#### 12 volts bulb and DCC

fernando nunes

I read that 12 volts bulb + DCC = melted shell.  The reason is because the lamp will get too hot, but that doesn’t happen in DC, so far as I know. And with a 16 volts bulb in DCC, is there any problem? Besides, how can one identify a 12 volts bulb versus a 16 volts?

Any comments on the subject would be appreciate. Thank you.

Fernando

Dale Gloer

A 12 volt lamp connected to a DCC decoder will likely melt a plastic shell.  This is because the lamp is operating all the time at approximately 12 volts that is supplied by the decoder.  The reason it does not happen on DC is that the lamp seldom or maybe never operates on 12 volts - it operates on whatever voltage is supplied to the motor to make it run at the speed desired, maybe as low as 6 to 8 volts.  A locomotive on DC with 12 volts supplied will run at very high speed.

In my opinion it is better to replace the lamp with an LED and suitable current limiting resistor when operating on DCC.  Some decoders are equipped with lamp outputs specifically designed for LEDs and do not require an external resistor.

Dale Gloer

john

Fernando,
You can use your 12 v lamp, actually any voltage less than track voltage. The trick is to install a resistor in series with it. I have a resistor substation box that makes it easy to find the right resistor. To find the value you need you need your bulb current. If it listed on the package just use the amp meter in your Volt Ohm Meter and use Ohm law. Make sure the wattage of your resistor exceeds the wattage of your bulb.
I am partial to using Leds. The only problem with them is decoders that put out 1.5 volts which is too low for any diode. The do take care of the heat when you can use them.
john

On Thursday, January 8, 2015 11:11 AM, "dale.gloer@... [WiringForDCC]" wrote:

A 12 volt lamp connected to a DCC decoder will likely melt a plastic shell.  This is because the lamp is operating all the time at approximately 12 volts that is supplied by the decoder.  The reason it does not happen on DC is that the lamp seldom or maybe never operates on 12 volts - it operates on whatever voltage is supplied to the motor to make it run at the speed desired, maybe as low as 6 to 8 volts.  A locomotive on DC with 12 volts supplied will run at very high speed.

In my opinion it is better to replace the lamp with an LED and suitable current limiting resistor when operating on DCC.  Some decoders are equipped with lamp outputs specifically designed for LEDs and do not require an external resistor.

Dale Gloer

Annette and Dante Fuligni

I have a Life-Like P2000 Alco S-1 with 12v, 50 ma bulbs, an Atlas RS-3 with 14-16v bulbs and a Bachmann Spectrum motor car with a 12v bulb, all with decoders running on DCC and no melting.

Dante

rg <richg_1998@...>

You are fortunate. I belong to about about twenty train forums. Some running 12 volt bulbs have not been so fortunate.

Rich

rg <richg_1998@...>

A few times I have seen a recommendation to install a 22 ohm, 1/2 watt resistor. This cuts down on the surge and lengthens light bulb life.
Many replaced the 12 volt bulb with an LED and 1k resistor.
Some do use a 1.5 volt bulb and resistor. The 1.5 volt bulbs run a lot cooler.
i have done measurements using an infra red temperature scanner.
Some DCC systems can run at a higher DCC voltage.

Rich

Failure is not an option. it comes bundled with Windows.
Dale Gloer

Annette and Dante Fuligni

I rather doubt that good fortune has anything to do with my experience with 12v bulbs. The principles of physics apply to matters such as lamp voltage (and the heat generated thereby) and the characteristics of materials such as plastic. These are not subject to luck. And before installing the TCS decoders, I checked their website installation examples. There were no warnings regarding bulb wattages (one example did change to LEDs but without mention of concern for plastic melting.

Dante

Robert Heroux

Dante -

I would say you did have good fortune smiling upon you and you may want to by some lottery tickets.. LOL  I have seen some get by with 12 volt only to find out later they were Brass loco’s with poor after market paint jobs and not plastic… Live and learn.

Bob

Robert Heroux
ACCU-LITES, Inc.
118 S. Main St. STE 5
Wauconda, IL 60084

Phone: 847.224.7914
FAX: 847.487.2089
NMRA Member # 143811

Annette and Dante Fuligni

Bob,

All the locos involved have plastic shells.

Dante

richg_1998@...

i did a Google search for

dcc 12volt bulbs plastic shell

Came up with many results and warnings. Experiences from a few.
i belong to 20 train groups/forums for some years.

Rich

richg_1998@...

i guess I should include the link. Some will never search.

http://tinyurl.com/m35c6ac

Rich

Mark Gurries

The problem is easy to understand for there is no difference between burning the locomotive shell and burning your hand with a normal light bulb.

All filament bulbs radiate both light and heat at the same time.  The heat is a byproduct.  The question become how much heat?   Just like our standard light bulb we halve in our homes have watt ratings, so do the small bulbs we used in our locomotives.

Watts = Volts x Amps.

Simple example of the heat output differences between two bulbs which only differ in voltage rating.

So a 0.1 Amp (100mA) bulb with a voltage rating of:

1.5V would dissipate 1.5V x 0.1A = 0.15Watts.  Warm to the touch.

12V would dissipate 12V x 0.1A = 1.2 Watts.   You would not be able to touch this bulb.

So by just dropping the voltage to 1.5V, we ALMOST reduced the watt rating or heat generated by 10X.

In the real would, 1.5V bulbs draw about around 0.01 Amps for a watt rating of 0.015W.   Now we are approaching almost a 100X reduction in heat from a 12V bulb.

This is why 1.5V bulbs running at 1.5V are always cool to the touch and 12V bulbs will burn your hand running at 12V.

One of the characteristics of model railroad light bulbs are the fact they are so physically small they represent a point source (concentration) of high temperature heat.

Additional factors that make this 12V lamp a big problem for DCC that did not exist with DC.

1) Introduction of Engineering Plastics.   DCC appeared during a time frame where high tech engineering plastics have been introduced too.  These new plastics offer supper detailed shells for engines.  This same plastic also appears to have a lower heat or melting threshold that the older thick plastic shells.  They also are much thinner which makes the thermal melting problem worse since thinner plastic cannot carry as much heat away from the heat source.   It has a poorer heat dissipation capability which means the plastic will get hotter from the same heat source than the old thick plastic did.

2) DCC allows one to have constant full power lighting without the engine moving.  That means when a given bulb is turned on, it is receiving the full track voltage which is a regulated voltage someplace between 12V and 16V depending on the scale.   As was stated before, you never had a DC system running at that voltage because that would force the engine to run at full speed at that same track voltage.  Track voltage = Motor speed.  In other words, at typical running speeds, the light was a lot dimmer putting out a lot less heat due to the track voltage was a lot less than 12V.

LEDs do not generate any heat of any consequence, are a lot brighter and unlike a bulb, will never burnout in the locomotives lifetime.

On Jan 12, 2015, at 12:14 PM, richg_1998@... [WiringForDCC] <WiringForDCC@...> wrote:

i guess I should include the link. Some will never search.

http://tinyurl.com/m35c6ac

Rich

Best Regards,

Mark Gurries
Electrical Engineer
DCC Website & NMRA DCC Clinics: www.markgurries.com