ECN Forum Forums General Topics of the Trade General Discussion Area Volt-Amp Conversion - Please Help

Posted for Todd

Todd:

VA is the mathematical number you come up with when you multiply the voltage at a piece of equipment by the current that is being drawn by the equipment.

We would need to know what your givens are and what you are trying to convert from. The relationship between Wattage and VA is a little complicated so if that is what you are trying to convert I think you will need to know the power factor of your facility.

I will try to provide a brief over simplistic view of how the power factor relates to power. If you search this site you may find a detailed discussion about the subject, barring that I am sure someone will come along with a better explanation shortly.

VA is "apparent power" the equipment is using. This is the same as the "true wattage" ONLY when the power factor is unity (current and voltage exactly in phase).

In most cases the power factor of the system is less than unity (phase shift occurs whenever you are feeding a reactive load) and since the current and voltage are out of phase the apparent power (VA) that must be supplied to the equipment will be greater than the actual wattage required so VA is used to size the supply components to compensate for the out of phase relationship of the voltage and current.

Let us know exactly what are your know facts and what you are trying to convert to VA. Tom R.


[This message has been edited by Tom R (edited 12-21-2001).]

I would also like to see any information anyone has on the subject on sizing UPS systems and also on what types you would recommend. When is a central system with dedicated circuits practical versus small individual stand alone units?
I don't want to lead this original post off course, I just thought maybe we could expand it

Thanks