Calculating amperage and wattage? Answered
So I'm doing an energy inventory on our house to see how much electricity we use, and maybe see if we could cut down on some costs.
Being Christmas right now, we have a long multi-string chain of lights going across our living room. I'd say it's about 50 feet long. They are just regular incandescent lights. typical normal size, no LEDs or flashers or anything. When you plug them in, they come on, and that's all they do. I wanted to figure out their wattage, so I started with finding the amperage. My multimeter isn't very good when it comes to measuring amps, so I decided to use a roundabout method by finding the resistance of the circuit. The resistance came out to be 13.3 ohms. Plug that into ohm's law and you get around 9 amps of current and therefor, about 1080 watts of electricity. That sounded right to me...after all, it is a long string of lights, and even though they don't individually suck up a lot, I figured it adds up.
I tried this same method with a single bulb that I knew to be around 300 watts. The resistance came out to be about 4.5 ohms giving a whopping 26.7 amps with a wattage of around 3200 watts! That can't be right. I want to know what I'm doing wrong. I'm pretty sure it can't be my multimeter because I just bought it brand new about a month ago. What am I doing wrong?