#122262 - HyperHacker - Sun Mar 18, 2007 5:38 am
Just wondering if anyone can recommend a method to power three strings of LED Christmas lights (each rated at 120V, 60hz, 0.04A, 4W) for about 5 hours, using a very small, lightweight power source (think something that fits in a large pocket)? They won't be on steady, so 5 hours is a theoretical maximum. I was thinking several 9-volt batteries connected together? I doubt AC/DC matters with simple LED lights.
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#122283 - keldon - Sun Mar 18, 2007 10:15 am
LED = Light Emitting Diode, so it has to be DC. Battery life is measured in Watts/hour. Energizer, then Duracell, not sure who is next. If it is AC then you will need to create a bridge to convert it to AC (just google for the circuit diagrams).
#122389 - HyperHacker - Mon Mar 19, 2007 3:54 am
Hm, actually 120 x 0.04 = 4.8. Would I just multiply that by 3 for 3 strings? So I need enough batteries to pull 14.4W/hour for ~5 hours. Since they'll be blinking on and off at varying intervals I might get away with as little as 2.5 hours.
Duracell's website may be the most useless website ever. It is completely devoid of information. Energizer's has nothing regarding the specifications of the batteries, only some general battery usage tips.
I really don't know enough about electricity to figure this out on my own. The batteries would need to total 120V and be able to supply 0.12A for 2.5 hours? Looking at Wikipedia's battery article, a typical 9-volt battery is rated for 625 mAh... 120/9 = 13.333... so I'd need 14 of them to reach 120V, and that would add up to 8.75 Ah. At 0.12A they'd last for 72 hours? No way that can be right... :-S
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#122399 - tepples - Mon Mar 19, 2007 4:31 am
| HyperHacker wrote: |
| HI really don't know enough about electricity to figure this out on my own. The batteries would need to total 120V and be able to supply 0.12A for 2.5 hours? Looking at Wikipedia's battery article, a typical 9-volt battery is rated for 625 mAh... 120/9 = 13.333... so I'd need 14 of them to reach 120V, and that would add up to 8.75 Ah. |
When you put batteries in series to increase their voltage, the current does not increase, and neither does the total charge (1 ampere hour = 3600 coulombs). Batteries in parallel have a higher charge. If you want to increase both the voltage and the charge by a factor of 14, you'll need to use 196 batteries.
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#122410 - HyperHacker - Mon Mar 19, 2007 4:48 am
Ouch. Well I certainly don't need them to last for 72 hours. I could also give each string its own, separate battery pack if that would make a difference.
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