Re: [CAD_CAM_EDM_DRO] Home shop power for a big machine

My brother is running a Mornarch VMC-75 (I think) with the 15 hp spindle
as you mentioned in a home shop, he also is running a lathe with 15hp
motor on a 10hp home made rotary phase converter. The VMC has a large
transformer on the front end. He occasionally trips the breaker when he
powers up the machine (in rush on the transformer we suspect) with no
load on the machine. We had to do some matching capacitors on the
transformer when we installed it due to the large induction load with
the transformer. We are considering going to a slightly larger breaker
(on the single phase side) in hopes to reduce the trips. I think he is
at 70 A now considering 80 (that is what I use on my 10hp converter).
Input power to the shop is 200A 230, single phase. Point is it can be
done. I have also seen a 10hp lathe on a 5 hp RPC with no problem.
Rule of thumb is a RPC will start a motor the size of the converter and
run 3 time that. With a lite load I have seen them start at least twice
their hp.

Beau

Jim Fleig - CNC Services wrote:

>
> Hi Roger,
>
> Just a thought: the power you may need to run the machine may be much
> lower than the power you will need to start the machine. Most three
> phase motors have a surge of power that starts the motor and then the
> current draw drops way down while the motor runs at its rated rpm. It
> may be more helpful to try to address the question about starting the
> machine. After the machine is started, then it may take very little
> power to run the machine to do what you would like to accomplish.
>
> Happy New Year!
>
> Jim Fleig
> CNC Services
>
> machine tool service from casting to control
>
> ----- Original Message -----
> From: vrsculptor
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> <mailto:CAD_CAM_EDM_DRO%40yahoogroups.com>
> Sent: Wednesday, December 31, 2008 10:10 AM
> Subject: [CAD_CAM_EDM_DRO] Home shop power for a big machine
>
> I was lusting over a big VMC that would never fit in my home shop and
> got to wondering about power. The machine's data plate says 230 volts
> 3PH @ 80 AMP's, 18KVA. It has a 15 HP spindle.
>
> I could use a rotary phase converter to generate the three phase but
> don't have anywhere near 80 AMP's available. 18KVA/750 watts equals a
> 24 HP phase converter.
>
> If you where using this machine in a hobby environment and not trying
> to get production feeds and loads how small of a phase converter could
> you get by with?
>
> Roger
>
> [Non-text portions of this message have been removed]
>
>