# Solution for “Fan Dimmers” malfunctioning problem with UPS

People, who have square wave UPS, commonly have a problem of malfunctioning of fan dimmers, some time fans also and other electronics items such as mobile chargers. Reason of that malfunction is “High voltage Spikes” produced by fans.

When an inductor switches on or switches off in a DC circuit, it produces high voltage for a very short time which is technically called “inductive kick-back” as you can see in below wave form. Remember that few years back, a toy like a book was very famous that when someone opened it, he got a powerful shock. Actually that book consisted of a coil, and a 1.5V cell. When coil switched on or off, high voltage generated and the guy who opened the book got a shock while there was just a 1.5V cell in the book to supply the current to coil.

Same theory is applied at fans which run at square wave UPS. The voltage in that UPS suddenly rises and falls and during that rising and falling, high voltage produces by the coils of fan which damaged the dimmers etc. I did an experiment to overcome on high voltage spikes by connecting a simple capacitor and succeeded.

So if one can not replace the square wave UPS (due to that problem and also a very low efficiency) with a good one, for the time being, I would suggest, connect capacitor with those fans which run with UPS. I hope the problem would be removed.

For ceiling fan 75-90W = Capacitor 1.5uf.

For pedestal fan 125-150W = Capacitor 2.5uf.

^^ Fans already have capacitors.

Extra capacitors are you talking about?

Only voltage spikes are not responsible for burning or decreasing the life span, it is the noise of modified sine wave current also which heats up the devices, its components and they gets malfunctioned.

Dear blogger,

In fan, there are two windings, one is running and other is starting but starting also works all the time with running winding. The running winding is directly connected with mains and starting is connected via capacitor. The images are the real one not an imaginary. So as you seen in first image, the fan's "running winding" is caused by creating high voltage spikes which can be minimized by connecting capacitor as you can see in second image.

Did you ever put an osciloscope on any UPS? on no load, there is no noise even in daisi UPS but as you connect inductive load, you could see the noise. But if you connect a linear load such as filament lamp, the wave form is as smooth as during no load condition.

In what way capacitor should be connected? Any description shall be appreciated.

I have the same problem with my Homage UPS . What should i do ?

Signode is right. Adding capacitor to the ups will improve noise generated by inductive loads (Fans, motors etc). Now the question of blogger is "where to add capacitor". Its very simple. you can connect a capacitor at any plug which is fed by UPS. ( For dummies: Capacitors have two legs. Insert one leg in one hole of socket and other into the other one). Theoretically capacitor should be closer to UPS side. Normally desi UPS have two sockets on their back side. So you can use spare one. I will like to add something to what signode has told. Adding a capacitor to your UPS load will put some extra wattage on UPS (e.g. 2.2 uF capacitor is almost 35 Watt load). You can prevent your dimmers by another mean. Simply remove the dimmer and bring it to a technician ( if you cant use soldering iron) and ask him to replace the tiny 3 pin TRIAC with a BT136 TRIAC (available just for Rs. 20). So you will never face a burnt/damaged dimmer again inshallah.

to avoid damage to mobile chargers, simply make sure that you have some load already on UPS. It means you never put a charger as a only load of desi UPS as the square wave is enemy of switch mode power supplies. by adding some load (Fans or lights ) you are actually changing the square wave little bit in shape.

@ Signode. The ringing in start of square wave trace (the upper one) is telling that your UPS has no built in capacitor at its AC output. Nowadays almost all desi UPS have a 1 uF capacitor on their AC output socket.

I have heard about a more simple solution for dimmers, malfunctioned because of UPS. There is some carbon layer inside it causing the malfunctioning, use WD 40 for cleaning and dimmer will be like new one.

[quote=“waheed_shah, post:6, topic:17228”]

Adding a capacitor to your UPS load will put some extra wattage on UPS (e.g. 2.2 uF capacitor is almost 35 Watt load).

[/quote]

Hello Waheed Shah,

Your statement is not correct. “(e.g. 2.2 uF capacitor is almost 35 Watt load)” is too much. I have measured the energy of a pedestal fan running on daisi UPS and the results are;

Without capacitor =126W

With capacitor =132W

Difference 6W.

In above case, capacitor is working as a “snubber”.

I have also tested the capacitor on wapda and found it consuming just 3W. So what is the bases of your statement?

[quote=“signode, post:9, topic:17228”]

Hello Waheed Shah,

Your statement is not correct. “(e.g. 2.2 uF capacitor is almost 35 Watt load)” is too much.

… So what is the bases of your statement?

[/quote]

He is right, a 2.2uF capacitor is around 33-34 VA load on the UPS.

Following equation gives you the Xc (capacitive reactance which is equivalent to resistance on DC)

Xc = 1447 Ohms,

I = V/R ----> I = 220/1447 = 0.152A

Now W = VI ----> W = 220 x 0.152 = 33.44 VA

This is called Reactive Power and not the Real Power, but it is kinda load on UPS.

Can you give instruction for dummies?

I have a 2000 homage UPS. On UPS fan make noise and slows down. Do we have to put capacitor with every dimmer and which type?

thanks

Dear Experts,

I am facing the same problem as @Tramper, that is fans slows downs and makes noise on UPS, my UPS is quite old with Square Wave output. What size of capacitor should be placed at UPS, as mentioned by waheed_shah so that it can take load of 3 to 4 fans and 4 Energy Savers.

Thanks

Moiz

Dear Signode, Waheed Shah sb,

I got your mean as a manufacturer of fan dimmer. But could please let me know about the 1.5uf capacitor more? Before we are using 683 J capacitors. But we still have complaints that it burns on UPS means the dimmer burned or damaged. We use so many ways to fix this problem but still not succeeded. We have upgraded the BT-134 to BT-136 and we are also using good kind of capacitors but the problem is still there. So according to you by using 1.5uf instead of all other capacitors can give us a sigh of relief? Please let me know the best solution? I searched on interned there are many tipes of 1.5uf capacitors. Could you please let me know the specification in detail. My MSN and email is goal_achiever89@hotmail.com. You can talk to me there if you have time. And then I can show you the pictures too of all components of fan dimmer. Hope any one of you assist me and give me a chance to say thanks..

[quote=“signode, post:9, topic:17228”]

Hello Waheed Shah,

Your statement is not correct. “(e.g. 2.2 uF capacitor is almost 35 Watt load)” is too much. I have measured the energy of a pedestal fan running on daisi UPS and the results are;

Without capacitor =126W

With capacitor =132W

Difference 6W.

In above case, capacitor is working as a “snubber”.

I have also tested the capacitor on wapda and found it consuming just 3W. So what is the bases of your statement?

[/quote]

Dear Signode,

I got your mean as a manufacturer of fan dimmer. But could please let me know about the 1.5uf capacitor more? Before we are using 683 J capacitors. But we still have complaints that it burns on UPS means the dimmer burned or damaged. We use so many ways to fix this problem but still not succeeded. We have upgraded the BT-134 to BT-136 and we are also using good kind of capacitors but the problem is still there. So according to you by using 1.5uf instead of all other capacitors can give us a sigh of relief? Please let me know the best solution? I searched on interned there are many tipes of 1.5uf capacitors. Could you please let me know the specification in detail. My MSN and email is goal_achiever89@hotmail.com. You can talk to me there if you have time. And then I can show you the pictures too of all components of fan dimmer. Hope any one of you assist me and give me a chance to say thanks

In order to be able to modify it one needs to understand the theory behind the working of a commercial fan dimmer. These dimmers are ESSENTIALLY designed to be used with 50 Hz sine-wave as supplied by the AC mains. The curve of the rising portion of the sine-wave is used to control the amount of input power to the fan. In the the UPS the output is a square wave which has an almost vertically rising leading edge. This can easily be seen in the oscilloscope trace photograph given above. Since the circuit is not designed for this kind of wave shape it does not function.

There is no simple solution to the problem and at the least the circuit needs to be re-designed to cater both for sine as well as square wave.

Sorry for posting off-topic..

I have a Pure Sinewave UPS installed at home but in my home there are a few Dimmers malfunctioning (not precisely controlling fan speeds), what's the reason behind this? Also, how can I check if my UPS is really Pure Sinewave? PS: I don't have oscilloscope.

Where should be the capacitor connected ?

Especially

@Asad and @Ijaz Ahmed

All Homage, Mercury or similar inverter type Chinese UPS already have this capacitor installed inside.

If anybody wants to attach such a capacitor, then it should be connected at the output of UPS just like you connect any load to the UPS.

[quote=“nictor, post:16, topic:17228”]

Also, how can I check if my UPS is really Pure Sinewave? PS: I don’t have oscilloscope.

[/quote]

There is no sure fire way except by looking at the waveform on an oscilloscope. One crude method that I can suggest is to connect take a 220/3 VAC step down transformer. On its 3 VAC secondary winding connect a resistor of about 5-10 ohms in series with an ordinary loudspeaker. First connect the primary to the AC mains and listen to the sound. Try to keep the level of ‘harshness’ in your mind. Now connect the primary to to the o/p of the UPS. If the harshness/smoothness of the sound coming out of the loudspeaker is about the same as the one with AC Mains then you can be sure that the UPS is producing sine wave. Harsh and ‘rough’ sound indicates sudden changes in voltage levels as encountered in square or near sine wave inverters.

[quote=", post:18, topic:17228"]

All Homage, Mercury or similar inverter type Chinese UPS already have this capacitor installed inside.

If anybody wants to attach such a capacitor, then it should be connected at the output of UPS just like you connect any load to the UPS.

[/quote]

A capacitor for each individual fan or just one will do ?