Re: Inverter question

Jon, et al.
We fit quite a large number of invertors on our range of machines,
enough to qualify as OEM's
[Original Equipment Manufactures ]
Firstly a few words about invertors. Currently there are roughly
three types doing the rounds based purely on age. The older ones are
very limited usually with just min speed, max speed, ramp up, ramp
down options. The mid range , usually about 1/1/2 to 3 years old
have a lot more options but usually what both of these types don't
have is current limiting options.
The latest type have more options that you can poke a stick at. The
ones we are currently using have 83 main options with sometime up to
7 sub options in many groups. These are current limiting and these
are the type to get if possible. The mark up on invertors is usually
about 100 percent on the modern stuff so shop around.
If you are forced to used any of the earlier options then feed the
single phase supply to the invertor by a DOL starter with the thermal
set to the motor current. This way and with the later type you can
use a smaller motor on a large invertor, but not the other way round.
With the later type you can usually specify the motor load in amps
and they are very good.
What invertor can't do is to start/stop/reverse instantly. Even with
the ramp up/down set to minimum there is always a delay. Trying to
get them set too fine often causes a trip out and you them have to
either reset or wait for the auto reset to latch back in. Switching
the output lines whilst under load is a definite no-no.
If plug reversing is an issue then you would be better off with an
convertor rather than an invertor.
A note about cost when buying, don't just look at the invertor but
the whole package needed.
Some invertors cannot do more than 60Hz without an add on speed
board. Some need an extra programming panel. If you need to run
remote stop start a lot can't latch the remote switches in and need a
remote relay to do this. Add all this up to get total cost. On the
mid models I have described above some with all these options are far
more than a new modern unit. Buyer beware.

As regards the two speed motor with US motors I am assured it can be
done as you have 220v two speed, three phase motors as standard. In
the UK all our 3 phase motors are 440v and so because you need to
switch to 220v delta wiring we cannot use two speed motors on
invertors and I cannot advise on this subject as it's unknown to me.

--- In CAD_CAM_EDM_DRO@egroups.com, Jon Anderson <janders@n...> 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.
>
> 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?
>
> Thanks for any advise,
>
> Jon