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billtee

Resistors needed for Just Plug lights?

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I have bought some very nice O gauge ‘wooden pole street lights’ (JP5646) for my goods yard. I do NOT want all the other parts of the Just Plug lighting system, as I am quite able to solder resistors (if necessary) into a simple 12volt supply. However, I am a little confused/puzzled as to whether I need to add a resistor to the feed for each lamp.

Can anyone offer some advice about this, please? I don’t want to burn out the LED in each lamp, so I could just put a 1K resistor in the positive (red?) lead and apply some 12v, but I’d rather  know beforehand rather than ‘oops, too late!

Thank you, everyone,

billtee

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One resistor per LED is safest, otherwise you can't test anything until everything is wired up.

12 volt supplies for model railways are rare, computer 12 volt supplies give 12 volts but model railway ones are typically rated at 12 VA and give 12 volts when the load is 1 amp, and up to and even over 21 volts on minimal load.

The power units supplied for model railways are such a pain in the neck when used with LEDs that I use computer power supplies instead. Not forgetting to use a circuit breaker or fuse in circuit to protect the wires.  I use 1/2 amp polyfuses these days.

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If I was in your position, I'd obtain a selection of resistors and LEDs, and start testing them from the highest value resistor downwards, until the brightness of the lamp is just as you want it. It then doesn't matter what type of power supply you use.

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Thank you, lads! I agree about model railway power supplies - it is difficult to purchase a 12v supply unless you pay a lot of money for it, something I am reluctsnt to do to just power a lot of lights! 

billtee

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2 hours ago, billtee said:

Thank you, lads! I agree about model railway power supplies - it is difficult to purchase a 12v supply unless you pay a lot of money for it, something I am reluctsnt to do to just power a lot of lights! 

billtee

Agree.   I have used Laptop Computer and mobile phone  power supplies for LEDs simply because I have scrapped the item and have (a box full) of power units.    Wall warts are my preference because they can't get buried under junk so easily  and overheat.    I set up low voltage "Bus Bars" and add resistors as required,  Yellow / Orange / Green seem pretty much the same resistor wise needing 2.2 volts (ish)  Reds need more resistance as they light at around 1.8 volts and in my experience, Clears less as they need around 4 volts to light at all so you need a 5 volt supply for clears but can get away with 3 volt for the coloured ones.

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I always put a 1KΩ with each of the LED lights. 

 

However Just plug are designed to be plugged into a Just Plug base unit without necessity for any resistors plus there are controls to adjust the lighting.

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Bought some 1K resistors  (1000ohms) and temporarily attached two in series to the red lead coming from the LED. Applied 12v from a ‘wall wart’ power supply and hey presto, LED lit up. When I tried reversing the power supply leads, LED didn’t work, but this was what I was expecting (LEDs are polarity sensitive!). Then I tried just one 1K resistor, and everything OK. LED is brighter, but not much, so obviously a 1K resistor is sufficient for each LED!

Sorted!!!

billtee

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Do the resistors have to be on the positive side of the circuit?

I have a black/white wire set up in a building but I can't see whether it's an LED or not, or if it has a resistor so gonna put one in anyway.

 

White wire = positive.

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Resistors can go in the positive or negative but it's best to keep to a standard.  I always try to fit them in the positive feed as that is my preference.

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