Fully Variable Speed Control Unit for Lasko 2155A Window Fan



For those that don't understand induction motors. An induction motor is both a trasnformer and a motor. It's really a clever idea that recognizes that both motors and transformers are made of two coils. The speed of the rotor is important in an induction motor so speeds are controlled by the design of the motor. That's why multiple speed induction motors have mutliple sets of stator windings. Which winding you energize determines the speed. And also why messing aorund with the voltage, particularly with controls that simply clip the sine wave doesn't work very well. You can vary the speed by changing the frequency. But only to a point because low frequencies don't work so well with a transformer.
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The OP here isn't interested in any information from people who know what they are doing -- he/she/it/they are looking for something which does not exist (a cord mounted VFD control) to try and precisely regulate the speed of a $35 dollar consumer grade window fan...
Let the OP figure it out on his own -- clearly doesn't like being informed that his desired device doesn't exist, or that the fan he wants to control won't work with the controller or that the motors which work with VFD controllers are expensive...
The OP is ignoring all of that and is therefore a troll...
~~ Evan
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On 6/23/2011 2:01 PM, Evan wrote:

Correction, Evan, the OP (as it happens, that's me) wants information, information which you refused to provide outright. So Evan, fuck off.
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Umm... You want information on something which does not exist for the application and device you want to redneck-engineer...
Rather than accept that INFORMATION and try to find another way (i.e. not in a window mounted, speed controlled [with the control cord mounted] fan) to accomplish your desire to move air quietly you continue to ask pointless questions and balk at the fruits of your own explorations as costing too much...
That sir is the textbook definition of trolling...
~~ Evan
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On 6/25/2011 4:47 PM, Evan wrote:

Accusing others of being a troll is a defining characteristic of trollish behavior. Another defining characteristic of trollish behavior is the total uselessness of the contribution to the discussion. It seems therefore that you have some introspecting to do, Evan.
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I think the point is that you initially did not seem very receptive to the suggestion that there is not a practical solution to your problem given the constraints you placed on the solution. Pont could have been made without calling you a troll though.
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On 6/24/2011 12:15 PM, jamesgangnc wrote:

I think the point is that Evan initially did not give a fuck about the subject and decided then and there that it was useless to even try to give me the information that I asked for. I've had a lot of experience with smart asses who will simply not give proper advice and the only advice they will give is "don't do it". Even is just one more smart ass. Well, fuck him.
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Movng on. I presume you've gotten all the information on the subject now. Or do you still have questions? And what's your plan next?
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On 6/24/2011 12:32 PM, jamesgangnc wrote:

I got all the info I wanted I think, thanks. My plan is to stick with what I got and look for a bargain VFD or a window fan with the feature I want. Thanks again.
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Evan wrote:

Film at 11, of the fire department trying to put out the fire and drag his corpse out of the building.
--
It's easy to think outside the box, when you have a cutting torch.

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The problem is that you can't simply continue to lower the frequency as the lower the frequency the less effective the induction is. Also you will find that variable frequency controllers are pricey.
Your best bet is to find a motor with brushes that you can vary the speed of with common speed controllers.
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On 6/21/2011 7:52 AM, jamesgangnc wrote:

I did find that. Cheapest VFD at a glance was $325. Although I don't see why they should be. Maybe these things are too specialized to be made cheaply.
It's a fan and there's little I can do about its design. It must be quiet and that is partly why I want full control over the speed.
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"Martin Levac" wrote in message
On 6/21/2011 7:52 AM, jamesgangnc wrote:

I did find that. Cheapest VFD at a glance was $325. Although I don't see why they should be. Maybe these things are too specialized to be made cheaply.
It's a fan and there's little I can do about its design. It must be quiet and that is partly why I want full control over the speed. ------------------------------------ One problem with using a solid state voltage controller (fairly cheap in small sizes) is that you have to set the minimum possible speed to some reasonable value in order to avoid stalling/overheating. It may not be quiet enough at that setting. Depending on the nature of the controller that is built in , there could be a problem if the built in controller was set to its lowest setting and the external controller limit was set for the case of the built in controller at a higher setting. in any case using an external controller, might not give you any advantage over the lowest speed setting built in.
There is also the possibility that the manufacturer is covering its legal ass.
Don Kelly cross out to reply
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That's part of it. There is not a high demand. Theoretetically an inverter design could be adapted to a variable frequency output. But you still have to convert to dc, then convert back to ac with a variable frequency switching supply of some sort. And you are still limited by the ability of the induction motor to operate at lower frequencies. Even 30hz, which is just half, is far worse at induction.
Practically all small fans will be built with an induction motor and speed control will be done via multiple sets of windings. Brushed motors are more costly and have issues with brush wear and electrical noise. They are seldom found in home appliances. I have seen them in blenders though. Probably because blenders have a lot of speeds.
Your most effective solution, barring finding a fan with a non induction motor, would be to replace the motor. That will probably involve some minor fabrication unless you are really lucky. Another option would be a DC motor and a variable output dc power supply.
But as you have found, there is no simple plug in solution for your problem.
Perhaps a smaller fan. Or put the fan in a window further away from you. If you leave the nearby window open you will still be in the cross breeze.
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On 6/21/2011 8:38 AM, jamesgangnc wrote:

I just want to say thanks for the reply and effort. I appreciate it. That goes for the other useful posters too.
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+1 to this...
A DC motor in a fan will be easier to control in the manner you desire and wish to control your fan in for whatever unknown and insane reasons.you have yet to disclose...
~~ Evan
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There's little you can do? Come on, Sparky! Design and build one yourself. It's not magic. Build a bank of 12v computer fans - they're quiet enough. Or spring for a fan that does what you want without 'fixing it'.
BTW, I'd never tell someone not to do something that has the potential of keeping me entertained.
R
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On 6/21/2011 8:55 AM, RicodJour wrote:

We all know what you did. It wasn't your smartest move.
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@Martin:
You can not turn a consumer appliance with a cheap induction motor into a perfectly adjustable device with the same precision of a VFD motor... First off, the variable frequency controller would cost more than the fan you want to run with it...
The cheapo motor the fan is currently equipped with has several windings in it which are energized in the same way a 3-way light bulb is configured... Low setting is a smaller winding -- Medium speed is a larger winding and Hi speed is all windings on at once...
The bigger question here is why you need to have a totally adjustable window fan unit -- and just how insane you would be trying to obtain something which just doesn't exist...
~~ Evan
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In article

There may be some tricks I do not know about but the only way I can think to make cheap three speed induction motors that are also reasonably efficient and without costly electronics is to switch the wiring to change the effective number of poles.
I am now curious enough to look that up.
--

Sam

Conservatives are against Darwinism but for natural selection.
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