Subject: Re: VAX7000 3-phase
To: Brian Hechinger <>
From: Gunther Schadow <>
List: port-vax
Date: 03/04/2002 19:09:50
Brian Hechinger wrote:

> On Mon, Mar 04, 2002 at 03:06:22PM -0800, Chuck McManis wrote:
>>Of course something like a TEMCo phase converter could also be used. These 
>>types of devices are used in lots of places (machine shops, etc) and can be 
>>found used for often 1/3 to 1/2 of their list price. For a small circuit 
>>(40 amp) the converter is often < $1000. It opens up a whole new class of 
>>machine for collecting ...
> that's cool and all, but how do i convert HP to A?  

That's the easy part! Use the following equations:

P = U * I  and 1 W = 1 V * A

1 HP = 550 ft*lbf/s ~ 745.6999 W

> i would need to be able to
> figure out how much HorsePower my VAXen have.  how does one do that?  is it
> based on size?  it takes three horses to pull my vax?  so it's a 3HP model? ;)

One kW are 1.341 HP, so 1 kW at 110 V are 9.09 A.
And then 1 HP at 110 V mounts to 6.72 W. There is
something about the phase issue and how you calculate
effective power (and there is where some conventions
make a difference between VA and W even though they
are the same physical unit.) But I forgot the detail.
It's got something to do with P really not being
U * I but there are integrals involved and capacitance
and inductance turn the phase differences between
U and I around, which makes for differences under
idle vs. load conditions. This was all nice and clear
to me when I did it in school but I forgot most of it
since :-(


Gunther Schadow, M.D., Ph.D.          
Medical Information Scientist      Regenstrief Institute for Health Care
Adjunct Assistant Professor        Indiana University School of Medicine