How to manage battery life in small area

Thread Starter

Jlwoodfloors

Joined Apr 2, 2016
17
First I hope I'm in the right forum. I am running 2 3w leds with a 5v rf transmitter. Having problems fitting enough voltage and mah in a small area. I'm trying to fit all this in a 1inch square aluminum tube by 2inches long. Batteries are a big issue was wandering if there is anything I can do toto prolong batteries it seems the rf transmitter draws a lot of juice. Have tried li-poly batteries but die out to quick. Trying to get at least 6 hours of work out of the leds. With the 2 3.7 volt lipoly in series only getting 1hr 250 mah per battery . Also tried aaa rechargeable 1.2v with 800 mah per battery. Maximizes space leds last for about 4 to 5 hours but can only use rf in the first hour. Please help me it's driving me crazy.
 

Dodgydave

Joined Jun 22, 2012
8,589
Start by measuring the current drawn by the transmitter and leds, this will give you a start as to how long these batteries will last,
Only then can you select your battery, size and capacity.


Try looking at 2/3 aa nimhi 1800maH, or 18650 lion.
 

John P

Joined Oct 14, 2008
1,782
For the LEDs, it sounds as if you need 36 watt-hrs from a battery that occupies 2 cubic inches of volume, so 18 wh/in^3, and there are 61 cubic inches in a liter, so it would be 1098 wh/liter.

Supposedly the LiPo battery in an iPhone 6s has an energy density of 703 Wh/l, so you may be too ambitious there, but not by a huge amount. Are you running your LEDs with an inductor-based constant current regulator, or just a resistor? If it's just the resistor, you've wasting a lot of power.
 

Alec_t

Joined Sep 17, 2013
10,604
If you can pulse the Tx and/or LEDs with a low duty-cycle you can reduce the average power consumption dramatically.
Just curious; is this a recovery beacon you're building?
 

John P

Joined Oct 14, 2008
1,782
The LED brightness can be traded off for longer battery life, to any extent you want, but I assumed 2 3W LEDs meant 6W power consumption. Actually if it is a beacon being used for maximum visibility, a flashing light would probably work better than a steady light, and would use less power.
 

Thread Starter

Jlwoodfloors

Joined Apr 2, 2016
17
For the LEDs, it sounds as if you need 36 watt-hrs from a battery that occupies 2 cubic inches of volume, so 18 wh/in^3, and there are 61 cubic inches in a liter, so it would be 1098 wh/liter.

Supposedly the LiPo battery in an iPhone 6s has an energy density of 703 Wh/l, so you may be too ambitious there, but not by a huge amount. Are you running your LEDs with an inductor-based constant current regulator, or just a resistor? If it's just the resistor, you've wasting a lot of power.
No just a resistor can you tell me more about this current regulators
 

Thread Starter

Jlwoodfloors

Joined Apr 2, 2016
17
If you can pulse the Tx and/or LEDs with a low duty-cycle you can reduce the average power consumption dramatically.
Just curious; is this a recovery beacon you're building?
Not a beacon how would I pulse the TX and or LEDs with a low duty cycle please tell me more
 

Thread Starter

Jlwoodfloors

Joined Apr 2, 2016
17
Start by measuring the current drawn by the transmitter and leds, this will give you a start as to how long these batteries will last,
Only then can you select your battery, size and capacity.


Try looking at 2/3 aa nimhi 1800maH, or 18650 lion.
How do I measure draw of current I have a voltage meter.
 

bertus

Joined Apr 5, 2008
20,180
Hello,

Do you also have details on the leds to be used?
The 3 Watt leds I know of use a current of 700 mA.

Bertus
 

atferrari

Joined Jan 6, 2004
3,580
The 200 mA setting of the DMM could be not enough. Betjer to do a first test with the higher setting which is quite often, unfused. 10A maybe?
 

Alec_t

Joined Sep 17, 2013
10,604
how would I pulse the TX and or LEDs with a low duty cycle please tell me more
The pulse circuit could be based on the ubiquitous '555 IC, but the details would depend on how much current the LEDs and Tx need and the duration of acceptable 'on' and 'off' periods.
 
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