Is my math right? LED and electricity usage.

[inthemix8080]

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)

 

[hyroot]

(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.

 

[BigEasy1]

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

 

[puffenuff]

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.

 

[inthemix8080]

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.

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.

 

[Green Thumb MN]

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.

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.

 

[Moldy]

(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.

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

 

[bigbillyrocka]

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...

 

[bigbillyrocka]

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...

 

[Mechmike]

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.

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.

 

[lax123]

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

 

[Mechmike]

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

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.

 

[SupraSPL]

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!

 

[SupraSPL]

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).

 

[Mechmike]

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).

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.