Using either 9 volt or 12 volt plug in adaptor

Hi All.    I have a choice of adaptors, either 9 volt DC  or 19 volt DC , as these are obosolete from a radio or WHY I thought either of them could be used to power a "separate DC LED circuit on my layout". So I set off for my local Maplin electrical store, where I asked about a suitable socket, all I got were blank faces and gobbledygook .Now I am turning to the forum for help, Straight forward ? Any advice please.  Kevin

Kevin, the adaptors - they plug into the mains power & have a plug on the end?
 cut the plug off and terminate the wires onto a  terminal strip -
http://www.maplin.co.uk/p/30a-terminal-strip-12-way-3-pack-n66eg


use the 9v unit for LEDs with say 500 ohm resistors
http://www.instructables.com/id/LEDs-for-Beginners/

I assume you're talking about "wall warts"  those usually black blocks that have a 13 amp plug and a wire coming out ending in a connector. just cut the connector off, strip back the ends of the wire and use one of those screw terminal blocks sometimes known as "chocolate block"

http://www.originlive.com/magento/media/catalog/product/cache/3/image/800x600/9df78eab33525d08d6e5fb8d27136e95/u/k/uk_1.jpg
wall wart

http://au.rs-online.com/largeimages/R4649744-01.jpg
terminal strip

You will need to either connect a number of LEDs in series, or add a resistor in series with LEDs, as 9V would probably blow a single LED connected directly

EDIT - oops great minds think alike!

Hi Ron.  Thank you for your reply, the LED' s four in total must be wired "Positive" first in a circuit? otherwise they will suffer damage ? I'm not brill on LED wiring and I was worried about the differentiating positive from negative. That is why I thought a socket would be better/easier for me.     all the best. Kevin

Hi Mike.  Thank you for your reply. I had never heard that term before, but yes that is what I mean. If the wires were colour coded? That would be straightforward , but they are both "White" and as I don't know how to separate positive from negative  Of course I don't want to cut off the plug not knowing which is which. The LED's are yard lights, four in total and they are bright but I can live that(modern or not), but the circuit must be Positive First otherwise I will damage them.    all the best  Kevin

Kevin, led lights only work with dc pos,you will not damage them if the wrong way they just will not light,whiich wiil solve your prob of not knowing the wireing,ie if no light then you have the + on the neg side
, but do not forget the resisters
:thumbs ;-) :cool:

Hi Owen.    Thank you for your reply. The reason for my mention of positive and negative, I was going on the the words of the supplier (C R Signals?) He said that they should be wired that way.  all the best.  Kevin

Hi Kevin

If the resistors are the right size, then it doesn't matter if they are wired back to front.  If it's a DC supply, then the worst thing that can happen is that the LEDs won't light.  Then just swap the leads over.

If it's an AC supply (like your DCC track power), then the polarity isn't an issue.

Hi Kevin,

Test the output from the transformer to make sure you know your anode from your cathode (and the actual voltage). The anode on a regular LED is the longer wire. Cathode is the shorter one on the flat side. It doesn't matter which side the resistor goes. It's worth while getting a selection of resistors to determine what light intensity you want.

If you use the 19v transformer something near 1000 ohm might be more appropriate.

What color(s) are you going for?

Nigel

Hi Max, Ron and Nigel.   Thank you all for your replies. It is rare for me to answer in multiple?  But here goes.I have been doing some serous thinking:oops: to save the worry. "Pro Tem, I am going to wire a 9 volt battery into the circuit . If it works? all well and good, if not then it doesn't matter too much as it isn't going anywhere, as it is only for me.  Thank you for your answers, I will check out the links.  all the best. Kevin

Hi Kevin,

Nothing wrong with a battery if you only have a few LEDs. 4 LEDs in series and you won't need a resistor (4 x forward voltage will be about 9v). Pop a reed switch into the circuit and you won't need to keep disconnecting the battery.

Nigel 

Nigel, I had read that a LED requires a resistor in 99% of the time & the value depends on supply voltage, LED volts and current.
See the link
http://www.hobby-hour.com/electronics/ledcalc.php 

Hi Nigel Thank you for your reply. I have just read the instructions for the lamps (info@crsignals.com)"The lamps are fitted with resistors to allow connection to a 12v DC supply. Connect the lead with the red sleeving to the positive of the 12v DC supply and connect the lead with the black sleeving to the negative of the 12v DC supply"
Which does sound simplistic? to say the least. Reading that, sounds like the lamps can be wired in parallel?
But I believe that the lamps with a 12v supply may be very bright.   all the best. Kevin

Hi Ron.   Thank you, I have just read that the lamps are already fitted with resistors, "info@crsignals.com"all the best Kevin

[user=1801]Passed Driver[/user] wrote:

. Reading that, sounds like the lamps can be wired in parallel?   YES
But I believe that the lamps with a 12v supply may be very bright.   Try them and see but I doubt it as the resistor reduces voltage so the LED get only 2-3v

Hi Ron,[user=606]Sol[/user] wrote:

Nigel, I had read that a LED requires a resistor in 99% of the time & the value depends on supply voltage, LED volts and current.
See the link
http://www.hobby-hour.com/electronics/ledcalc.php 

Hi Ron,

Yes….but only if there is an initial surge. Works best with the circular Li batteries (inherent internal resistance), or good (brand-name) AA's (especially the Li-polymer ones coming onto the market). Depends on the LED color as that is what governs voltage drop and current requirements. White ones need a lot more than red or green. If in doubt use a limiting resistor of around 220 ohm with a battery.

Kevin, it looks like you have a RTR solution. If each lamp has it's own resistor then you should have no problems in running them in parallel as every one will get 9-12V. The only issue is that for example 20 with a current draw of 20 mAmp each will require at a minimum a 400 mA supply. I can see why you would want to drop to 9V if they are too bright.It's easier to use a resistor with more ohms to change the light intensity.

A 9v battery has a capacity of around 500 mAh at best, a yellow platform lamp will draw around 20 mA, 5 lamps will last 5 hours or less (probably 3 hours). If you go the battery route it's worthwhile using rechargeable ones (if only for the environment). Best bet is still a small transformer (9V, 0.6 Amp would be OK and leave some spare capacity and will cost around £7.00).

Nigel

Nigel

Hi Nigel.   Thank you for your reply, but, your understanding of the complexities of "amps and ohms" is much better than mine. Which takes me back to the start of this thread, but now that I have read the instructions about"Each lamp has a resistor fitted" and " wire red to positive " etc. I still don't know (with both wires being the same colour) if I cut off the plug which would be positive and which would be negative. Whereas if Maplin could supply me with the correct socket it would be straightforward . I do have terminal blocks/strips to spare, but, it still takes me back to "positive and negative" .   all the best. Kevin

Just because you get a socket, won't mean it will be labelled, I assume you know to use multimeter,  how the meter reads using a battery that way by comparing it to the wall plug output will tell you positive vs negative.
Now if you don't know how to use a multimeter ( an essential tool in this hobby ) http://www.ehow.com/how_8516583_use-multimeter-beginner.html

plus Using a multimeter

Hi Ron.   Thank you for your reply. Yes, funny you should say that , I do own a multi meter, but, I don't know how to use it. I should really understand it. And will investigate it.  All the best. Kevin