3 phase motor/ vfd / phase converter question

[stryder]

Hi all, first post here.
I have read the other 2 posts about 3 phase, and vfd and have questions.
I was given a Baldor 3hp 3 phase motor, i intend to build a KMG style grinder and use this to power it.
My question is, which is better, a static phase converter, or a VFD ? i got the impression that the vfd was better but didn't quite understand. is this a speed control as well as a phase converter?
I want to use a variable speed controller, can i do this with a static converter?
Thanks, George

[DC KNIVES]

George,get the VFD, static phase converters suck.The phase converter would also not give you variable speed without adding something else .All this can be accomplished with a VFD.You will need a single phase input with three phase output and probably one rated at 5 hp would be best.I don't know where you will be picking up the VFD but make sure you get a manual, you will need it to set your parameters to operate the motor.The wiring is easy.I hope this helps.Good luck. Dave

[stryder]

Dave, thanks! that is what i was trying to understand. I am not an electrician, so i have been reading all the posts i can on the subject. The articles i have read seem to be described for journeymen to masters level.
George

[Rob Frink]

static phase converters suck.

In my opinion, this couldn't have been said any better. Especially if you are talking about "Phase-a-matic" phase convertors. Those devices are a simple capacitor circuit used to start the 3ph motor. Once the motor is started, the phase convertor drops out and the 3ph motor runs on a single phase. ...making 1/3 of its rated hp. "Phase-a-matic" promotes their products with less than accurate claims.

On the other hand...a VFD generates 3phase power that the motor runs on...all 3 legs all the time. Some are analog and others use micro-processors. They also offer motor protection in terms of monitoring the power output to the motor with programmable shut-off faults when the motor is overloaded. They monitor the motor speed and adjust thier output to keep the motor running at the selected speed.

Yes a VFD is a speed control. It varies the AC frquency to change the speed of the AC motor. VFD stands for Variable Frequency Drive. Even if you don't need speed control, a VFD would be a better choice over a static phase convertor for running your 3ph motor at a constant speed....and it will cost more as well.

Good luck with your project.

[stryder]

Rob; I wish i could purchase one of your amazing machines!! It's the crawl before you walk thing. Thanks for the input. George

[AcridSaint]

Rob, you are truely a stand-up guy. Not many folks out there are so helpful to people who can't buy their stuff. Guess that's why you'll stay successful with folks in the community.

Back to the topic!

[Rob Frink]

I'm truly a "shop-guy" at heart. I love machinery, tools and gadgets.

Selling belt grinders is just my day job.

[Mike Krall]

Rob,

I'm trying to help a tool & die maker with his Hardinge Precision Lath. He is running a phase convertor on it now (1 1/2 hp 3-phase). The lath has it's own variable speed dials (and two speed gear box) and there are two other motors down stream... one AC and one DC, both 1/4 hp. Can a VFD be used in a situation like this?