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With the current heatwave it seems a good time to take a look inside a fan controller.
As is very predictable with grey imports, it is very basic and lacks any electrical noise suppression. The triac also lacks a basic snubber network, which is usually desirable with inductive loads. Such a simple circuit may have stability issues with some inductive loads.
The spare component positions could have been intended for a couple of things. A crude locator with neon and resistor for finding the controller in the dark, or a snubber network.
If they were intended for a snubber network then it's possible that it was left off because it takes very little current to make a fan rotate, and it may have leaked enough to keep a new fan turning slowly. If it had been on the other side of the switch it would have been less of an issue.
I'm not sure if these are made in 120V versions. It's possible that the simplest fix for timing might be to adjust the capacitor value down so it charged faster on each half cycle.
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Is a classic fan speed controller from ebay probably works like a standard dimmer. I i would expect but when i connected it in sears with the tungsten load just lamp it did not dim it clicks it turns. But nothing happened at all let's explore and see if we can work out what went wrong so for a start. Let's get the face plate off to pull the knob off first that will that will help there's a screwdriver um can i clip this off non destructively.

Yes. I can so off comes the faceplate. The module these usually pop out these modules. Let's try gently pricing that down like that scrunching plastic imminent.

Oh. It's out that's good right. Let's get these out the way and let's pop. The module open.

It's got some clips at the side is this going to come out or to have two screws out. I shall try taking it out first and if it doesn't pop out what not just comes out just comes out the first thing. I'm seeing is a reflection off here is that broken track. Oh that is a broken track.

That's probably what the problem was okay i'll tell you what let's continue reverse engineering. It and we'll take a look at the circuitry so i can see a die hack here. I shall unscrew this and i shall take the module out that way we're free of this gray piece of plastic. Now we can take a closer look at it these often just work like a normal dimmer and as in many of the imported gray market products.

There's no suppression notes of a inductor and capacitor required for radio interference suppression. I suppose if it's a fan. The inductance of the fan may limit that to a degree. I'm not really sure so there's a potentiometer with a switch uh.

There's what is probably a track the diac in line with that the timing capacitor and then just a smattering of resistors uh around this potentiometer for the actual control of the speed right taiwan. I'm just going to take a picture of this and we'll take a closer look at it one moment. Please okay let's explore this is the back of the circuit board. There is the crack that was in the track that's not uncommon when you've got large components like pretend shorters if they're not seated down fully onto a circuit board.

There's a risk that any pressure against it will break that solar connection. It's really common with big components particularly when things are dropped in shipping. It used to be a major thing uh in older television sets with uh heavy transformers that if they get dropped. It would break the solar joints.

Easy fix all i did was put a wire link between the two broken parts to provide a flexible movable joint. So this effect this actually goes in line with the load. The neutral will go directly to the road. The line will come in here.

And then the load will be connected to here and the switch switch is a power. Interesting to note these tracks here are to the triac and they're beefed up with solder. But then it goes through the switch to the output terminal. And nothing is beefed up the soda here in fact.

This is probably the thinnest part of the track. So that's the bit that will blow when there's a short circuit. Because there is no fuse in this there's no air suppression components in that either it's quite odd. There's a couple of uh positions down here that look as though they're for a snubber network.

The circuit board has a little diak on it which uh feeds up to the base of the at the gate of the triac and then there's a timing circuit based on some discrete resistance. Which resistors. Which are all tucked under here. And a timing capacitor.

Let's just cut straight to the schematic. Because that's going to make it a lot clearer because uh you can't really tell too much from that circuit board so i shall zoom in on this a little bit so here's how it works. The triac is connected directly across load and live so that when it switches on it shorts live to the load. Which then powers the load.

Which is getting its neutral from the elsewhere. So say for instance. If this is neutral and say we just actually powered a lamp. A tungsten lamp.

It would be hooked up like that so to turn the triacon. We have a diac a diak is an interesting little component. It is a voltage threshold device. But it's bi directional and in each half of the sine wave this capacitor here charges up via these resistors until it reaches 30 volts.

When it reaches 30 volts. This diox suddenly turns on and it clamps on and discharges this capacitor into the gate of the triac and that turns on and brings the load on so if i was to show you say for instance. If if i was to draw a bit of a sine wave sine wave. What actually happens if you set it to half intensity or half speed in the case of the fan.

And it's coming on roughly in the middle of the uh of each half of the sine wave on each half. These resistors pass current to charge the capacitor and the position of the potentiometer determines how fast it charges before it triggers. It's interesting to note that there's a 680k resistor in parallel with 500k potentiometer. Which is very reminiscent of lighting circuits to make it so it's not a linear.

Response it gives a very weird logarithmically type response and this 82 k. Resistor. 8200 ohm. Resistor is to set the absolute maximum speed this capacitor can charge up if that potentiometer is put right over to the full scale.

So to speak. So what happens is it charges up the diac triggers triggers. The track and the triax by their very nature latch on they don't turn back off again until it reaches the zero crossing point as soon as the current flowing through them goes to zero. They should normally turn off then the polarity swaps to the other half of the sine wave.

And it does the same again there's usually a slight difference in symmetry. But more or less the same position it'll turn on again and it'll stay on for that part of the sound wave. So it just basically turns on for 50 of the time. And that is it the number network was actually if that's what it was it could have been a couple of things.

But a capacitor and a resistor 100. Ohm 100 nano. Very common they make the operation of the track more stable with inductive loads. And by suppressing sort of high speed switching transients that can cause the track to turn on unexpectedly that is it it's super simple isn't it right tell you what i shall put this back together.

And i shall find a load a suitable load for it uh. That's interesting then we'll power up and see if it works one moment. Please let's test this here's the setup. I have the cliff quick test for providing temporary power and the live from it is going to the fan controller and then to the socket.

A standard british socket. The neutral from the power supply goes straight to the socket. So this is basically just breaking into the live. The socket has a lamp plugged into it and when i turn the power on here let's make sure.

This is off first turn the power on noting that there are live connections under here when i turn on it initially lights the lamp at full brightness and then as you turn it up it actually turns the lamp down the reason for that is it's because it's a fan controller as opposed to a lighting dimmer. It's designed to start the fan at full speed to give it a good head start to give it a bump to actually start. It spinning sometimes if you start fans when they're at a low setting. They just they'll just sit there and hum and not rotate um.

So i'm not sure how compatible this should be with all fans with standard basic ceiling fans it should be okay. But there is no radio interference suppression on it maybe the inductance of the fan itself would help there. But this is probably quite a popular thing in china our gessler fans that's really probably the market. It's designed for but there we go a very standard simple circuit based on a dimmer um.

That is just being used in this case to phase angle control a fan motor. Very very simple and straightforward.

13 thoughts on “Inside a cheap ebay fan controller with schematic”
  1. Avataaar/Circle Created with python_avatars GrrDraxin1 says:

    You should see if you can get a hold of one of those dimmers that has the sine wave cut in the other direction. Those as I understand it make motors sound a lot less buzzy when you use them, as the sine wave is cut off instead of cut on for the dimming function.

  2. Avataaar/Circle Created with python_avatars Rafael Gomes says:

    I have a similar unit hooked up to my ceiling fan. It causes the fan to make a terrible humming noise at pretty much any position other than full speed, so it's basically useless.

  3. Avataaar/Circle Created with python_avatars Tinkerbot says:

    Has anyone noticed the gradient marking on the knob is the wrong way round for this application?

  4. Avataaar/Circle Created with python_avatars adebabay tech says:

    Friend love it

  5. Avataaar/Circle Created with python_avatars Om nOm says:


  6. Avataaar/Circle Created with python_avatars edquin8 says:

    I really want to try out that pen!

  7. Avataaar/Circle Created with python_avatars Aaron Brandenburg says:

    One thing I do agree with with big Clive is that in cases where something like this is used for fan speed control versus lighting that the starting with high gets the motor going because it would be harder on a motor to start on low this is much better reason why and some other people say about about how I being used the most I'm sure their differences of opinions but I'm sticking with this one since probably most accurate

  8. Avataaar/Circle Created with python_avatars Rakesh Pai says:

    Here in India, we've all but phased out (get it?) triac-based dimmer controls for inductive loads like fans. The choppiness it introduces at the lower speeds makes the fan hum noisily, makes the motor coils heat up, and reduces its life. Instead, we now use a 5-position (usually) capacitor bank to switch speeds, and it has the same form-factor as a triac dimmer. Sure we lose out on the smooth step-less speed control, but it's a lot quieter and saves sending fans to the landfill.

    In fact, now that we're all moving to LED lights, and traic-based dimmers don't work well with LEDs either, the utility of traic-based dimmers has diminished to the point of all but vanishing from home use. It''s amazing – just 10 years ago these dimmers were everywhere. Now they've vanished.

    The 5-position capacitor bank based dimmers are very interesting in their design too. They usually have only 2 or 3 caps to keep the cost low, and the dial switches them into various series-parallel combinations to give 5-position speed control.

  9. Avataaar/Circle Created with python_avatars dpmott says:

    Running an induction motor with a triac ensures that the motor incurs an inrush of current at a rate of twice the line frequency. The motor can never get to its full speed, so it is always lagging behind the line frequency, and when the triac activates, the motor will draw extra current to accelerate. Both the motor and triac will run hot (and inefficiently) as a result.

  10. Avataaar/Circle Created with python_avatars No music RC says:

    This was FANtastic

  11. Avataaar/Circle Created with python_avatars Piper Cessna says:

    Just wondering if the chinesium manufcturers could really get any dimmer? 🤷‍♂

  12. Avataaar/Circle Created with python_avatars twocvbloke says:

    I just run my wall fan through my 240-120v transformer, otherwise it just spins too fast and sounds like I have an aeroplane on my wall, and it doesn't really push much air as a result, gotta love "quality" these days… 😛

  13. Avataaar/Circle Created with python_avatars Tom Luque says:

    Confusing…… You have showen that the Dimmer start out at full power to the bulb, but the printed icon wedge on the knob indicates low power start ???

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