Running 120V/60 hz Single Phase Motor on 230/50 hz

[ahmetkazici]

I have 3 ventilators that are rated for 120V/60 hz however my supply is 230/50 hz. I can use a step down transformer 230/120V however because of the frequency change i won't be able to have the same rpm. I was thinking to use a step down transformer and a vfd to overcome this but could not find any products that does both.

 

[jraef]

http://www.invertek.co.uk/product_optidrive_e21.aspx

A VFD can be programmed to put out any voltage BELOW the incoming line voltage. So you would feed the VFD with 230V 50Hz and program it to put out 120V at 60Hz as the top speed. But be careful, a 120V packaged unit like that is going to expect to get a hot and a neutral, and sometimes they bond the neutral inside of the unit (they are not supposed to but it happens). That would be very bad for the output of a VFD.

I'll warn you though, this is likely FAR more expensive than just buying a new ventilator motor that will run correctly at 230V 50Hz.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
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[ScottyUK]

It's single phase too, which will probably not suit the VFD.

Some types of single phase motor can run on a 'dumb' scalar drive but we are getting into specific types of motor and types of drive to do this. For the cost of a ventilator is it really worth it?

 

[jraef]

That Invertek drive I linked to is for single phase motors, albeit with a butt load of caveats. One of the problems is the TYPES of single phase motors; it can only be used on PSC and Shaded Pole motors. But that covers most vent fans.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
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[macmckim]

If the single phase motors are capacitor start type with centrifugal switch - you would have to find out from motor mfg
if their switch is a 50/60 design. If not, then you will need a 50HZ motor.

 

[ScottyUK]

How good are those Invertek single phase VFDs, assuming a suitable motor for it to drive? Obviously it won't have the tight control of a three-phase vector drive but I have never had the chance to play with one. I've hung single-phase motors off the output of an old scalar drive which was too dumb to care and had varying degrees of success (from kinda worked through to capacitor fire).

 

[jraef]

They sell them here in the US through two companies called Anacon and Bardac. I've only done a couple, they seemed fine, but you are right, scalar drive performance. Their big market for those seems to be vent fans because HVAC companies need them for air balancing when there are a lot of bathrooms in a facility with a shared air space. Too many people gassing up the bathrooms after a Mexican food working lunch and leaving the fans on will mess up the larger HVAC system so that nobody can open the front door against the vacuum!

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[iceworm]

"I'll warn you though, this is likely FAR more expensive than just buying a new ventilator motor that will run correctly at 230V 50Hz."

Buying a 50hz motor won't do you any better than using the one you have. Transform the voltage down to keep the V/Hz ratio the same and the motor you have will run the same rpm as new 50HZ motor.

If the ventilator fan is mounted on the motor shaft you will either have to find a VFD that will work with your motor or get another fan. Unless it has pulleys and a belt.

At 120V, it can't be much of a ventilator. How about just buying a new one rated for 230V, 50HZ and the CFM you need.

ice

 

[ScottyUK]

iceworm,

You're correct up to a point, but you're overlooking some other effects of the change in frequency: at 5/6 of the original speed the fan won't require as much power and won't move as much air, and won't develop as much pressure if in a ducted application. Overall it's performance will be significantly reduced. If the OP selected the fan based on a requirement for a certain airflow then the fan which had adequate performance running on a 60Hz supply probably won't be adequate running on a 50Hz supply.

 

[iceworm]

but you're overlooking some other effects of the change in frequency: at 5/6 of the original speed

You're absolutely correct. But no, I didn't overlook the speed change ingerent with the changing frequency. Aparently I didn't say it very well.

As I recall:

Transform the voltage down to keep the V/Hz ratio the same and the motor you have will run the same rpm as new 50HZ motor.

How about just buying a new one rated for 230V, 50HZ and the CFM you need.

ice

 

[ScottyUK]

No, you got the speed change bit nice and clear, but didn't mention - because I'm sure you understand - that the slower fan won't move as much air, which is after all the whole reason the motor is turning in the first place.

 

[iceworm]

You are correct. I did not specifically mention the expected changes in CFM, pressure, or power. No, I don't consider myself a wizard on the mechanical.

ahmetkazici mentioned the rpm change so I figured he knew there would be a change in the cfm ~5/6, pressure ~25/36, and a change in the power ~125/216. He did not appear to need a basic physics lesson.

My post was aimed at: Why engineer a $500 fix when a $100 fan will fix the issue, have less parts to fail, easier to T-shoot down the road. Its only installed once - but it has to be repaired for the next 30 years.

ice

 

[jraef]

Hence:

I'll warn you though, this is likely FAR more expensive than just buying a new ventilator motor that will run correctly at 230V 50Hz.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[ScottyUK]

I completely agree with your last sentence iceworm.

 

[iceworm]

jraef -
Yes, you did say that. And I read what you said. Hence the reason for my post. A new 50hz ventilator motor won't fix the problem. (Well, unless you have a source for 1.7 pole motors) It won't turn any faster than the existing. As already noted, takes an impellor (fan) change as well - or pulleys and belt change to get the CFM/pressure back to design.

However, you are correct, I did not say, buy a new "ventilator". I sloppily use "new one". Bad on me.

ice

 

[jraef]

Yep, you're right. I said motor, I should have said fan. Good catch.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376