# COMMUNITY FORUM

sailor86

04:28AM | 04/24/09
Member Since: 04/08/08
I'm trying to do some math and figure out what various devices around the house are costing us. Our rate is 9.7 c/kwh. I rounded it up to .10/kwh. So a 60 watt bulb costs roughly .006 to light for an hour. If I dim that bulb to 50%, does that translate to 50% the cost? Also I'm not sure how to figure the A/C. I looked and it's rated for 31.9 amps minimum and a 50 amp max. Naturally the voltage is between 197v and 250v. How do I go about figuring that out?

TimBonham

01:26PM | 04/24/09
Member Since: 01/09/07
Dimming depends on the efficiency of the dimmer used. None are completely efficient, so dimming it to 50% will probably still use roughly 75% of the 60 watts. And human perception of light brightness is not linear -- a light at 50% electrical power will seem to human eyes to be about only 25% brightness.

But the power consumption of a single light bulb is pretty meaningless anyway. It's really minor compared to things like refrigerators, stoves, clothes dryers, etc. Even all the lights in your house burning 24 hours a day would be less electricity than your refrigerator.

You can certainly save money & power by replacing incandescent bulbs (that are used more than an hour or two) with CFL or LED ones, but it's not going to be a really major change in your electricity use. Nationwide, it would make a huge difference for the utility companies (and the planet) if everybody did this. but individual savings are pretty minor.

For something like air conditioning, all you can do is make some estimates. Assume 40A on average x 240V = 9600W = approximately \$1/hour to run your air conditioner.

But they usually run for only 1/2 to 3/4 of the time. That depends on the temperature of the day outside and what temp you have set your thermostat at inside. Your local power company may have figures available on how many cooling hours an air conditioner ran in your location for the last year, which might help to get a more accurate estimate.

There are devices available which let you plug in an appliance, let it run for a day or so, and record the actual electricity used. That would give you some real data for your usage. But I don't think these would work for hard-wired things like air conditioners, only smaller window plug-in units.

sailor86

04:52PM | 04/24/09
Member Since: 04/08/08
Very interesting stuff. I'm almost OCD about turning out lights. Here's a combo scenario: Putting the PC on standby for an hour or so versus shutting it down completely. And who carries the gizmo that records power consumed?

TimBonham

07:44PM | 04/24/09
Member Since: 01/09/07
Lots of people carry them.

Search Google for brand names Kill-A-Watt or Watts-Up and you will find local suppliers.

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