Re: [CAD_CAM_EDM_DRO] Rotary phase converter

On Tue, 29 Jan 2002 09:20:49 -0500, "Carlos Guillermo"
<carlos@...> wrote:

>Thanks Fitch -
>
>Yikes. I was trying to avoid having to set up a phase converter
>in order to run a VFD. My lathe has a pretty nice selection of
>gearing, and I would be happy with one or the other. The nice
>thing about a VFD is that I could easily control the spindle speed
>with the IndexerLPT / G-code interface combo. It is my preference
>for this reason, although this would require quite a bit of
>rewiring to implement the forward reverse and spindle "inching"
>controls as they currently exist on the lathe.

The rotary converter will allow you to use the inching controls just
lime the lathe was plugged into the wall. Unless you have a specific
problem with the lathe speed increments as designed, there really isn't
much need to use a VFD on a manual lathe. The only exception would be
if the electrical supply is marginal and the slow speed ramp behavior of
the VFD avoids installing a higher amperage service.

>The Hitachi specs say that the VFDs are capable of 150% load for
>60 seconds. Does anyone know WHY they warn against running a
>bigger motor? Couldn't we just pretend the motor was just rated
>"conservatively"?

If pretending is what you want to base an relatively expensive decision
on, go for it. Its your wallet. You pick your pony and take your ride.
As one of my favorite people, Richard Feynman, once said "For a
successful technology, reality must take precedence over public
relations for mother nature can not be fooled."

>The VFD is pretty well protected, and when the
>current limit is exceeded, it will fault. It's got enough smarts
>to make sure you don't get 5hp out of a 3hp VFD (but 4.5hp for 60
>seconds is OK!)

Its your money. I would not do it.

>Fitch - could you point me to a 5hp VFD that will run on 1-phase?
>It should work on my 20-amp circuit, right?

The on line sources I know about are:

http://www.kbelectronics.com/ Model KBVF to 1 hp.
www.dealerselectric.com/
www.automationdirect.com

>Another issue - reading up on static phase converters, I found
>that they only allow your motor to run at 2/3 rated power because
>they only provide 1-phase once the start up circuitry cuts out.
>Why don't they do like VFDs and generate 3-phase constantly?

For the same reason a VW four cylinder doesn't put out the same torque
and speed as a Cummins N14. The static converter and the VFD are
totally different products. i.e. because static converters aren't
designed like VFDs. There is a reason a 3hp static converter costs
about $150.00, and a 3hp VFD costs several hundred. If you look inside
a static converter you will find a circuit that looks for all the world
like the motor starting circuits on the Houston Metal Shop WEB page -
although I can't seem to find the URL at the moment. you can't make a
VFD out of a voltage controlled switch, a resistor, and a capacitor.
That is essentially what is inside a so called static converter.

>Thanks for the help,
>
>Carlos Guillermo
>VERVE Engineering & Design
>
>-----Original Message-----
>From: Fitch R. Williams [mailto:frwillia@...]
>Sent: Tuesday, January 29, 2002 8:36 AM
>To: CAD_CAM_EDM_DRO@yahoogroups.com
>Subject: Re: [CAD_CAM_EDM_DRO] Rotary phase converter
>
>
>>I've never used
>>one, and I'm trying to figure out how and when they "self-start".
>>Can someone please explain? Also, can I run a 5hp motor at 3hp
>>with a 3hp VFD? The Hitachi literature warns against running a
>>motor rated higher than the VFD's rated HP, but I can't
>understand
>>why.
>
>I would not recommend running a 5hp motor on a 3hp VFD. Hitachi
>builds
>them, and they know their product, and its limitations. The VFD
>market
>is very very competitive, cut throat in fact. If they had any
>hope that
>their 3hp VFD would actually run a 5hp motor with out causing them
>to
>lose money on warranty claims or create upset customers, they
>would sell
>it as a 5hp VFD!
>
>You can feed a 5hp 3 phase input VFD from a rotary converter with
>a
>balanced rotary converter based on a 7.5hp idler motor and it
>should
>work just fine. You can buy 5hp single phase input VFDs but they
>are
>more expensive than the three phase input ones at that HP. You
>might
>get away with feeding it from a 5hp idler if the acceleration
>ramps were
>programmed for it in the VFD, but it isn't a good idea.
>
>Fitch
>
>
>
>
>Addresses:
>FAQ: http://www.ktmarketing.com/faq.html
>FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
>
>Post messages: CAD_CAM_EDM_DRO@yahoogroups.com
>Subscribe: CAD_CAM_EDM_DRO-subscribe@yahoogroups.com
>Unsubscribe: CAD_CAM_EDM_DRO-unsubscribe@yahoogroups.com
>List owner: CAD_CAM_EDM_DRO-owner@yahoogroups.com, wanliker@...
>Moderator: jmelson@... timg@... [Moderator]
>URL to this page: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO
>bill,
>List Manager
>
>
>
>Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>