REACTIVE POWER

Page title already turn you off? best you read on.

There will never be a more important thing in life than for you to do your own measuring. Counting on others to do it for you can be costly, and you generally find out it's at your cost not someone else's. Once you accept the responsibility to do your own measuring, you need to learn how to measure.

One of the greatest little devices going is the Kill A Watt, the outfit that conceived, and marketed it?, I hope they're rich!

Now we're going to keep it simple here, you only need to remember one simple thing.

When you have pure resistive loads like an incandescent light bulb, or an electric stove top burner, it's easy to calculate the energy you are using to power it. It's simply voltage (times) the current, or in Ohms Law, the expression is E*I=P.  Lots of us know this and we also know that P stands for Power, or Watts, and WATTS is a real power figure.

When you get into AC power, you need to consider another VERY important FACTOR, and that is the PF or POWER FACTOR.

In the AC world, E*I*PF=P, and IF PF= 1.0 then E*I in your case will equal P as well

But don't quit reading, this gets easier, and you will know why it's so important for you to know.

I recently bought a SW4048 Xantrex inverter, this  older model and many like it have a reputation of being tough and reliable. I placed the Kill A WATT between the power plug and the AC input of the Inverter. With the batteries fully charged and in FLOAT (just laying around doing nothing), and the inverter function turned off, I saw 673 VA on the meter. Yikes! this can be a lot of power I'm being charged for! The next thing we ask ourselves is... "Can we afford to allow this inverter to float this battery?"

Well, now, this is the time to look at the rest of these buttons on the Kill A Watt. push the power factor button, it's reading (.15), push the WATTS button, it's reading a little over 140 watts, hey that's a lot less!

So.... our real power consumption is 140 watts. I go back the next day and see that it's at 100watts.

So what?

What we are seeing is a rather large inductor across the line, it's the Primary side of that BIG transformer we're using as a battery charger, the reactive power is high, but we are not being charged for the 673 watts, had we simply read the voltage, and current, and figured Voltage X Current,   we might have assumed so..

The Kill A Watt tells us the real story, and more, we can even allow it to accumulate the KWHs and run a total for us, this is a great and simple tool, you can't afford NOT to own it.

Now if you think of our situation, it may have been your generator powering the inverter's charger, and you might have assumed you were carrying a real .673 KWs had you used a simple volt meter and amp meter to measure the load. You can see above the potential magnitude of your error!

As for this battery charger, it is fairly efficient when it's bulk charging the battery, but as per floating the battery, it's not very efficient at all, we could float our batteries with a purpose built charger, and do it at a fraction of the cost, that's another topic, but it could save you a lot of energy over a year's time. 

When you see a Person post that he's modified his Indian made engine, added Graphite pushrods, and trick valves, he may also claim he's now making BIG power. IF he's using anything other than a resistive test load. he may be fooled into thinking he's a Master of tuning up generators.

With all this said, there's no better place to learn about this topic than reading Bill Roger's book,  he wrote it just for us DIYers.

I hope this page helps a least one person find reality, and come to think of it, Electrical Reality is what Bill's book is all about!

All the Best,

George