SCR Motor Speed Control made from salvaged parts

[Paul Jones]

Christophe,
I wish I had kept the schematic but I am pretty sure it is "phase angle control" using thyristors for controlling the phase angle or trigger angle thus allowing the output RMS voltage of the load to be varied. I think a more efficient method would use TRIACs instead of thyristors but I don't think these were available in the early 70's.
Thanks for asking, Paul

[PJs]

PJ,
I thought I could help you with the part numbers and pulled the board from its edge connector. Some of the transistor cans are too corroded to read all the printed markings. The big SCR is a 2N3669, the four diodes are 1N2860A, the three transistors are 2N3754 (middle right), 2N26?9 (lower left),and unknown in upper middle position.
Paul

Thanks Paul for specs...I thought those diodes might be mil spec. and they were. Also that TO-3 SCR still has an equivalent out there but wonder if they'll last 40+ years¿ Shouldn't be hard to find everything based on these numbers and still have a big box of 1/2 & 1W resistors. Loved the heatsink too by the way! Thanks again for the post! ~PJ

[Paul Jones]

PJs - thanks for the spec confirmations. Yes, the heat sink was cut from a piece of scrap aluminum sheet and the corners thinned a little to allow bending without breaking. It is crude but effective. Years ago, I would use the motor speed controller for a one-speed saber saw for cutting metal and the controller would become extremely hot but never burned out. Now I use it for the Unimat lathe which has very little load on the controller so that is probably why it has lasted so long (see http://www.homemadetools.net/forum/m...00-lathe-10111 ). Thanks, Paul

[Paulo Bonini]

congratulations Paul, but, do you send-me eschematic diagrans?

[Paul Jones]

Paulo,

I no longer have the schematics or the original construction article that I used to fabricate the SCR motor speed controller. The circuit design came from an electronics construction article in either Popular Electronics or Popular Mechanics sometime in 1968 or 1969. If you can find the archives to these magazines, I am sure you will find the details on how to construct this. The speed controller has been very reliable for now close to 47 years and still in use every week for my Unimat lathe (see my publication http://www.homemadetools.net/forum/m...00-lathe-10111 ).

Thank you for your interest,

Paul Jones

[pfredX1]

These are a lot easier to make today with triacs and diacs. http://i.imgur.com/GE3ZXqP.png Here's a commercial one I repaired that is almost that exact circuit I'm making a holder for it in this image https://i.imgur.com/BWiLc5Z.jpg It has an extra resistor and cap for inductive loads. But if you use the right triac you don't even need those parts.

[pfredX1]

I replied to this post before so this would have been a duplicate comment.

[Christophe Mineau]

Yes,
And obviously, a simple vacuum or hand drill speed controller can be salvaged or even an halogen light dimmer, I have tried it already,
but for a real use of a washing machine universal motor in a shop made project, it is not really convenient, as it does not drive
at constant torque . As soon as you apply load, the speed drops and you have to readjust.
The only way to do it properly, according to me, is to regulate in close loop, using the signal from the tachometer, just like what does the washing machine control board.
But this takes more than a few components and requires a micro controller.
I already found on eBay a Russian seller who sold PCBs and instructions for such a controller, but I never managed to arrange the payment, there was something wrong at the time between Paypal and Russia, maybe it has been solved since.
One day, if I only had time, I may try to make one with an Arduino, I think I it is doable, but no more time ...

But if someone has already done it, it would be really nice to share

[wizard69]

Nice work, brings back memories! Back in my youth I did a lot of salvage to build things like a control panel to launch my rockets with. This was most likely the early 1970's, I remember becoming obsessed with linear regulators and built a bunch of power supplies and then tried to blow a few of them up. Those regulators where tough. Unfortunately most of the surplus I got was second hand form junk dealers with a big markup, even those sources dried up after a bit. At this point I don't know of any surplus shops in the area.

[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