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2.3 – Motor Speed Control (part 3 – thinking about heat)


The triac is going to need a way to cool off during continuous use. You could buy a standard heatsink from Maplin or similar or make your own. As my triac is rated at 26amps I am not too worried about it- but something to lick the heat away is needed.

I used a section of aluminium channelling (same as used on the lathe bed) bolted together with a bit of old heatsink rescued from a discarded computer PSU, with a bit of flattened copper pipe.

As far as I know copper is better at conducting the heat, and aluminium at radiating it to the surrounding atmosphere. Hence the copper helps disperse the heat throughout the sink and the aluminium radiates it off.

Whatever you find to use, cut your metal to a sensible size with a hacksaw , or similar (if you only have a junior hacksaw make or buy a full size one or you will waste a lot of time). Drill your holes, then, clean and polish all joining surfaces. The cleaner and flatter the meeting surfaces the better the heat will transfer. If you have some, apply thermal paste before bolting up the assembly.

The triac needs something to dissipate heat

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Responses to Motor Speed Control (part 3)

  1. Fsousa
    April 26th, 2013 at 12:11 pm

    hello!
    congratulations on your articles!
    I have not got knowledge to make a circuit to control my motor washing machine want to buy one at ebay, do you think maximum power: 4000w (connected resistive load) is enough??
    is it gets enough power and speed?
    link:http://viewitem.eim.ebay.pt/4000W-AC-220v-Power-SCR-Voltage-Regulator-Speed-control-Dimmer-Thermostat-4KW/300889241184/item

  2. Bongo
    April 26th, 2013 at 3:38 pm

    Hi Fsousa,
    I haven’t tried, so wouldn’t like to say for sure… On the face of it 4000W seems like it would cope with a ~750W washing machine motor, BUT the motor will draw much higher surge current on start-up. Also, it is an inductive load not a resistive load – it will create back EMF…
    If it stays cheap, you could give it a try, but I would advise against it, unless you contact the seller and tell them what you plan and ask them to advise. Let us know if you do…
    If you do try it, I would recommend only starting the motor on the lowest speed and gradually increasing.

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