I have the old school electric meter with the (far too rapidly) spinning disc. I already know how to read five little clock faces for cumulative KWH.
I want to know the instantaneous kilowatts my house is drawing right now. How can I figure that out by timing how fast the disc spins?
Yes. You can determine your instant watts or kilowatts by using a stopwatch to time how long the disc takes to go around. Then you need to do a little bit of math. Not too much, promise :)
First, look for a figure somewhere on your electric meter called Kh. 7.2 is a common number, so you'd see a marking like 7.2 Kh or perhaps a different number. **
Take the Kh number and multiply it by 3600. You can call this number Ks. You might as well write this number on the meter, you'll be using it a lot. ***
Use a stopwatch/phone to count the number of seconds per 1 revolution of the disc. (If it's moving too fast or you want more precision, time 10 revolutions and divide by 10.)
Start with the Ks number (Kh x 3600) and now divide by the number of seconds. That is the number of watts being used right now. **** For instance if Ks is 25920 and it took 6 seconds, 25920/6 is 4320 watts.
If you want kilowatts, divide watts by 1000 (4.320 kw).
** gory details: Kh is the number of watt-hours per revolution. A watt-hour is 1 watt for 1 hour. *If you had only a 1-watt LED nightlight burning, it would take Kh hours to turn.*
*** gory details: multiplying Kh by 3600 gives the number of watt-seconds per revolution, since there are 3600 seconds in an hour. By the way, for a 7.2Kh meter, this number will be 25920.
**** gory details: Ks is the watt-seconds per revolution. Divide by the number of seconds per revolution, the result is watts!
***** gory details: another example picture.
