Best Decoder for Athearn F3

skeet06 wrote in news:326a3176-d284-4016-b78b- snipped-for-privacy@b64g2000hsa.googlegroups.com:

All of them; None of them. The decoder's function output wants to put out around 12V for the headlight, so if your headlight is rated for less voltage than that they'll fail.

What voltage and current are your headlights expecting? If it's not 12-

16V, you'll probably need a dropping resistor of some value. Determining the value is easy, use Ohm's Law.

V = C*R (Just remember VCR. Standard Ohm's law format uses I in place of C.)

Voltage = Current * Resistance Resistance = Voltage / Current

The current should be listed on the packaging, if not you'll have to measure it yourself with an ammeter. It's not to hard usually. It'll be the value in "Amps" or "Milliamps"

The May 2008 Model Railroader has an article that explains this.

One more thing: Does your locomotive have an 8-pin DCC socket? It's probably best to get a decoder to fit that rather than hardwiring it yourself.

Puckdropper

Puckdropper skriver:

No, you can dim the output on many decoders.

Klaus

Dimming isn't what's needed here. Most decoders have a function output of around 12v and Athearn Genesis has 1.5v bulbs. With this situation you need to use drop resistors using ohms law as was described. There are some decoders that do have a function output of 1.5v -- TCS A6X is one. There may be other manufacturer's decoders with this feature but you would have to check the specs to find them. Personally for the Genesis F units I use a TCS T1 and a 910 or 1000 ohm drop resistor for each bulb -- I also dump the Genesis circuit board, which takes up a lot of room, and make my own small connection board on top of the motor.

Jim

On 5/11/2008 1:50 PM Jim Bright spake thus:

In this case, wouldn't it be a better idea to replace the lamps with

12-volt ones? You can "drop" the voltage with a resistor as you describe, but you're going to end up dissipating a lot of power as heat, depending on how much current the bulb draws. Could end up cooking something.

12V bulbs get pretty hot compared to 1.5V bulbs.

An alternative would be to replace the 1.5V bulbs with LEDs.

On 5/11/2008 2:48 PM Wolf Kirchmeir spake thus:

So, on that subject: anyone know if non-blue "white" LEDs are available yet? A lot of people don't like those psuedo-white ones; not very realistic-looking.

wants to put

rated for

situation

cooking

available

Go over them a couple of times with a yellow high-lighter. Definately improves the look.

Len

Of course, only when you run your train at night because until almost the end of steam, steam locos ran with the headlights "off", something most modellers these days don't realise.

-- Cheers

Roger T. Home of the Great Eastern Railway at:-

48° 25' North Longitude: 123° 21' West

For " White " LED go to Train Control Systems they have some very nice LED that burn pure white, start out at 650 ohms and try up or down until you get your desired light out put. I am useing them in steam engine head lights [ brass ] and they are great.

David Nebenzahl wrote in news:48276254$0$11167$ snipped-for-privacy@news.adtechcomputers.com:

You might get around the heat issue by using a 780x series voltage regulator. (The 78L0x series is low current and small package size.)

There's also the LM317LZ adjustable regulator (that can work as both a voltage or current regulator.) MR had an article in April 2000 about LED headlights that used this. (The same basic circuit is in the LM317LZ's datasheet.)

The nice thing about resistors is they're able to be placed inline with the wire, so they don't take up much extra space. If heat dissipation is an issue, one can use series resistors to spread the heat out across several smaller resistors.

Puckdropper

On 5/11/2008 9:46 PM Puckdropper spake thus:

You could, but keep in mind that even a voltage regulator will dissipate some heat; it's just a linear device, and that extra voltage (12 - 1.5 v) has to go somewhere. Bigger voltage drop = more heat.

Jim hit the nail on the head when he mentioned the A6X.

The A6X actually has an active regulator circuit, not just resistors, so it plays very nicely with even those notorious 1.5v Genesis bulbs.

I've put them in all my Genesis locos, and have never had any of the original 1.5v bulbs fail.

Stevert

Jim Bright skriver:

Yes it is.

Yes and then you dim the brightness so the average output is 1,5 volts. But it is better to use voltage drop by a 1kOhm resistor and then dim to get sufficent light level.

Klaus

David Nebenzahl skriver:

No 19-volts ones....

Klaus

Wolf Kirchmeir skriver:

A 1,5 volt 0,1 watt and a 12 volt 0,1 watt have pretty much the same temperture.....

And then you have the resistor problem again.

Klaus

David Nebenzahl skriver:

There is Yoldal sunny white or warm white, in Europe many of us buy them at

Another dane has replaced all lightbulbs and LEDs in his trains with the Yoldal LEDs, it looks great!

Look at:

Or this one and forward:

Klaus

This idea works fine in theory but I wouldn't trust it. Dimming on standard decoders is done by controlling a width of a pulsating DC which in oths "on" state is close in value to the track voltage (minus

1.4V). That is about 12 volts. This pulse is not guaranteed to always stay pulsing at an average voltage of 1.5V.

For example when the decoder is being programmed it'll apply the full voltage to the function outputs during the programming packet acknowledgment. Or when the decoder "blows its brains" (which does happen), it will reset the outputs to full brightness. In either case the 1.5V bulb will be blown instantly. You'll end up changing those

1.5V bulbs way too often.

More reliable solutions are to use voltage dropping resistor or changig the lights to either 12V bulbs or LEDs with a current limiting resistors.

Peteski

On May 12, 2:47 pm, "Klaus D. Mikkelsen" wrote: ...

Why are resistors such a problem? I work in N scale and I have no problem installing resistors in the LED circuits in locomotives. Lately I've been using SMD 1206 or 805 size resistors. They are very tiny. I've also noticed that certain decoders already have empty pads on the circuit board designed to accept resistors in series with a function output. I think I've seen that on some N scale Digitrax decoders.

Peteski

On 5/12/2008 10:08 PM Peter W. spake thus:

Guess it isn't that big a problem after all; doing a little back-of-the-envelope calculation shows that to divide* 12 volts down to

2 for a LED requires an 1/8 watt resistor, so it looks like even a surface-mount one would be good enough.

• To be technical about (and lord knows we like to be technical round heah', don't we?), one doesn't "drop" voltage; one divides it. In this case, with a resistor in series with the LED, the divider puts 10 volts across the resistor and 2 across the LED.