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SCR Motor Controller - Cheap on Ebay
First off, this seems way too simple for me to be the first to recommend it, but I can't find anything on this site with a search, so I thought I'd throw up a quick post. I was using a triac motor dimmer for my vacuum blower speed control, but the minimum speed was still pretty fast.

I picked up an SCR motor controller from ebay. This is the one I got: http://www.ebay.c...0910260596 , but there are a great many others, some much cheaper from china. Just search "SCR controller". Some of them only list that they control 80-220V, but these ones with enclosures, (that cost a few more dollars), list 10-220V. It's all "chinglish", so tough to tell if they are talking about teh OUTPUT voltage, or the INPUT voltage. Anyway, I spent $10 to get the one that lists 10-220V.

It's got 4 contacts on the side, labelled in chinese. Looking at the underside, two of the contacts are just wired to each other, and the other two go off into the circuitry. I assumed the two wired to each other were the neutral contacts, (they were also the ones in the center), and the two outer ones were the hot contacts. I wired it up in series with my 6.5 amp vacuum motor and fired it up. Beautiful. I can dial voltage down so low with this little $10 unit that my monster blower can idle along at around 60 rpm, (slowwwwww, 1 revolution per second). Or I can crank it up to max.

I'm not sure if I'm getting the "full" max power out of it. To be honest, I think my motor is so overpowered that I'll never need full out of it - but if I feel like it a simple DPDT switch will bypass the SCR controller and give full mains voltage to the motor.

For $10, it's great, goes from zero speed to (as far as I can tell), full speed. No words on longevity yet, but it's rated for 4000 watts, (which is way more than anything can pull on my 20A 120V service), so with any luck it'll last. Plus it's TINY! It's about the size of a deck of cards.
I found the single board DC drives also work very well. Not quite as efficient as a variable auto-transformer, but more efficient than a router controller.
KB Electronics makes/made several models and most have min-max speed, min-max torque, and current sure and look for:
__Correct input voltage
__Required output voltage
__Required current
oldgearhead attached the following image:
I've been using one of the 3800 watt scr speed controllers for years. So far it has done over a 1000 roasts controlling the 1500 watt heating element. The only problem I had was that the plastic part that holds the connecting terminals is subject to a lot of heat and will eventually become warped and brittle. It happened to me around the 500th roast. I ended up removing the plastic and soldering the wires directly to the board, which is just about the limit of my electronic fabrication skills.

The lack of discussion surprised me too in the past, when everyone was using those (IMO) worthless router speed controls. Now the emphasis has switched to TC4 boards to integrate logging and controls, leaving manual controls to Luddites like me. Grin
Well SCR simply refers to silicone-controlled-rectifier. Most, low voltage. AC voltage-controlling devices have SCRs inside them, router controllers, light dimmers, and so on. As I mentioned before the single-board DC drives will also control an AC/DC motor and they might have an SCR or two inside. Some 120ACV input DC drives have 0-90VDC output, some 0-110VDC, and others 0-130V.

The better devices use PWM. PWM is not a part, like SCR but is a control method. In fact pulse-width-modulation is also used in electric-car RC racing speed controllers, they can deliver over 100 amps to a tiny DC motor, and they might have as many as 6 SCRs inside.
The SCR unit that I would buy, if I needed one, is called a solid-state voltage regulator. However, in my experience, nothing beats a quality variable auto-transformer.

Edited by oldgearhead on 10/18/2014 4:26 PM
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