AC Fan speed control

[haxan]

Hi,

I am opening a thread again for AC Fan speed control. The FAN i want to control operates on 220V AC and speed can be dimmed using triac by firing it at correct time durations.

First task is how to design a Zero Crossing Detection Circuit. Is it possible to detect ZC without using a transformer, directly from the power line somehow?

 

[haxan]

anyone ?

 

[ericgibbs]

anyone ?

hi,
There is this option.

 

[haxan]

This has the ZCD circuit built into its IC, i want to detect the crossing pulses and feed it to the microcontroller.

 

[DirtyLude]

Search for dimmer in here or google it. Zero crossing detectors are part of regular uC controlled dimmer circuits. I use a 4N25 and bridge for a zero crossing detector. Similar to this:
Andrew Kilpatrick Interfacing: AC Line

 

[Hero999]

I assume you're talking about a phase control dimmer?

A zero crossing SSR or opto isolator can't be used for that.

How are you powering the MCU?

You need a transformerless PSU or a non-zero corssing opto isolator.

 

[haxan]

Yes it is a phase control dimmer for a Fan (inductive load)

The MCU will be powered separately with independent source.

So there will be practically no link with the MCU power phase and AC live phase.

Yes i understand that i will need non-zero crossing opto isolator such as MOC3021. I just want to concentrate on how to get Zero crossing pulse on both parts of one cycle. DirtyLude posted a link which contains pdf file with such circuit works without a transformer. Just a bridge connected with opto transistor 4N25. Will check it out tomorrow if available from local market.

 

[Hero999]

If you know that the live and neutral conductors are not going to be reversed, you could use a couple of Y1 rated capacitors and diodes. The neutral must be connected to C2 and the live to C1, otherwise it won't work if the DC supply becomes connected to the earth/ground connection which could be caused simply by touching the DC supply.

**broken link removed**

The phase shift is nearly 90° due to the phase shift in C1 and C2 so this circuit shows you when the voltage is at its peak, not zero but it should be easy to compensate for this using software.

**broken link removed**

Here's a link to a similar thread.
https://www.electro-tech-online.com/threads/detecting-presence-of-mains-safely.106061/

 

[Gayan Soyza]

In my precision dimmers I use this method.

ZX detection is via 2 diodes, 1N4001's, which draw current from the main 230v supply via a 4M7 1/2 watt resistor. They are clamped to 0v and 5v. They produce a roughly square wave (0v / 5v) which goes through two 40106B Schmitt inverter gates

 

[haxan]

You mean something similar to this:

**broken link removed**

 

[Hero999]

No, I think Gayan is talking about a similar circuit to the one I posted but using high voltage, high value resistors, rather than capacitors, to couple the mains to the MCU input.

I've just realised that D3 an possibly the other diodes aren't needed with my design because they're built into the MCU.

Don't worry about using capacitors to couple the mains as long as they're low value and Y1 rated, they're perfectly safe as long as there are suitable clearances between the mains tracks and MCU side.

If you go for the resistor option, the resistors should be able to withstand a 8kV spike without breaking down and turning into a low resistance, select high voltage resistors and look at the datasheet for the withstand voltage - ask the manufacturer if you're not sure.

 

[haxan]

I am facing one problem. I have attached an LED where i get the Zero Cross detection pules. The LED stays on when the power is on MAINS however when i change it to UPS, the LED goes off?

The MAINS voltage is 220 where as UPS's is 240. Can anyone diagnose the problem?

 

[Hero999]

What sort of waveform does the inverter inside the UPS produce?

If it's squarewave, then maybe that's what's causing the problem?

 

[haxan]

I am not sure how to check the waveform. I do not have an oscilloscope. Does this mean that Zero Crossing Detection wont be possible on UPS systems?

 

[haxan]

anyone ?

Why is the circuit not detecting ZC on UPS

 

[Hero999]

I don't know.

As I said before, it depends on what sort of UPS you're using.

I'd suggest looking at the datasheet or manual for the UPS.

If you have an oscilloscope, you can measuring the output waveform by connecting a mains transformer to the UPS.