Furnace Blower Motor Wiring Question

[dwall174]

Not really a heating or ac related question, But I'm looking for some basic wiring information on a furnace blower motor.

A friend of mine gave me a nice running blower unit from his old furnace, The motor was just replaced about two years ago. Unfourntaly he just found out this year that his heat exchanger was now bad, So he needed to replace the furnace.

I'm planning to use this blower unit to build a ambient style air cleaner for the fine wood dust in my garage.

I've seen several DIY designs on the web where the people building the air cleaners just use 3 wall switches to control the speeds! However none of them show the actual wiring for this style set-up?

At about 11:40 minutes into this Video
the builder shows turning on one the switch at a time to control the three speeds.

Does anyone have an idea of what type switches he's using (3-way?) & how he possibly wired this up?

Doug

 

[freds fuel]

red low blue medium black high white common

 

[MikeF2316]

I have one very similar. I haven't used it for anything yet, but I did test it. White was neutral, the black, red and blue were speeds 1,2 & 3, I don't remember which was which. But I do remember only one of the wires could be powered at a time. So if you use 3 single pole switches, you have to remember to make sure only one was in the on position at a time. Looking at your 6th pic, it looks like red, blue, black are speeds 1, 2, 3.

 

[dwall174]

red low blue medium black high white common

Looking at your 6th pic, it looks like red, blue, black are speeds 1, 2, 3.

Yeah I understand that part of the wiring!

But I do remember only one of the wires could be powered at a time. So if you use 3 single pole switches, you have to remember to make sure only one was in the on position at a time.

That's where I'm getting confused!
In the video I posted above, It looks like he's turning each switch on in series?

Doug

 

[Innovate1]

You only want to energize one speed at a time. You could use two 3 way switches and a regular switch to set up three switches. The first one gets power on the common terminal and one of the others go to the motor. The other non-common terminal hooks to the next switch common terminal. Again, another terminal goes to a motor connection and the other non-common terminal goes to the last switch. The other terminal on the last (standard) switch goes to the remaining motor terminal. Or, probably better, you could use a standard switch first in line for on/off. Then two three way switches to direct the power to one, and only one, speed connection on the motor.

If you only need two speeds you can eliminate one switch with either arrangement.

 

[MikeF2316]

...

That's where I'm getting confused!
In the video I posted above, It looks like he's turning each switch on in series?

Doug

To me it looks like he has one power wire and it connects to black, red or blue, depending on which speed he wants. The ideal would be a 4 position rotary switch, to include an off position.

 

[dwall174]

The ideal would be a 4 position rotary switch, to include an off position.

Yeah something like this one would be ideal

But they cost about $40 & I already have some wall switches on-hand.

Doug

 

[dwall174]

You only want to energize one speed at a time. You could use two 3 way switches and a regular switch to set up three switches. The first one gets power on the common terminal and one of the others go to the motor. The other non-common terminal hooks to the next switch common terminal. Again, another terminal goes to a motor connection and the other non-common terminal goes to the last switch. The other terminal on the last (standard) switch goes to the remaining motor terminal.

So if I understand you correctly it would look something like this.

After actually drawing it out & getting a visual image of the switches wired up, It looks like it should work!

Doug

 

[yeldogt]

I used on of the 3 in 1 switches from leviton -- had around from another project.

I see they are $20 bucks now. nothing is cheap



Your picture is showing 3 way -- you only need to have singles. The rotary is nice since no two can be on at once.

I have had mine for years -- just flip off and then next speed on

 

[dwall174]

Your picture is showing 3 way -- you only need to have singles.

Yeah but then there's a chance that more than one lead could be powered at a time.

The rotary is nice since no two can be on at once.

The 3-way switches should function like the rotary switch & only one lead would get power at a time.

Doug

 

[LS6 Tommy]

I second the rotary switch. Also keep in mind, regular wall switches are not motor rated.

Tommy

 

[Bert_]

I just use a double throw toggle switch (on-off-on). Pick two speeds, that's usually fine anyway.

 

[nadogail]

Would that be a Single Pole Double Throw switch?

 

[LS6 Tommy]

Would that be a Single Pole Double Throw switch?

Yup.

Tommy

 

[dogdog]

Yeah I understand that part of the wiring!

That's where I'm getting confused!
In the video I posted above, It looks like he's turning each switch on in series?

Doug

Those different speed wires are just different tap on the same motor winding to give different speed. The highest speed would have highest resistance, and lower speed would have lower. Medium is well in between... those are usually in ohms (tenth)

It's usually better if you just use a selector switch or 3 relays with a "digital" controller to energize each relay for speed you wanted ( most fan that have remote are controlled this way)

but let's say you want to do it for fun and the heck of it.
3x spst... one end connect to hot... the other connect to the speed wire respectively...

so the logic should go like this...

If all three are on.. the motor would go low speed... electricity go to the least resistance.. so low speed winding would have least resistance.. The other two would have done nothing...even if you shut off high / medium... on/off doesn't matter.

If you shut off Low, and high / medium on.. then fan would be medium... same logic. so high speed switch on/off doesn't matter.. fan will be medium.

if you turn off LOW and MEDIUM... then fan speed would be high, well... that is because it is the only point in the winding that have power.

Pretty sure you can draw up your logic table and use your K-map(Karnaugh Maps) to reduce down the scenarios

 

[raddksn]

So if I understand you correctly it would look something like this.

After actually drawing it out & getting a visual image of the switches wired up, It looks like it should work!

Doug

this would work! but by time you buy the 3 switches an enclosure and cover, you're more than half way to the rotary switch that is motor duty rated!

 

[stingry]

Yeah something like this one would be ideal

But they cost about $40 & I already have some wall switches on-hand.

Doug

Ebay has a bunch of rotary switches. Search 4 position rotary switch. I bought one to do exactly what you are doing. It was only 7 or 8 bucks.

 

[dwall174]

Those different speed wires are just different tap on the same motor winding to give different speed. The highest speed would have highest resistance, and lower speed would have lower. Medium is well in between.

Yeah after seeing this schematic;

I kind of thought it would not really make a difference if all three switches were on!

let's say you want to do it for fun and the heck of it. 3x spst... one end connect to hot... the other connect to the speed wire respectively...

Being I have several switches on hand (regular & 3-way) I'll probably just use those for now to test things out.

3 relays with a "digital" controller to energize each relay for speed you wanted (most fans that have a remote are controlled this way)

Thanks, I hadn't really thought about a remote option!
Being this filter unit will probably be mounted to the wall up near the ceiling, A remote control could come in handy.

Doug

 

[dogdog]

Yeah after seeing this schematic;

I kind of thought it would not really make a difference if all three switches were on!



Being I have several switches on hand (regular & 3-way) I'll probably just use those for now to test things out.



Thanks, I hadn't really thought about a remote option!
Being this filter unit will probably be mounted to the wall up near the ceiling, A remote control could come in handy.

Doug

You'll needed to find a 3 channel remote, probably plenty on Ebay or some chap here will design one for you with Adruino and ESP8266, few very knowledgeable chaps with adruino and electromatronics here, probably a fun project. or 2 channel is more common, just select the two speed and cap off the other.

as far as utilizing those 3 way switch... it's just ensuring only one of the wire is on... if you work through the logic... from left to right. say A (SPDT) B (SPDT) C (regular on/off)...

A ON.. no electrical to B and the screw on the terminal to the fan speed 1 is energized., if A off, Electrical is to B, screw terminal to fan speed 1 is de-energized.

A off, B on screw terminal on B to the fan speed 2 is energized. .... and so on so forth..

A off, B off and C on terminal to fan speed 3 is energized.

If A off, B off, C off then system is off...

it's weird logic but it's stepping though one by one with switches.

Pretty sure it will be a fun logic for DIY your own remote , You'll just have to know how those fan winding works and bob is your...



This 4 channel would fit your bill if the relays are good enough for the load.



https://www.ebay.com/itm/12V-4CH-Ch...rol-Relay-Switch-With-2-Receiver/183856642969


why 4 channel... leave 1 for immediate on/off



the other 3 just follow the same logic as those 3way switch setups... It'll still be weird to operate, but hey at least it's "Remote" ...

 

[jlv03]

Inexpensive rotary switch on Amazon: https://www.amazon.com/dp/B00NTROK8Y/?tag=atomicindus08-20

I have the old 4 speed fan from a previous furnace set aside for a similar project. One of these days...

 

[dwall174]

2 channel is more common, just select the two speed and cap off the other.

More than likely that's what I'll end-up going with!
I'm thinking I'll probably only need the low & medium speeds?

Doug

 

[dwall174]

Inexpensive rotary switch on Amazon:

Thanks for the link!

It may come in handy, A lot better price than the $40 one I shown before
Also the one I shown before is only rated at 10 amps & my blower will draw 9 amps.

Doug

 

[LS6 Tommy]

Those different speed wires are just different tap on the same motor winding to give different speed. The highest speed would have highest resistance, and lower speed would have lower. Medium is well in between... those are usually in ohms (tenth)

It's usually better if you just use a selector switch or 3 relays with a "digital" controller to energize each relay for speed you wanted ( most fan that have remote are controlled this way)

but let's say you want to do it for fun and the heck of it.
3x spst... one end connect to hot... the other connect to the speed wire respectively...

so the logic should go like this...

If all three are on.. the motor would go low speed... electricity go to the least resistance.. so low speed winding would have least resistance.. The other two would have done nothing...even if you shut off high / medium... on/off doesn't matter.

If you shut off Low, and high / medium on.. then fan would be medium... same logic. so high speed switch on/off doesn't matter.. fan will be medium.

if you turn off LOW and MEDIUM... then fan speed would be high, well... that is because it is the only point in the winding that have power.

Pretty sure you can draw up your logic table and use your K-map(Karnaugh Maps) to reduce down the scenarios

The highest resistance would be the lowest speed and as impendance decreases, rpm increases.
Speed windings are not shunts, so energizing more than one is not going to work the way you describe. The motor will run at the highest speed and still engergize the other windings. They are one winding tapped at different impedances in series with eachother. Energizing more than one speed winding at the same time will burn out the motor.

Tommy

 

[dogdog]

The highest resistance would be the lowest speed and as impendance decreases, rpm increases.
Speed windings are not shunts, so energizing more than one is not going to work the way you describe. The motor will run at the highest speed and still engergize the other windings. They are one winding tapped at different impedances in series with eachother. Energizing more than one speed winding at the same time will burn out the motor.

Tommy

so what happened if I power all three speed wires? ELectromaticaly ?

 

[LS6 Tommy]

You will burn out the motor. I don't fully know the dynamics of why it happens electrically speaking. I think it's beacuse the winding is energized, but the rotor is not operating at the speed of the field the winding generates.

Tommy

 

[metlmunchr]

With even 2 of the wires energized at the same time the motor will burn up and it'll happen in a minute or two.

I had a college dorm job with about 150 fan coil units with factory supplied speed switch and stat for wall mounting on a jumbo box. One speed switch was defective internally and powering both hi and medium at the same time. I set the fan speed to hi when checking things out and immediately noticed the fan didn't seem to be coming up to full speed. Checked wire connections and everything looked good. Turned it back on, and in maybe a minute and a half at most, the motor fried.

After diagnosing the problem and talking with the motor shop we used for large motor repairs, I learned a PSC motor with power on 2 motor leads tries to run at both speeds at the same time with the result being heat generation the same as if the motor is severely overloaded.