Dcc, Lights, Resistors & Install

[Woofda]

Could someone suggest a decoder for a HO Athearn SD70mac with ditch lights and no sound?  I tried a NCE DASR decoder.  This decoder doesn't have resistors for the lights and promptly burned out all the lights. My guess is some kind of six function decoder with built in resistors for the lighting system?

As always thanks for the help.

[tstage]

Woofda,

For 6-function decoders, you might try a Digitrax DH163 or DH165.  (The 165 is the replacement for the 163 and has the capacity to add sound, if desired.)  For Proto 2000 locomotives, the recommendation is the DH165L0.  I don't know right off hand which one the Athearn would take.

Tom

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I just checked the Digitrax site.  For an Athearn SD70, they recommend either the DH163A0 or DH163D.  Again, the 165 series is the replacement for the older 163 series decoder.  However, you might be able to still find some 163s somewhere.

[Woofda]

Thank you for the reply I checked the web sight and those are the recomended decoders. The question now is "do you have to wire resistors into the lighting circuits?"

[tstage]

Woofda, 

You can always download the instruction manual for the DH163A0 decoder.  (The link is at the bottom of the page.)  Since it doesn't make mention of any onboard voltage regulator (like there is on the DH163L0 decoders for the Proto 2000 locomotives), my guess is that you'll need to add a resistor for each LED or bulb.

Tom

[jim22]

I normally replace the 1.5v bulbs in the locos with directional lighting with 13v 30ma bulbs.  Then you don't need the resistors.  This would be a good option, considering you've already blown your low voltage bulbs.  Resistors can be used to drop the voltage so the low voltage bulbs can still be used, and some decoders have resistors on them for at least some of the bulbs, but the resistors dissipate quite a bit of power.  If you use them, you need to use big ones (1/2 watt at least) and you need to keep them from melting the plastic shells.  LED's with resistors is another option.  LEDs stress the decoders less, and I think the resistors dissipate less power.

Jim 

[jktrains]

Could someone suggest a decoder for a HO Athearn SD70mac with ditch lights and no sound?  I tried a NCE DASR decoder.  This decoder doesn't have resistors for the lights and promptly burned out all the lights. My guess is some kind of six function decoder with built in resistors for the lighting system?

As always thanks for the help.

The Genesis SD70MAC has a built 9 pin socket for a DCC decoder. The Genesis SD75M's have an older light board desgin without a socket. You should have used a NCE DA13SRJ or DA15SRJ which would plug into the 9 pin socket.  For working (alternatively flashing) ditchlights you need to relocated one of the wires to another connection of the factory board.  NO resistor need to be installed.  By using the original light board, all the voltage  from the decoder function still flow thru the orginal circuit board and is dropped by the orginal board's circuitry before going out to the bulbs.  You only need a 4 function decoder (1-front headlights, 2-rear headlights, 3-left ditchlight, 4-right ditchlight).

The problem you now have is that you've blown the original bulbs and need to replace them.  The ditch lights will be a chore, but can be done if you work slowly.  Still use 1.5v bulbs because the 12v bulbs will be larger and generate more heat which might melt the small, thin ditchlight housings.

[steve58]

A word of caution, if you read the Digitrax site very carefully, the decoders only have current limiting capability for the Front and Rear lights. All the other function hookups STILL require resistors.

TCS makes a six function drop in board that has current limiting on ALL the outputs. It's the A6X. I haven't used one yet, but have other TCS decoders and they seem to work really well. Their warranty is excellent too, no questions asked.

[Woofda]

Thanks for the inputs and I will look up TCS.

[betamax]

Current isn't the issue here, voltage is.

The lamps will only draw as much current as they need. But if the voltage is too high, that'll blow the lamps and fast.

If you are using a 12V lamp with a 16V source, you need to lose 4 (or more) volts. Installing a resistor will acomplish that. If the current draw of the lamp is 40mA, you need 4V/.04A which is 100 ohms.

If you use a 150 ohm resistor, the drop will be 6V, and the lamp will see 10V across it. It won't be as bright, but it will last a lot longer.

[steve58]

TCS states that pretty clearly:

http://www.tcsdcc.com/decoder/A6X.htm

I understand from reading that the new Digitrax will run front and rear lights without resistors. BUT if you read on the Digitrax site, it's extremely difficult to figure out exactly what the decoder will and will not do.

Just my opinion.