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Discussion Starter #1 (Edited)
I'm trying to wire a dimmer to two 12-volt LED reading lights.

I'm using this dimmer: https://www.amazon.com/Volt-Dimmer-LED-Halogen-Incandescent/dp/B01C4UBMY6/ref=cm_cr_arp_d_product_top?ie=UTF8

I'm using two 12-volt LED reading lights from Scandvik.

When I make the connections, there is a distinct hum coming from my lifeline 6v batteries when the dimmer is turned low. Voltage tested at 12.9.

Any idea what causes this? When the dimmer is all the way up, the noise goes away. When dimmed, it comes back. It's faint, and I have good hearing, but it definitely is there when I am close to the batteries.

No other electronics hooked up.
 

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You sure it's the batteries humming? I've seen complaints about dimmers humming. Also, I've read some LEDs are not truly dimable.
 

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I second the led’s might not be dimmable. That dimmer for $30 is pretty expensive vs the one RR & I got from China for under $2 that work great (you do need to use the remote that comes with them however).
 

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The dimmer is probably using pulse-width modulation (chopping up the DC supply voltage into pulses), because it's more efficient to do it that way as opposed to a simple resistor ... but an inherent side effect of using a DC PWM chopper is that it introduces an AC noise component at whatever the PWM frequency is (and harmonic multiples of it).

LEDs generally don't like having their supply voltage played with. They conduct (and emit light) when above a certain threshold voltage, and they don't conduct at all (and emit no light at all) if the supply is under the voltage threshold. This will kinda-sorta work with PWM (and the associated electrical noise!) but will not work with a resistor or equivalent voltage-divider if it is supplying below the threshold.
 

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