temperature-controlled variable speed ac motor controller

Thread Starter

steamngn

Joined Aug 26, 2012
14
Ok electronics -Gods,
i need some help designing a controller for a piece of equipment we have. I have an inline 120v A/C blower that draws 295 watts at full speed. I am looking to have the blower run CONTINUOUSLY at ~80%, and have a thermostat monitor the cabinet temperature. As the temperature goes above 95 degrees F the fan needs to increase in speed until and reach full speed should the internal temperature go above 100-110 F.
As the temp comes back down the blower should stay at speed until below 95 F then back to 80%.

Can someone help me out? Thanks in advance!
 

MaxHeadRoom

Joined Jul 18, 2013
25,469
First you need to ascertain the type of motor.
Sounds like it might be a Universal (brushed) motor, if so, a simple Triac controller could do it.
If you want a slightly exotic control, some kind of micro processor may be the answer to control the Triac.
 

LowQCab

Joined Nov 6, 2012
2,171
The first thing You need is a proper VFD, ( Variable-Frequency-Drive ),
this will change the AC Frequency ( and Voltage ) to keep the Motor happy at
lower than it's rated RPM.

It's possible, that You could replace the Motor with a multi-speed Motor,
if this is possible, it would be much less expensive than a VFD.

We know very little about your Motor, so it's not possible to speculate on
whether or not a suitable replacement Motor is readily available.

You might try contacting the Blower-manufacturer to see if they can give You
a recommendation for a Multi-Speed-Motor.

Or,
You could replace the entire Blower with a new Blower with a Multi-Speed-Motor already built-in.
.
.
.
 

Thread Starter

steamngn

Joined Aug 26, 2012
14
Hi all- thanks for the input. I will get more info on the motor Thursday and post it here. There isn't much we can do with replacing this unit, so we'll have to build around it as needed.
 

Thread Starter

steamngn

Joined Aug 26, 2012
14
Ok gang- not a ton of info from the manufacturer on this motor but here we go - It is an external-rotor design:
fan motor.jpg

There is a variable speed controller the company lists- there is no data with it but it is solid state with a third wire that goes to the motor capacitor. The cap wire is normally connected to L1 when no speed control is used.
Hope this helps!
 

MaxHeadRoom

Joined Jul 18, 2013
25,469
So from what you indicate, it is AC induction motor with start/run capcitor, IOW a PSC motor,
They are normally speed controlled by Triac control, but often you have to start at a higher speed then lower to what you need.
1ph AC motors do not take well to variable frequency as they tend to drop out of run at low rpm's. But sounds as though you are using the higher rpm range?
You would need a thermal sensor circuit that regulates the rpm by control of the triac.
 

Thread Starter

steamngn

Joined Aug 26, 2012
14
So from what you indicate, it is AC induction motor with start/run capcitor, IOW a PSC motor,
They are normally speed controlled by Triac control, but often you have to start at a higher speed then lower to what you need.
1ph AC motors do not take well to variable frequency as they tend to drop out of run at low rpm's. But sounds as though you are using the higher rpm range?
You would need a thermal sensor circuit that regulates the rpm by control of the triac.
Yes sir- I think you are 100% correct on triac control. And the intention is to have this unit run continuous at 80% or above so we should be ok there. I am lost as to how the thermal circuit will integrate with the VSC - thats why I'm reaching out to the Gods here lol
 

MaxHeadRoom

Joined Jul 18, 2013
25,469
It depends on whether you want to monitor different points and take action for every setting or just a simple room type temp i.e. on/off at a manually set point.
There is 555 based one in the Fairchild APP-3006 that you could adapt.
 

Thread Starter

steamngn

Joined Aug 26, 2012
14
I think there needs to be just one temp sensor inside the cabinet - no real benefit in multiple points as the enclosure is airflow from bottom pulled through the top. I suppose we COULD put a second sensor in the air-inlet to the room and monitor what is inbound as well....
 

Thread Starter

steamngn

Joined Aug 26, 2012
14
So- OHD3 make-contact would probably be good for our application. How do I integrate this into a VSC? i'm having a serious case of mental-meltdown over this....
 

MaxHeadRoom

Joined Jul 18, 2013
25,469
What you could do is pick up a standard ceiling fan controller from local HW store, find the level manually that you want use, when the sensor detects 80° , the sensor would operate a small relay which would short out the in/out terminals of the fan controller in order to run full on.
BTW, you want the type that fits into a normal switch box.
Or you can get the type with a manual shorting switch that operates the fan full on, and do the relay mod on it.
 

LowQCab

Joined Nov 6, 2012
2,171
Just for interest .................
Here's a very simple way You can do it with no Electronics at all, just Thermostats and a Transformer ........
It also generates zero Electrical "Noise" unlike a Triac-based Controller.
There are actually a wide variety of ways that a Transformer can be used.

Edit .....
For a tight budget situation, a M.O.T. ( Microwave-Oven-Transformer ),
can be used instead of a nice shiny new "store-bought" Transformer.
Just wind your own Secondaries and experiment with the number of Turns.
.
.
.
Motor Auto-Transformer FLAT .png
 
Last edited:

Thread Starter

steamngn

Joined Aug 26, 2012
14
Just for interest .................
Here's a very simple way You can do it with no Electronics at all, just Thermostats and a Transformer ........
It also generates zero Electrical "Noise" unlike a Triac-based Controller.
There are actually a wide variety of ways that a Transformer can be used.

Edit .....
For a tight budget situation, a M.O.T. ( Microwave-Oven-Transformer ),
can be used instead of a nice shiny new "store-bought" Transformer.
Just wind your own Secondaries and experiment with the number of Turns.
.
.
.
View attachment 270052
Not only is this a great idea, I'm laughing out loud at the MOV reference- we're an appliance sales and service company, have a limitless supply of magnetrons laying around!
 

Thread Starter

steamngn

Joined Aug 26, 2012
14
Just for interest .................
Here's a very simple way You can do it with no Electronics at all, just Thermostats and a Transformer ........
It also generates zero Electrical "Noise" unlike a Triac-based Controller.
There are actually a wide variety of ways that a Transformer can be used.

Edit .....
For a tight budget situation, a M.O.T. ( Microwave-Oven-Transformer ),
can be used instead of a nice shiny new "store-bought" Transformer.
Just wind your own Secondaries and experiment with the number of Turns.
.
.
.
View attachment 270052
A question about this idea: The motor has a run capacitor, and according to the manufacturer there is a speed controller that goes between the L1 and capacitor wire to control speed. Normally the capacitor is connected directly to L1 - so in your example the capacitor would stay connected as-is? Would this have a tendency to produce "hum"? That really isn't a deal-killer as the environment is noisy to begin with.... just trying to wrap my head around everything.
 

LowQCab

Joined Nov 6, 2012
2,171
If You "design-in", an extremely low, "Low-Speed" setting,
it's very likely that the Fan-Motor will not start-up at that Power-Level
without some help from some fingers.

But most likely .............
at anything more than about "Half-Power" Speed,
the Motor will always start-up just fine with no modifications to anything.

Once the Motor is spinning, You can slow it down to a crawl, and then speed it back up,
all very smoothly with no drama.

If You find that it's advantageous to run the Fan extremely slow most of the time,
a "Start-Button" can be added.
This is basically a temporary "High-Speed-Button" for kick-starting the Motor,
which is wired in parallel to the "High-Speed-Thermostat",
which just completely bypasses the Transformer for full-Power.
Once the Motor is spinning, it won't stop unless the Bearings are very "sticky" and need Oiling.
.
.
.
 
Last edited:

Thread Starter

steamngn

Joined Aug 26, 2012
14
If You "design-in", an extremely low, "Low-Speed" setting,
it's very likely that the Fan-Motor will not start-up at that Power-Level
without some help from some fingers.

But most likely .............
at anything more than about "Half-Power" Speed,
the Motor will always start-up just fine with no modifications to anything.

Once the Motor is spinning, You can slow it down to a crawl, and then speed it back up,
all very smoothly with no drama.

If You find that it's advantageous to run the Fan extremely slow most of the time,
a "Start-Button" can be added.
This is basically a temporary "High-Speed-Button" for kick-starting the Motor,
which is wired in parallel to the "High-Speed-Thermostat",
which just completely bypasses the Transformer for full-Power.
Once the Motor is spinning, it won't stop unless the Bearings are very "sticky" and need Oiling.
.
.
.
That's what I thought- We're not looking for super-low speed, more along the lines of 60-80% continuous and then 100% if/when required. I think I will go down this transformer route as the design makes for super-easy mounting in this cabinet. As the Hammond transformer isn't terribly expensive I think I will grab one in the interest of saving time winding my own. I am going to use some Altech APT-CNOF thermostats for control, will start with 3 and see if "low" speed is too low to start (or too low to move enough air) and if that is the case then I will parallel the windings for medium/high only.
Will post back when I have this up and running to let everyone know the outcome!
 
Top