Go Down

Topic: Battery life... (Read 1 time) previous topic - next topic

fubbi


Hi

I have 4 transistors pwm'ing 5 LEDs each, so all in all 20 LED. I want to run it off a rechargeable 9V block and I am trying understand how long the battery will last.

Can I assume that 20 led at ? 20mA (mixed 2 types and have no specs) with 220? R is 400mA and how does that relate to the
200maH that the 9V block has? I am considering using several batteries in parallel but how many would get my through the day. Its an art installation and I could have the batteries swapped every morning.

The arduino needs some juice too, its a pro micro and I don't know its requirements. http://www.sparkfun.com/products/10998

Most thankful!

Fubbi

majenko

The 200mAh basically means that, if you draw 200mA then it will last 1 hour.

You need to know the total current draw.  I would suggest placing an ammeter in between the battery and the power input (in series in the positive line) and measure the actual current requirements.

Then you can calculate how long 1 battery should last.
Get 10% off all 4D Systems TFT screens this month: use discount code MAJENKO10

Grumpy_Mike

Quote
how does that relate to the 200maH that the 9V block has?

It says the absolute maximum time is half an hour, in practice it is likely to be half this.

Quote
I am considering using several batteries in parallel

Don't do it, you will get all sorts of problems with the batteries cross charging each other, even with non rechargeable ones.

Those small 9V blocks are very poor at current, you are best off using some AA NiMh rechargeable ones.

fubbi


I thought 20 LED would be easy to run for a day... What would you use? I really want to avoid using a power cable for aesthetic reasons

I am "in the field" and the little pocketmeter i brought can't measure A :(

thank you

majenko

If you're "in the field", then connect it via a cow.  The louder it moos, the more current you are drawing.

I would probably use a lithium based power source for that kind of life time.

It's hard to advise without knowing actual current draw.
Get 10% off all 4D Systems TFT screens this month: use discount code MAJENKO10

Go Up