Re: [CAD_CAM_EDM_DRO] Inverter question

Jon Anderson wrote:

> Have a question regarding sizing VFD inverters. I have an old Hardinge
>
> chucker with 1hp 2 speed motor. I'm having problems with the antique
> relays and contactors and would like to replace all that with an
> inverter. There's a couple 1.5 and 2hp inverters coming up on eBay.
> Given that I frequently do a LOT of repetitive start/stop at max rpm,
> should I oversize the inverter and go for a 2hp?
> Given that I want to put a 3-5hp motor in it eventually, could I run
> the
> 1hp motor off a 5hp inverter?
> I don't mind buying a smaller one now and buying another when I go for
>
> the larger motor, I can use the 2hp on my Bridgeport.

I would recommend getting the newest inverter you can find. The options
on
the digital programmer modules are far better than the old ones with 5
pots.
Make sure you can get the braking resistor, or know how to obtain and
install
your own. Decelerating a lathe, the inverter needs to get rid of a lot
of
energy, and will use the braking resistor heavily for that. A small fan
might
be all you need to keep the inverter and braking resistor cool, so it
may
not be necessary to oversize the inverter.

>
> Also, given that I have a two speed motor and what I know of
> inverters,
> I'm just going to have to wire it for the high speed windings. I have
> a
> Toshiba 1hp inverter and I recall reading in the manual that one
> should
> never disconnect it from the motor under load, which would seem to
> preclude switching windings. Correct?

Most inverters have such a warning. I did this with my 1/2 Hp inverter
on a
Bridgeport M head mill, and never had a problem. But, you could use the

two-speed switch, just never change it when the inverter is running the
motor.
You shouldn't need to power the inverter off, just have it in the 'stop'
mode
when you change windings.

Jon