How To Convert 12vac To 12vdc

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Thought this was simple but struggling to wrap my head around it. Trying to figure out how to connect a string of 12 VDC LED lights to my 12 VAC outdoor landscape light circuit...

I got a decorative string of LED lights that made to use plug into the wall (110V). The lights include a plugin transformer that outputs 12 VDC 1A. There is also a mention of 7.2 W on the box (though not sure if that is the max load of the transformer or the actual load of the lights.)

The LED lights also include a mode controller (with IR receiver) that can be plugged between the transformer and the lights. The controller is operated via an IR remote to dim or blink the lights. Controller label shows input at 12 VDC, output at 6A (max). It also mentions "connecting mode: common anode (+)".

So...

What do I need to get the 12 VDC LED lights connected to my 12 VAC landscape circuit? I would like to keep using the controller too (to control brightness level.)

From all the Googling I've done, I am inclined to think all I need to a "bridge rectifier" and on Amazon I found "DB101 Single Phase Full Wave Diode Bridge Rectifier 600V 1A 12 Pcs" for $5.65 with free shipping.

Is that it? Any other advice?

Last edited: Mar 13, 2015

Harvey

Administrator<br>Elite Member

From your post, I'll assume you don't have any experience actually building a rectifier - filter circuit, and buying the parts, AND a chassis, AND a piece of perf board, AND the cable and connectors you want will probably cost you more than just buying the 12 volt 6 amp supply you need for the LED controller.

For example, I found this one on Ebay for $7.99.

I have no idea about the quality of this particular unit, but searching Google for power supply 12 volt 6 amp will give you more leads.

I'm an electrical engineer, and for eight bucks, I'd rather buy it than build it, unless I needed right now, and it was after hours on a weekend, and I happened to have all the parts lying around my shop area.

Hope that helps. :cool:

Harvey,

Thanks for helping me out. You are right that I have no experience on this topic. Note though that my landscape circuit is already providing me 12V, just that it is AC. The LED lights *may* need DC, since they came with a 110V-to-12VDC transformer.

So wouldn't I just need to somehow convert my existing 12 VAC to 12 VDC?

I intend to have these lights outdoor and I have easy access to my 12 VAC circuit there. Not sure what I need to do in order to plug these lights directly (without the transformer they came with) into my landscape light 12 VAC circuit.

Harvey

Administrator<br>Elite Member

Harvey,
Thanks for helping me out. You are right that I have no experience on this topic. Note though that my landscape circuit is already providing me 12V, just that it is AC. The LED lights *may* need DC, since they came with a 110V-to-12VDC transformer.

So wouldn't I just need to somehow convert my existing 12 VAC to 12 VDC?

No for a couple of reasons:

1. Your 12 VAC transformer supplies a max of only 1 A (ampere) of current. Your LED setup requires 6 amps, five more than your transformer can deliver.

2. The LED system may require a regulated voltage. If so, you'd need some overhead (>15 VAC) for various losses to allow a linear (the simplest) regulator chips to work. You could make/build a switching supply that can provide an output greater than the input voltage, but it would be more complicated and far more expensive to build a single hobby project, and it's still not as simple as buying the right part for eight bucks.

I must be missing something... Not sure why you say my 12 VAC transformer supplies a max of 1A. The transformer specs I provided before were for the transformer that came with the string lights. I will not be using that transformer. I mentioned those specs just to be able to infer what the LED lights may need.

I just looked at my landscape light transformer and it shows that it takes in 120V/5.1A and puts out 12V/600VA on a dual circuit (two separate circuits, each allowing a load of up to 300W).

From search on Amazon I wonder if these are the components I need:

- DB101 Single Phase Full Wave Diode Bridge Rectifier 600V 1A
- 25V 1000UF 105C Radial Electrolytic Capacitor 10x20mm

What do you think?

Oddly enough - I'm trying to do the exact same thing. The obstacle is the power packs that are reasonable in price - aren't rated for outdoor use. Also, if I use a separate 12vdc supply, it involves running yet another wire 'over the river and through the woods'. I know ...sounds lazy...

(Running the wire is easy. Hiding the wire is the chore.

In the meantime, I have this humongous 12vac/300watt outdoor landscape lighting power pack that appears to be languishing with 250 spare watts....so surely I could slap a fullwave bridge rectifier, and a cap or two into a sealed box of sort - even with some rude and crude point-to-point wiring/soldering.

My 'want' has to do with outdoor use - and - the directional aspect of LED's. I live out in the sticks and really do try to limit/avoid lighting up the sky.

A 5 meter reel of waterproof 3528 LED's is rated at 4.8W/meter. Even if I hook up a couple reels in parallel - it would/should still be less than 50 watts @12vdc.

And I look at that landscape transformer and wonder "there's gotta be a way!" ...or have I missed something completely? ( i hate getting stuck between genius and idiot! lol)

Last edited: Mar 14, 2015

If I use a separate 12vdc supply, it involves running yet another wire 'over the river and through the woods'.
In the meantime, I have this humongous 12vac/300watt outdoor landscape lighting power pack that appears to be languishing with 250 spare watts....so surely I could slap a fullwave bridge rectifier, and a cap or two into a sealed box of sort - even with some rude and crude point-to-point wiring/soldering.

And I look at that landscape transformer and wonder "there's gotta be a way!" ...or have I missed something completely?

Mark,

Bigger pain than I imagined... surprised the LED strings don't just come ready to go for 12V AC. I assume LED just needs DC and that MR16 LEDs I see on the market have embedded the circuitry to provide them DC internally :confused: ... and that would be too expensive to provide with the string lights? :'(

I have some threads on Amazon, trying to get advice on specific products. The most complete thread (see comments on first answer) is at: http://www.amazon.com/connect-decorative-operating-landscape-circuit/forum/FxQVN0H8XYO549/Tx1YHKEYXML2GTT/1/

I'll try it out and see what I get... If you find a better solution or have some practical feedback on results for whatever you end up using, please post.

My landscape light transformer is by my outdoor BBQ "island" so I could put a 110VAC-to-12VDC transformer inside the enclosed island cabinet under the grill, inline but before the transformer+light switch. Two of the LED strings I plan to use (inside gazing globes) would be around there so I could run separate wires to them. But for other locations, like in front of the house, it just will not be practical to run a whole new set of wires...

I find it hard to believe there is no off-the-shelf AC-to-DC converter meant for 12V circuits, that can be used outdoor for landscape lighting applications!! o_O

I find it hard to believe there is no off-the-shelf AC-to-DC converter meant for 12V circuits, that can be used outdoor for landscape lighting applications!!

So far, I have spent numerous hours googling keywords and phrases. I've scoured aliexpress and ebay hoping to find a OTS solution. And so far...nothing. Not even a 'here's how I did it'.

What i don't know for sure is if the problem is the landscape power packs. Most of the larger ones are 'switching' (vs linear). And, if I understand correctly, switchers don't develop their full output without a proper load. So i am guessing a simple bridge rectifier circuit just doesn't cut it.

Last edited: Mar 14, 2015

Can you link us to the exact LEDs you bought?

Their power requirements might be too much for a 1-amp bridge.

And if you're going to be buying parts, go to Digikey. Amazon's going to cost a lot. $6 for a single 1A bridge rectifier? 50 cents at Digikey, and then do first-class mail for $3-4. You'll also have a better chance of avoiding counterfeit parts than from random sellers at Amazon or eBay - Digikey is an authorized reseller for a lot of major manufacturers.

Last edited: Mar 19, 2015

Ken g6

Programming Moderator, Elite Member

: Dec 11, 1999

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In my youth I used to play with electronic kits from Radio Shack. As I recall, when I rectified AC to DC, the DC voltage was different from the AC voltage. I can't remember if it was lower or higher. Either way you should probably get some voltage converter, either on the AC side or the DC side.

In my youth I used to play with electronic kits from Radio Shack. As I recall, when I rectified AC to DC, the DC voltage was different from the AC voltage. I can't remember if it was lower or higher. Either way you should probably get some voltage converter, either on the AC side or the DC side.

It depends on what else was on the circuit.

Yes, you'll drop some voltage across each diode crossed in the bridge. However, there's also RMS voltage to think about.
If you're talking just simple sine wave, 120VAC's peak is actually close to 170V. 12VAC's is nearly 17V.
So if you rectify 12VAC and stick a beefy capacitor across it, you'll read something above 12V. You'd see this on heavy wall-wart power supplies: Measure the voltage with no load, and you might see 17 or 18 volts. But once it's loaded with something, the voltage drops. Those things were just a transformer, some diodes, and maybe a capacitor, with no regulation. Newer supplies use a different circuit inside in order to make them more efficient, so that they can comply with various regulations. They usually have some degree of regulation on the output. (Some degree: Consumer product manufacturers try to shave out every fraction of a cent, and decent voltage regulation costs money.)

Looking at the datasheet for this Vishay bridge (sorry, Vishay fanboy), you will get....oh, let's say 0.78V drop per diode.
So on the output side, your peak voltage would be:
(1.4142 * 12) - (2 * 0.78) = 15.41V.

If you put a capacitor across that, it'll help filter out some of the ripple, but your average voltage will be higher than 12V.
Your LED strip is probably just a bunch of strings of LEDs with a resistor on each one. Feeding it unfiltered rectified power will make it flicker, though that depends on your eyes. My eyes seem to be weird - I can see an LED flickering if it's PWM'd at up to around 4kHz; by 5kHz it's finally not visible. Some people can't see flicker at 60Hz.

If you want to turn rectified AC into clean DC, you need a regulator.
Three basic types:
- Buck: Takes a high voltage and turns it into a lower one: Turn 15V into 12V.
- Boost: Takes a low voltage and turns it into a higher one: Turn 9V into 12V.
- Buck-boost: Can take a range of high or low voltages and turn it into a specific output. Could take 9V or 15V and turn it into 12V.

Cost depends on how much of a load you're trying to drive.

Last edited: Mar 19, 2015

Do you have 120VAC outdoors? Is there some reason you're forced to use the 12VAC landscape power?

According to the OP:

Two of the LED strings I plan to use (inside gazing globes) would be around there so I could run separate wires to them. But for other locations, like in front of the house, it just will not be practical to run a whole new set of wires...

oOk..I'm hoping I can cover all the bases.

Why 12vac to 12vdc instead of 120vac to 12vdc. - - - the converter module I am hoping for will be incorporated into a design for yard ornaments.
#1 Running a 120vac extension cord across a yard for days on end is pretty stupid. Very stupid.

#2 Most folks have landscape lights - so tapping their existing power makes practical sense. AND, in some cases, they have gobs of power going unused (i.e. they bought a 600 watt system and they have 3 - 10 watt halogens on it. #4 Most landscaping systems have photocells and/or timers.

#3 Most folks don't have 47 exterior outlets. Usually, they have a single duplex in the back area...and if they are lucky, one in the front.

Here's a link to the LED strips I have bought for the prototypes:
http://www.amazon.com/gp/product/B00QVAE1HQ/ref=oh_aui_detailpage_o07_s00?ie=UTF8&psc=1

I looked at a whole slew of power packs - from warts to bucks and back again. Virtually NONE are weather proof, unless you get a "special" LED driver IP65 (very expensive) and it's right back to running the extension cord.

And lastly, I'm just plain old tired of buying every danged thing from China. It lasts a few weeks...and you got nothing. Or - you get to wait 4-6 weeks for a slow boat to bring it over. Over it.

Last edited: Mar 23, 2015

A very simple way is to simply get a premade bridge rectifier or you can make your own with some diodes (make sure you get proper current rating but for what you're driving pretty much any should do). AC in, DC out. You will get a 120hz flicker unless you add a capacitor on the DC side but keep in mind this may increase the voltage as AC is always a bit more peak to peak than what you get with a meter. For example 120vac is actually about 170v on the high side.

On similar subject this is a little project I made for Christmas lights:

I wanted to keep this universal so I skipped the capacitor to avoid the voltage increase, as not all sets may like to be driven at that higher voltage or at constant rate (they might put some undersized LEDs in there knowing they will be running at a low duty cycle). Worked great for my tree, it was much brighter, and no crazy flicker.

For the kind of voltage and current you're dealing with, I would probably just free hand solder the diodes in proper configuration, shrink wrap, and call it a day. Keep in mind that the device I showed would not work if you were to plug a 12v AC adapter into it, just in case that's what you're thinking. in fact I'm not even sure what would happen to the adapter, it would probably actually fry it. So don't try that.

You can google bridge rectifier for diagrams of what it is. it's mostly self explanatory if you know that a diode only allows current to flow in one direction. It basically takes the negative wave and inverts it so it's positive so you get a full positive "sine" wave which is basicaly a bunch of bumps like this: /\/\/\/\/\/\ instead of this: /\_/\_/\_/\ (remember LEDs only work one way so the negative wave is not seen by them)

Hope this helps.

This unit would work fine.....indoors.

It would likely be alright outdoors too for quite some time if placed inside of a plastic bag. If he really wanted to waterproof it, cans of conformal coating spray are readily available from electronics suppliers.

Last edited: Mar 23, 2015

Oh well I guess I missed that. Still seems a whole lot easier to run a single extension cord to the location as opposed to rolling his own special power supply with components/enclosures etc. Unless of course he doesn't have any outdoor AC available.

Last edited: Mar 23, 2015

Running an extension cord (if they have an outdoor receptacle) is by far the easiest - and the most dangerous.

But! (there's always a but!) I ain't giving up.

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