Buck converters

If they are the ones I'm thinking about, press down semi hard while turning the screw. counter clockwise. must have DC input.

Will give that a try, I didn't want to break anything, if you know what I mean, I was already being sorta firm with it, cause was thinking the same thing...

Marty

Those adjustment potentiometers have something like a 25 or 30 turn range where 1 turn changes the output by about 1 Volt.  Usually for a step down converter you turn it CW to increase output, CCW to decrease output. 

If the output had been set to maximum (say, 30V DC), and you you only feed it 15V then you might need to turn the screw over a dozen times CCW to set the voltage to something below 15V...since a step down can only lower the voltage even if you tell it you want more.  If you ask for more than it can deliver, it will just put out whatever it can which is your input Voltage less a Volt or so.

Here's an example. Does take some turning just going down 10v.

You need a load at the output. Try something you don't care to much about. Like a light bulb.

I Can't play the video, and I do have a led connected on the output side...

Marty

Note that this adjustment pots do not have a "hard" mechanical stop at the CW or CCW end-points.  That is, you reach the end of the range and you can continue turning with no effect on the adjustment.  There is a clever slip/clutch inside that allows this behavior without breaking anything.  If you listen really carefully you can usually hear a (very) faint "click" on each turn when you attempt to turn beyond either end-point.  This is the slip mechanism in action.

Note that I have a number of these modules that actually adjust CCW for increasing voltage.  It's certainly not universal that they use CW for increased voltage and CCW for decreased voltage.

Well I do hear the CLICKING noise,  I have turned it many times clock wise, only thing left is to go the other way....

Marty

Keep trying - I use these guys for LED lighting in O and Standard gauge cars. I add a bridge at the input end (AC to DC) and another capacitor at each end to keep down the flickering, as some cars only have a single roller pickup. Work very nicely. One caveat - at first I bought the really cheap ones and they fried. Use the LM 2596 versions. (shown in photos and in the video. They seem to be able to handle any AC noise passing through as well as 2 feet of LED lighting on 1 inch centers on the larger cars. Also, check out the 16 foot long strips of LED's available through your favorite Chinese ebay merchant. Different colors (warm/cool, etc), giving different effects. You can cut these every 3 inches (3 LED's have their own resistor on the LED tape..

Just confirming - I use the same parts as in the tutorial, but the bridge rectifier he used was way overkill. I bought a bag of 50 bridges (I think 35V and 3 amp) for a couple of bucks, enough for forever. Makes the overall volume of the circuit smaller too.

Yup, have to agree, that is one big rectifier...Must be over6amp probably closer to 8amps...

Marty

Here's the bridge rectifiers I used. No failures yet after a lot of running with 25AC in standard gauge cars, over 2 feet of LED strip per car.

4kAAOSwxH1T-zjG" target="_blank">http://www.ebay.com/itm/50pcs-...a:g4kAAOSwxH1T-zjG

I would certainly hope a 2A bridge wouldn't fail!  The 5 meter strips (that's 16 feet) will consume less than 2 amps at 12 volts.  Of course, if you're driving those LED's with 25 volts, you're pushing them to at least twice their ratings, and they'll soon fail anyway!

With 18" of LED strip in passenger cars, I use from 25 to 30 milliamps for a car.  Here's one in pretty bright florescent lighting, the interior is certainly bright enough for me.

Well, went back to the drawing board and tried the only thing I hadn't done.  The sellers instructions were wrong, can you believe it???   Turned the screw counter clock wise, and EUREKA, it worked, with 18volts going in, I was able to get it below the 10 volts in the article,  in fact with the LED's it is pretty hard to notice the voltage drop,  but very obvious with a regular bulb...  Thought that I would bring you guys up to date, now on ward to step two, do a install...

Marty

 Congrats!   

Martin Derouin posted:

Well, went back to the drawing board and tried the only thing I hadn't done.  The sellers instructions were wrong, can you believe it???   Turned the screw counter clock wise, and EUREKA, it worked, with 18volts going in, I was able to get it below the 10 volts in the article,  in fact with the LED's it is pretty hard to notice the voltage drop,  but very obvious with a regular bulb...  Thought that I would bring you guys up to date, now on ward to step two, do a install..

I guess you didn't believe me two days ago or you would have saved yourself some time.

gunrunnerjohn posted:

Note that I have a number of these modules that actually adjust CCW for increasing voltage.  It's certainly not universal that they use CW for increased voltage and CCW for decreased voltage.

See second post.

Excellent point Chuck!   I missed that as well.

Thanks everyone for your support in this.   Due to health reasons unable to get to work bench as often as I like to.  John it isn't that I didn't believe you, but the seller gave me bad info.....

Marty

Marty, it's eBay and they're translating from Chinese.  No telling if they know what CW or CCW means!