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AC fan speed control by periodic on/off switching

E

ectoplasm

Jan 1, 1970
0
I have a fan (110 V AC) that I want to control the speed of.

I want to do this by periodically switching it on/off. Say, period of
about 5 seconds; and the 'on' period can be controlled as 10-100% of
this time. I already have a fan that has this built in, and it works
great, silent too. Basically it's variable pulse width control of an
AC appliance.

I probably need a thyristor / triac circuit for this, switching on the
null-crossings. Would be nice if the period time could also be
variable.

Searches on Google failed because I don't know what keywords to look
for. Can someone help me out?

Thanks,
E.
 
R

Roger_Nickel

Jan 1, 1970
0
I have a fan (110 V AC) that I want to control the speed of.

I want to do this by periodically switching it on/off. Say, period of
about 5 seconds; and the 'on' period can be controlled as 10-100% of
this time. I already have a fan that has this built in, and it works
great, silent too. Basically it's variable pulse width control of an
AC appliance.

I probably need a thyristor / triac circuit for this, switching on the
null-crossings. Would be nice if the period time could also be
variable.

Searches on Google failed because I don't know what keywords to look
for. Can someone help me out?

Thanks,
E.

Should be able to cook something up with a solid state zero crossing
switching relay and a simple op amp based pulse width modulator. you could
also use the ever-popular dual 555 to generate the PWM waveform and power
can come from the mains via a dropper resistor/rectifier/zener regulator
arrangement. Safety first; plastic enclosure, plastic shaft on control
potentiometer, plastic mains switch housing and operating lever. Proper
cord anchorages (get the proper clamping grommets for this). Build it in
the fan housing if you can to save some trouble. Five seconds for the
switching cycle seems a bit long; a couple of seconds would reduce
hunting. Watch for overheating of the fan motor.
 
G

GPG

Jan 1, 1970
0
I have a fan (110 V AC) that I want to control the speed of.

I want to do this by periodically switching it on/off. Say, period of
about 5 seconds; and the 'on' period can be controlled as 10-100% of
this time. I already have a fan that has this built in, and it works
great, silent too. Basically it's variable pulse width control of an
AC appliance.

I probably need a thyristor / triac circuit for this, switching on the
null-crossings. Would be nice if the period time could also be
variable.

Searches on Google failed because I don't know what keywords to look
for. Can someone help me out?

Thanks,
E.

Integral cycle control. Triac drivers wwith this feature are available.
 
L

LVMarc

Jan 1, 1970
0
ectoplasm said:
I have a fan (110 V AC) that I want to control the speed of.

I want to do this by periodically switching it on/off. Say, period of
about 5 seconds; and the 'on' period can be controlled as 10-100% of
this time. I already have a fan that has this built in, and it works
great, silent too. Basically it's variable pulse width control of an
AC appliance.

I probably need a thyristor / triac circuit for this, switching on the
null-crossings. Would be nice if the period time could also be
variable.

Searches on Google failed because I don't know what keywords to look
for. Can someone help me out?

Thanks,
E.
ep,

the idea for speed control is good. However, instead of crating a few
cycles of 120 60 hz and then a few off and aFEW ON ETC,, CONSIDER THE
WAY THAT LIGHT DIMING IS PERFORMED... in this case each 1/2 cyle of the
60 hv power is allowed to fow of 180 degrees (full speed, or 90 degress
1/2 speed etc.)

marc
 
R

Rich Grise

Jan 1, 1970
0
the idea for speed control is good. However, instead of crating a few
cycles of 120 60 hz and then a few off and aFEW ON ETC,, CONSIDER THE
WAY THAT LIGHT DIMING IS PERFORMED... in this case each 1/2 cyle of the
60 hv power is allowed to fow of 180 degrees (full speed, or 90 degress
1/2 speed etc.)

Integral-cycle control dramatically reduces the hash.

And it could be better for the fan motor, as well, assuming that this
is the kind of motor that can be controlled that way in the first place.

Cheers!
Rich
 
E

ectoplasm

Jan 1, 1970
0
Thanks for these great tips, Roger Nickel.

power can come from the mains via a dropper resistor/rectifier/zener
regulator arrangement.

I would like to get power from the mains, yes. What do you mean by
'rectifier', by the way?

To get a low voltage DC supply from the mains, more must be needed
than just only a resistor + zener diode, right? Could you elaborate?

Thanks.
 
E

ectoplasm

Jan 1, 1970
0
Integral cycle control. Triac drivers wwith this feature are available.

I found a triac driver, the MOC3041, a 6 pin DIP. It has a zero
crossing circuit, LED optocoupling. I can use this one; I'll need to
have an extra triac that does the main switching.

But you say there are triac drivers that have integral cycle control
BUILT IN. Could you tell a model number? I couldn't find it in Google.
Are there any online searchable electronics parts catalogs?

Thanks !
 
H

Homer J Simpson

Jan 1, 1970
0
ectoplasm said:
I have a fan (110 V AC) that I want to control the speed of.

I want to do this by periodically switching it on/off. Say, period of
about 5 seconds; and the 'on' period can be controlled as 10-100% of
this time.

You'd do better with a cycle control system using full cycles.
 
J

John Fields

Jan 1, 1970
0
I have a fan (110 V AC) that I want to control the speed of.

I want to do this by periodically switching it on/off. Say, period of
about 5 seconds; and the 'on' period can be controlled as 10-100% of
this time. I already have a fan that has this built in, and it works
great, silent too. Basically it's variable pulse width control of an
AC appliance.

I probably need a thyristor / triac circuit for this, switching on the
null-crossings. Would be nice if the period time could also be
variable.

Searches on Google failed because I don't know what keywords to look
for. Can someone help me out?

---
If you could settle for an on and off (both variable) period of 255
seconds or less it can be done with a single 8 bit down counter, a
"D" type flip-flop, the TRIAC driver you have now (I'm not psychic,
I read your later post ;)) a TRIAC, some switches, and some pullups.

And a power supply of some kind. Since it's not going to be
dissipating much power, something using a capacitor straight off the
mains, a rectifier and a Zener ought to work fine if you can stand a
non-isolated supply.

Want a schematic?
 
M

MooseFET

Jan 1, 1970
0
I have a fan (110 V AC) that I want to control the speed of.

I want to do this by periodically switching it on/off. Say, period of
about 5 seconds; and the 'on' period can be controlled as 10-100% of
this time. I already have a fan that has this built in, and it works
great, silent too. Basically it's variable pulse width control of an
AC appliance.

I probably need a thyristor / triac circuit for this, switching on the
null-crossings. Would be nice if the period time could also be
variable.

Searches on Google failed because I don't know what keywords to look
for. Can someone help me out?

Thanks,
E.


There is something that I have wanted to try out for quite a while.
It is a variation on dropping cycles that I think would lead to lower
losses in the motor. I will explain it and others can shoot it down
if I am wrong.

To decrease the operating speed of an induction motor, it is best to
lower both its voltage and frequency. A device like a triac can be
fired to allow an alternation through or not.

The triac it fired on the positive alternation.
The negative alternation is skipped
The positive alternation is skipped
The triac is fired on the negative alternation
The positive alternation is skipped
The negative alternation is skipped
.... repeat

This lowers the frequency to 1/3rd that of the mains frequency.

The RMS voltage on the motor would be 1/sqrt(3) of the normal line
voltage. However, the frequency content will be a bit funny. If I
did my math right, only 0.4 of that will be at F/3.
 
E

Esther & Fester Bestertester

Jan 1, 1970
0
I have a fan (110 V AC) that I want to control the speed of.

Use a light dimmer.
 
E

ectoplasm

Jan 1, 1970
0
Use a light dimmer.

Nah. LVMarc also suggested it. Not so good to cut up the phase (HF,
net pollution, might have bad effect on motor). See also Rich Grise's
reply.
 
J

jasen

Jan 1, 1970
0
Use a light dimmer.

Don't they aren't good for fans. they make triac based speed controllers,
use one of them.

Bye.
Jasen
 
E

ectoplasm

Jan 1, 1970
0
Yes. A better solution than mine if you don't need to count
individual cycles, so I won't waste my time designing and posting
the circuit I had in mind.

OK. And if later I have a working solution I'll post it. Thanks for
your offer for the schematic!
 
T

Tony Williams

Jan 1, 1970
0
ectoplasm said:
I want to do this by periodically switching it on/off. Say,
period of about 5 seconds; and the 'on' period can be controlled
as 10-100% of this time. I already have a fan that has this built
in, and it works great, silent too. Basically it's variable pulse
width control of an AC appliance.
Searches on Google failed because I don't know what keywords to
look for. Can someone help me out?


We used to have an electric cooker where the heating
elements was controlled like that..... Bursts of
full sinewaves separated by gaps.

Try the keywords "burst control heater" as a starting
point. You might even be lucky and find a complete
knob-controlled module that does it.
 
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