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Adjustable AC power source for 5 fans of 115VAC 60hz 16w (fans connected in parallel)

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Marc Champagne

New Member
Hi Folks,

I'm not a big electronics buff, but I do manage little, practical, projects.

I'll be using an arduino to control these fans based on temperature readings.

My thoughts was to have 2 different power sources, one at full power and another source that is pre-adjustable (tweaked to have quiet fan operation), the arduino would trigger relays to select which power source is used based on temperature readings.

My question: what is a good non-resistive circuit that I can use/build for this adjustable power source?

I'm open to suggestions as well.

Thanks!
 

MaxHeadRoom78

Well-Known Member
If these are standard shaded pole induction motors, about the only way is via a triac circuit.
You need an opto triac driver such as MOC316x etc, see Fairchild app note AN-3006.
Max.
 

Marc Champagne

New Member
Thx max.
This is the type of fan (not exact model, mine are 115v 60hz 16w): http://images2.qianyan.biz/qy/5/4/9/20123115243057376139.jpg

I did some digging on the opto triac, it's over my head.

My initial idea (keeping things simple) was to use an old analog light dimmer to preset a certain voltage and have 2 relays (controlled by arduino)
where one relay would switch the full voltage and the other would switch the preset(dimmed) voltage to the load.

But old analog dimmers tend to get hot and/or are noisy and am looking for something more elegant. then again the load pulls 0.7 amps total, should I even worry about heat?
 
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MaxHeadRoom78

Well-Known Member
If using an arduino the Triac (light dimmer) switch should be isolated so the Opto triac MOC device performs the isolation between Arduino and switching triac.
The fans look like small shaded pole motors so a dimmer/triac should control them.
You probabally would find many other circuits Triac by Google
Max.
 

dr pepper

Well-Known Member
Most Helpful Member
I dont know if its in your experince range however you can take a light dimmer, remove the control pot and replace it with a photocell, then place said photcell in a tube with a led at the other end, then you have a opto isolated power controller.
Might take a little fiddling with values.
If these are synchronous motors then its not going to work, as speed is controlled by frequency not power.
 

Marc Champagne

New Member
Hi Folks,

Well, seems all are on the same field for they being shaded pole motors and I did try a modern 4-setting dimmer (off,25%,50%,75%,100%)
and the motor span in all settings, although barely usable at 75% or less.

Been looking at Max's opto triac suggestion, I get the sense of it (don't need mechanical relays to drive AC with DC)

I looked at the specs for the MOC316X: http://www.pselectronic.cz/pdf/1114/1114014.pdf and seems straight forward enough, 2 pins to drive
with DC and 2 pins as the switch for AC, what is unclear is how the "dimming" aspect is done, different DC voltages on the trigger affect how much AC will pass?

Thx
Marc
 

MaxHeadRoom78

Well-Known Member
In the Fairchild App notes it shows two methods, zero cross switching which means once on the triac stays on for the full cycle and is always switched when the cycle transitions through zero, this is usually used in full ON/OFF situations and burst heating of element type loads.
The other is phase angle firing where the exact point on the phase cycle needs to be known in order to repeat the cycle at the same point every time, in a simple dimmer this is taken care of with the RC circuit.
When using a μp type or other IC control, then the mains have to be sampled and the phase point fed to the micro or other IC, in the app note this is done with a 555 (fig 3).
Max.
 

MaxHeadRoom78

Well-Known Member
The Arduino link explains it to a degree, I am not sure of some of the terms used, maybe English is not the writers 1st lang?
e.g. They mention detecting zero cross over then 'opening' the triac, whereas zero is detected and at some later point in the sine wave phase angle the triac is turned on, it turns itself off when the sine wave traverses zero again.
Max.
 
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