remember the variable speed dc motor control circuit in HSM?

[metalmagpie]

The HSM circuit I mentioned probably came right out of some thyristor databook back in the day. It's just a variable RC generating a voltage which goes to one terminal of a diac. The other terminal of the diac goes to a SCR. Couple of diodes, a rectifier and a DPST to reverse motor direction and that's it. 20 amp 600 PIV SCRs are available down the street from me for less than $10.

I asked George for permission to reprint the circuit itself so we can talk about it.

metalmagpie

[metalmagpie]

Have a treadmill motor on my lathe- been going strong for well over a decade now. I run it from a a switched multi voltage source with bridge rectifier and capacitor filter. This is, or was, a variac- but now it doesn't have a travelling pickup brush, it has multiple secondary taps selected by a rotating switch. It's crude, but effective. What it doesn't give is precise speed regulation- it gives a range of fixed voltages to drive the motor. I get the usual slowdown under load- which I kind of like anyway as it gives an intuitive sense of the loading I'm putting on the motor. No electronics involved. Old school. But I'm one of those guys who likes 'enmeshing himself in yards and yards of wire' as an old saying goes. This approach is not for everyone.

I run my motor now with a variac and full-wave rectifier. Yes, it works, but I want back emf sensing and I want something I can build into the head of the drill press.

metalmagpie

[darryl]

Have a treadmill motor on my lathe- been going strong for well over a decade now. I run it from a a switched multi voltage source with bridge rectifier and capacitor filter. This is, or was, a variac- but now it doesn't have a travelling pickup brush, it has multiple secondary taps selected by a rotating switch. It's crude, but effective. What it doesn't give is precise speed regulation- it gives a range of fixed voltages to drive the motor. I get the usual slowdown under load- which I kind of like anyway as it gives an intuitive sense of the loading I'm putting on the motor. No electronics involved. Old school. But I'm one of those guys who likes 'enmeshing himself in yards and yards of wire' as an old saying goes. This approach is not for everyone.

[MaxHeadRoom]

Yes, I made some PWM boards up for them, I am working on a solution to interface direct to the Mach3 CNC spindle control (M3,M5, Sxxxx) etc.
Keep an eye out for local market places that offer curb side pick up of T.M.s Any that does not fit the bill drop them off at the re-cycling plant!
.

[metalmagpie]

If this a T.M. version, the MC2100 offers one PWM solution.

Yes, it appears that an MC2100 board could be made to drive my TM motor. I see them on ebay from about $80 up. I'd still have to fab a board to feed a PWM signal to the MC2100 which is about as much trouble as making the HSM circuit itself. I will try to get permission to post the actual circuit I'm talking about.

What would be helpful is a list of treadmill brands that use the MC2100 control board, so I could watch for those on craigslist. I'd feel much better about using one if I didn't have to pay big bucks for it. Apparently Icon and Nordic Trak both make treadmills that use the MC2100 - any others?

metalmagpie

[metalmagpie]

How big is your motor?

2.3 horsepower, or 16.8 amps. This is typical of the size motors I found when I tore down 5 or 6 treadmills recently. Clearly a 5 amp speed control is far too small.

metalmagpie

[macona]

Like most treadmill motors, mine is too big for that 5A power supply.

How big is your motor?

[MaxHeadRoom]

Like most treadmill motors, mine is too big for that 5A power supply.

If this a T.M. version, the MC2100 offers one PWM solution.

[metalmagpie]

Personally I would just buy a PWM controller off ebay. SCR controllers kind of suck at low speeds from the ones I have used. Maybe something like this. It depends on the motor you want to use though , https://www.ebay.com/itm/13378962062...AAAOSwNP5dSPcM

Like most treadmill motors, mine is too big for that 5A power supply.

[J Tiers]

Personally I would just buy a PWM controller off ebay. SCR controllers kind of suck at low speeds from the ones I have used. Maybe something like this. It depends on the motor you want to use though , https://www.ebay.com/itm/13378962062...AAAOSwNP5dSPcM

Yes, they may get coggy, and in any case do not slow down well for larege recductions

[macona]

Personally I would just buy a PWM controller off ebay. SCR controllers kind of suck at low speeds from the ones I have used. Maybe something like this. It depends on the motor you want to use though , https://www.ebay.com/itm/13378962062...AAAOSwNP5dSPcM

[wierdscience]

Post#20 by Barrington has the basic circuit layout for an SCR based controller, which is what the control in that issue of HSM was IIRC.

https://bbs.homeshopmachinist.net/fo...l-breakthrough

[MaxHeadRoom]

Never saw the article, but was it a simple Triac controller with a bridge on the output maybe?
Just thinking it may not have been PWM from back then?

[metalmagpie]

In the May/June 1996 "Home Shop Machinist" magazine, an author named C. Eyer published a DC speed control circuit with which he controlled the speed of a permanent magnet lawn mower motor. This circuit was much discussed back in the day on groups like rec.crafts.metalworking.

Do you remember the discussions about this circuit? I also remember someone (I think it was a Berkeley engineering student) who simulated the circuit using SPICE and suggested some component changes to improve stability. I had thought he posted his suggestions to r.c.m. but I can not find it with google, who supposedly archived the old newsgroups.

I'm looking for those suggestions or any hints or ideas where I might look for them.

metalmagpie