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How to convert 2hp AC blower motor to variable speed

How to convert 2hp AC blower motor to variable speed

How to convert 2hp AC blower motor to variable speed

(OP)
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.



RE: How to convert 2hp AC blower motor to variable speed

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.

RE: How to convert 2hp AC blower motor to variable speed

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.

RE: How to convert 2hp AC blower motor to variable speed


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

RE: How to convert 2hp AC blower motor to variable speed

(OP)
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.

RE: How to convert 2hp AC blower motor to variable speed

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

RE: How to convert 2hp AC blower motor to variable speed

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.

RE: How to convert 2hp AC blower motor to variable speed

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

RE: How to convert 2hp AC blower motor to variable speed

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!

RE: How to convert 2hp AC blower motor to variable speed

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?

RE: How to convert 2hp AC blower motor to variable speed

(OP)
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.

RE: How to convert 2hp AC blower motor to variable speed


Is the duct "oil-canning?"  
  

RE: How to convert 2hp AC blower motor to variable speed

(OP)
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

RE: How to convert 2hp AC blower motor to variable speed

Offhand, 2hp seems kind of large for a 1ø HVAC "permanent split capacitor" air-handler motor, but if it is, something like this may be considered:  http://www.crydom.com/pdf/lpcv.pdf {Signal conditioning by others.}
  

RE: How to convert 2hp AC blower motor to variable speed

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.

RE: How to convert 2hp AC blower motor to variable speed


Oops.  
  

RE: How to convert 2hp AC blower motor to variable speed


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

RE: How to convert 2hp AC blower motor to variable speed

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

RE: How to convert 2hp AC blower motor to variable speed

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.

RE: How to convert 2hp AC blower motor to variable speed

rickr,
I hate to tell you this, but from your description it does appear that you have a permanent split capacitor 1 phase motor and you will not be able to use an electronic soft start device with it. The soft start components would be damaged by the capacitors in the motor. This will also prevent you from using a VFD as well, even if you found one that works on 1 phase motors. I have in the past used a soft start on a temporary fan with full knowledge that it would not last long, but it made the problem go away for a few months anyway. Baldor makes a cheap 1 phase soft start controller that you can simply mount and wire downstream from whatever is controlling your motor now. It may only last a few months, or you might get lucky and it will last a year or so, you never know. Your only alternative electrically is to change out the motor to 3 phase and add a VFD which will convert your 240V 1 phase power to 3 phase for the motor. FDigure $300-500 plus labor minimum.

Another approach would be a "mechanical soft start" clutch device such as a Torque Tamer, shot coupling or fluid coupling that will slowly allow the blower to accelerate even though the motor is started at full speed rapidly. Contact a Power Transmission distributor such as Motion Industries or Kaman Industrial for advice.

That pop you here is probably the sheet metal or even the fiberglass duct "oil canning" as busbar suggested, so another option may be to solve the problem mechanically, perhapse with spray-on sound dampening material or something like that.

Good luck.

Subvert the dominant paradigm... Think first, then act!

RE: How to convert 2hp AC blower motor to variable speed

Suggestion: There may be something suitable related to your application available on web. If there happen to be some proven similar application, then it shall get serious consideration. Visit
http://www.toad.net/~jsmeenen/motor.html
http://www.achrnews.com/CDA/ArticleInformation/features/BNP__Features__Item/0,1338,26558,00.html
http://www.braschmfg.com/Download/cabinet.pdf
http://www.lsicsi.com/appnotes_files/body_application_notes.html
etc. for some interesting ideas, perhaps some higher power rated dimmer could perform the motor controls.

RE: How to convert 2hp AC blower motor to variable speed

If you can get away from a capacitor start motor there are small soft starts called torque limiters available for single phase.  They are used in conjunction with existing starter.  Cost is < $200US in small quantity.  It will give you a time band of .5-5S and torque adjustment of 0-85%.  Size is 2"Wx4"Hx5"D, mostly heatsink.  It's really designed for conveyer applications but may be the best cost item available.

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