GoFuckYourself.com - Adult Webmaster Forum - View Single Post - who here knows about batteries and electronics?

rowan · 03-07-2007, 06:37 PM

Oh yeah, with regards to you using a 9V battery... if you're supplying 40 LEDs then it's unlikely it will last long. 40 LEDs at 10 milliamps each is a total draw of 400 milliamps (0.4A), and if you want more light you could probably go up to 30mA each which is 1.2A. I did a quick search and found a 9V rechargeable battery rated at 400 milliamp hours (0.4 amp hours), which means - in theory - it can supply 400 milliamps for an hour, 200 milliamps for two hours, 100 milliamps for four hours etc. Your 9V battery would probably provide useable output for less than 10-15 minutes, assuming it was even able to discharge at a 1.2A rate.

That's why D cells are bigger than AA; they have the same voltage, but they will last longer and/or provide a higher current.

03-07-2007, 06:37 PM
rowan Too lazy to set a custom title Join Date: Mar 2002 Location: Australia Posts: 17,393	Oh yeah, with regards to you using a 9V battery... if you're supplying 40 LEDs then it's unlikely it will last long. 40 LEDs at 10 milliamps each is a total draw of 400 milliamps (0.4A), and if you want more light you could probably go up to 30mA each which is 1.2A. I did a quick search and found a 9V rechargeable battery rated at 400 milliamp hours (0.4 amp hours), which means - in theory - it can supply 400 milliamps for an hour, 200 milliamps for two hours, 100 milliamps for four hours etc. Your 9V battery would probably provide useable output for less than 10-15 minutes, assuming it was even able to discharge at a 1.2A rate. That's why D cells are bigger than AA; they have the same voltage, but they will last longer and/or provide a higher current.