Constant Brightness Lighting

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Woodie

Active Member
Mar 23, 2001
2,093
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Northern Rivers NSW Australia
One of my locos that I want to decoderize has 1.5 volt globe directional constant brightness lighting. (uses diodes/resistors on the internal circuit board) Lighting at each end of the loco is headlight, and red/white marker lights. Forward has white marker lights and headlight, with red marker lights at the rear. Lighting is reversed when direction is reversed. This is on DC.

There are 3 1.5 volt globes at each end. ( 1 for red marker lights, one for white marker lights, and one for headlight).

The globes are mounted into the chassis, with "funnels" (if that's the right word) on the body that"funnell" the light to the appropriate marker lights etc. I really don't want to pull this mechanism apart. I really should put a pic of it up, to help describe it, but never mind.

If I just wire the decoder up for motor only (into the relelvant point in the loco), will the constant brightness lighting still work properly? i.e. do NOT wire up the decoder headlight functions. Although it would mean I cannot turn headlight on/off, nor have the lights on when stationary.

But I see no reason why the DC current supplied by the decoder would not also power the constant brightness directional lighting as well. The draw of current by the motor & lighting from the decoder shouldn't exceed the capacity of the decoder. The decoder (NCE D13SR) is rated at 1.3 AMPS.

Any thoughts? I don't think I'll blow the globes, or constant brightness circuity, as it's designed for 12 V DC anyway. (I run a DCC track voltage of the default of 14.5 V AC)
 
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pgandw

Active Member
Jul 9, 2005
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There are 2 ways to wire up the constant brightness unit - 1) in series with the decoder input, and 2) in series with the motor on the decoder output. Both have drawbacks.

1) The constant brightness unit will see essentially a 14V AC signal. The unit is designed to drop 1.5 volts from the input, but there should be enough remaining for the decoder. The issue will be that due to the AC input there will be no directional control of the headlights - they all will be on at all times. They may flicker some depending on the frequency and duration of the "wrong polarity" pulses.

2) The constant brightness unit will see a 12V pulse width modulated DC signal. The constant brightness unit will impact the top speed of your engine, since you will have about 1.5V less than the decoder can put out (probably around 10.5V). You will also have to adjust your speed curves, since the pulses to the motor will be 10.5V instead of 12. The light reversal portion will work correctly, but at slow speeds with narrow pulses, the lights may flicker or stay off. As you point out, the lights will be off when the motor is not turning unless you do some fancy programming of the start point of the decoder.

Constant brightness units are designed for an analog DC signal. Some decoders have lighting circuits designed for 1.5V bulbs, others use 12V bulbs. LEDs can be run off decoder 12V lighting circuits with a 1K resistor in series with the LED, but that would mean taking yur lighting unit apart. No answer is without its drawbacks, so I would try option #2 first (least amount of effort and change to the locomotive).

yours in lighting
 
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Woodie

Active Member
Mar 23, 2001
2,093
0
36
Northern Rivers NSW Australia
Thanks for that fred.

Option 2 is really the only option I have. However I will look at the constant brightness circuitry, and see if I can slot the output funtions (1 & 2 : headlights) in after the rectifier diodes, and before the voltage adjust resistors/circuitry (that drops the voltage to 1.5 V). If I can wire it in that way, then I can use the headlight function of the decoder. That's provided the circuity allows me to do that, of course. I'm assuming the voltage supplied by the decoder's function 1 & 2 would be equivalent to DC track voltage. Just slot it in at the appropraite circuitry point. But it probably has the voltage drop circuitry before the rectifiers. :rolleyes: Which rules that idea out!

But first things first. I'll just wire it in between the track pickup and the decoder motor output to the motor/circiutry supply and see how it goes from there.

I am aware of the PWM (pulsed) voltage supplied to the motor from a decoder, and the voltage is usually about 1.5 volts less that the track voltage. FWIU, the use of Constant Brightness Lighting circuitry also affects the top speed/voltage available to the motor on ordinary DC as well.

Thanks for that Fred. It's good to get others' confirmation of thoughts. :thumb:
 
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