Newb Q: Are Resistors Needed for Head & Effect Lights With Decoders?

[tehachapifan]

...or do the decoders already provide reduced voltage for LED's....or does it depend on the brand, etc?

If it depends on brand, let's use a TCS decoder as an example.

If a resistor is still needed, would it be the same value of resistor as if power was being taken straight off the frame?

Thanks!

[victor miranda]

ah where is the opinionated peteski when you need him?

when I install LEDs I use the resistor needed to limit the current for that LED
and expected voltage.

.... I use 16v for the calculation and most LEDs use 10ma
a 1k resistor is about right for most modern and tiny LEDs

the decoder may be able to limit the current, and if it gets re-programmed
and there is no resistor.... things may get hurt.

I may have to test some things now....

victor

[wazzou]

ah where is the opinionated peteski when you need him?

victor

I was just wondering that myself.  Maybe he's suspended.   

[mmyers]

For the most part, resistors are not included. Circuit board type replacement decoders will provide resistors for board installed led's but that is it. You really have to check the documentation for each decoder but as I said, assume no resistors. BTW, the resistors limit current for led's. Assume voltage on the blue wire to be same as track voltage when doing calculations. TCS has a nice resistor sheet on their web site.

Martin Myers

[Ken Rice]

Generally, read the manual and google for the specific decoder you care about.  For example, since you mention TCS, I'll pick the TCS AMD4.  The manual is downloadable from the TCS web site:
http://www.tcsdcc.com/Customer_Content/Literature/Decoders/N_Scale/Atlas_N/AMD4_Web.pdf

It includes a note that says: "This decoder features onboard 1K ohm 1/4 watt resistors for LED's!"

And if you either poke around on the TCS site or do some googling you end up here:
http://www.tcsdcc.com/Customer_Content/Installation_Pictures/N_Scale/Atlas/8-40CW/8-40CW.html

Which shows exactly where you solder the wires for ditch lights on the AMD4, and no extra resistors used.

- Ken

[victor miranda]

read the manual?

that seems farfetched.

victor

[tehachapifan]

I did read manual but still can't tell for sure if the resistors indicated are for the existing board-mounted LED's or for any additional LED's the modeler may wish to add. I have also noticed that the decoder manuals I have seen so far are written for electrical engineers and not a basic hobbyist.

[victor miranda]

tehachapifan,

believe me I have noticed...

at some point one sets up a test or two and decides what to do.

back a while ago when I thought I might take up installing decoders.
one fell showed a photo of his test rig

think motor and a few LEDs with resistors
more or less a loco that will not go anywhere
that is easy to attach a decoder.

last and not least  aligator clips to attach it to the programming track
or to the regular track

then you can test the decoder before you install it.

it is not an easy read those manuals...

[tehachapifan]

Thanks, Victor!

Testing makes sense prior to installation but I also want to arm myself with the best knowledge as to reduce the chances of letting the factory smoke out of said decoder during said test.

[Ken Rice]

If you're worried about letting out the magic smoke, and you're not sure if you need to add a resistor, hook it up temporarily for testing as Victor said with the added resistor.  With an extra resistor you'll probably get a very dim led, but you won't let the smoke out.  If it's not dim, then the resistor is probably not extra.

[tehachapifan]

More good advice. Thanks!

[jagged ben]

Ken has it right.   It really depends on the board.  Bigger boards that have extra space are more likely to have them.   Some TCS decoders have them and they are documented and some Digitrax decoders have them and they are not documented (except in various hard to find forum threads!). 

Best to ask the question of a specific decoder.

[tehachapifan]

Thanks, Ben. In this case I am using the Digitrax DN163A3 for the Atlas MP15DC and I did have to add resistors for the LED's. As mentioned in another thread, I now have lights that are bright.