Thread: speed controller

Thanks Gerhard, you're a gem!

Hi Watson,

as promised, here are the first two schematics. One is an industrial design by Thomson of France, which is actually used in arc welding transformer. This in itself is quite a hefty application, since arc welding features very violent fluctuations in both peak currents and peak voltages (caused by e.g. induced counter-EMF in the windings and the occasional short-circuits). Besides, Thomson should know, since they have a relation with the very reputable French electric locomotive industry (with Alsthom being one of the great names, they also made the TGV). Thomson semiconductor parts may be subject to very poor or no availiablity in Austrialia, but Texas Instruments devices and the likes may be more easy to find. The second schematic is an adaptation of the Thomson schematic with more ordinary part types. By replacing the TIC 263 triac by an equivalent with the same characteristics and gate current, but with higher Amp capabilities, the motor Wattages of 1200 Watt in this example may be cranked up beyond 2000.

The design is reasonably sophisticated, the little 221/206-triac fires a series of trigger pulses at the larger current switching triac ("pulse train"), instead of the usual single pulse at each sine half wave in ordinary dimmer designs. This guarantees reliable firing and switching of the main triac even under adverse circumstances, of which there are many with inductive loads.

I'm searching for another design i know well, somewhat simpler, but it is my standard control box which i've used for more than 15 years now, on virtually any machine that has to be examined and tested. When i found it, i will also post it, as well as some pics from the mentioned homemade box and the parts layout inside.

till next time

gerhard

Thanks for posting the circuits Gerhard

Interesting.......

Does anyone happen to know the major differences between these circuits and the one in this thread https://www.woodworkforums.com/showth...854#post912854 that talks about the silicon chip design feb 2009

http://www.siliconchip.com.au/cms/A_111129/article.html

Given that lots of power tools have speed controls that seem to not take up a huge amount of space, how are the power tool manufacturers circuits different from the ones in the kits. Surely it couldn't be too hard to replicate the circuit in the tools that have speed controllers, though obviously the rating will make a difference.

Blouis79,

They are the same thing. It's a Silicon Chip design supplied though Jaycar as a kit.

It is a 10A rated unit but it does have some issues.

Watson, Batpig and myself have built it. It will do the job on my big Makita router 3612 that doesn't have speed control but the amount of control before cogging occurs is not that great. I only have to get my router down to 2/3 to 1/2 max speed and the unit does that ok.

Originally Posted by The Bleeder

Blouis79,

They are the same thing. It's a Silicon Chip design supplied though Jaycar as a kit.

It is a 10A rated unit but it does have some issues.
...

The Gerhard circuits are not the same as the Silicon Chip/Jaycar design.

This GoogleBook has several speed control circuits in the chapter. http://tinyurl.com/cb3wdx

I would like to build one that doesn't have issues - to use on compound slide saw (brushed) and angle grinder. Don't need it for drill. I made a drill motor speed controller from a Dick Smith kit about 20 years ago that also had issues.

Exactly the same kind of circuit that's on my variable speed triton router or bosch sander or festool saw would be fine. They don't seem to have issues with the knob position and control from full power to slower.

Thanks Gerhard!

Sorry about the delay in replying. I wasn't subscribed to the thread and only just found this...

Wouldn't mind paying for a finished unit if it was able to run a Makita 3612BR and had a decent speed dial...

Damien

Hi Damien!

General answer to all posts above: the discussion seems to revolve around which type of circuit fits the bill for the most types of power tools, and if the control is of such quality that there is preferably no power loss in low rpm-regions.

The best answer to both wishes is to disappoint straight up-front, to avoid too high expectations. Any power control either conducts or blocks parts of the fed power, meaning that the controlled motor can't possibly deliver full power at reduced feed, ever! Any manufacturer of either controls or power tools lies through his teeth when claiming that.

I'm in the process of making a small historical oversight of power control technology, including features and drawbacks of all the means ever applied in power tools. This may take a while, but i'll try to deliver soon. It's rounding up the proper examples and easy to follow schematics that takes up most of the time. In practice i end up making much of that myself.

There is a lot of humbug and half-knowledge messing up this particular field of technology, part of which is caused by the tool manufacturers' own marketing jargon and stiff promises, just to look good in brochures. It's time a bit of this humbug got cleared away.

Greetings all, and 'til soon

gerhard

Gerhard,

I have to agree with you. They love to push their product.

Damian,

Check this thread. It may be of some help.

https://www.woodworkforums.com/f15/router-speed-97218/

Hi Steve,

as for electronics delivering wavering rpm, i found that in many cases dust inside the regulating wheel (between the carbon resistor strip and the sliding contact) is the cause of the trouble. Blowing clean the inside of this wheel with compressed air solves the trouble in most cases. E.g. the vintage Elu MOF 77 had a reputation for behaving erratically when soiled, since its large regular mounted in the middle of the airstream was relatively exposed and therefore sensitive. The 70-series electronic AEG drills were also known to have dust-sensitive regulator wheels in their handgrips.

The resistor regulates the loading and unloading times of a timing circuit capacitor, the voltage threshold values of which are used to trigger the thyristor or triac switch at exact partitions of the sine wave. So if there is dust between the sliding contact and the resistor strip, the resistance value alters spuriously, therefore the capacitor loads and unloads spuriously and the triac fires spuriously, noticeable as unstable wavering rpm. Anyone will remember crackling noises on old radios and amplifier, when turning the volume. There is probably no better way to illustrate spurious behaviour of electrical contact than that.

When cleaning the regulator doesn't help, it's probably wear of the resistor strip. The thin layer of carbon can be scraped off by the sliding contact during use, or get damaged over time by gritty of corrosive dust. Replacing the regulator is the remedy. Spurious electronics triggering can also be caused by a faulty feedback system. Motor rpm is sensed through a disc magnet on the motor axle and the magnet's field is picked up either by a coil (to be converted into a voltage) or by a Hall element (a sort of magnetic field sensitive transistor). If this coil or Hall sensor is loose, its connections are unstable or if the disc magnet is flawed in any way, the feedback is unstable, which results in unstable circuit triggering.

Pictures: first model Elu MOF77, later grey/orange MOF77, AEG SB2E-600 drill. When you squint your eyes and look at the cutaway presentation on the lid's inside of the drill carton, you can see the actual regulator with the resistor strip (silvery things behind the orange wheel) as mounted in the handle grip. This is the part that often starts to misbehave because of dust trapped inside.

Greetings

gerhard

Gerhard,

Thanks for that. Must look at a cleaning schedule.