Speed control of a leaf blower

[eptheca]

Hello
I have a leaf blower, 2400W, 220V (abt.11A) with a speed control.
The speed control circuit is based on a TRIAC BTA12 600B, a diode, a capacitor, a 100K resistor and a potentiometer.
It's a 490K poteniometer with a 390K resistor between the legs, I measure it to 220K

Does anybody have a good idea for how to control this circuit with an arduino?
My "safe" solution is to have a servo turn the pot back and forth, but I would like a better, less mechanical solution.

Would it be possible to use a photo resistor in stead of the pot, and an LED to control that?
I assume the 220V is running through the pot, so are there photo resistors that can take that?

I appreciate any suggestions on this
thanks in advance  

[MarkT]

In theory a suitable _high voltage rated_ LDR could be substituted for the potentiometer, then you can control the circuit optically from a light-pipe and white LED.  An extra series resistance might be required to stop too much current (and heating) in the LDR...  However I don't know if high-voltage LDRs exist...

Finding an existing opto-isolated (or remotely controlled) dimmer circuit rated for universal motors of that power would be an off-the-shelf solution (light dimmers and motor speed control for universal motors are basically the same circuit).

But if you are not confident working with mains voltages think twice.  Mains voltage shows no mercy and can easily kill.

[eptheca]

thanks for the tip
I have found high voltage LDR's up to 600V, but I don't think they are suitable for 2400W
dimmers have the same problem, most of them are for lights up to 500W
I have a router speed control that works up to 20A, but it's with a pot as well, so...

I think maybe my first idea, to turn the pot with a servo is the safest, cheapest and easiest solution, but I'm open to all suggestions

[MarkT]

The LDR doesn't take anything like 2400W!  In fact nothing in the circuit does except the motor.  However you will need to ensure the LDR can take the current/power involved, which is a bit of calculation once you know the min resistance needed.

[eptheca]

here's a quick schematics and photo of the circuit



would it be possible to control the TRIAC with an optocoupler with a PWM pin?

[retrolefty]

There seems to be something missing in that schematic drawing. The 490K pot, 390K and 100K resistors don't appear to make a complete circuit, just kind of hanging out in free space with just one connection to the main circuit?

Lefty

[eptheca]

yes, you are right
I have edited the image now with the correct connection

[triven]

you could use a multiplexer, preferably 4:16. and on each output pin of the available 16, you could connect a resistor that suits the speed you want to attain at different intervals. these outputs will be connected to your motor, the multiplexer will have to be bidirectional(both positive and negative half cycle) and will have to have a high current withstanding capacity. for this i suggest using power transistors at the output of your multiplexer.(the resistances previously connected will act as base resistance to limit the base current) , and therefore you will have a safe and precise control of your blower....