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Forum Index : Microcontroller and PC projects : How to variable speed control a Galanz GAL4P19A-KND motor

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rogerdw
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Joined: 22/10/2019
Location: Australia
Posts: 904

Posted: 06:24am 28 Dec 2024

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Hi Guys, I’m looking for some help with a fan speed controller please.

When I built my Warpverter I scored a barrel fan from the indoor section of a split system aircon … as well as the circuit board and supply.

I thought I’d be able to cobble something together but no success so far.

It will definitely run flat out … and I can use a cheapie on/off controller to switch it … but it would be nice to have it run at a civilised speed rather than flat out or stop.

The motor is a Galanz GAL4P19A-KND 240V 19W

Apart from the 3 motor winding connections, it also has a 3 wire connector with 5V, Signal and Gnd.

If I power the signal wires with 5V, I get 3 nice clean switching pulses per revolution. Goes from gnd to 5V cleanly.

I have the circuit board … but it is for the whole aircon control and not just the fan … so not much help in this situation.

I also have a circuit diagram I found which is the same or extremely close to the board I have.

Any suggestions as to how I can arrange variable control of the motor please?

Thanks

Cheers, Roger

phil99

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Joined: 11/02/2018
Location: Australia
Posts: 2606

Posted: 07:45am 28 Dec 2024

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The circuit is conventional leading edge phase control of a split-phase motor.

Power to the motor is varied by synchronising the MCU with the 240VAC zero crossings and delaying switching the optocoupler to trigger the triac.

Compare the frequency of the feedback signal with the desired speed and vary the trigger delay accordingly.

How well this works depends on what you are using the motor for.
The smoothly rising, predictable torque/speed characteristics of fans and centrifugal pumps give good stable speed control with this method.
Loads that require a higher torque at low speed than at high speed may require a variable frequency drive.

If driving a fan and you don't need exact speed control you can ignore the feedback signal and still get good results, except at very low speed. That may require starting at a higher speed then slowly reducing to the desired low speed.

rogerdw
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Joined: 22/10/2019
Location: Australia
Posts: 904

Posted: 08:42am 13 Jan 2025

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Thanks Phil,

I'm sorry, I forgot I put this in the wrong section and didn't see your reply. I don't come in here very often, a bit out of my league.

Thanks for the explanation. I do want to use it simply to run a fan and even just a slow, medium and high would be great.

I can apply 240AC across the motor and it runs at full speed nicely ... but I'm not sure what method to use to run it slower. I bought a motor speed control from aliexpress which uses a feedback system similar to this, but I couldn't get it to work even slightly.

So should I just try a basic light dimmer/ac motor control circuit using phase control with a triac. I can see it not starting too well at low speed like you say ... but anything from medium and up should still run perhaps.

Thanks.

Cheers, Roger

phil99

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Joined: 11/02/2018
Location: Australia
Posts: 2606

Posted: 10:57am 13 Jan 2025

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Yes, you can use a conventional leading edge triac light dimmer, I have done so a couple of times.
There is a small mod you need to make though. Add a 220nF 250VAC capacitor with 2.2kΩ 1/2W resistor in series in parallel with the dimmer.

The reason for this is the trigger method used in the dimmer only delivers a very brief pulse to the gate. The anode current must reach its minimum holding current before the pulse ends or it will switch off. But the inductance of the motor slows the rate of rise of the current so much it become unreliable. The RC combination supplies enough current for long enough to keep the triac conducting until the motor current rises.

Option B is get a bathroom exhaust fan speed controller from an electrical trade outlet such as Middy's.

rogerdw
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Joined: 22/10/2019
Location: Australia
Posts: 904

Posted: 01:18am 14 Jan 2025

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Thanks again Phil, I was writing a reply last night when the site disappeared. Was worried.

I think I'll just try Option B. Hopefully will be quicker and easier.

Cheers, Roger

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