# Power Factor for Capacitive Loads

Discussion in 'General Electronics Chat' started by quixote, Oct 24, 2012.

1. ### quixote Thread Starter Member

Jan 15, 2007
12
0
Please look at the following company website:

http://www.prodisplay.com/intelligent-glass-technical.html

At the bottom there is a diagram showing a transformer with the smart glass (DVG) as a load. The smart glass is basically a capacitor.

So my questions:-

Q1. The manufacturer claims the power consumed is 7W. Should this not be 7VA?

Q2. Also, what power rating should the transformer have in this case? For a capacitive load, the Power Factor would be 0, is that right?

Q3. Or does the transformer mean that the load (as seen from the mains) is purely inductive?

Help..!

2. ### GetDeviceInfo Senior Member

Jun 7, 2009
1,571
230
are you sure that the panel represents a capacitive load? I'd think that an alternating current would not give you a net change in the panels properties, unless it was clipped through some quadrant. I'm thinking variable DC is passed through the panel, with 'transformer' being a generic term. I could be totally wrong however.

3. ### quixote Thread Starter Member

Jan 15, 2007
12
0
Hi

Yes, I am quite sure the smart glass panels act as a capacitor - I have seen the 90º phase lag between current and voltage in my own lab. The transformer I am using is either an autotransformer (BLOCK SAT100) or (preferably) an isolating transformer (BLOCK TIM 100).

4. ### Sensacell Well-Known Member

Jun 19, 2012
1,183
276
The glass must dissipate some power through the lossy dielectric material combined with IR losses from the resistance of the conductive electrodes.

5. ### The Electrician AAC Fanatic!

Oct 9, 2007
2,300
335
The spec also says .1 amp per square meter and "power" (does this mean applied voltage?) of 110 VAC. This tells you that the VA required is 11 VA. If the real power consumed is 7 watts along with a VA of 11 VA, there should be a phase shift between current and voltage of something other than 90 degrees.