24VAC LED flood with 12VAC driver works on 12VDC—how?

Question

I bought some cheap RGB flood lights from aliexpress.com. They were supposed to be DC24V (I intend to run them off a solar/battery setup) but I ended up with AC24V instead. What clued me in was the brown/blue connecting wires, when I was expecting red/black for DC.

Opening the thing up though, I find this:

An AC12V LED driver! And, curiouser and curiouser, when I hooked it up to a DC12V power supply it lit! I could only get red light and the IR remote control didn't work, but the magic smoke didn't leak out.

What is going on?

• Why does something sold as an AC24V device contain an AC12V driver?
• Why did applying a DC voltage to an AC device not blow it up?
• Why could I only get red out of the LED and not any other colours, and why did the IR/control circuitry seem to not work?

Answer 1

What is going on?

 Why does something sold as an AC24V device contain an AC12V driver?
 Why did applying a DC voltage to an AC device not blow it up?

 Why could I only get red out of the LED and not any other colours,
 and why did the  IR/control circuitry seem to not work?

If it doesn't use a transformer for lowering the supply voltage there's a very good chance is does work from DC. Most wall-warts will run from a DC input because (like your LED panel) they have a bridge rectifier that converts ac into dc. Bridge rectifiers pass ac or dc exactly the same - they are just steering diodes that always push the most positive input voltage to the +Vout and the most negative input voltage to -Vout

It did not blow up (or not-work or get too warm or short the supply out) because it doesn't use an input voltage transformer (as per the answer in the paragraph above).

When you powered it from 12V dc I suspect that there isn't enough voltage to allow all the circuits to work correctly. AC 24V will produce a peak voltage of about 34V and this will likely feed through a bridge rectifier to give about 32Vdc - a lot higher than 12V dc you fed in and this I suspect is the main reason.

Ditto for AC 12V - it has a peak voltage of 17V and after a couple of diode drops in the bridge will settle at 15.6VDC - if you had a bench supply and fed it with 17Vdc I'd bet it would work.

Answer 2

That "driver" is just a bridge rectifier and a voltage regulator. LEDs are DC bulbs. They don't work with AC. A bridge rectifier is just 4 diodes that force alternating current into a direct current pattern. If you apply DC to a rectified circuit intending to feed DC lights, it will work just fine. In fact, if you determine the total load of the actual bulbs and size the input correctly, you can probably toss the driver in the trash and directly connect.