I've been designing an interactive lighting system for my girlfriend.
A little bit a back story about this project --
My girlfriend is a master's student in the arts and she will be having a showcase of her artwork at a venue and it will be a week long. I told her that I could build her an interactive lighting system for her art pieces.
The design is such --
it uses a sonic range finder with an Arduino Uno. I use a powerful LED light with housing on a PWM pin, it goes from 15% lighting (ambient lighting) to 100% lit once someone is within range of the range finder, in this case, 3-4 feet. Once the Arduino and range finder know that the subject is in rage, it does this slow transition to 100% brightness and slowly illuminates the art piece until the subject leaves and then transitions back down to 15%.
I'm currently using a 9v battery on this project but I realized that after some tests, it only gave me about 10 hours of use and then just died.
So here's the problem --
I need a battery system for the arduino that's not TOO hefty that can make it last for a week. I know, this sounds extreme, but I'd like to see if anyone has any suggestions other than "plugging it in" to a source, that's my last-ditch effort if the battery option will not work.
Thanks folks! I'll post pictures of it once its up in the venue and maybe even a youtube video, it's pretty neat in a simplistic way.
You have not said how much power your "powerful LED light" draws and what portion of the time the light will be at 100% vs 15%. Do you have a multimeter you can connect in series with the battery to measure current draw?
A 9V battery going through a 5V linear regulator will throw away almost 50% of the power. You might want to use a lower voltage battery (3.8 to 5V) and power the equipment directly with that.
johnwasser:
You have not said how much power your "powerful LED light" draws and what portion of the time the light will be at 100% vs 15%. Do you have a multimeter you can connect in series with the battery to measure current draw?
A 9V battery going through a 5V linear regulator will throw away almost 50% of the power. You might want to use a lower voltage battery (3.8 to 5V) and power the equipment directly with that.
Oh, my apologies! It's a 3w, 800mA LED light.
As for 15%/100% time, it should be about:
15% brightness - 80% of the day
100% brightness - 20% of the day
Since people will be approaching the art pieces for only minutes at a time and then leave.
In regards to the 9v battery, how do you think a latern battery would fare? since they're about 6v anyway, right?
Yes, LiPo for instance. With an efficent step down module, you will not have much loss in converting down the voltage. See eBay for tons of step down voltage converters.
Tobbera:
Yes, LiPo for instance. With an efficent step down module, you will not have much loss in converting down the voltage. See eBay for tons of step down voltage converters.
What would be the point of the step down voltage converters if I get a LiPo battery that's 5v or 6v? They do make them in those voltages last I remember. Unless you're talking about the big LiPo batteries, like the 12-19v ones?
I just picked up a Alkaline 6v lantern battery from Radio Shack (R.I.P Radioshack...)
Running a test since 1:00PM PST we'll see how long that lasts, any estimations as to how long it may last? Remember, this unit is constantly on and a 9v battery lasted 10 hours.
Single cell LiPo batteries have a terminal voltage of nominally 3.7 V, but it is as high as 4.2 V when freshly charged and drops to below 3.0 when discharged. If you let the battery voltage drop much below 3.0 V, it will be permanently damaged. Two cell LiPos have twice those voltages, so you need a voltage regulator to have a constant voltage.
There are "boost/buck" regulators that give 5V regardless of the battery voltage (within limits), and one of these could directly power the Arduino and LED through the 5V terminal. See for example Pololu - Step-Up/Step-Down Voltage Regulators
A 9V alkaline battery has about 500 mAh capacity at 50 mA so we can guerss that your circuit was drawing an average of about 50 mA for the ten hours the battery lasted. To supply 50 mA for 30 days you'd need 36,000 mAh of battery capacity.
A 6V alkaline lantern battery has about 13,000 mAh of capacity so to get 30 days of life you'd need three in parallel.
36 Ah would be a pretty good sized lead acid battery, larger than most motorcycle batteries.
Lead acid is actually the battery of choice for long term use, due to low price, durability, ease of charging and overall capacity.
Tobbera:
Yes, LiPo for instance. With an efficent step down module, you will not have much loss in converting down the voltage. See eBay for tons of step down voltage converters.
What would be the point of the step down voltage converters if I get a LiPo battery that's 5v or 6v? They do make them in those voltages last I remember. Unless you're talking about the big LiPo batteries, like the 12-19v ones?
Yes, I was thinking about the bigger ones. If you buy one of a common size and voltage, it might have a resell value when your project is over.
johnwasser:
A 9V alkaline battery has about 500 mAh capacity at 50 mA so we can guerss that your circuit was drawing an average of about 50 mA for the ten hours the battery lasted. To supply 50 mA for 30 days you'd need 36,000 mAh of battery capacity.
A 6V alkaline lantern battery has about 13,000 mAh of capacity so to get 30 days of life you'd need three in parallel.
Thanks John! That was very informative.
Right now I have been running the unit for about 36 hours roughly on the 6v lantern battery. I just need it to run for a week, so 7 days.
if my unit is drawing 50mA
then that would be 50mA * (24 hours * 7 days) = 8,400 mAh
which looks like it's well below the rated 13,000mAh of the 6v alkaline lantern battery, so this test should be very successful! If that' the case, I'll be getting lantern batteries instead of LiPo, simply due to cost.