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### Topic: somebody please explain this? sketch attached (Read 1 time)previous topic - next topic

#### zacmackra

##### Apr 13, 2014, 07:40 pm
hi guys i found this circuit diagram an how to control ac fan with arduino. however what i could not understand is there is a well defined path ABCDEF along which the current can flow and hence the inductive motor or fan will remain on all the time instead of being controlled by the gate pulse to the triac. can somebody explain this?

jpg attached

#### Runaway Pancake

#1
##### Apr 13, 2014, 07:56 pm
In both of those examples, as long as the opto input is on then the triac will be on.
"You gotta fight - for your right - to party!"
"Who is like unto the beast? who is able to make war with him?"
It's "bipolar transistor" or "junction transistor" - "BJT" is stupid.
When all else fails, check your wiring!

#### Jack Christensen

#2
##### Apr 13, 2014, 11:48 pm
Only a fraction of a milliamp will flow C-D-E. The capacitive reactance of a 100nF capacitor at 60Hz is around 26K Ohms.

#### zacmackra

#3
##### Apr 14, 2014, 04:22 am
Thank you jack.  Btw what should be the power rating of the resistor and capacitor to be used?

#### Jack Christensen

#4
##### Apr 14, 2014, 02:11 pm

Thank you jack.  Btw what should be the power rating of the resistor and capacitor to be used?

I'd need to know the mains voltage.

BTW, what was the source of the schematic? It wasn't indicated there?

#### Jack Christensen

#5
##### Apr 14, 2014, 02:59 pm

hi guys i found this circuit diagram an how to control ac fan with arduino.

Can you give the link to where you found the circuit? Sounds like you got off on the wrong foot right from the start. Triac circuits aren't well suited to controlling AC induction motors, which is the type used on most of the fans around here anyway.

#### zacmackra

#6
##### Apr 15, 2014, 05:46 amLast Edit: Apr 15, 2014, 06:43 am by zacmackra Reason: 1
mains are 230v, 50z
the control is not specifically for ac fan, it can be any ac motor depending upon the requirement of the circuit. i just want some rotation control.

here it is

it is done by chopping the sine wave

here is another one-
http://www.bristolwatch.com/arduino/arduino_power_control.htm

#### Jack Christensen

#7
##### Apr 15, 2014, 01:50 pmLast Edit: Apr 15, 2014, 01:52 pm by Jack Christensen Reason: 1

the control is not specifically for ac fan, it can be any ac motor...

Well, no. There are different kinds of AC motors.

Induction motors (typically used in mains-powered fans) run at a speed determined by the mains frequency and the load on the motor, but their speed cannot vary by more than a few percent or they will stall. On/off control of an induction motor with a triac may be OK but don't expect to control speed very much.

Universal motors are found in things like power tools (drills, saws), kitchen appliances (blenders), etc. They can actually run on AC or DC. They are very noisy as compared to induction motors (so not usually used in fans) and have a relatively shorter life. Their speed can be controlled with a triac circuit.

There are other kinds of AC motors as well but those are the most common. Good luck. Be careful, keep your sneakers on and one hand in a pocket.

#8
thankyou

#### retrolefty

#9
##### Apr 16, 2014, 08:04 pm
Also be aware that triac type switches (which include most of those AC solid state relays) can have problems controlling AC motor loads due to the induction of the motor windings and give problem symptoms like turning on but not turning off or not turning on. The 'fix' is usually wiring a series R/C network across the load terminals but the component values must be 'sized' to the specific motor load.

#### michinyon

#10
##### Apr 17, 2014, 04:38 pm
How do room fans that have a selection of three speeds work ?

They have been around a long time,   and I somewhat doubt that they have variable frequency drives.

#### retrolefty

#11
##### Apr 17, 2014, 04:51 pm

How do room fans that have a selection of three speeds work ?

They have been around a long time,   and I somewhat doubt that they have variable frequency drives.

Fans with a few fixed speeds usually have different windings switched to the power source. Variable speed fans use triac type controls but with properly sized R/C filters across the triac load terminals.

#### Jack Christensen

#12
##### Apr 17, 2014, 05:48 pm

Variable speed fans...

As in continuously variable? Hadn't noticed those, but haven't gone shopping for fans lately either. Will have to be more observant

#### retrolefty

#13
##### Apr 17, 2014, 06:02 pm

Variable speed fans...

As in continuously variable? Hadn't noticed those, but haven't gone shopping for fans lately either. Will have to be more observant

Yea, both types avalible as well as some now even use IR remotes to control speeds/on/off. IR remote control using Arduino would be a simple project and keep one from having to deal with household AC voltages.

#### Jack Christensen

#14
##### Apr 17, 2014, 07:02 pm
I've got a three-speed with IR remote in front of the treadmill, works great. I may have to take it apart, hmmm!

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