VFD? New Motor? What?
March 27th, 2009Next Hurdle
I ended the weeks-long turmoil of trying to choose a metal lathe, and I thought life would be free from puzzles and dilemmas for a while. WRONG. Now I have to figure out what to do about the 3-phase motor, and I have to get a minimal amount of tooling.
I can get a phase converter for $100, but I don’t know much about it. I don’t want something that will harm the motor or cause it to produce less power than it would on a true 3-phase system.
The mechanical speed controls on these old lathes sometimes give up the ghost, and when that happens, I think it’s best to scrap the gears and go VFD all the way. If I had a VFD already, I would not have to worry about ordering a new one, and I would not have to toss a phase converter for which I have no use. A VFD containing a phase converter would work as a phase converter, but a phase converter with no VFD stuff would not control speed. See what I mean?
I’ve asked about this before, but I have the memory of a gerbil who just mistook a sack of coffee beans for sunflower seeds, so every time someone explains it, I forget and have to ask all over again.
People always tell me to build a rotary phase converter, but it seems silly to run one huge motor just to provide juice for another motor.
I’ll figure it out. I think the best thing is to have them ship the lathe as-is, and I can worry about the electrics on my own.
“The electrics” is how we he-man tool people describe motors and starters and so on.
I can get a single-phase motor cheap. That’s probably the easiest thing to do. But I am told they generate less torque than triple-phase, so I’m not sure what size to get. The original is 2 HP.
Arrgh.
March 27th, 2009 at 12:51 PM
you will not notice a difference in single or three phase at this skill level. you will always lose hp with a vfd or phase converter. Motor driven phase convertors are perfectly legitimate systems and are in common use everywhere.
March 27th, 2009 at 2:09 PM
Unless you’re planning to use three phase a great deal,a rotary converter might be the easiest way out. If you power company doesn’t have “real” 3 phase close to your house,you might ask them about the” Delta Wye” type 3 phase. It’s artificial,but it works. I’m familiar with the facilities of one such user,it’s done with transformers off a single phase line,because true 3 phase isn’t available.4d3
March 27th, 2009 at 3:57 PM
Well, your normal motto is “always overbuy”.
A 2-HP single phase motor is, as you say, fairly cheap, especially if you’re willing to accept a used one. But that’s a minimum solution, not an “overbuy” one. It would allow you to use the lathe, and as og points out, at your skill level you wouldn’t notice any problems (note: my skill level, too).
A simple phase converter, rotary or electronic, is the middle way. Rotary phase converters are big and noisy, by the way. You might not like having one in your garage.
The overbuy solution is the VFD. One thing you might think about: if you had one VFD, and bought some plugs and sockets, you could move it from the lathe to the mill and back again as needed. You probably won’t be using both of them simultaneously, hmm?
The only real problem is finding a 2-HP VFD with single-phase input.
Regards,
Ric
March 27th, 2009 at 7:03 PM
The amazing thing is, I can’t think of an example where I have succeeded in overbuying.
March 28th, 2009 at 9:08 AM
Well, yes, exactly.
Regards,
Ric
March 28th, 2009 at 12:32 PM
Delta VFD022B21A
March 28th, 2009 at 4:03 PM
By the way, a VFD doesn’t mean your motor will be lower horsepower. The horsepower on the motor will be what you get- but it will cost you more to get it in terms of electrical use.
March 29th, 2009 at 9:30 AM
Then why do people keep claiming VFDs “derate” motors? It never made any sense to me, since the motor will always produce the same horsepower at the same voltage and current.
March 30th, 2009 at 2:15 PM
If you use a 3 hp VFD on a 3hp motor, you will get less than 3hp. If, on the other hand, you use a 100 hpvfd on a 3 hp motor, you will get 3hp. So: Overbuy. The VS one I linked to would work fine. Most places will try to sell you a 3hp VFD for a 3HP motor.
There are other issues with VFD’s. A VFD doesn’t provide “true” three phase. It takes single phase, rectifies it, and chops it back up into three phase- but it’s digital, and a digital output is not a true three phase sine wave- not really. The only way to get “real” three phase is to use a motor-generator combo. That will output proper three phase AC- but a VFD does the job as close to the real thing as is necesary for the work possible. I guess I could have made this clearer, sorry f I was not being crystal clear. If you want 2 hp of 3 phase power, get a VFD at least capable of 3hp or above, and you should still get the full 2hp. However, it’s going to cost almost as much as a 3 hp single phase motor. Clearer? I hope so. This is confusing stuff and as I’m usually posting from a phone I may not be able to be as complete in my explanations as I should be, apologies.
March 30th, 2009 at 2:48 PM
No problem, Og. I shouldn’t complain about free information.
.
The VFD I chose is 3HP. It’s a TECO. A guy who owns a 5914 said TECO worked fine for him.
March 30th, 2009 at 3:12 PM
oh heck that will be plenty then.