Adding a trim pot to a fan motor

[ranckie]

Greetings, My name is Ranckie and I'm new to this forum. I have a small fan motor that I'd like to add a trim pot to to slow down the high speed on it. Right now, when the fan is on high, it sounds like you're standing next to 747! I have a basic understanding of electronics but not enough to know for sure where to add the pot. Here is a description of the motor I'd like to control; it's a small, 120 V, 60 Hz, capacitor start motor, with five colored motor leads coming out of it; a white, a black, and a blue to control the motor; plus a yellow, and a brown going to a small, externally mounted 250v, 4μF capacitor, (followed by the number 1803, but I'm not sure what that number represents). The data plate on the motor states that the white is the common, the black is the Hi speed, and the blue is the Low speed. The name on the motor is "EUROKA" and the model number is CR8225-1204, followed by the number 1B5560640B. I can't imagine that a motor of this size would draw much amperage but there is no amperage, (or wattage) listed. I do have a "Kill-O-Watt" meter and could get a wattage reading if required. Any help getting me started on this would be greatly appreciated. Thanks. Ranckie

 

[Alec_t]

A trim pot won't handle enough current for that task. You could try an incandescent bulb (not a LED or CFL bulb) in series with the high-speed winding.
One of e.g. 60-100W rating might do.

 

[PETERDECO]

Try a motor speed controller for an attic fan. You may need to mount it in a box but be careful! You don't want to play with line current if you don't EXACTLY know what your doing. Paying someone to do the wiring for you will cost a lot less than a hospital stay.

 

[shrtrnd]

I'm wondering about your application. What is this small fan supposed to be cooling? If it's some particular instrument that is
being cooled, it might be engineered for a specified airflow, and if you slow the fan down, the instrument/equipment might overheat
and cause you a different problem. Is this just a stand-alone fan that is for personal comfort use, or is it cooling some equipment
that should not be overheated?

 

[ranckie]

I apologize for not clearly stating what my "small motor" was used in. It's a fan motor on a room size humidifier and I just tested it for amperage draw. With the fan on Hi, it draws .6 amps (six tenths of one amp) so you can see the current draw is small. What made me think that a trim pot would work is, (realizing that the type of motor might prevent its use) the trim pot I have, shown in the attached picture, is a replacement pot for controlling the air distribution blower on a Harmen pellet stove.

Years back Harmon had a few issue's with those pots on a few stoves so I purchased a few spares just in case but never had to use them. I'm guessing that the distribution blower in that pellet stove must draw at least as much amperage as the fan motor in the humidifier, and those pots run forever; (the issue on the pots that failed is a few of them had "flat spots" on the wipers. (You should hear what that blower sounds like on Hi speed) The fan motor on the humidifier has 3 speeds, or # 3 which is Hi (.6 amps), #2 which is Med. and only a tad slower than Hi, (.53 amps), and then the slow speed, or # 1 which is way too low for effective humidification IMHO, (about .25 amps). I was hoping to be able to add one of my spare Harmon trim pots to slow down the Hi speed a bit. The humidistat and speed control on this humidifier are digital and most likely all mounted on a tiny circuit board encased in a small plastic case. By the way, the only marking on the trim pot that I have is "Spain", and it is used in the stove as a "daily pot control" as opposed to a trimmer that is only adjusted a few times; I've read that the wipers in pot "controls" are supposed to be more robust. I hope this clarifies things a bit. Thank to all for taking the time to comment.

 

[shrtrnd]

Your pot is not going to last long in your application, as noted by Alec_t.
I kind of like PETERDECO's idea of looking for a commercial speed controller.
It sounds like you have basic electrical skills.
Things like box fans usually have low-medium-high, they do that by putting resistors between the switch contacts.
Your potentiometer idea is sound, but you need a larger wattage pot.
I guess it's up to you if you want to get a pot and experiment, but you'd be guessing about the pot resistance value you'd need.
In my mind, back to PETERDECO'S idea of buying something commercially.
You can look for a variable controller, like your pot idea, or a low-medium-high switch type with the resistors.
Maybe someone else here will have a better idea for you.

 

[ranckie]

Because I'm curious by nature, I'd like someone to explain why that small trimmer pot that I have, will handle the load of a blower on the pellet stove, On and Off every day for years, (the very same pot that is in my picture) but can't handle the current load of my small fan motor that only draws .6 amps on high speed. Please understand that I'm not asking that out of arrogance, I would never do that, ever. Rather, I'd really like to know what the difference is. Is it because the two motors may be different, like one (mine) is a capacitor start, and the other might be an inductance motor? By the way, I found a video on you tube where someone wanted to do almost exactly what I want to, and he found this speed controller on Amazon, so I'd like to know if this would work as "Shrtrnd" and Alec T suggested. here is the link to Amazon; https://www.amazon.com/gp/product/B00LODGP2E/ref=ppx_yo_dt_b_asin_title_o07_s00?pldnSite=1
I also feel very comfortable working around electricity and have done so for many many years; I'm probably older than most of the nice folks on this forum and my skin is still "flesh colored" LOL. Also, here is the link to the You Tube video I spoke of;

Thanks again.

 

[Bluejets]

Just because the input device to the speed control may be a pot, it does not mean it is connected directly to the motor.
It may be (and most likely is) via a thyristor or similar.
2 reasons upfront, 1 is the pot will not handle the mains current or the voltage directly, and 2 , it would create a hazardous situation due to the construction of the standard metal shaft pot.

 

[ranckie]

Thank you Bluejets for your explanation. As I started to read your answer, I had a good idea where you were headed and told myself if I had pondered my question a bit longer, I might have concluded that other components were involved in the Harmon blower circuit. All of my knowledge is rooted in electricity, so while I don't have enough knowledge to design an electronics circuit like the one you described, I understand the concept. I am still curious though if the speed control at Amazon would do what I'm looking for. Here is the link to that control: https://www.amazon.com/gp/product/B00LODGP2E/ref=ppx_yo_dt_b_asin_title_o07_s00?pldnSite=1
Thanks again for your input.

 

[shrtrnd]

Also, the small pot you showed in your picture typically is designed for .5W
As noted by Bluejets, we don't know how your pellet stove blower and humidifier circuits are designed.
Whenever I try something like this, I always plan for a worse-case situation, because I don't want to do the same repair twice.
Your blower fans may have specifically designed protective circuitry, but when a motor first starts up, you are
not looking at a steady voltage/current flow, The old 'ELI the ICE man' adage comes into play.
Voltage(E) before Current(I) in and Inductor(L)
Current(I) before Voltage(E) in a Capacitor(C)
You have a spike in power when a motor FIRST turns-on, before it settles down to a steady voltage/current state, and enough of those will fry your small trimpot.

 

[kpatz]

The pellet stove fan had a speed controller of some sort, and the pot just controlled the controller. A small current through the pot (or voltage coming out if the pot was wired as a voltage divider) told the controller how fast to run the fan, using some form of PWM similar to a dimmer switch.

The pot itself won't work for controlling the fan, you'd need the entire circuit. You can probably find a speed control box complete with the knob at a place that sells fireplace inserts, pellet stoves or similar products.

 

[ranckie]

You are correct kpatz, and that is same thing that other members have suggested as well. And as I mentioned earlier in this thread, I found such a controller on Amazon for about $6.00 by watching a video on You Tube where the author was doing almost the exact same thing that I want to do. Here is the link to that controller on Amazon;
https://www.amazon.com/gp/product/B00LODGP2E/ref=ppx_yo_dt_b_asin_title_o07_s00?pldnSite=1
Thanks for the suggestion kpatz.

 

[Bluejets]

Maybe...

 

[ranckie]

Maybe...

Maybe as in, the speed controller on Amazon may work? Yesterday you stated, "That control is for dc motors not ac split phase." Please explain to me how you determined that the fan motor is a split phase, and again, that is a genuine question on my part. One of the sellers pictures that accompanies the speed control on the Amazon site, shows the four screw terminals as, "AC in AC in", and "AC out, AC out". Did you make that statement because its split phase? Just curious. Thank you again for your input Bluejets, but I would still like to know how I can change the speed of that small fan motor.

 

[ranckie]

I realize that it has been several weeks since I made my original post about something I could use to control the speed on a small humidifier fan motor and specifically, if I would be able to use a small trim pot. After many members pointed out to me why that wouldn't work, (a trim pot requires a supporting circuit to handle the amperage) I finally did find a great inexpensive solution at Lowes. It's a fan Speed Control that I picked up for under $8.00, Lutron Rotary Fully Variable 5-Amp White Rotary Fan Control in the Fan Controls department at Lowes.com (now around $10.00) and it works great. It allows me to set the fan speed to whatever I want and solved my problem. I simply cut the high speed motor lead and put the fan control in series and mounted it in a small PVC hobby box I picked up at Home Depot with a blank cover and attached it with Velcro to the back of the humidifier. Thanks again for everyone's help.