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Discussion Starter · #1 ·
Hi,

Does anyone know whee I can get a 12vdc power supply in a case with the screw terminal connectors on the the outside for connecting the wires too.

I am looking for something similar to those produced by Gaugemaster but with a more amps. About 12vdc 5 amps would be OK.

It's to run all the lighting on my layout via a distribution board.

Thanks

Simba
 

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Just another modeller
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*** If you are in UK then Maplin have a suitable transformer

Richard
 

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Discussion Starter · #4 ·
Hi, Richard,

I am in the UK. I have had a look on the Maplin site and can only see a 12v AC transformer. I need DC. Can you post the link to the one you have seen.

Many thnaks

Simba
 

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Just another modeller
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***Its all in the description - Once built into a case etc it ceases to be a "transformer" and becomes a power supply (PSU)

5A 13.8V DC PSU Code: XM22Y £21.99 - showing as In Stock

regards

Richard
 

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Discussion Starter · #6 ·
Richard,

Thanks found it. For the extra cash I think I will go for the 7amp version.

I am no electrician so what is 13.8V going to do to my 12V LED's?

Regards

Simba
 

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Paul Hamilton aka "Lancashire Fusilier"
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Simba,

Dunno about 12V LEDs, most are closer to 1.5v and require appropriate resistors to be safely used often around the 1000 or 1k ohms mark as a minimum. Please check to avoid dissapointment.

As to the resistance value required based on say 20 milli amps draw for the LED at say 1.5 volts across the LED then using Ohm's Law the resistor required would be calculated as R = (13.8 - 1.5) / 0.02

Therefore R = 615 ohms. This usually results in a light that is far to bright for most applications and therefore experimenting with the higher resistor values is often sensible.

I found that a small variable resistor in the form of what is known as a trimpot with a range of up to 10,000 ohms (10k) gives a good range of brightness that when you achieve the desired result by turning the trimpot you can then read the resistance across the terminals with a mutlimeter and there you have your resistance value to enable you to purchase the correct nearest resistor.
 

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Just another modeller
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9,983 Posts
**** If using "bare" LED then just use a 1k resistor - the difference in brightness between 650 and 2k ohms is nothing, and 1k is universally safe at model railway voltages.

Most un-ballasted (bare) red/green/yellow LED are closer to 5~10mA and 1.5v, although green is slightly higher - about 2v - most Whites are 15~20mA and 3.2 volts. If you use these as guides you will be fine.

if you have "12V" LEDs they will have a resistor built in. I cannot know WHAT they used value wise so can only suggest that you try one. It will probably be fine - when we make them, we always use a "safe"value for 12~18 volts.

Richard
 
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