# Electricity consumption

Discussion in 'Grow Room Design/Setup' started by spaga, Aug 10, 2011.

1. Hey gc, can't find a consistent answer to this anywhere. Although I find it fairly intuitive, I've heard many different answers.

If I'm running a 120 w centrifuge fan (400cfm) with a fan speed controller (120 v with max 15 amp) at around 50% speed, how many watts is that for the day assuming it's running at the same speed 24/7.

Is it simply half the watts of the fan since it's running at half speed?

Does it still use all 120 w while only running slower?

Or is it somewhere in between assuming the fan router uses some watts?

The same question goes for 600w light with a digital light timer. If in 12/12, does the light only use the 600w every hour it is on, and it and the timer use 0w when it's off?

Thanks for help with these novice questions!

2. everyone can sit around and make guesses...

P3 - Kill A Watt

this is the only real way for you to know without a shadow of a doubt how much power each and every thing you have plugged in is using and at what time

found at home depot for less than 30

3. Thanks, that will be helpful to monitor, but I'm looking for some estimates so I have a good idea how many kwh I'll be using a month. I'd rather have a general estimate than before see a massive spike on my monitor

4. unless you plan on pushing massive lighting your fine...

1k watts and all the trimmings is about 60 dollars a month, more or less

5. Ok, sorry if this gets a bit long but I will try to keep my explanation as short as possible. If you are using a speed control and running the fan at 50% you will use 50% of the power that you would at full speed. Power companies meter your power by Kilowatt hours. In simpiliest terms that means that a 1000w device, ran continuesly for one hour will consume 1 kilowatt hours worth of power. Where I live a Kilowatt hour will cost you 7 cents. Your power bill should tell you what they charge in your area per kilowatt hour. Are you certain its a 120Watt fan and not a 120VOLT fan? You can figure the wattage of any device by using the formula P = I x E (Power, or watts they are the same thing, is equal to voltage times current) All devices will have a placard that will tell you their amperage draw and voltage. Assuming you do have a 120WATT fan, at 50% speed it will be drawing 60w. 60 x 24(hours in a day) = 1440 watts in a 24 hour period. That is equal to 1.44 kilowatts or about 10 cents per day to run a 60 watt fan 24/7. Hope this answers your question.

6. And to answer the second half of your question simply...yes the light only consumes power when it is on. The timer will consume a very small amount of power to run it's internal clock but it is miniscual. Again 600w is equal to .6 kilowatts. So .6 x 12 = 7.2 kilowatt hours or about 50 cents for that 12 hour period. so around \$15 a month. Switch that light on 24/7 and it will cost you around \$30 a month.

7. ^Agree with abrooks both posts above, with a few additional comments:

The fan through a speed controller set to 50% will use somewhere around 50% of the wattage of operating at full speed. Hard to say it literally would be exactly 50% because of the variables involved: how accurately is the speed controller in determining the "percentage" being allowed through, the speed controller can get warm which means it's absorbing the consumption of a bit of electricty so is that from the 50% or in addition to it, etc -- but I agree that whatever the effect of things like this, they are miniscule, so in calculating monthly cost yeah just think of it as 50%, close enough.

Abrooks, you said watts = voltage x current. Actually it's voltage x amps, current is voltage. I think you meant amps by "current", you clearly know this stuff.

8. #9
Last edited by a moderator: Aug 11, 2011
current is not voltage bro. P = I x E Its Ohms law. Power is wattage. I is amperage which is a measure of current. And E is voltage. Amperage and current are two terms for the same thing. Just like power and wattage.

9. And yes you are absolutley correct when you say that there are always losses and that my 50% is an approximation. Heat will cause some losses but I really didn't feel like getting into an explanation of copper loss and efficiency.

10. thanks all, very helpful. my power should then be in pretty good shape. i'm not so much concerned with the cost of the bill, but the relative increase in the bill. even if i only add \$50/month, i want to make sure that's not going to double or triple my bill for tip-off purposes. i only have 1 600w light, 2x 120w fans with dimmers, and a few miscellaneous things. i think that should be just fine. i also bought a kill-a-watt device to get more exact measurements for estimates as someone recommended.

11. I stand corrected on the terminology. Wonder why when you are going to travel to another country and you buy an adapter for your electric appliances that the "currency converter" lets you step between voltages, not between amperages.

I think we are both saying the same thing about what watts are and how they are measured, watts = volts x amps.

12. Beats the hell out of me. But yes wattage is determined by voltage and amperage (or current)