Is this motor brushless or brushed? Want to speed control the motor. Suggestions?

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,267
Comes out of an HVAC unit. power requirements are 115V @ 7.8A (897VA). It's the blower motor; half horse.
Forgive the dirt, but why clean it if I can't use it as a variable speed fan. Looking on Amazon for a motor speed controller and I've found one but it says not to use on brushless motors. Not certain what they're calling brushless; could be BLDC type they're referring to.
1624132978795.png
This is the controller I'm referring to. I can go a different route, not locked into anything just yet.
 
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Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,267
Yes, appears to be THIS motor.

Been looking at motor speed controllers on Amazon. So far it seems these controllers I'm finding are for brushed motors, not induction motors.

The motor-in-hand draws 7.8 amps. I ran it on an autotransformer that is rated for 2.5 amps. It got hot but controlled the speed of the motor. Since mine is rated for only 2.5 amps - I can't use it. But it DID give me nice control with a nice gentle airflow on about half voltage. Intended use is for higher airflows, say 75% to 100%. But I might want to turn it down to 50%. So I'm looking for a controller that will achieve my goal.
 

nsaspook

Joined Aug 27, 2009
8,678
Yes, appears to be THIS motor.

Been looking at motor speed controllers on Amazon. So far it seems these controllers I'm finding are for brushed motors, not induction motors.

The motor-in-hand draws 7.8 amps. I ran it on an autotransformer that is rated for 2.5 amps. It got hot but controlled the speed of the motor. Since mine is rated for only 2.5 amps - I can't use it. But it DID give me nice control with a nice gentle airflow on about half voltage. Intended use is for higher airflows, say 75% to 100%. But I might want to turn it down to 50%. So I'm looking for a controller that will achieve my goal.
https://www.plantservices.com/articles/2002/48/

These types of motors are not designed for variable speed operation but there are some single-phase output VFD controllers on the market.
 

MaxHeadRoom

Joined Jul 18, 2013
23,632
Comes out of an HVAC unit. power requirements are 115V @ 7.8A (897VA). It's the blower motor; half horse.
Forgive the dirt, but why clean it if I can't use it as a variable speed fan. Looking on Amazon for a motor speed controller and I've found one but it says not to use on brushless motors. Not certain what they're calling brushless; could be BLDC type they're referring to.
This is the controller I'm referring to. I can go a different route, not locked into anything just yet.
That controller is a plain Triac controller I believe. Some add a bridge and run a universal motor with it.
Also looks yours is a 6 pole motor by the RPM's.
Single phase VFD's are just about suitable for fans etc, but any kind of variable load or low RPM's, they tend to drop out of run.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,267
Get a 3-phase motor and a single to 3 phase motor controller. That's the best way. You should be ableto find one with 120V in and 208 3-phase out.
Looking to use what I have. The motor did vary with speed through my autotransformer, but the AT is not rated for that high an amperage. The motor itself is three speed "High", "Nearly High" and "Almost High". There's very little difference between high and - um - low. The testing I did with my AT was using the "Medium" winding and as reported in post #3 with the AT set to about 50% the motor began to spin slowly and build to a nice gentle breeze. As I turned up the voltage the fan speed increased what seemed to be a linear taper. When set to about 90% the motor was running close to full speed but the AT was getting hot quick. Within a minute it was hot enough that you didn't want to hold it. So being that the AT is rated for 2.5 amps and the motor appears to be a max of 7.8 amps, the AT is not the solution. However, the motor DID vary in speed. I could get any level of airflow desired up to full speed. But I don't want to sacrifice my AT.

Perhaps I need to build a speed control circuit that can handle the amperage and vary the voltage from around 60 to 120VAC. Isn't there some sort of transformer configuration whereby you can control the AC voltage? Thought I saw something like that a year or so back. Perhaps something to do with Diesel Electric Locomotives (full version, not hobby).
 

MisterBill2

Joined Jan 23, 2018
9,292
First, the speed variation will be greater when the motor has a fan load, probably a lot greater. Often the different speed taps just vary the motor power, and so with a load there is more phase slip and it spins slower, but with no load the change is much less.
If you can live with a few speeds then the three taps will probably be adequate, if not, get a transformer of the 240 to 120 step down type, and put the two windings in series. Then you can have full line voltage, 1/3 line voltage, or 2/3 line voltage . Between those three levels and the three speed taps that will be a very wide speed range. With a bit more switching you can also have half line voltage.
 

nsaspook

Joined Aug 27, 2009
8,678
No, you don't want a 'Mag AMP' for induction motor control.

A voltage only (with a Triac or auto-transformer) solution to control that type of motor speed is version of slip control.
https://circuitglobe.com/slip-speed-in-induction-motor.html

It works (with low power motors designed for this type of high slip operation) to a point but increasing slip for much lower speeds causes copper losses to quickly heat the coils and is unstable under changing load without rotational speed feedback. This means low efficiency of the drive, acoustic noise, and electromagnetic interference.
 

MisterBill2

Joined Jan 23, 2018
9,292
Before you invest in any controller you should put a fan load on the motor and see what speeds you get. You may be very happy with hi, medium and low. Cheap, easy, and all the hard work is already done for you.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,267
the speed variation will be greater when the motor has a fan load, probably a lot greater.
Before you invest in any controller you should put a fan load on the motor and see what speeds you get.
There IS a squirrel cage fan on the motor. Sorry if I failed to mention that. And yes, I know that an unloaded induction motor will spin virtually the same RPM with low, medium or high inputs.
 
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