Genesis F9A decoder

Jim

Unless you find a decoder with 1.5 volt outputs, you need a series resistor. With a series resistor the dim and Mars light functions will not work correctly. Below is the text from two previous posting that may help.

Genesis F-3 DCC decoder & sound installation 03/06/02

I did things a little different when I installed the decoders in a ABBA set of Santa Fe F-3's. I installed a Soundtraxx DSD-AT100LC sound decoder in one of the B units. While this decoder would fit in a A unit, it only has two light outputs. The NCE DA-SR decoders which I installed in the other B units and both A units has four light outputs.

The headlight was connected to the first output set to operate from F0 (normal use of F0). F8 was set to dim the headlight. It's the only function number that can be used for dimming that is the available on both the NCE decoders and the Soundtraxx decoders.

The red and clear gyralight bulbs were connected to outputs 2 and 3. Both of these outputs were set to be controlled by F1 (I normally use F1 to control the rear or backup light). The red light output was set to come on only when the engine is in reverse and the clear light only in forward. This way I only need to use one function to control both. Both outputs had their EFX lighting function set to simulate Gyralights. The 1.5 volt bulbs require resistors in series to work with DCC decoders. Unfortunately the headlight dimming and Gyralight functions do not work well (if at all) with

1.5 V bulbs and their series resistors. See my separate posting titled "1.5V Bulbs and DCC EFX lighting effects" for a way to improve their appearance.

Since there is one more output on the decoder, I drilled a small hole at the top of the bulkhead at the rear of the cab. A 12V bulb was installed here to illuminate the cab. I used F3 to control this output as that is what I use to control interior lights on my doodlebug and RDC's. A engineer and fireman were installed in the cab. The cab seats are too narrow (12" between armrests) and too high (the top of the seat cushion is at the height of the side window sill). I cut one armrest off where needed and filed the bottom of the figures as much as possible so that they would fit.

1.5V Bulbs and DCC EFX lighting effects 03/06/02

When you use 1.5 volt bulbs (It is not always possible to substitute 12V bulbs which is the preferred solution) with DCC decoders you must use a series resistor with the bulb. Unfortunately this combination requires more voltage to start to glow than a 12V bulb. As a result when the headlight is set to dim, it may not glow at all with 1.5V bulbs as opposed to 12V bulbs. The same problem occurs when the output is set to simulate a Mars, Gyralight or Rotary Beacon. The simulation is done by varying the output. Sometimes the bulb just appears to flash as the bulb does not light until the output is high.

To correct this I experimented with lowering the resistor value and putting diodes across the bulb to prevent the bulb from seeing more than 1.5 volts. Most small 1.5V bulbs are meant to draw 15ma. This would require about a

680 ohm resistor in series if your DCC output is 12V. Instead I used a 330 ohm resistor in series with the 1.5V bulb. I then placed diodes across the bulb. You can use a small bridge rectifier for the diodes by connecting the

• and - terminals together and the AC terminals across the bulb. This combination looked almost as good as using a 12V bulb when the output was set to simulate a Gyralight.

How it works: The decoder varies the output from off to full on in varying patterns in order to simulate these effects. By lowering the resistor value I enabled the 1.5V bulb to start to light sooner. Since more current is flowing, the bulb would reach it's maximum before the decoder reaches full output. The diodes across the bulb act like a constant lighting circuit and prevent the bulb from seeing more than 1.4 volts as the decoder goes to it's maximum output.

You can experiment with different resistor values to get different effects but be careful not to exceed the decoder output current (usually 100ma per function). At 12V output this would mean no lower than 120 ohms, at 15V output, no lower than 150 ohms. A lower resistor value then what I used will give you a different effect but not necessarily a better one. When you lower the resistance, at some point the bulb will just appear to be flashing on and off rather than varying in intensity. Make sure you connect the diodes across the bulb before you start lowering the resistor. If you don't you will most likely blow out the bulb as it will see twice the voltage that it was designed for.

Different Explanation

Ignore the various special effects and just consider the headlight when turned on bright and when turned on dim. 12V bulbs work fine in this case but 1.5V 15ma do not. To see how they work, I connected a 12V 30ma Minitronics bulb to a variable DC power supply. The bulb would just start to glow at about 3 volts, at 7 volts it looked like a dim headlight and at

12 volts it was at full brightness. I then took a 1.5V 15ma (Athearn bulbs worked the same), I connected a 680 ohm resistor in series (this would be the correct value for my lower than normal 12V track voltage) and connected this to the variable DC power supply. In this case the bulb did not glow at 3 volts, did not glow at 7 volts, started to glow at 9 volts and of course was at full brightness at 12 volts. It was at full brightness at 12 volts because the 680 ohm allows the correct current at this voltage. The decoder must put out about 7 volts when set to dim, as this is the correct range for the 12V bulb but it is too low for the 1.5V and 680 ohm resistor.

I can make the 1.5V bulb light at any voltage (over the minimum that will cause it to light) by using the correct resistor in series. At 7 volts I would need a lower resistor than at 12V. By trail and error, I found that

330 ohm resistor would allow the 1.5V bulb to look like a dim headlight when connected to the decoder output set to dim(a lower resistor value would make the bulb come on at full brightness or even burn it out, but that is not what I wanted).

The problem now is, that if I set the decoder head light output to bright (the output voltage goes back up to about 12 volts),the 330 ohm resistor would allow too much current to flow through the bulb and burn it out. This is where the diodes across the bulb come into play. If the voltage across the bulb tries to go above 1.4 volts (which it will because of the low resistor value), the diodes will conduct and hold the voltage to 1.4 volts. This prevents the bulb from burning out when the output is set to full brightness. When the output is set to dim, it is like the diodes are not in the circuit because the combination of the lower output voltage and 330 ohm resistor keep the voltage across the bulb lower than 1.4 volts. The bulb therefore looks dim.

The special effects Mars, Gyralights etc. are just a variation of the above. Instead of two voltage outputs (bright and dim settings) the output voltage is continually varying.

Stuart Sabatini Palm Coast, FL

----- Original Message ----- From: "Stuart Sabatini" Newsgroups: rec.models.railroad Sent: Monday, April 05, 2004 4:57 PM Subject: Re: Genesis F9A decoder

The explanation was great for the resistor value, but what does a person want in the way of a diode (this coming from someone who is electronically challenged)?

Frank Eva

Frank

Any low voltage rectifier diode above 100 ma current and 25 volt rating would be OK. I would think all rectifier diodes are above this rating. The smallest in my old Radio Shack catalog is a 1N4001 which is rated for 1 amp and 50 volts.

Stuart Sabatini Palm Coast, FL

Stuart,

Have you got a diagram of how you wired this? Is the 'bridge' between the lamp and the resistor, or ahead of it? you mention tying the +/_ terminals together, and using the AC pair across the lamp.- I am confused here...

Jim Bernier

Stuart Sabat> Frank

Jim,

He is protecting the lamp from excessive voltage with the diodes; two diodes in series drop 1.4 volts - in one direction. The 'bridge' is just a convenient package of 4 diodes wired to protect both directions and may not be needed in a DCC application since function outputs are already DC.

(-)-------\/\/\/\/\------|-------| ................light>..O......./\

Thanks,

I got it figured out after some doodling on my note pad......I was sending up the 'alarm' too fast.

Jim Bernier

"KTØT" wrote:

reposting Jim's diagram in hopes it lines up than what I saw ....

(-)-------\/\/\/\/\------|-------| .................light>..O....../\

Dang! My repost doesn't look any better on my end. Well I guess you all get the idea from Jim's diagram.

Is this correct?

"

"

Use a fixed font when you read it, and it looks fine.

You guys have the right idea. Two diodes in series can be used in place of a bridge rectifier. When using a bridge rectifier you do not have to worry about polarity but the bridge rectifier is larger than two diodes. When using two diodes you must check that the polarity is correct or you will burnout the 1.5 volt bulb. Before connecting the bulb, connect a voltmeter across the diodes. If the polarity is correct you will never see more than 1.4 volts. If incorrect you will see the full output voltage. Just reverse the directions of the diodes in this case.

Stuart Sabatini Palm Coast, FL

Well I thought it was fixed but find it didn't. ;-)

Stuart,

Thanks for the info. I got MARS lights working using 2 bridge rectifiers, and 330 ohm resistors. I just used the 680 ohm resistors in series with each headlight bulb. The 'dim' feature really was not high on my list. The big problem is trying to get the Athearn wire retainers on the Digitax DH163A0 decoder. I finally tinned all of the leads and soldered them to the decoder with a 25w soldering pencil. Does anyone know a source for the small black wire retainers that fit on the Digitrax decoder? The ones supplied with my Atlas RS-1's light board work fine on the decoder. The Athearn Genesis light board has ones are are really too small to fit on the DH163A0 decoder. I am going to send a note to Atlas too see if I can get their wire retainers, but I wonder if there is a source of these 'in bulk'.....

Jim Bernier

Stuart Sabat> You guys have the right idea. Two diodes in series can be used in place of