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Topic: somebody please explain this? sketch attached (Read 916 times) previous topic - next topic

zacmackra

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

In both of those examples, as long as the opto input is on then the triac will be on.
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Jack Christensen

Only a fraction of a milliamp will flow C-D-E. The capacitive reactance of a 100nF capacitor at 60Hz is around 26K Ohms.
MCP79411/12 RTC ... "One Million Ohms" ATtiny kit ... available at http://www.tindie.com/stores/JChristensen/

zacmackra

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

Jack Christensen


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?
MCP79411/12 RTC ... "One Million Ohms" ATtiny kit ... available at http://www.tindie.com/stores/JChristensen/

Jack Christensen


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.
MCP79411/12 RTC ... "One Million Ohms" ATtiny kit ... available at http://www.tindie.com/stores/JChristensen/

zacmackra

#6
Apr 15, 2014, 05:46 am Last 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
http://www.alfadex.com/dimming-230v-ac-with-arduino-2/

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 pm Last 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.
MCP79411/12 RTC ... "One Million Ohms" ATtiny kit ... available at http://www.tindie.com/stores/JChristensen/


retrolefty

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

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


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


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 :smiley-eek:
MCP79411/12 RTC ... "One Million Ohms" ATtiny kit ... available at http://www.tindie.com/stores/JChristensen/

retrolefty



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 :smiley-eek:


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

I've got a three-speed with IR remote in front of the treadmill, works great. I may have to take it apart, hmmm!
MCP79411/12 RTC ... "One Million Ohms" ATtiny kit ... available at http://www.tindie.com/stores/JChristensen/

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