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LED Power supply Amp variation

DerekCuenod

Jun 13, 2023
2
Joined
Jun 13, 2023
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Hi all.

I have a few strings of LED lights that I need to power from a 12v Battery to get a longer run time. They run off 2 x CR2032 3v batteries for a total of 6v when supplied from the factory.

I have built a small power supply using a 7805 voltage regulator. I get 4.8-5v when running from a 12v power supply. This is working perfectly for me but I have a small query.

The 7805 can only supply 1.5A so I wanted to check the amp draw of the LED strings.
Using the PSU (measured at 5v) my multimeter is giving me 0.7A.
When using batteries (measured at 5.8v) the same string only draws 0.1A.

Is there an explanation for this?
Have I missed something? This is a big difference.

Thanks in advance for your input.
 

Harald Kapp

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Nov 17, 2011
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Measure the voltage on the LED string when powered by the batteries. I'm confident you will find that it is much less than 5 V.

The CR2032 battery has a comparatively high inner resistance which means the output voltage drops proportionally to the current drawn.
The 7805 on the other hand can deliver a high current without a decrease in output voltage.
The LED string surely is also much brighter when powered from the 7805 than it is when powered by the batteries.

Next step: use another regulator to decrease the voltage from teh PSU-regulator circuit to the same voltage when using batteries.
 

DerekCuenod

Jun 13, 2023
2
Joined
Jun 13, 2023
Messages
2
Measure the voltage on the LED string when powered by the batteries. I'm confident you will find that it is much less than 5 V.

The CR2032 battery has a comparatively high inner resistance which means the output voltage drops proportionally to the current drawn.
The 7805 on the other hand can deliver a high current without a decrease in output voltage.
The LED string surely is also much brighter when powered from the 7805 than it is when powered by the batteries.

Next step: use another regulator to decrease the voltage from teh PSU-regulator circuit to the same voltage when using batteries.
Thanks Harald
I will do so. Much appreciated.
 
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