SCR Motor Speed Control made from salvaged parts

**pfredX1** · May 6, 2018, 09:45 AM

If you want to buy parts there has never been a better time for that than now. Today we have the Internet. So you can get parts shipped right to your door cheap. Mostly I buy direct from China. There's some waiting involved with that but the prices can't be beat. I'm patient. Right now I could get 10 more of the triacs I used in the dimmers I made for $1.64. They're probably counterfeit but they still work just fine. https://www.aliexpress.com/item/10PC...844754301.html

**nhengineer** · Sep 8, 2018, 07:53 AM

Paul Jones, It would be appreciated if you'd share of provide a link for the schemagic for this project.

**pfredX1** · Sep 8, 2018, 12:24 PM

Originally Posted by nhengineer

Paul Jones, It would be appreciated if you'd share of provide a link for the schemagic for this project.

Just looking at the circuit board I'd say there are better schematics for making SCR phase fired converters today. We have higher performing parts we can use now. I found this circuit works well http://i.imgur.com/GE3ZXqP.png That's all you really need. It can even handle inductive motor loads. I've run a 600W router on one that I made. You can even get a heavier triac for larger loads. Here's the same circuit with a snubber http://i.imgur.com/iiuSn8H.png Though with the right triac you don't really need a snubber.

**nhengineer** · Sep 10, 2018, 12:45 PM

Thank you.

**Nick79** · Dec 27, 2018, 08:44 PM

Nice work. I am having a little trouble translating the solder "circuit" into a working diagram. Would you be able to post a circuit diagram with a list of components so I and others could build one too? Thanks so much - Nick

**pfredX1** · Dec 27, 2018, 11:01 PM

Originally Posted by Nick79

Nice work. I am having a little trouble translating the solder "circuit" into a working diagram. Would you be able to post a circuit diagram with a list of components so I and others could build one too? Thanks so much - Nick

Here is a schematic to a circuit that works fine and is easy to build http://i.imgur.com/GE3ZXqP.png
You want to get a "snubberless" triac for inductive loads like motors. I used a BTA24-600BW and a DB3 diac with the dimmer I built and it worked fine to speed control a 600W router here. This is what the circuit I built looks like https://i.imgur.com/M7WENhG.jpg
Quite frankly I wouldn't build the original posted circuit today unless I had a time machine and went back 40 years in it. Then it wouldn't be today though.

**trigger** · Dec 11, 2020, 11:36 PM

Chocolate out of sh....... The only way

**lest21** · Dec 11, 2020, 11:40 PM

Paul,

Neat write up. It was an SCR that got me into a career path that served me well. In June of 1967, with my fresh AA in Electronics Technology, I went forth seeking a job that paid more than my gas station one. It was a boom time for electronics, so I hit every company in Costa Mesa and Newport Beach that had an opening. First question was always, 'what's your draft status?' As soon as I said 2S, I would get come back when you're not draftable. Then stopped in at Borg Warner Controls in Santa Ana. Asked about a tech position, their question back was a new one. Do you know what an SCR is? Why yes I do.

The last week of class our instructor came in and held up this odd little object. This is an SCR and it can control 5 amps, had a hex base with a 1/4" stud. We were in awe, having been warned, now this will run at 1 amp and can hurt you for two years. He described how it worked in a circuit.

So the Borg Warner guy said draw the circuit, which I did. You're hired, start next Monday. I too naive to realize that was too easy. The next Monday when I arrived, I found out the SCR's in the equipment they were building had 3/4" studs and controlled up to 500 amps. The core equipment was motor speed controls using 3 phase motors for process lines instead of DC motors. Cheaper and a lot cleaner. They also had just gotten a contract from Comsat for Uninterruptible Power Systems to be used at their satellite base stations. Single 125 kVA modules, 480 volts, 3 phase.

Turned out I enjoyed the work and at the time, there were probably less that 500 techs world wide working with this type of equipment. We used joke that we were basically Edison linemen with a solid state background. While working for Borg Warner, later Emerson Industrial Controls, I did jobs in Mexico, Canada, Brazil, then in 1976, the Soviet Union. We did the motor controls for the Kamaz truck plant and I was the field engineer doing the start up. Then while working on a UPS at Hughes in Fullerton, they asked me to come to work there. Went from electrician to plant engineering to systems engineer there and it all started with an SCR.

Hope I didn't bore you with the tale, but you can see why I have a very fond bond with SCR's.

Cheers,
Les T.

**trigger** · Dec 11, 2020, 11:44 PM

Problem with the cheap Chinese knockoffs they tend to fail.I order a lot off MOSFETs and similar components for inverter charger repair jobs and then have returns due to component failure,not a happy experience when sailing way off grid.When taking a job I now cost Chinese/original with risks, advantages .Latest 20N60 batch received where second hand with new legs soldered on,the ingenious skullduggery will never cease to amaze me.