Researching Switch type for a fan

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,896
I have a fan from a furnace. Fairly large, 12 inch outlet, motor probably drawing around 8A. I can look to be sure, but that's not the issue. I'm looking for some rocker type switches for a project I'm putting together in my woodshop. The fan is three speed. So I'm looking for three SPDT switches rated for about 10A 120V, just two position "ON-ON". With the switches wired properly I can turn the high switch on and get the high output. However, if I want Medium, the High must be in the OFF position (that is to say "Not ON", hence the DT) and the medium switch can be on. IF I want Low, both high and medium must be in the off position for the low leg to get power. I have a drawing I could post but that drawing is up in the shop and I'm in the basement right now.

So I'm looking for a Rocker type SPDT ON-ON switch rated for 120V 10A on an inductive load. I'm finding a lot of ON-OFF-ON switches which will work (I think with an inductive load) but I don't want the center off feature. And I don't want lighted switches either. If anyone knows of a source in the US that would be helpful. I'll continue to search, but so far I'm finding plenty of toggle switches, but if I build my project with toggles then I'll need a mounting plate. The rocker switches should be able to fit into the appropriate size rectangle as yet to be cut into the project.

Thanks.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,896
Learning a little more about switches: Said I'm looking for a rocker switch. I'm learning that toggle switches ARE rocker switches. I'm looking for the type of switch that looks similar to this:
1640608178611.png
These are SPST switches, I'm looking for SPDT type switches LIKE these.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,896
Here's where I'm going: With three switches, all in the "Down" position the fan doesn't run. When the high switch is in the up position the medium and low switches are not active, so you can't try and power the fan with two different speeds at the same time. With High in the down position either the Medium or Low can operate. Low can only operate if both High and Medium are in the down position.

The whole reason for asking this question is because I believe I've heard that inductive loads are harder on switches than resistive loads. I don't want to get a switch that is good for resistive loads but not reliable for inductive loads. Maybe I need snubbers on the switches - I just don't know. That's why I'm deferring to you folks who know the answers I seek to the questions I have.
1640613579151.png
 

MisterBill2

Joined Jan 23, 2018
12,440
LowQ beat me to it. Why the insistence of rocker switches? Most multi speed fans use a rotary switch like shown.
For multi-speed motors, especially fan and blower motors, connecting more than one speed at a time will usually cause destruction by means of burning up one winding. So multiple rocker switches is not recommended.
 

MisterBill2

Joined Jan 23, 2018
12,440
It might be unusual but only one speed can be activated at a time using the 3 rocker switch scheme from post #5.
View attachment 256206
Certainly this is correct, it would work and be safe for the motor as well. But cutting three rectangular holes for those three rocker switches will be a lot more work than punching one round hole for the collet and a small round hole for the anti-rotation key. AND some fans always want to hit the high speed setting first to get the blade spinning which is important as the lubricant ages and gets sticky.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,896
Looking for those rectangular switches because they can be mounted directly in my project. Going with toggles means I have to construct a plate and cut a large hole in my project.
That would be ideal, but again, not looking for something that has to go through 3/4" of material. That's a long shaft, and probably hard to find. That switch and knob profile will not mount on anything other than an aluminum plate (or other material of similar thickness.

I've gone ahead and ordered three toggle switches at a cost of less than $9.00. So with the arrangement of wiring I showed in an earlier post, I'll have the control I want. It's part of an air filtration system in my new woodshop. The large fan will move a lot of air. I have yet to learn just how much dust will be pulled out of the air and how often I'll have to replace the filters, but hey! It's a wood shop and I can make anything I want of it.

On high, the fan is rather noisy. Even on low it's still moving quite a lot of air AND it's still noisy. I may end up going with some sort of industrial fan speed controller to slow it down to where it moves plenty of air without all the noise.
 

MisterBill2

Joined Jan 23, 2018
12,440
Aside from the air noise there is possibly vibrating metal noise. That can be reduced by adding dampening material to the parts that are vibrating. (but not any rotating parts)
Adding to the mass of any vibrating surface will lower the resonant frequency and increase the energy needed to make it vibrate, bot reducing the noise generated. And an additional cheap and easy thing is just cleaning off any dust and fuzz that have accumulated on the surfaces.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,896
When I bench run the fan there's no vibration that I've noticed.

One thing I'm considering - and maybe wrongfully so - is to put a light bulb in series with the motor in an effort to achieve a milder air flow (slow the motor). Yes, I know an induction motor wants to run at a constant speed. However, the amount of work it does is moderated by the power applied. The fan itself will reduce the RPM. Reducing the amount of current to the motor will result in a lower wattage at the motor, slowing it down. But again, I may be on an entirely wrong approach. There seems to be very little difference between the three speeds. High is high. Medium is damned near high and Low is near high as well. Of the four wires there is White (Neutral), Black (high), Blue (medium as far as I can tell) and Red (low, but almost as high as high and medium).

This squirrel cage fan came out of a gas furnace. It's from the 80's and I don't have the electronics it came with. I don't know if the electronics were used to further moderate the fan operation, but just plain high is just plain too much. I think. I have to finish the build to see just how much noise and air flow I achieve. The goal is to clear the air of airborne sawdust. It will be mounted above my dust collection system, which right now, before upgrades, is more of a dust pump than anything else. Sure, it captures the large stuff, but the fine stuff - that's what's in the air and the reason for wanting to build this thing.

As for the switches, I wanted the rectangular type so they could be fit into 3/4" plywood. Using toggles means cutting out a larger cavity and building a mounting plate for the switches. Just this morning it occurred to me that perhaps I can slow the fan a little with the addition of a lightbulb. However, I also wonder if what I'll achieve on a major portion is to moderate the amount of light rather than the amount of air flow.
 

MisterBill2

Joined Jan 23, 2018
12,440
Certainly lowering the voltage will slow the motor. That effect is rather non-linear, though and so you will find it an interesting exercise. I suggest using an autotransformer scheme to lower the voltage instead of light bulbs. A 12 or 24 volt transformer can be used to subtract voltage from the mains supply by series connecting the windings with the correct phasing, and it will cost a lot less than a traditional step-down transformer. And all of the experimenting can be done with only your AC voltmeter, so it will not be complex nor expensive. You will need to have the transformer secondary rated to provide the motor current, though.
There are also fan speed controllers available that function similar to light dimmers except that they are designed to control induction motors. They were available from Grainger a few years back, I have not checked recently. Combined with the 3-speed selection the combination should be able to run your blower at any speed you want. Those controls are simple two-terminal series connections and thus very simple to add.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,896
I suggest using an autotransformer scheme to lower the voltage
So happens - I have a few 2A autotransformers hanging around with no specific purpose. One experiment I did with that was to power the fan directly through the AT. However, the AT got hot, and I was using the low speed line on the motor.

Can you tell me a little more about hooking up a "Subtracting" transformer (you didn't call it that but I assume you mean opposing voltages detract from overall voltages).
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,896
You got me thinking about transformers now. I have a multi-tapped transformer. It's primary is for 125V and though it's not specifically equipped with a lead, there IS a point where I could tap off a center-tap from the primary. But that would drop my voltage by half. Without doing the math I think that would probably result in approximately 25% of the power I have when under full unreduced power. The secondaries consist of many multi-tap coils ranging from 5.1V to 65V, each with multi-taps (except the 5.1V). Here's a schematic of the transformer. The 65V appears to have the heaviest gauge wire, and it's out of a stereo system. Using the 65V secondary as a voltage divider (autotransformer) again I cut power by 1/4th. Is that right? Let me check the math: 65V @ 10A is 650VA. 32V @ 5A is 160VA. Am I applying logic correctly?

Here's that transformer:
1640705543109.png

Assuming the motor at 1/2 HP draws 7.8A (probably on high), if Low draws 75% of thats 5.85A. @ 120V that comes to 700VA. I don't know that this little transformer would handle that. Core measurements are:
3" x 2_5/8" x 2" and a guesstimated weight of about 8 pounds.

Transformer part number is
1-431-655-11
751022HD
TAM MALAYSIA
(backwards) UR . M 9819
 

MisterBill2

Joined Jan 23, 2018
12,440
That logic is sort of correct, although adding and subtracting voltages is more an issue of current than wattage. It is actually vector math, made much simpler because all of the angles are either zero or 180. One challenge is that the motor current varies with the load, but not in a convenient manner. And blower power varies with the cube of the flow rate, so the relationship is not so very predictable..
Using half of the 65 volt winding in series and then connecting across the 120 volt winding will provide still another lower voltage. That is using it as an autotransformer. So there are quite a few options for somewhat lower voltages.
 

shortbus

Joined Sep 30, 2009
9,444
I may be on an entirely wrong approach. There seems to be very little difference between the three speeds. High is high. Medium is damned near high and Low is near high as well.
Without a load on your blower, like the duct work would have been in it's past life, you probably won't see much difference in the perceived speed. Most multiple speed motors like that the speed is changed by the number of coils in use for the speed. Changing the voltage to the motor will probably make it over heat.
 

MisterBill2

Joined Jan 23, 2018
12,440
Can you offer a solution?
REducing the speed of a blower by some small amount also reduces the required power, which will tend towards reducing the heating. Some motor applications are far more sensitive than others. Whenthe load stays constant,like in an air compressor, then certainly overheating will result.
 
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