Triac on multi speed fan motor ?

I would like to use whole house fans to ventilate my workshop but it would be nice if I they were computer controlled variable speed.




I have done zero crossing, triac thing, once or twice back in the dark ages but never for an inductive load so I am asking for advice.

Suggest circuit/schematic. if not what do I need in the way of a snubber?
Do I want to just use the high speed wire or should the low speed wire be used for lower RPM? Thinking that using the lower speed wire will be more effective at low speeds because the triac can be triggered sooner for a longer on period.

Random info
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A PIC or ESP8266 will be used for this controller.

As I understand either 2 separate sets of poles or a transformer is used in motors like this to obtain more than one speed. I have no idea which it is.

3v0

That looks like a rotary guillotine waiting for a victim. I hope safety screens smaller than a child's hand (finger?) are a part of this project. I also hope I don't hear, "children won't be here" because children eventually find there way everywhere - even if it is the day after you start "pushing up daises".

gophert said:

That looks like a rotary guillotine waiting for a victim. I hope safety screens smaller than a child's hand (finger?) are a part of this project. I also hope I don't hear, "children won't be here" because children eventually find there way everywhere - even if it is the day after you start "pushing up daises".

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This greatly concerns me too. I've opted for a 5 foot deep moat rather than a screen. That way I can stock it with alligators. Well still dithering between gattors and crocks!



Current plan is to construct a metal frame for the fan with grills on both ends. Am looking at having the frame rotate so I can reverse air flow.

3v0

Fans are typically used in a phase angle control mode, not burst firing as in heating applications, you can get ceiling fans controllers from any hardware store, worst case scenario you might have to up the rating of the Triac.
Max.

MaxHeadRoom78 said:

Fans are typically used in a phase angle control mode, not burst firing as in heating applications, you can get ceiling fans controllers from any hardware store, worst case scenario you might have to up the rating of the Triac.
Max.

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Phase angle is what I want to do, delayed turn on after zero crossing. Tried to say that in the original post but forgot the term. I would rather build than buy.

3v0

EDIT As I have said I need to control the fan speed via a uC. That way I can also monitor motor temp and RPM. If it gets too hot running slow it can speed up. If the bearing are going dry and slowing it down I will know.

Checked amazon did not see anything that would easily work. Could take an existing one and replace the pot with a digital pot but I'd rather not have Line Voltage Chinese-um stuff where it is unattended.

If this passes the justification phase can we talk about the circuit?

I have used the Picmicro based on as per their app note for both burst and phase angle control.
AN958, also Fairchild AN-3006 for phase controlling.
Max.

Hmm I was only aware of the control where you detect zero delay then fire the triac. Twice a cycle. Reading up on the alternatives.

Ah I did not know about the burst mode. Both require zero crossing detection.

Burst control in an induction motor will create very significant vibration.

The reason is simple, the rotor speed will be well below slip speed, and you will be applying full RMS voltage at each burst. This means high inrush pulses as the rotor attempts to accelerate.

Phase control also operates a motor below slip speed, but at least the applied RMS voltage is significantly reduced.
There will be vibration but it will be far less. Use phase control.

Additionally:
For uP control you will require an optocoupler. Make sure that you select a NON-ZERO CROSSING device. Using the incorrect optocoupler is the number one error.

Thanks Schmitt trigger. Looks like the H11AA1 opto coupler is a reasonable choice on the optocoupler to do zero crossing detection as shown here. Reduce the 4.7K and 470R current limit resistor if I go with a 3.3 V processor. Was concerned about the caps connected to the mains but found KEMET R75LI3100AA00K "Film Capacitors 560V .1uF 10% " for 34 cents each.

If this is reasonable all I have left to do is find a reasonably priced triac with sufficient headroom. Motor says 3.8A so maybe 2X or 3X that. So 8 to 12A.

I have previously used the H11AA1 to detect zero crossing. It is a good choice.
But I have always employed purely resistive current limiters. The capacitive limiter will introduce a phase shift with respect to zero.

Lastly, try to get the MOC3011 optotriac. The MOC3010 requires significantly more trigger current, and may not work reliably with the resistor value shown.

Will take a look at the M0C3011. Regarding the shift it really does not matter. We could fix it in software
But I would be happy to loose the caps.

Also forgot about the snubber !

Time has marched on. Found sunbberless triacs.