Justin Klein
New Member
Hey all,
I'm working on a small DIY project, and am a bit confused about the current draw I'm measuring from a roll of SMD5050 LEDs. The full roll (150LEDs, 16ft/5m) is supposed to be 21watt/12V (as stated by the seller, and from other references I've found online). As I understand it, this means it should draw 21W/12V=~1.75A. However, when I hook it up to a 12V battery pack (8xAAs) I'm only measuring ~500mA (it's on full brightness, white color aka all 3 RGB LEDs active). What could explain this large discrepancy?
The reason it matters is I plan to run them off of batteries, & am trying to calculate a reasonable balance of length vs runtime vs battery size vs cost (ultimately I'll use li-ion). All the resources I've found (i.e. https://www.reddit.com/r/DIY/comments/3abnek/trying_to_fix_my_electrofur_running_led_strips) say that I should estimate runtime as above: i.e. 21watts/12v=1.75A, so running this amount of LEDs off of a 2000mah battery pack (aka 8 AA's) should last for a bit over 1 hour. But the fact that I'm only measuring 500mA means it would run considerably longer. So then...if I need it to run for, say, 8 hours, does that mean I'd actually need a 1.75A*8=14000mah li-ion battery (as per calculations)? Or a 500mA*8=4000mah (as per measurements)? Or if I get a 8000mah battery, could I just double up the length of the strip?
Something tells me I'm missing something fundamental here, I just want to make sure that before I commit to a LED-length & battery size, I'm actually getting the numbers right...
I'm working on a small DIY project, and am a bit confused about the current draw I'm measuring from a roll of SMD5050 LEDs. The full roll (150LEDs, 16ft/5m) is supposed to be 21watt/12V (as stated by the seller, and from other references I've found online). As I understand it, this means it should draw 21W/12V=~1.75A. However, when I hook it up to a 12V battery pack (8xAAs) I'm only measuring ~500mA (it's on full brightness, white color aka all 3 RGB LEDs active). What could explain this large discrepancy?
The reason it matters is I plan to run them off of batteries, & am trying to calculate a reasonable balance of length vs runtime vs battery size vs cost (ultimately I'll use li-ion). All the resources I've found (i.e. https://www.reddit.com/r/DIY/comments/3abnek/trying_to_fix_my_electrofur_running_led_strips) say that I should estimate runtime as above: i.e. 21watts/12v=1.75A, so running this amount of LEDs off of a 2000mah battery pack (aka 8 AA's) should last for a bit over 1 hour. But the fact that I'm only measuring 500mA means it would run considerably longer. So then...if I need it to run for, say, 8 hours, does that mean I'd actually need a 1.75A*8=14000mah li-ion battery (as per calculations)? Or a 500mA*8=4000mah (as per measurements)? Or if I get a 8000mah battery, could I just double up the length of the strip?
Something tells me I'm missing something fundamental here, I just want to make sure that before I commit to a LED-length & battery size, I'm actually getting the numbers right...
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