G Scale Model Train Forum banner

1 - 10 of 10 Posts

·
Premium Member
Joined
·
25 Posts
Discussion Starter #1
I have converted a LGB loco with the older type of circuit board to DCC operation. I have attempted to adapt the board as a voltage/current regulator for the return path for function outputs without too much success, the headlight was fine but I was unable to reduce the voltage to the back-up and cab light. I literally burned my fingers on a resistor I added to the circuit as a last resort


Any views on whether it would be simpler to upgrade the bulbs from 5 to 18 volts or advise on a simple voltage/current regulating circuit and component values. I recorded a function output of 20V from the Digitrax decoder used.

John
 

·
Premium Member
Joined
·
25 Posts
Discussion Starter #4
Dan.

I have had the European version of the DRGW diesel switcher in use for about 12 months with a Digtrax Decoder. The basic idea was to provide a direct function feed to the individual lamps F0 head and back up Lamps, F1 cab light and utilise the voltage and current regulating circuitry for the return. The circuitry seemed to work fine for the headlight F0 but not the back up or cab light.

Yesterday after finally obtaining some replacement bulbs, I decided to try science and test a 33Ohm 5W resistor in the circuit whch got so hot that it physically burnt my finger.

What has me puzzled is whether the heating occurred as a result of choosing an incorrect value of resistor or whether it started fighting with th board circuitry.


I will probably end up discarding the board and installing a resistor in series with the bulb, a principal which seems to work fine with LED equipped locos.

John
 

·
Premium Member
Joined
·
3,883 Posts
When choosing a resistor I would look at the voltage output for the function that drives the light, and then the voltage/current rating of the light.

If you have the Original LGB D&RGW diesel switcher, I believe it was designed for 18 volts and used the screw in type of bulb that is 18 volts.

The newer D&RGW has a circuit board inside and ha 5 volt bulbs (these are plug-in and have a flat top). Round top LGB plug-ins are 24 volt.

What replacement bulb did you use for the install, and what is the part number on the bottom of the loco. I have both the new and old versions and can look at mine for more specific information on your engine.
 

·
Premium Member
Joined
·
25 Posts
Discussion Starter #6
Hi Dan

Thanks for your advice the loco is the 21620 model with 5v plug in bulbs and the circuit board is under the cab.

John
 

·
Premium Member
Joined
·
3,883 Posts
Since you have the 5 volt flat top bulbs, you can swap them to the 24 volt versions and not use a resistor. LGB lists 33ma as the current rating for the 5 volt bulb.


24 volt LGB bulb is rated at 15ma.
 

·
Master of Disaster
Joined
·
867 Posts
If you have used a resistor that burns to the touch..try using a 1 watt resistor sold at Radio Shack this will dissappitate the heat better and may not get as hot to the touch...they are quite large compared to the lesser ones...they also have other ones you can get to expirement with as far as brightness.

Make sure you mount it away from touching anything...

I have found that you have to be very careful ADDING ANYTHING to an LGB circuit..as it is easy to get majic smoke..I do not mess much with LGB circuitry, BUT anyone's else I can do most anything I need .

I have used the 1 watt resistor on my Accucraft K-26 lights and it works fine

MHO

Bubba
 

·
Super Modulator
Joined
·
20,511 Posts
On thing people commonly forget to do is calculate the power (wattage) resistor needed.

P = I(squared) R or V(drop) I

Take the current you are running through the resistor, square it, and then multiply it by the resistance. Alternatively, the voltage drop across the resistor times the current.

Do NOT put 1/2 watt through a 1/2 watt resistor! You need to at least DOUBLE the wattage of the resistor over what you calculate.

And, no matter what the size of the resistor in wattage, if you are "using" 1 watt in the dropping resistor, then 1 watt of heat will be coming from it. A larger resistor just spreads the heat out over a larger area.

Regards, Greg
 
1 - 10 of 10 Posts
Top