How can I make a meter to display the number of watts being used in my house? 120v, 2 phase system.?

Question

I am able to contruct electronic circuits

I should have mentioned that I require a circuit diagram to produce a low cost watt display from the 2 incoming phases. I am not concerned with the high acuracy of purchased meters and want something I can hook up to a large display. PS I know that the meter outside the house reads kwH.

Thanks for the replies. I think I need to make more clarification.

I don't want to do any math, especially since there are 2 phases.
I don't want to visit my basement anytime I want see real time power usage or have clamp meters etc hanging out of my breaker panel
Amps times 120 doesn't equal watts.
CT's are safe for measuring current especially if they are hall effect although I would hope that someone suggesting hall effect type for the circuit has a low cost supply of them.

ps I know hall effect CT's will not give phase angle to enable true power and since my biggest power consumption (aircon) is an inductive load, this may not be a good solution

Answer 1

There is a meter on the outside of your home that does just that.

Answer 2

You can read the meter base yes. That will show you a total of kWH consumed over a given period of time. What it won't tell you though is any kind of indicator of peak load.

If my 1200 watt microwave were to run for an hour on high, the meter base would reflect 1.2kWH's consumed over a period of one hour.

Realtime wattage however, isn't so easy. The easiest way would be with a power meter, with voltage probes and a current clamp. A true power meter, will show voltage, current, and phase angle, giving you a real time analysis of what's being drawn at any given moment, (kVA, kVAR, kW)

I wouldn't recommend fiddling with DIY circuits, unless you have a true "hard core" reason to do so. Current capacities, even on a small home's feeder, can make quite the fireball. You can rent power meters online if it's an absolute must.

Answer 3

Well, that is whaat your electrical meter that the city uses to figure out your bill does. It tells how many killowatt-hours (KWH) you have used each month. A KWH is 1000W being used for 1 hour. For example, if you had 10 100W light bulbs burning for an hour, that would be one KWH.
But the meter wont tell you how many watts you're usuing at any given point in time. For that, I would just go around the house and count them all up. You could Google a website that tells how many watts all the different appliances use. Then just do the math with a calculator.

Answer 4

I just did this because my electric bill was so high. Not the wiring method, the math method.

I looked at the total KwH used for the month, and divided by the number of hours in that "month" (last cycle was 31 days). It turns out I use an average of 2Kw all the time.

(since finding that out, i've turned OFF the A/C, opened the windows, and don't use any portable fans. I also started turning on my computer only when I need it.)

Answer 5

In order to get a reading on what your house is using, you would need to measure the current flow in the wiring before it branches out from the breaker box. That area of the wiring is not easily accessible, and not particularly safe to do.

However, you could buy an induction (clamp-on loop) type ammeter that would read current without cutting through any high voltage insulation. Multiply the amps by voltage to get watts.

Some examples of this type of meter are at this link:

Answer 6

Don't do this yourself; hire a registered electrician to do it. Explain what you want and ask for an AC ammeter to be connected to the house supply. Watts=volts times amps. The meter will tell you the total number of amps being used in your house, so if you multiply the meter reading by 120, that will be the number of watts you're using. You can buy watt meters that give you a reading directly in watts. Ask an electrician about them.