I have a Proto 2000 SW8 switcher that I am going to need to hire wire the decoder. Front light I should be able to use a LED. Rear light over the cab I will have to leave the bulb. How do I find out what mil-amp the bulb is. I do have a cheap Multimeter from Harbor Freight, what settings would I set it to to get the amps the bulb draws?
Far as decoder, I bought a Digitrax DZ 123, see any problems with me using it in the SW 8?
Thanks again, Ken
I hate Rust
Get an NCE SW9-SR. It's the closest thing to a drop-in decoder for those locos. There is already a resistor for the rear light so you don't have to rip out the cab interior to replace it, or find room for a resistor, and there are two pads ont he decoder to solder an LED to for the front light, also with the resistor already in place.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Don't' worry about the bulb ma. Decoders can handle the current. The current will be less than 100ma.
You can just put the meter in series with one bulb lead and set the meter to read current. I always start with the highest ma setting. In this case 200ma. or bulbs or LED's. If not sure, start with the 10 amp scale.
I have some of those meters as I have been a electronic tech for many years.
For motor current, I always start with the 10 amp scale as most motors will draw over 200ma.
The DZ123 is a good decoder. I use a DZ125 in a small diesel and a Mantua 2-6-0.
Right now I assume the loco is not DCC ready as you did not say. I do not have this loco so just guessing.
If there is a PC board for DCC ready, there might be a resistor on the board if the loco uses 1.5 volt bulbs.
With your meter on the volts scale, look for the operating voltage right at the bulb.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
to measure current you first remove one of the bulb leads from the decoder. You then put the meter in current scale. It should have the letters ma next to the numbers on the dial. Then place one meter lead on the decoder terminal and the other lead on the bulb wire and activate the bulb. You can then take the reading. If it's an analog meter and the arm pegs the wrong way simply reverse the leads. When done replace the bulb wire to it's original location. If you have to check for voltage, measure across the bulb after any resistors that may be in line.
The placement of the meter with any dropping resistor doesn't matter when measuring current since a series circuit has constant current throughout.
Good luck.
Springfield PA
Funny, after an hour wait 3 answers the same time. There were none when I started to post and 3 after I posted.
HamltnblueFunny, after an hour wait 3 answers the same time. There were none when I started to post and 3 after I posted.
Sometimes it takes a while for "stuff" to happen.
Problem is you don't know the voltage bulbs they use. I've blown enough to know that when it says Proto 2000, replacing the bulbs first saves trouble later.
They can use 1.5V or 12V, you are never sure what they used that day.
I use two multimeter's sometimes, one to read the voltage, the other to read the current. Multimeter's are under $10.00 that are ideal for this.
There are no excuses on why everyone in DCC should not have at least two meters and some double clip leads for testing.
For those who do not know how to use a meter, the meters come with instructions and there are many links on using multimeter's, just in model railroading alone.
P2K almost always use 1.5V or 3.0V bulbs. If you assume 1.5 you won't blow one - if it happens to be a 3V bulb it will either be dim or not light if the resistor is too big. If you err the other way and assume 3V, and it's 1.5V, it will be really bright - for a short while.
I've never seen a P2K loco with a 12V bulb , and I've put decoders into an awful lot of them, from GP-7's to SW's to SD7's to S1's to PA's to E units. Some with DCC ready circuit boards, some witht he kind you have to cut traces. Every one has the light bulb wired either across diodes or with a large resistor - definitely not 12V. Of course I also always replace them with LEDs so I don't much care about what's already in there.
Anyway the NCE decoder I mentioned handles the light problem AND fits nicely in place of the stock circuit board.
Randy, I am sort of stuck with the Digitrax decoder, I want to get the engine running this week.
richg1998Don't' worry about the bulb ma. Decoders can handle the current. The current will be less than 100ma.
So if I am reading this right, I don't need to added a resistor to run the factory light bulb?
Thanks for all the answers. Confused Ken
You definitely need resistors, the bulbs are 1.5 volts. You'll have to disconnect one and use your meter in series and a 1.5v battery to check the current and calculate from there. They'll probably need to be fairly large, 1/2 watt or better to handle the load and space is at a premium. I think they are 30ma, the NCE decoder has a physically large 100 ohm resistor attached to the bottom for the rear light, but they are using half-wave power (the bulb does NOT connect to the blue wire, but rather one of the track pickups for the common).
If you're determined to use the Digitrax decoder I'd go through the effort to get at the rear light and swap it for an LED as well and avoid any heat issues.