# How to build a kwh meter?

1. Nov 9, 2007

### Gyrobug

How to build a kwh meter??

I would like to seek some information on how to build a kwh meter to check the power consumption for my school robotic project? Please tell me what are the components that are required to build one?

Thank you.

Regards,
Gyro

2. Nov 9, 2007

### marcusl

I assume you can get by with knowing instantaneous power consumption? If so, then measure the voltage and current draw, their product is instantaneous power.

If you really want cumulative energy usage, I suggest sampling voltage and current again but with two DVM's connected to a PC, or getting a PC card with ADC's on it. Your PC will multiply to get instantaneous power, and integrate the samples continuously to give you cumulative energy.

3. Nov 9, 2007

### dlgoff

http://www.rp-l.com/meters.htm#How%20Meters%20Work

Power companies measure how many times the disk turns in any given hour. The disk has slots with a light emitter on one side and a detector on the other side(used when they want to telemeter the data to their office). If the disk has 10 slots and each rotation represents say 1kw, you will get a 10 pulses, each representing 100watt. So if they get say 25 pulses in this hour, you've used 2.5kwh of power.

Last edited: Nov 9, 2007
4. Nov 11, 2007

### Gyrobug

Thanks for the info. You guys been very helpful.

Cheers,
Gyro