G Scale Model Train Forum banner

1 - 8 of 8 Posts

·
Registered
Joined
·
1,602 Posts
Discussion Starter #1
When I kitbash my Bachmann center cab, I want to replace the blue LED headlights with some nice warm white LEDs. I also want to convert the lights to run on a small battery pack, so that the lighting remains constant and can remain lit even when stopped.


The only thing I like about the existing headlights is the fact that they are directional. Is there any way to keep that feature?
 

·
Super Modulator
Joined
·
20,526 Posts
Actually, I believe the problem to be solved would be the same, track or battery.

Ray, the primary problem is to set which light is on based on the track polarity, but still power from the batteries.

My thoughts are that if you want to go to this trouble, why not use the track power for something?

So, put a charge on the batteries / reduce the battery drain while track power is sufficient.

This may be getting more complex and expensive than you want.

What about the simple solution? Put a few diodes in series with your motor so that the lights come on before the motor. Then when you come to a stop, just throttle down enough for the motor to stop... the lights will still be on.

You can buy a couple or 3 full wave bridge rectifiers and put them in the motor lead(s) to do the voltage dropping to the motor.

If you think of a FW as haveing 2 inputs and 2 outputs, just tie the inputs together and tie the outputs together. You now have a 2 terminal "device" that drops voltage with basically no heat. put one or 2 of these devices in line with your motor leads (either side of the motor, does not matter).

Having LEDs will help get max brightness at lower voltages (because they sort have constant brightness at a wider range of current).

I think this solution is easy for you to do, inexpensive, and avoids the hassles of batteries, i.e. charging, placement, wearing out.... when your primary power source is track power.

Regards, Greg
 

·
Registered
Joined
·
3,384 Posts
I'd do it with a relay(s) and do in fact something quite similar on my goose to toggle the sound system. The relay is triggered by track power and can only be activated if proper polarity is applied through a diode. The relay armature is used to engage the batteries to the lights.

If a latching relay is used, the lights can stay on when no track power is applied.

Alternatively, in your case, you could power the lights off track power that would be keyed on by the relay when the voltage gets high enough. When the voltage is interupted, the relay shuts off kicking in the batteries. This could keep directional capability for forward and reverse, but just switch to the forward lighting when the relay drops out.
 

·
Premium Member
Joined
·
712 Posts
Posted By toddalin on 01/18/2009 6:56 PM
I'd do it with a relay(s) and do in fact something quite similar on my goose to toggle the sound system. The relay is triggered by track power and can only be activated if proper polarity is applied through a diode. The relay armature is used to engage the batteries to the lights.

If a latching relay is used, the lights can stay on when no track power is applied.

Alternatively, in your case, you could power the lights off track power that would be keyed on by the relay when the voltage gets high enough. When the voltage is interupted, the relay shuts off kicking in the batteries. This could keep directional capability for forward and reverse, but just switch to the forward lighting when the relay drops out.




so what votage relay did you use ?
 

·
Registered
Joined
·
811 Posts
Use Aristo PWC and you don't have to mess with the diodes. Put a 100 uF capacitor across the LED/resistor combination and the lighting will come on nearly full bright at the first tick of the throttle.

- gws
 
1 - 8 of 8 Posts
Top