is dangerous, I am old enough to know 240V is dangerous having mild electrocute myself many times hanging christmas lights. I will take safety precaution.

author: T4P
author_rank: Super Contributor
timestamp: September 19, 2012, 05:56:40 am
content: Check the brushes first, that was the problem i got with my clackity rotary toolWell i think a "light-dimmer" esque TRIAC will work? Like this :http://dx.com/p/2000w-scr-voltage-regulator-module-dimming-motor-speed-controller-thermostat-142344?item=3

author: amyk
author_rank: Super Contributor
timestamp: September 19, 2012, 07:29:13 am
content: Quote from: T4P on September 19, 2012, 05:56:40 amThat looks a bit wimpy for 2kW...

author: nukie
author_rank: Frequent Contributor
timestamp: September 19, 2012, 08:00:00 am
content: How about 4kW?http://www.prodctodc.com/4000w-220v-high-power-scr-speed-controller-electronic-voltage-regulator-governor-thermostat-dimming-dimmer-p-169.html#.UFl7LY3iYwAOr perhaps 10kW!http://www.prodctodc.com/high-power-10000w-220v-scr-electronic-voltage-regulator-moto-control-controller-thermostat-governor-dimmer-p-171.html#.UFl7sI3iYwA

author: T4P
author_rank: Super Contributor
timestamp: September 19, 2012, 08:20:19 am
content: Quote from: amyk on September 19, 2012, 07:29:13 amHardly ever is ...

author: Simon
author_rank: Unknown
timestamp: September 19, 2012, 10:03:28 am
content: I'm curious, how can someone patent a basic SCR circuit found in any text book ?

author: Psi
author_rank: Super Contributor
timestamp: September 19, 2012, 10:41:47 am
content: An angle grinder should not vibrate, even at full speed.If it does then there is something very wrong with it.To most people angle grinders seem relatively safe but they actually cause a lot of injuries.It happens when the grinding disk shatters (and they do), bits of it will fly out in all directions and embed themselves deep into anything they hit.An angle grinder that vibrates is much more likely to break a disk due to the sideways wobble stressing the disk surface.Also, side note: If you want to grind aluminum get a special grinding disk designed for it.The normal ones get clogged with chunks of aluminum very easy and it throws them out of balance leading to increased disk of shattering.

author: nukie
author_rank: Frequent Contributor
timestamp: September 19, 2012, 11:34:54 am
content: I don't know how they manage to patent the circuit and even shocking it was done in 1996 not 80s or 70s. Well, obviously that didn't stop them, plentiful source as posted.Regarding my angle grinder, it doesn't vibrate that much, it actually has damping system but I can still feel the tingling sensation like a overpowered women's toy strapped with rolls royce engine. It gives you hand orgasm. I own a few angle grinder over the years, I know how it shakes when something is off centered.I use a 5"/125mm tungsten carbide tip saw blade it is rated 11,000 rpm. My grinder works at 11,000 rpm. I am a bit uncomfortable running it at full speed. It's designed for wood but it cuts through aluminium stock like butter generates no heat at all. So I need a controller to limit the speed, so the blade won't self disintegrate.

author: saturation
author_rank: Super Contributor
timestamp: September 19, 2012, 12:27:06 pm
content: Most power tools use universal motors. You can speed control it with a triac aka light dimmer module rated for the current draw, as others have described. You can also use a variac.

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 20, 2012, 02:55:09 am
content: Quote from: nukie on September 19, 2012, 08:00:00 amThose are so cheap that if manual control is all you need, don't bother building your own. Go with the 10kW version to get more room for starting inrush.

author: G7PSK
author_rank: Super Contributor
timestamp: September 21, 2012, 05:58:00 pm
content: For softer material you need more power not less. You best move would be to buy a new angle grinder with ant vibration and soft start and sell your old one. I speak from experience as I have been using angle grinders since the mid 70's.

author: kyndal
author_rank: Regular Contributor
timestamp: September 29, 2012, 06:20:46 pm
content: im using that exact cheapo "2000w light dimmer" with my angle grinderdoes the job just fine... of course there is a "lower limit" where the grinder will still turngood for "alternative attachments" like wire brushes etc/Kyndal

author: G7PSK
author_rank: Super Contributor
timestamp: September 29, 2012, 09:17:30 pm
content: Quote from: Simon on September 19, 2012, 10:03:28 amI think due to it being 1970 when the patent was granted. SCR's were the cutting edge back then.