How to convert 2hp AC blower motor to variable speed

[rickr]

I have a 2HP 240V blower motor for which I would like to vary the speed from my plc. The motor is a standard HVAC type blower which is belt-driven from a motor.

Any inexpensive suggestions as to how I may use this motor or do I have to replace it with another type.

I'm in the process of upgrading the controls on this piece of equipment (Dectron Dry-0-Tron). It controls the environment in a swimming pool room.

 

[Lewish]

I assume this is an AC motor. You can use a VFD to give you variable speed. Some have provisions for inputs from a plc. Your motor is probably not Inverter Duty rated, so you will probably be wise to replace it with one which is Inverter Duty rated if you decide to use a VFD.

 

[peebee]

I'd re-examine the need for a VFD on such a small blower. The main reason for picking a VFD over an adjustable damper would be energy efficiency, usually due to cost savings. For such a small blower, though, there would probably be no installation savings or life cycle savings. Consider just using a damper.

 

[busbar]

If the blower is driven by a permanent-split-capacitor {PSC} 1ø motor, simple triac/SCR phase control may be applicable.

 

[nbucska]

Isn't bang-bang not good enough ? <nbucska@pcperipherals.com>

 

[rickr]

the reason for this question was the blower makes noise when starting and I was hoping to cut down on that by ramping up the blower to speed.

 

[xnuke]

Try a soft start as long as you're not looking for a turndown in operating speed.

 

[SteveKW]

On that application you could use resisters or even capacitors in series with the motor. A simple relay with a timer could short the resister/capacitor after a few seconds putting the motor across the line.

 

[dydt]

hi..
if you have enough budget for this modifications, i will recommend a VFD with inverter duty motor...you can use a miniature PLC to control the VFD's preset speed which i believe up to seven settings on standard VFD's...you can program the PLC for whatever time you want the speeds to kick in..

dydt

 

[jraef]

rickr,
Before you can act on any of these suggestions, you need to determine (and post) wether it is a single phase or 3 phase motor. If it is single phase as I suspect, the VFD suggestions are mostly invalid unless you replace the motor with a 3 phase version and that sounds a bit drastic for your purposes.

The simplest way to tell is to look at the circuit breaker or fuse box that is feeding power to this blower. If it is a 2 pole breaker or 2 fuses, it is single phase. If it is 3 poles or 3 fuses it is 3 phase. Don't trust just counting wires since ground wires are sometimes mislabeled.

If it is 3 phase, I suggest just using an inexpensive soft start device since you may not need to vary the speed continuously. At 2HP 240V however, there is not much of a cost difference to upgrade to a VFD, just more complex.

If it is single phase it is more complicated because of the different types of single phase motors. Some can be used with electronic controls, some can't. Find out and re-post.
Subvert the dominant paradigm... Think first, then act!

 

[peebee]

Be aware that both a soft-start and a VFD could increase your noise levels, depending on the specific source of your noise. The harmonics generated by both controllers tend to produce a ringing or whining sound in the motor.

What kind of noise problems are you dealing with?

 

[rickr]

The motor is single phase 2-pole, 240VAC. The offensive noise is the initial air rush through the duct work. If there is any play in the doors in the house I can hear one or two bang slightly closed ( i can fix that part of it ). There is a slight boom as the motor starts up. I think it is due to initial rush of air. I figured if I somehow dampen the starting of the blower, I may eliminate this noise. It would be nice if I didn't have to swap out the motor to accomplish this, but I may consider that, within reason.

Keep in mind -- i only have 24VDC digital inputs, digital output relays and 4-20mA inputs in the PLC. No analog outputs.

 

[busbar]

Is the duct &quot;oil-canning?&quot;

 

[rickr]

The duct work is fiberglass. Your question as to is it oil canninig gave me an idea. The blower itself is attached to its sheetmetal enclosure. Maybe the external enclosure wall that the blower is attached to is flexing due to the torque of the blower -- hence the noise. Not much I can do about that without a redesign.

Looking at the motor (not being a motor expert) it looks like a normal one with two coil size humps on the top of it. I'm hoping this will give a clue to the type of motor I have and my options. If only I could ramp this motor up to speed. This definately would solve my problem.

Question 1:
Is my description of the motor enough to determine if this motor can be ramped?

Question 2:
If so, what devices would I need to accomplish this?

Thanks
rick

 

[busbar]

Offhand, 2hp seems kind of large for a 1ø HVAC &quot;permanent split capacitor&quot; air-handler motor, but if it is, something like this may be considered:

http://www.crydom.com/pdf/lpcv.pdf

{Signal conditioning by others.}

 

[peebee]

bus, your device does look promising but note that it states that it's not suitable for AC motors, he'd have to change his motor out.

 

[busbar]

Oops.

 

[busbar]

I do not believe that a ceiling-fan controller has adequate capacity.

 

[rickr]

Thanks for your suggestions guys, i didn't realize that the difficulty of my problem was in the category of 'rocket science'.

 

[peebee]

It's not rocket science, just expensive. Any VFD or soft starter would take care of you. You're probably talking hundreds or thousands of dollars to buy one, though. Some heavy steel motor brackets would probably do the trick at much lower cost and with a much lower failure rate.