SCR Motor Speed Control made from salvaged parts

[trigger]

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.

[Paul Jones]

Hi wazard69,

It is more difficult to find surplus electronics stores these days let alone electronics junk yards. Locally we have the store Orvac Electronics in Fullerton, CA (see Catalog ) that used to have a large section of the store devoted to surplus electronics (the smell of the old electronics would bring back memories) but most of the materials are gone compared to what they used to have. Back in the late 1970's to early 1980's I built S-100 bus computers with 8080 and 8085 CPU chips as a hobby and bought many surplus parts from Orvac and several other stores in the area. I still have the computer with the S-100 bus backplane but hesitant to power it up with its old 12 amp power 12V power supply because the old large can capacitors could explode. The capacitors were pretty old when I bought them in the late 1970's but it would be fun to see the computer come alive again.

I remember it was such a thrill the first time I saw the blinking cursor indicator on the screen of an old 9" CRT monitor when the 8080 2MHz CPU computer started up and I gave it the command to clear memory and display all the RAM memory showing all zeros in hex. The first 8080 and later a 8085 (a 4 MHz CPU) could only address 64 Kbytes of memory but this type of static RAM drew several amps of power, needed a big fan for cooling, and you really only address 58 kbytes of real memory because the 4 Kbyte BIOS resided in a ROM address in the upper memory address space. Nonetheless, I eventually improved the computer capabilities and installed a 5 1/4 " floppy disk drive and ran a FORTRAN compiler and link editor on the computer. It was an amazing little computer in its day and built from S-100 bus board kits and surplus parts. As a hobby with the S-100 bus computer I programmed in 8080 machine code, Assembler, and FORTRAN (I had been using FORTRAN since 1968). It also ran LISP and a BASIC interpreter and but the compiled FORTRAN was always much faster to run.

Regards,
Paul

[nhengineer]

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

[pfredX1]

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]

Thank you.

[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

[pfredX1]

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]

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

[lest21]

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.