Variable control for 3 phase motor. 2

[Biff67]

I manage the shop on our large vegetable farm in Arizona. We inhabit what was previously the vegetable packing house, hence, there are many three-phase, gear motors available to me from old conveyors and packing lines. As I make plans to build a rolling-tubing-bender for making greenhouse bows I’m thinking about using one of these older motors. They are 1960's & 1970's vintage.

The most common motor we have is of the following specification:

(name plate reads as follows),

SYNCROGEAR MOTOR by US ELECTRICAL MOTORS
Los Angeles, CA.

¾ HP; 3 PH; 220/440 V; 1800 Motor RPM; 37.9 :1 ratio yields 45 RPM at output shaft


My question is: Can any three phase motor be controlled by Variable Frequency Drive etc? Is there a particular Variable speed drive that is better suited to this motor? I’ll want reversing capabilities.

Thank you for any help you can give me.

Biff

 

[rbulsara]

Yes. Talk to any VFD manufacturer or its rep..

Rafiq Bulsara

http://www.srengineersct.com

 

[sreid]

Try a Delta VFD-S up to 3 HP.

http://www.delta.com.tw/product/em/drive/ac_motor/ac_motor_product.asp?pid=1&cid=1&itid=5

 

[jraef]

There are a lot of opinions surrounding using older motors on VFDs. The insulation used in the 1960s magnet wire is not likely going to stand up to the rigors of VFD use, there are a lot of voltage stresses incurred by the technology. You can mitigate the effects by using filters on the output of the VFD, make sure you mention that you a potential VFD supplier, it's more important than a lot of people give it credit for.

Other than that, pretty much any modern VFD is going to work fine (and by the way, they ALL can reverse the motor, that's inherent). As to specific brands, we all have our "naughty and nice" list, it's pointless to get into specifics because the exercise usually degenerates into a series of sales pitches (for example, Delta is on my naughty list...).

What I always recommend generically is that you determine who is a good reputable supplier of VFDs IN YOUR AREA, one with an expert on staff, inventory available and access to a service organization. Because in my opinion no amount of discounting or bargain hunting is going to make up for not having someone to call if you get yourself in trouble. If you were an experienced VFD user who was comfortable being your own guru, then fine, shop on the internet for the cheapest thing you can find. Nobody in the business makes absolute junk or they would not survive. But there are a lot of suppliers who will SELL you their junk over the phone from 3000 miles away and then leave you twisting in the wind at the first sign of trouble. That is what you can't afford.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[ScottyUK]

"...pretty much any modern VFD is going to work fine..."

From the brand name and the speed listed as exactly 1800 rpm (i.e. no slip) I'm not so sure. 3/4 HP is a funny size for a synchronous machine - big for a permanent magnet rotor, and very small for a wound field rotor. Need some more detail, or better still a photo of the nameplate.


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[DickDV]

I would fully support everything jraef said in his post. Your application is not specialized enough to require a specific brand or technology but local support will make or break any project.

One little suggestion, if those motors are wound for dual voltage, ie. 240/480V, I would strongly suggest running them on the lower voltage and also take advantage of some of the newer drives that will output three-phase 230V with an input of single phase 240V.

This simplifies your supply wiring and, maybe most importantly, reduces the chance that the motor insulation will be damaged by the drive-generated power. It doesn't hurt either that, at 3/4hp, these drives are very economical to buy.

Good luck and have some fun with your project.

 

[waross]

Very good advice about the voltage Dick.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[CH5OH]

important to know is what is the expected most frequently used speed, if it's around 0 (lots of reversing, the motor might need some forced cooling (normally its cooled with a shaft mounted fan, running at 1800 rpm

 

[macmckim]

USEM Gearmotors - little right angle worm gearmotor were
called Synchrogear Gearmotors - just a brand name, nothing do do with Synchronous motors, DC motors etc.
As noted by DickDV - operate on 230V and winding should stand up to the PWM waveforms.

 

[ozmosis]

Good advice on the 230Vac winding DickDV!
It is the Peak-Peak voltage that would kill off any motor with inferior winding insulation when connected to a PWM VFD. P-P means (roughly) the AC supply x 1.42, meaning the P-P voltage seen at the motor would be in the region of 326V whereas the 460Vac winding would see 653V as a minimum.

 

[waross]

In case anyone missed the implications, a 230V/460V motor has all windings insulated for 460V. Using the motor on 230V gives the safety margin that ozmosis pointed out.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Biff67]

Thanks guys!

I appreciate your help.

I'm busy shipping tomato seedlings to California so they can make ketchup for us all. Will be in touch as I progress.

One of my Ag Engineering professors at the UofA,'Doc' Jacobs, ( he trained WWII navy fighter pilots), used to say:
"Experience is expensive whenever you can get it second-hand".


Biff