Power Supply

Vengenc

Hey all,

Noob question maybe but... how do you decide your best options for supplying power to your project. Specifically.. Say I had an LED array that drew 300mA and planned to run it off of battery power.

How do you know what type of batteries to use and how many of each type would give you the best battery life vs portability?

Sorry if this doesn't make sense.. but I·am a newbie still. [noparse]:)[/noparse]

Thanks.

·

Mike Green

You need to decide the maximum amount of current you will need, the average amount, and the amount of time you want your circuit to run. The battery capacity you will need is in ampere-hours (or milliampere-hours). Say you wanted to run your 300ma LED array for 8 hours and you wanted to use rechargable batteries. Say that the other circuitry you need really needs very little current for itself ... most of the drain is from the LEDs. That's 2400 mAH. Most rechargable batteries will deliver their capacity at around the 10 hour rate (divide the capacity by 10 hours to get the average current). If they have to deliver much more current (say 2A for 1 hour), their capacity will be less. Similarly, batteries self-discharge over time and will lose their charge over a period of weeks.

I would stick to NiMH rechargables or Alkaline non-rechargables. You can now get AA NiMH batteries with capacities on the order of 2.5AH. They're easy to charge and easy to use. You can use an external charger that'll recharge them in 1-4 hours or you can use a simple constant current (1/10 capacity or less) charger circuit in your device. Search the web for sample circuits.

Vengenc

Thanks Mike,

That's pretty much exactly what I needed to know.