Help with 12V COB LED power source

PROBLEM:
24 SMD COB LED has too much drop off in illumination over 3 hours.

PREFERRED SOLUTION:
To get my (24 SMD) 12V COB LED to last 2 or more hours with adequate illumination. Currently running off of 4-3 volt button batteries.

I’m working on a little project at home for a custom show car I built. I’m trying to get my interior lights to work independently with a small power source.
I have a few COB LED’s placed inside the car and can not run wiring without destroying my interior.
I thought I designed a perfect fix using four 3volt button batteries ran in series. The small batteries allow me to hide the power source without running more permanent wiring. It only needs to last a couple hours for the final judging.
Currently, they are lasting much longer then needed but the drop off is very dramatic. From over 100 LUX when first switched on, to 30 LUX after 10 minutes, 17 after 20 minutes, 15 after 30 minutes, then it starts to stabilize and remain around 13 LUX with very little drop off.
These lights do not need to be over 30 LUX. They are only decorative lights but the drop off can’t be so drastic that a judge can notice the difference over a 20 minute period.
QUESTION:
What are my options to get a more stable output with much less drop off in ilumination?

I would like to thank anyone in advance for any advice or possible solutions.

Hi,

The brighness drop is quite expectable.
It's also expectable that the COB LEDs are distroyed by fully charged batteries.

The problem is that all LEDs should be current driven and not voltage driven.
LEDs are not meant to be connected directly to a battery..

Battery voltage varies a lot when fully charged down to low charge. Voltage even varies with age and temperature. You need to consider this voltage variation.

When using a series resistor it will start at lower brightness but be more constant over time.
There is no simple solution around this.

All this is the reason why there are dedicated LED driver circuits. Do a search. You will find may ready to buy circuits, you will find many vendors selling thousands of different L.ED driver ICs. All come with datasheets to tell how to use them.

Klaus

Simple current limiting via NPN transistor. Although this is the same as resistive drop, it has an advantage (compared to plain resistor) because current drop is less drastic.



Battery voltage holds up better over a 3 hour timespan since you draw less current from the get-go.

On the other forum the problem is with the capacity of the tiny "button" batteries. They are SEVERELY overloaded since each special LED display draws 170mA from 12V.

My font has changed since the recent update here but I cannot change it back to normal.
EDIT: My font looks bad only when I am typing.
EDIT: Hey, I get an alert and extra points for each edit. What can I buy with all these points??