light bulbs : LUSENET : Wiring for DCC : One Thread

Hey gang.

2nd question... I am wiring half of my yard as a sub bus, and using the diagrams in your track wiring section. I am using the terminal block method. In order to test the wiring and the light bulb, I applied a 14 vdc power supply to the bus, and then deliberately shorted the track. The light doesn't light much, in fact it just begins to glow, when my aligator clips are getting pretty warm. Any ideas on what might be going on? The power supply is a 7.5 amp supply, and it doesn't even flicker when the short is applied. Seems odd to me.

-- John Hartline (, October 29, 2004



It sounds like you have too much resistance between your power supply and where you applied the short. I don't know why you are using a power supply instead of your booster. Go ahead and use your booster. It was designed to shut down when there is a short. YOu won't hurt it.

So look for any reason to have too high resistance. You didn't wire your layout with 24 AWG wire, did you? Do you have 2 or more bulbs in series with your track? Otherwise, look for poor connections.

-- Allan Gartner (, October 30, 2004.


It sounds like you have heavy enough wire and also it sounds like you have done a good job wiring the layout. Using your typical ohm meter, the wiring job you have done should not read any more than a few tenths of an ohm at most.

It also sounds like you have a serious enough resistance problem that you should be able to measure it. Your problem will probably read a couple of ohms.

Do this. Disconnect your power supply. Place a jumper across your light bulb to short it out. You are about to look for "high" resistance and you don't need to be reading the bulb and have it give you false readings.

Attach a lead from your ohm meter to ONE of the power supply/booster leads. Take the other meter lead and check the corresponding rail. If you read a couple of ohms, start working back to your other meter lead connection.

If you get a good, low resistance reading, check the other lead from your booster to the other rail.

-- Allan Gartner (, October 30, 2004.


It sounds like you have one of your set of feeders bypassing the bulb. So when you slide the joiner to join both rails, the bulb is not able to work as it should.

Why does the bulb work at all? Because you are getting a very poor electrical connection through the joiner. Let this be a lesson to all, do not trust joiners to provide a good electrical connection!

-- Allan Gartner (, October 30, 2004.

Hi John

If using your power supply, measure the voltage across the lamp and if not approx 12 volts DC then you have a problem with wiring. With the short applied and the light globe illuminated, measure voltage drop across ALL wiring lengths, one section at a time, and track joiners until you find the one with the highest voltage reading. This is the culprit to the fact that the light is not on bright. You could use your DCC booster and use a DCC volmeter or just use a multimeter set on AC and make voltage comparissons.


-- Marcus Ammann (, October 31, 2004.


Rereading your question, your problem is the aligator clips. If you are using an 1156 lamp, about 2 amps current draw, your aligator clips should not get hot. Heat is a high resistance. Change clips, solder leads to terminal block or use better termination. A short at the track does not necessarily mean a short to the power supply (or booster) All wiring, terminations, clips etc are in SERIES with the short and all of these impact on the TOTAL current flowing in the circuit. Remember Ohms Law is I (amps) = E (volts) divided by R (resistance). Another way of saying it is, current in circuit is determined by voltage applied and the resistance of the components.

-- Marcus Ammann (, November 18, 2004.

Moderation questions? read the FAQ