Speed Control For PSC Motor Question

Thread Starter

PGB1

Joined Jan 15, 2013
139
Hello To All!

I hope it is not inappropriate to ask this question at All About Circuits, but it seems like the best place to get an accurate answer.

Our air handler has a blower motor with a variable speed control. Using it allows us to always have the fan moving air across the filter and UV light. When the system calls for cooling or for humidifying, I have realys wired so that the speed control is bypassed and the blower goes into either humidifying or cooling speed. (Humidifying also has a speed control.) (Heat is by a separate boiler.)

I have to replace the speed control about once per year. My question is whether there is a better type of control with a more modern design for this motor than the one I keep buying. Attached is the datasheet for the speed control. Hopefully it will let you know what type of control it is.

The motor is a permanent split capacitor 1/3 HP 120 volt single phase with a run capacitor. There is no start capacitor. It has leads for 3 speeds, although the variable speed controls are on low winding only. (Cooling speed is the high winding & medium is not used.)

The make & model are Century FLD1034. I apologize but I can't get a datasheet, other than dimensions, to save so I can share it.

Thank You for advising. I certainly appreciate your help.

Paul
 

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LowQCab

Joined Nov 6, 2012
4,052
Why is a Lamp-Dimmer required ?
It's hardly saving enough Electricity to measure.
Just use the Lowest-Speed-Motor-Tap.
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Thread Starter

PGB1

Joined Jan 15, 2013
139
Why is a Lamp-Dimmer required ?
It's hardly saving enough Electricity to measure.
Just use the Lowest-Speed-Motor-Tap.
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.
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Energy saving wasn't the goal. We use it so that air can be constantly moving across the U/V light and the filter, or simply to have air movement in the house. Having the ability to control the speed or turn the fan off is something that we appreciate.

For example, at night we set the speed very low or off. During a warm day, we can set the speed slightly higher so a mini-breeze is blowing. (The air handler is a high velocity type so air mixes well.) Should we, perhaps, cook something odoriferous we can turn the speed faster to move the air. (The high intensity U/V light is quite effective at quickly removing odors from the air.)

The control was factory installed in the air handler, but I moved it into a two-gang junction box on the first floor. for easy access. It shares the box with the hallway light switch.
 

MaxHeadRoom

Joined Jul 18, 2013
28,669
What exactly is failing in the controller?, there is not a lot to them, the main component is the Triac.
At one time it was easy to contact KB, now they are owned by Nidec Japan, they do have a support line contact you may also get help from, it may help to locate the defective part also if making contact with them.
 

Thread Starter

PGB1

Joined Jan 15, 2013
139
The pdf indicates there's a range of controllers. What is the current rating of your controller?
Sorry for the omission: The rating is 5 amp full load and lock rotor is 10 amp.

Motor name plate indicates 4 amp and 6.2 max. In use at maximum speed setting with not new filter & evaporator coil in use (wet) is typically about 3.7 amps when tested.
 

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Thread Starter

PGB1

Joined Jan 15, 2013
139
What exactly is failing in the controller?, there is not a lot to them, the main component is the Triac.
At one time it was easy to contact KB, now they are owned by Nidec Japan, they do have a support line contact you may also get help from, it may help to locate the defective part also if making contact with them.
On a couple failed controllers, the circuit board had burns. Specifically what component failed isn't known. Symptoms of one of those failures was that the motor would not adjust speed and another failed to no voltage to motor.

On three controls, the "Off" detent in the rheostat failed to allow Off. Autopsy on one showed a mechanical failure. On another it showed burned parts of the winding. The detent held, but voltage continued to the motor.

Thanks for the idea to try to contact KB. They may have a product suggestion.

Paul
 

Thread Starter

PGB1

Joined Jan 15, 2013
139
Something Doesn't sound quite right, at those ratings I would not expect that damage?
I wonder if heat is damaging the control.
It does get warm in use and is in a 2-gang deep switch box with a light switch next to it. Per NFPA 70, the box is sized correctly, but touching the metal face plate provides warm to the touch.
 

MisterBill2

Joined Jan 23, 2018
18,426
If the motor has three selectable speeds, chosen by which is powered, then that is the scheme that I would choose to use. If the lowest speed is still too much, then add a controller in series with the slowest connection.
 

Thread Starter

PGB1

Joined Jan 15, 2013
139
I've read current at several speed settings. The numbers in the post above are at highest (cooling) setting on the high speed winding. The low speed winding that the speed control is in parallel with, the amperage readings are lower. Tested moments ago, dialed to the typical lowest speed we use, the amp reading is 2.01.

The motor body does get warm in use, but less so than when on the high speed winding during cooling. It's can become slightly above ambinet, but air moves over and through the motor to help cool it.

Could the fact that these controls fail simply be the nature of the device? (Heat + Time = Accumulated Deterioration) I remember in the way back days old style incandescent light dimmers failing every several years.

Something that did not occur to me was the possibility of unnoticed, transient voltage spikes getting past the surge suppressor and damaging the speed control circuitry. Is that a possible cause?
 

MisterBill2

Joined Jan 23, 2018
18,426
OK, I see one big problem: " The low speed winding that the speed control is in parallel with, the amperage readings are lower. "
The speed control is NEVER placed across a winding. It connects between the motor and the power supply feed.
The multi speed motor acts like a transformer , and when the high speed is selected there is about 300 volts present on the low speed winding connection, at least that is how it is on my furnace which has connections for high, medium, and low speeds. It appears that each of the windings are in series. So on the high speed selection, the motor becomes a step-up autotransformer.
 

Thread Starter

PGB1

Joined Jan 15, 2013
139
I apologize MisterBill2 for my poor explanation of how the speed control is wired.

A drawing from the manufacturer is attached. The only change is that the control, which comes mounted in the cabinet of the blower unit, was moved it to the first floor hallway as a wall switch for convenient access. Connections are the same and the wiring between is #12 thhn stranded.

Not clear in the drawing is that the winding is energized by the line side of the 120 volt input power. It is energized only when the machine is not calling for cooling (high speed winding is then energized) or heating/humidifying (high speed winding). Other than those times, it is available 24 hours a day. The medium speed winding is not in use & was capped at the factory.

I just realized that the other speed control, on the winding that is energized during heating/humidifying, is the original one from 17 years ago. But it is only energized during humidifying in fall & winter. (Perhaps 3 hours per day maximum). When cooling, that speed control is bypassed by the control board.
 

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MisterBill2

Joined Jan 23, 2018
18,426
What might be the source of the failings would be if there was a sneak path for current to flow through the low speed controller when the high speed is powered.Years ago a well meaning AC installer wired the transformer for the solenoid valve across the low speed motor connection. When winter cam it did not work. Running the motor on high speed had caused about 300 volts to appear across the low speed terminals, frying the transformer. Who would have guessed it?? So if there is 300 VAC at one terminal of the external speed control, and it somehow finds a connection to neutral or ground, that is fatal for the speed controller. .You can use your multimeter to verify that step-up. A report on a more recent motor should be interesting.
 

Thread Starter

PGB1

Joined Jan 15, 2013
139
What might be the source of the failings would be if there was a sneak path for current to flow through the low speed controller when the high speed is powered.Years ago a well meaning AC installer wired the transformer for the solenoid valve across the low speed motor connection. When winter cam it did not work. Running the motor on high speed had caused about 300 volts to appear across the low speed terminals, frying the transformer. Who would have guessed it?? So if there is 300 VAC at one terminal of the external speed control, and it somehow finds a connection to neutral or ground, that is fatal for the speed controller. .You can use your multimeter to verify that step-up. A report on a more recent motor should be interesting.
Thank You Mr. Bill for mentioning that possibility. I will test this to find out if this is the problem. If it's a problem, perhaps a relay used for isolation will solve it.
 
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