RE: [CAD_CAM_EDM_DRO] Re: VFD's / Skates

John,

It is sounding like you have made up your mind and want to use a static
converter. You have been given advice by a number of VERY experienced
people that a VFD is the way to go, but seem to not want to take it. Yes
a static converter will make the spindle turn. I have run Bridgett (4 hp
Bridgeport series II) on a static converter, rotary converter, and now
on a VFD. All three got the spindle to turn. There is no comparison, the
VFD is the way to go even if you are planning to use it as nothing more
than a fixed speed phase converter.

The primary drawback of a static converter is that you lose about 1/3 of
your power and it is very hard to get it to be balanced under all the
load conditions you will have with a big mill. The rotary converter will
give you full power and is much easier to get closed to balanced, but
you are paying a big penalty in current draw because you need the
current to run 2 motors simultaniously. In my case that means I need a
30 amp 220 VAC circuit plus I needed a 15 amp 220 VAC line for my air
compressor that has to run at the same time. That is a lot of juice and
many homes (most?) are not wired with that much current available. I had
to replace the electric close dryera and the electric range with natural
gas units to the tune of $2000 worth of gas plumming to free up the 50
amp 220 VAC line I needed in the garage. With both the static and the
rotary converter they were definitley not happy bringing the spindle up
to speed when it was stopped set to the anything over 2000 rpm or so.
The VFD is supplying real true fully balanced 3 phase electricity to the
machine. That by itself seems to make Bridgett run smoother.
Additionally with the ramping up to speed I can leave the spindle at
full speed and the VFD starts it up nice and smooth with no complaints.
Even better, the VFD I have has intrgal braking so when I stop the
spindle the VFD brings the speed down and it stops from a high speed in
probably 1/4 of the time it took by just cutting the power.

Summary is, do what you want but recognize that no one has pointed out
any reasons that a converter would be better than a VFD.

Tim
[Denver, CO]

> -----Original Message-----
>
> > Let me check and get back to you tomorrow but I think I have a 4 Hp
> > VFD kicking around spare.
>
> Thanks. I phoned Yaskawa and asked for a:
> 1.5kW triple phase, 500 - 3000rpm, single phase in, VFD.
> They called back and mentioned a few things like that running
> it at low end speeds around 500rpm would heat the motor over
> time which'd short the inverter or knock it out so I should
> fit a fan to the top (I instantly ignored their own personal
> kit idea, I'm not paying £400 for a plastic fan put on by
> someone else). What else, the motor would need to be wired in
> Delta Star as opposed to Star. The inverter came to a pretty
> awesome £371, or $540 (On 4 pole putting out 100hz to get to
> 2880rpm). If you have a inverter that'd do John I'd still be
> interested but otherwise can I not just use a static phase
> converter and a step up transformer after it? There are belts
> on the machine, I'm not sure I need a £200 button to change
> speeds. The man said the inverter would be for 230v so I'd
> need to put the step up on that as well, but I'm not buying
> it I don't think.
>
> Regards,
> John He
>
>
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