Thread: Speed Control for brush motors

Is this possible without affecting the torque, example in the case of a router?
Zelk

Originally Posted by zelk

Is this possible without affecting the torque, example in the case of a router?
Zelk

Sorry, just realised that this was for DC motors only

Zelk,

No it's for 240v AC brush type motors up to 10A.

Trying to get info from the silicon chip web site. Looks like i'll have to go and buy the mag.

Originally Posted by The Bleeder

Zelk,

No it's for 240v AC brush type motors up to 10A.

Trying to get info from the silicon chip web site. Looks like i'll have to go and buy the mag.

In that case, is the torque affected on say, a router?
Zelk

Zelk,

The torque will obviously be affected. By how much I don't know. Not enough info on the web site, so it's off to by the mag.

G'day Bleeder,
I got the same flyer and ordered a kit straight away.
Its just arrived, and from what I can see (haven't constructed) there will be a distinct difference in speed between when the device is switched to Full, and when the controller is in circuit without any speed control applied, due to the use of diodes prior to the control circuitry.
Torque loss should be minimal, however these controllers don't like working with machines that already have speed control wired in...like some routers and jig saws and drills.

I'll now stand by for incoming from the usual experts.

Haven't seen the unit refered to or read the construction article, but it sounds like a typical high power light dimmer style unit to me. As such, the unit should be able to pass a complete sinewave waveform at max speed, so shold not affect max seed significantly.

However when the speed is reduced, the waveform will blanked for increasing portions as the speed is reduced. This creates significant distortion and harmonics in the waveform, and high inrush currents into the motor. As a consequence, the motor can overhead more easily as it can absorb similar power levels with much less airflow for cooling, unless it was designed for use with this style of speed control.

In comparing a fixed speed router plus controller of this type with a true variable speed router, the true VS unit is preferable as they tend to include feedback to maintain the speed with load variations, whereas the addon units don't. There is nothing to maintain torque while reducing speed. Consider a variable speed drill, load it up with a large bit, slow it down to an optimum speed for the drill bit and put it to work, pretty soon you will increase speed at the trigger as the unit gets loaded down. This is the point where they tend to overheat. Better to run with something that can provide the right speed with decent efficiency, either through design or mechanical gearing.

Here's my copy drawing of the output waveform from the Silicon Chip article.
also, when switched into circuit the motor speed is reduced to 70 - 80% from full speed.
The article also notes fan cooling speed may be reduced.

Also, the unit works on two kinds of EMF feedback .

Malb,

No its not a high power light dimmer style. If it is based on the previous 5A one then it does have back emf sensing. The original 10A one didn't have back emf sensing but was a bloody good unit. Emailed my mate in the UK to find out if it is still going.

Noel,

Ordered mine so should be with me by the end of the week. Just ordered the Feb Silicon Chip mag as it is in there. Find out more in the mag.

Dear Gents,

Looks like I'm first to the Power-Point with this one, so here's a few comments regarding the unit - for the purpose of tempering any excessive expectations...

1) If you (or the staff at Jaycar) are looking for the thing hanging on the wall where the kits usually are, look down at the shelf instead. That's because instead of being packaged in the usual plastic hanging-blister, the things are just shipped with all the componentry inside the unit's aluminium case, which is then just shrink-wrapped in plastic. So don't be put off if they say to you "The computer's showing some in stock, but it must be mistaken because we've looked everywhere and can't find any!", because the whole kit is just sitting somewhere disguised as an aluminium Case...

2) Steve - don't bother buying the relevant issue of the Mag as well as the kit, because a photocopy of the whole Mag article is included with the kit as instructions (and as far as instructions go, they're not very detailed...)

3) Don't use the photocopied Case-Face templates as marking-guides for the various holes and penetrations that need to be made, because the photocopy is of a scale that is not quite 1:1.

4) She's not a terribly easy kit to build; the aluminium for the Case itself must be anodised, and it's quite thickish as well. The shapes of the cutouts for the Input and Output power-leads are a little irregular, and were hard enough to get just right with a Rotary Tool (long live the unkillable $40 Ozito! ), let alone if you were doing it all by hand with just a file. Either way, you'll definitely need sharp Drill Bits...

5) The supplied wiring is only in the form of Mains Flex, so if you haven't got any 10A rated individual wiring lying around (or a decent wire-stripper), prepare to be bogged down in some fully-serious manual stripping .

6) As well as the wiring, the rest of the supplied hardware in general seemed a little "skin-flint" in nature; I ended up using all of my own screws because the supplied units didn't seem quite appropriate, and they don't even give you "crimp" style lugs for connection to the sockets (they just give you some "heat-shrink" to go over your solder joints to the terminals). They want you to put some rubber Feet on the thing (obviously to allow a Case-mounted transistor on the bottom of the thing to dissipate heat), but they don't actually give you the four cheap little rubber Feet...

7) There is a transistor-like component that ends up getting surface-mounted on the inside-bottom face of the aluminium Case with heat-sink compound for cooling reasons. Thing is - you wont see how well the thing mates with the bottom of the Case when looking down on it from above. Therefore, after drilling your holes for the main PCB in the bottom of the Case...
(a) Turn the Case upside down
(b) Mount the PCB on its little nylon spacers on the upturned bottom face of the Case
(c) Bend the legs of the transistor to suit the height of the PCB
(d) Drill an accurate fixing-hole for the transistor while its legs are protruding up through the PCB
(e) Secure the transistor to the surface of the upturned Case with a screw
(f) Solder some little locking-blobs of solder onto the legs of the transistor where they come up through the top side of the PCB in order to hold it in position
(g) Unscrew the PCB off the upturned bottom face of the Case
(h) Turn the PCB back over and solder the transistor to it properly
(i) Turn the PCB back over again and screw it again onto the underside of the Case through its little nylon legs, and see whether the transistor is indeed sitting flush on the surface of the Case (some minor bending of the transistor legs may still be required in order to "spring" the unscrewed end of the transistor onto the Case surface - the screwed end will take care of itself when the screw is eventually tightened into place)
Hope that all makes sense...

8) Wiring to the Input Socket and Switch are soldered, but these two fittings are eventually pressed into place from the outside. Therefore, allow enough extra length of wiring for the PCB to sit inside the Case while the wiring runs out through the penetrations with enough slack to enable you to complete the soldered joins onto the terminals of the said fittings while they are un-mounted and outside the Case.

9) I tested it on an incandescant lamp last night, and Lo! - the thing actually strobed at low "speed"... And then I tested it on both my Recipro and Circular Saws this morning, and they both "cogged" (ie. ran roughly) at low speed.

10) When testing the unit, I noticed that the running speed of the said tools only appeared to decrease when the Speed Dial was operating down in the lowest one-third of its range (ie. the upper two-thirds of the Speed-Dial seemed ineffectual...)

11) The thing needs a Power Cord of its own to run - namely the style that you plug into the back of a Computer. And guess what?- Despite the $65 price tag, it's not supplied...

Photos below...

Best Wishes,
Batpig.

Batpig,

I hear you. I ordered mine through the 1800 number as my local Jaycar didn't have any. Got it last friday. (took a week to turn up)

Couldn't get the mag anyway and yes the instructions are a bit light on.

In regards of the 'cogging' did you adjust the trim pot to see if it went away. (haven't test mine)

Started the build on Sunday (only free time I got). It's a lot simpler than the one from 1997 that I built even though some of the solder points are really close (eyesight not what it used to be).

I went and bought some crimp terminals for the IEC and switch. This made it a lot easier even though I had to put heatshrink over the IEC terminals as the connectors were bare ends for that size.

I had a larger case that I put mine in and used some solid core copper wire to go from the PCB to a terminal block for the connections to the other components.

They could have suppiled the power cord but I have plenty of those. (Just got to ensure they are 10A rated)

I'll take some pics when it's all finished (before I test it and hope it's not charcoal after that).

Great Report Batpig

Hi Folks,

From the wet, cold UK so I don't know the Jaycar company you are all discussing but I've been looking at this item with the same idea.

http://www.quasarelectronics.com/cr0008.htm

Anybody got any ideas if I can use one to drive my 3/4 hp lathe motor without any problems?

Yes, I've noted the 'Contact Us' tab at the top but never had a response to any e-mail I've sent them.

Any technical knowledge dispensated will be gratefully received,

G'day Dragonfly,

The controller you linked to is for a universal (Brush type) motor, and I reckon your 3/4 hp motor would be a capacitor start 2 or 4 pole motor and these type of controllers dont work with them.