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Author Topic: Can I run a 4.5 volt LED headlamp on 5 volts?  (Read 428 times)

N1AUP

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Can I run a 4.5 volt LED headlamp on 5 volts?
« on: October 09, 2021, 02:47:17 AM »

I have a headlamp that runs on (3), AAA batteries.  I use it when doing barn chores at night.

The AAA batteries don't last very long, so I was thinking of attaching a 4.5 volt, rechargable pack that is larger than the 1 amp hour AAA cells that it currently uses.

I thought that using a rechargable USB pack might be an easy way to do this, but USB is 5 volts.

Can my LED light handle 5 volts instead of 4.5, or is that going to eventually destroy the circuit?  If the latter, what is the simplest way to drop the voltage?  A resistor?  What wattage?  Use P=I*E?  I'm guessing I can use ohms law, while measuring the current draw of the light to figure out the required resistance as well.

Thanks
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K1MMI

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Re: Can I run a 4.5 volt LED headlamp on 5 volts?
« Reply #1 on: October 09, 2021, 03:34:32 AM »

A rectifier diode like a 1N4001 thru 1N4007 drops the voltage by .6 volts.
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W1RKW

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Re: Can I run a 4.5 volt LED headlamp on 5 volts?
« Reply #2 on: October 09, 2021, 04:23:04 AM »

Use Eneloop rechargeable batteries. 
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N1AUP

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Re: Can I run a 4.5 volt LED headlamp on 5 volts?
« Reply #3 on: October 10, 2021, 02:28:55 AM »

A rectifier diode like a 1N4001 thru 1N4007 drops the voltage by .6 volts.

You're right.  Forgot about that.  The perfect solution.
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N1AUP

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Re: Can I run a 4.5 volt LED headlamp on 5 volts?
« Reply #4 on: October 10, 2021, 02:29:54 AM »

Use Eneloop rechargeable batteries.

I'd like to use something with more capacity.  The AAAs start running down after a few hours, and light gets dim.
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N7EKU

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Re: Can I run a 4.5 volt LED headlamp on 5 volts?
« Reply #5 on: October 10, 2021, 04:00:05 AM »

Hi,

I'm pretty sure that these lights already use an internal voltage converter to reduce the voltage to a precise lower value. It would be fine to run on a 5V pack as is. Anyway, the three cells probably make close to 5V when brand new.

73
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Mark -- N7EKU/VE3

W9IQ

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Re: Can I run a 4.5 volt LED headlamp on 5 volts?
« Reply #6 on: October 10, 2021, 06:03:27 AM »

Always keep in mind that the simple (bare) LED is biased with current, not voltage. The resulting voltage drop is merely a byproduct of the current passing through the diode.

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

N7EKU

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Re: Can I run a 4.5 volt LED headlamp on 5 volts?
« Reply #7 on: October 10, 2021, 07:02:09 AM »

Right,

It's more likely current limiting used in these lights.  As such, a bit more supply voltage would still be OK as long as the regulator can dissipate the bit extra heat OK.

More coffee :-p
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Mark -- N7EKU/VE3
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