Is my math right? LED and electricity usage.

I just calculated what my leds cost per month and it seems really low ( i know leds are efficient but didnt think they were this efficient)

So I have a 135W blackstar led. For arguments sake because of the fans and everything on it lets say it draws 150w. Also presume i am doing 24/0 and 12/12. Also by the website for my electric company kWh is .05847. Also presume 31 day months. I am trying to overestimate things to produce an above average estimation.

(150w*12/1000)(31)(.05847) = $3.26/month (on 12/12 light)

(150w*24/1000)(31)(.05847) = $6.52/month (on 24/0 light)

(watts x hours x days) / 1000 x kwh

so you pretty much got it right. This order gets the same answer..

5 cents per kwh is awesome. I was paying 19 cents. Since I moved paying 13 cents. It will go up after summer is over.

It's like .35 cents an hour here that's why I have a LED.

This led doesnt really pull 135w though. It has (45) 3w leds in it but they arent driven to full 3w's. You'd need to hook it up to a killawatt meter to know for sure, but it probably is only around 90w.

puffenuff said:

This led doesnt really pull 135w though. It has (45) 3w leds in it but they arent driven to full 3w's. You'd need to hook it up to a killawatt meter to know for sure, but it probably is only around 90w.

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oh, im not sure if thats depressing or not considering i get a good amount of growth from it. im starting a new grow soon and i'm hoping its enough for just one plant. but if not i'll probably supplement it with cfls since i have a ton left from my cfl days.

5 cents is what im showing from the energy co's site for my city. i have to double check the bill to get an exact amount.

inthemix8080 said:

oh, im not sure if thats depressing or not considering i get a good amount of growth from it. im starting a new grow soon and i'm hoping its enough for just one plant. but if not i'll probably supplement it with cfls since i have a ton left from my cfl days.

5 cents is what im showing from the energy co's site for my city. i have to double check the bill to get an exact amount.

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Yes, for 3w LEDs the actual electric draw is ~1.8. so 45x1.8=81 watts. I have a "240 watt" light and with internal fans pulls less than 150. My local electric is 10.9 cents per kw.

hyroot said:

(watts x hours x days) / 1000 x kwh

so you pretty much got it right. This order gets the same answer..

5 cents per kwh is awesome. I was paying 19 cents. Since I moved paying 13 cents. It will go up after summer is over.

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Yeah, mine is 0.09465 per KWH. Pretty cheap juice there!

Idk much about led but I do know my electric is more expensive than even in california yet where I'm at is considered the energy capital of the usa. Makes no sense. I grow with my 150 hps to start then add in my 400 (removing the 150) and my bill has shot up $80 a month extra. That's twice what it was in idaho. Lame!
I too have been looking for led as a substitue...

Idk much about led but I do know my electric is more expensive than even in california yet where I'm at is considered the energy capital of the usa. Makes no sense. I grow with my 150 hps to start then add in my 400 (removing the 150) and my bill has shot up $80 a month extra. That's twice what it was in idaho. Lame!
I too have been looking for led as a substitue...

Green Thumb MN said:

Yes, for 3w LEDs the actual electric draw is ~1.8. so 45x1.8=81 watts. I have a "240 watt" light and with internal fans pulls less than 150. My local electric is 10.9 cents per kw.

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That's a pretty good ballpark figure! I build my own panels and had to learn the math to be successful.

The equation is: volts x amps = watts used. Most commercially made Chinese grow lights that use 3w diodes run them at 550ma and the common average forward voltage of the leds is about 3v. ~3v x .55a = ~1.65w Anything more is consumed by cooling fans and driver inefficiencies.

One can get more efficient leds and drivers and large heat sinks to eliminate fans and DIY a panel to eek out more light for less dollars but all of that stuff is pretty costly. The really good Cree and Luxeon ES diodes are about 3-4 times the price of the Chinese Epistars and the most efficient drivers are 2-3 times as much. I plan to run my DIY lights until the wheels fall off so the steep upfront cost works out for me.

~3v x .55a = ~1.65v Volts x Amps = Volts

lax123 said:

~3v x .55a = ~1.65v Volts x Amps = Volts

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Ooops! My typo. I shouldn't medicate before posting! It should have read ~3v x .55a = ~1.65W
Original post is now edited.
Thanks for the heads up.

The 5 cents/KWH is probably jut the delivery charge. There is 5-10cents more for the supply charge and there is a monthly fee of 15-20 just to get service so total cost is probably 12-15cents/kwh

The driver is (hopefully) at least 70-80% efficient so input wattage is probably ~100w. You can do a lot with that on the veg side but only in a micro grow would it be much use in flowering. Good luck!

According to this thread to late 2011 the 240w blackstar had an input power of only 133w. Maybe just a fluke? I replaced my kill-a-watt with an ensupra because it is much more precise (cheap on eBay).

SupraSPL said:

According to this thread to late 2011 the 240w blackstar had an input power of only 133w. Maybe just a fluke? I replaced my kill-a-watt with an ensupra because it is much more precise (cheap on eBay).

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That's about right. The Blackstar 240 has 80 diodes. Assuming an average of 3v use per diode that's 240v. If they drive the leds a .55a it would work out to 132 watts.
240v x .55a = 132 watts.

They may be driving the diodes at .5a which would be 120w for the diodes and the rest for fans and driver loss. Most drivers operate at ~85% efficiency. Some of the more expensive ones go over 90% but it's unlikely that Blackstar uses expensive drivers.