Trying to install "Landscape" lights in the flowerbed. Failing to read carefully, I bought a Timer/Transformer with 12v AC output, and LED fixtures that want 12v DC.
So, since upon inspection the Timer unit had empty space behind the connector panel, I says, let's put a 4-diode rectifier in there and have our DC.
Said & done. But where I expected 12v DC (minus diode loss), I get a 23.8v AC indicated -- until I reverse the meter leads, then I get zippo!
Can't imagine the lights will really like that. See pix.
What gives??

 

Trying to install "Landscape" lights in the flowerbed. Failing to read carefully, I bought a Timer/Transformer with 12v AC output, and LED fixtures that want 12v DC.
So, since upon inspection the Timer unit had empty space behind the connector panel, I says, let's put a 4-diode rectifier in there and have our DC.
Said & done. But where I expected 12v DC (minus diode loss), I get a 23.8v AC indicated -- until I reverse the meter leads, then I get zippo!
Can't imagine the lights will really like that.View attachment 290946View attachment 290947View attachment 290948View attachment 290949View attachment 290946View attachment 290948View attachment 290949 See pix.
What gives??

(Sorry about duplicating the pix. Operator error.)

 

To get DC from a 4-diode bridge rectifier you need a capacitor sized to limit the droop between peaks of the rectified waveform. This is what you get with no capacitor:

You will notice that the frequency is twice the input frequency of 60 Hz.

This is what you get when you add the capacitor.

See the difference?

 

I think your meter is giving bad readings because it is low quality. No insult intended. If you measured it with a better meter there would be less confusion.

12VAC rectified should be about 17V. Then there should be about 1.2V drop across your rectifier, finally ~15.8V.

 

12-VAC, has a peak-Voltage of ~16.8-Volts.

After Full-Wave-Rectification, ( minus 0.7V + minus 0.7V = minus 1.4V ),
and routing the Output into a Bulk-Storage-Capacitor,
You will have around ....... 16.8V minus 1.4V = ~15.4-Volts, with no Load.

This Voltage will drop to some degree when a Load is applied.

Adding a "Low-Dropout-Voltage" Voltage-Regulator,
after the Capacitor, is the best solution.
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What gives?

Connect one of the LED lamps and measure again.

 

12VAC rectified should be about 17V.

The average DC value of the full-wave rectified, unfiltered output is 0.637/0.707 * 12V = 10.81V.
The RMS value is 12V (both values ignoring diode drops).

If the LED lights can tolerate the ripple, just power them directly from the bridge rectifier without any filtering.
If the ≈1.4V drop from the bridge rectifiers is too high, try Schottky rectifiers, which should reduce the total drop to <1V.

 

and LED fixtures that want 12v DC.

Are you sure they are 12 volt DC only? Post a link or part #.
Most 12 volt LED landscape lights work on both AC and DC.