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12 volt transformer to power over 80 layout lights


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My OO Gauge layout now has over 80 led and grain bulb lights on it. They are all powered through a cheap 12v three pin adaptor. I have noticed that the lights have also

dimmed since I first started adding the lights and therefore assume that the adaptor is not 'fit for purpose'.  What sort of 12v power source do I need that is capable of

dealing with so many lights and where can I buy one from. Thanks Kevin.

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Depends on the rating of the lamps and exactly how they're connected. A quick google shows 12V GOW lamps with ratings between 60mA and 100mA

 

80 60mA lamps connected in parallel would draw approx 5A this means a 60VA transformer

80 100mA lamps connected in parallel would draw 8A this requres a 96VA transformer.

 

If you've been adding lamps over time you might also find the wire size in parts of the circuit is now too small, causing a voltage drop. 

 

Try Maplins

 

Jeremy

Edited by JeremyC
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A 96VA transformer could supply 8 amps, which can make things get pretty hot if there is a short circuit somewhere and either the cutout isn't up to scratch or the wiring resistance is enough to keep the current below the cutout limit but still quite high.  Might be better to keep your existing power supply but transfer some of the lamps to a new one of similar power rating. 

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Try to use LED rather than filament lamps  A typical LED with 1k resistor takes 12ma of current or 83 LEDs to 1 amp  Hobbys (www.hobby.uk.com) produce a nice LED bulb for dolls houses that have an LES screw in fitting part no K53509 and produces enough light to light buildings etc

 

Grain of wheat bulbs typically take 80ma or 9 lamps to 1 amp.  80 filament lamps requires 6.5 amps of current

 

If you are using LED and filament on same circuit, you will need DC voltage and hence equally large rectifiers.  You could run the filaments of AC but beware the voltage.  DC is typically 3/4 the voltage of the AC input, ie 16v AC transformer produces 12v DC when rectified.

 

Gaugemaster do a range of transformers and G Scale controllers that can provide this sort of power

 

 

Rgds

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Depends on the rating of the lamps and exactly how they're connected. A quick google shows 12V GOW lamps with ratings between 60mA and 100mA

 

80 60mA lamps connected in parallel would draw approx 5A this means a 60VA transformer

80 100mA lamps connected in parallel would draw 8A this requres a 96VA transformer.

 

If you've been adding lamps over time you might also find the wire size in parts of the circuit is now too small, causing a voltage drop. 

 

Try Maplins

 

Jeremy

Totally agree with Jeremy re wire size. At these curent consumptions we are talking about the size of cable found in a car. It is not only the current you need to consider but the volt drop. 80 lights sugests a big layout.  which would sugest running a thick buswire, 2sqm to groups of lights then connecting each with a dropper I would sugest ditching the 3 pin plug, what is its current rating? Are the pins burnt. You may also need to look at the wires directly connected to the transformer.Have you fitted thermal cutouts on the 12V side.

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Even if the load were 10A at 12V on the output side, the three pin plug is only passing 500mA on the mains side. No problem there.

 

A transformer can be used to power LEDs from AC so long as an extra diode, or another LED, is connected in "reverse parallel". If using two LEDs, they can share the same current limit resistor. You may need to adjust the resistor value compared to DC use due to each LED now only being powered 50% of the time and the higher peak voltage.

 

Depending on the voltage available and the type of LEDs, you can connect two or more in series to use even less current.

 

Andrew

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No one seems to have mentioned it, but why try to use a single power supply for all your lights (regardless of type)? A much better option is to power them from different power supplies.

 

For 2 reasons.

 

1/ Gives you  a backup, in that not all your lights will fail if your one large unwieldy power supply stops working for any reason.

 

2/ With multiple power supplies, its much easier to configure different parts of your model to light up at different times, especially if the lights are spread amongst the supplies. Whoever sees a real town, have ALL the lights coming on at once?

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2/ With multiple power supplies, its much easier to configure different parts of your model to light up at different times, especially if the lights are spread amongst the supplies. Whoever sees a real town, have ALL the lights coming on at once?

Either way, you need a switch somewhere, for that one :)

 

Andrew

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