# 3 vdc from 12 vdc? Possible?



## Rod Fearnley (Jan 2, 2008)

I have recently bought some street lights for my outside RR. The power supply for ancillary items out there is 12 vdc. The street lights are rated at 3 vdc. What do I need to put between the 12 v and the lights to achieve the correct voltage?
Thanks in advance.


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## dbodnar (Jan 2, 2008)

Rod - that is a fairly simple conversion with a switch mode DC-DC converter - have a look at this article on my web page:
http://www.trainelectronics.com/artcles/DC-DC_Converter/SwitchMode.htm
I use these little devices for many, many projects - best price I have found is here:
http://www.banggood.com/LM2596-DC-D...wer-Supply-Module-With-Display-p-1005123.html
Less than $4 each and fairly fast shipping
You can also use a voltage regulator but they dissipate excess power as heat and can get REALLY hot! The DC-DC converters stay quite cool and have an LED resadout to boot!

dave


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## toddalin (Jan 4, 2008)

Great idea Dave.

I was going to use a regulator for my voltage reduction during the motor delay for the sound system enhancement, but at $3.14 each for three, with more versality and a readout, these are too good to pass up and I'll surely find uses for the other two. For $9.32, I have three on the way.

Thanks


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## dbodnar (Jan 2, 2008)

I think you will like them, Todd - I use several on my HO module - they pull 19 volts DC off of the auxiliary bus and supply 12, 10 and 5 volts to various accessories and gizmos on the module. Even going from 19 volts to 5 at the better part of 1 amp produces almost no heat.
dave


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## armorsmith (Jun 1, 2008)

Rod,

Another option, depending on the arrangement of the lamps, is to run 4 in series. 3Volts time 4 bulbs equals 12 volts. This will only work if the lamps are good ole fashion incandescent bulbs. And this has a zero cost factor.

Bob C.


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## Beddhist (Dec 17, 2013)

... and the bulbs have to be the same wattage.


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## JPCaputo (Jul 26, 2009)

It will also work with LEDs as well. Get as close as you can to the supply voltage in series, and add a resistor to limit the current to 15-20 mA.


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## Dan Pierce (Jan 2, 2008)

MAny of the dollar store lights can run from AA batteries and will work on 3.4 volts (2 alkaline batteries that are fresh) and down to 2.4 volts (low level of 2 rechargable batteries in series).
So, a 12 volt source may let you run 5 of the led units in series if they are all identical.


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## Rod Fearnley (Jan 2, 2008)

Thanks Dave. I checked out the website that you gave me. It immediately transferred to £ Sterling. With free postage. £2.31
I have just ordered a couple.


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## dbodnar (Jan 2, 2008)

Excellent! Keep us posted on your progress - hopefully this will take care of your power settings.

Note that the little button on the board toggles between showing the input voltage and the output voltage - I would test the output voltage with a volt meter just to be careful!

dave


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## Paul Burch (Jan 2, 2008)

Dave,
I didn't see in the description anything about the physical size.


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## dbodnar (Jan 2, 2008)

Paul Burch said:


> Dave,
> I didn't see in the description anything about the physical size.


Paul - the boards are about 2.5" x 1.5" x 0.5

FYI, the grid paper that I use for most of my photos has 1cm squares on it.

If you need something smaller for a lower current application this unit is very small http://www.banggood.com/10Pcs-Mini-...ly-Buck-Module-Step-Down-Module-p-999753.html

Note that the price is for 10, not for just one!

dave


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## toddalin (Jan 4, 2008)

And they ship fast. Mine got ordered yesterday and shipped today (Mon).


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## CliffyJ (Apr 29, 2009)

Thanks Dave, I just ordered a couple to play with. 
(And thanks Jerry B. for alerting me to this).


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## Rod Fearnley (Jan 2, 2008)

Mine just arrived, 15 days from Hong Kong to the UK.
Start experimenting tomorrow.


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## toddalin (Jan 4, 2008)

Mine came yesterday. Linda thought they looked quite substantial for $<3.50 each.

I haven't tried them yet, but lets hope the quality is better than the price would indicate for a Chinese piece.


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## dbodnar (Jan 2, 2008)

toddalin said:


> Mine came yesterday. Linda thought they looked quite substantial for $<3.50 each.
> 
> I haven't tried them yet, but lets hope the quality is better than the price would indicate for a Chinese piece.


Todd - the only issue I had with some of mine was that the LED display was fairly dim - I compensated for that by placing a small piece of translucent red acrylic over the display - brought the display right out of the mud!

dave


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## MikeMcL (Apr 25, 2013)

I found a pack of 6 LED streetlamps in Lowe's Christmas section for about $6.60. In my garden RR I run lights off an old Malibu landscape transformer at 12VAC. The streetlights, as purchased, run in parallel off two AA batteries, I put the streetlights in a series based on the LED wizard found here, www.led.linear1.org/led.wiz Just use 3.3 forward voltage at 20ma and add your starting voltage (12), and the number of LEDs in your array and it will give you a schematic with resistor value.


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## Greg Elmassian (Jan 3, 2008)

That's a great scene Mike! I had to look a couple of times to make sure it was not real!

Greg


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## Naptowneng (Jun 14, 2010)

Great idea Mike. Looks good

Jerry


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## MikeMcL (Apr 25, 2013)

Greg Elmassian said:


> That's a great scene Mike! I had to look a couple of times to make sure it was not real!
> 
> Greg





Naptowneng said:


> Great idea Mike. Looks good
> 
> Jerry


Thanks guys! Still a work in progress. Just got the trolley (streetcar) line running last week!


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## Greg Elmassian (Jan 3, 2008)

I went to your facebook page, some great photos, and I must also compliment you on your exposure control for the night shots.

Thanks, Greg


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## MikeMcL (Apr 25, 2013)

Greg Elmassian said:


> I went to your facebook page, some great photos, and I must also compliment you on your exposure control for the night shots.
> 
> Thanks, Greg


Whatever exposure control you speak of is purely accidental, LOL! Other than using a small tripod and keeping the perspective low, it is an automatic snapshot without flash (but utilizing the timer function to keep steady) from my Samsung galaxy note 3 phone. I do have an advantage (if you want to call it an advantage) of a nearby 1:1 scale streetlight for fill lighting!

But thank you for taking the time to check out my page, send me a friend request if you do FB.


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