On Wed, 20 Jan 2010 16:57:41 -0600, Ignoramus29895
wrote:

On 2010-01-20, Wes wrote:
Ignoramus29895 wrote:

Given your ability to find a deal, is there any reason you can't come up with a rpc? I'm
running mine on a Rotophase my uncle found in a dumpster at a oil location he maintained
portapotties at. A motor, a few caps, you are good go to.

I already have a phase converter, but I was hoping I would not need to
use it for the lathe. I have a pile of variable frequency drives, some
are in a bad cosmetic shape (hard to sell) that are quite usable.

i

I don't know enough about VFD's in your application to help you.

It would seem that a motor that is 230/460 which I belive yours in could handle whatever
extra strain a vfd would put on it.

I don't know but would adding some load side capacitance mellow out how your motor reacts?
I'm hoping our EE's on the list have comments on that one.


I am pretty sure that you cannot put capacitors on the output of a
VFD.

Actually right now, the lathe is on a Phase-A-Matic static phase
converter. The Phase-A-Matic came with the lathe. It runs, but I am
getting only 2 HP out of 3. Maybe I should just leave it as is. I
would not be likely to use all of the HP without coolant.

I want to do the right thing, and it is not immediately obvious what
is the right thing. I know for sure that I do not need to vary input
frequency.

It seems that the phase converter route is nicest to the motor, and
lathe, but is less convenient for me.

i

There's now way of being sure but the odds are pretty good.

VFDs increase the peak voltage stresses on the motor insulation,
Most older motors survive (all that I have used) but a few fail.
Capacitors do NOT help.

The yard stick I would use is simply based on the mechanics
of the motor installation. If it's difficult or impossible to
replace it with a modern motor then it makes sense to stick with
an RPC.

If on the other hand it's a fairly standard motor that
could be replaced if disaster struck I would chose the VFD drive
on the basis that the increased convenience outweighs the small
increase in risk.

Jim