bus wiring

[heinz]

hello,i've been told to finish off my main bus wiring with a resitor and a capacitor for each end for smoother operation.how is this done,exactly,and what size resistor and capicitor must I use.I purchased a bag full of capacitors(ceramic)with many different numbers on them.Which is which?.The store does not know and I find no  good results on the internet.Is the value that important?(the info for all of them says accuracy +-20% temp.+10 to +85C,withstand 2.5  rated voltage.(15pf 50volts.for some)others 1pf 50v and some more .01uF50v.The resistors are rated 1 watt 100 ohm.Will those do the job?It's the capacitors i am not so sure about.(NO RADIO SHACK HERE).Thank's Volker

 

 

[retsignalmtr]

there's no reason to add a resistor and or a capacitor to the ends of the buss wires. just keep the ends away from each other.

[Texas Zepher]

heinz

hello,i've been told

By whom?  And why aren't they helping you?

to finish off my main bus wiring with a resitor and a capacitor for each end for smoother operation.

It has nothing to do with smoother operation.  It has to do with a phenomena called "ringing".  Different manufacturers dcc units have different "ringing" characteristics.  When the DCC signal rings it can put a higher voltage onto the track than the DCC unit is set to do.  That is if the unit is set to put 15V onto the track a ringing signal can spike to 30V.  Voltage spikes can damage decoders, lamps, and any other electronics connected.  Anyway this should not be happening if your bus is shorter than 30 feet.  And that does not mean actual length of the bus.  it is length of wire from the DCC command unit.  So if the DCC unit is in the center of a 60 foot bus it should still be fine.

how is this done,exactly,

Simply put the resistor and capacitor in series across the end of the bus.

what size resistor and capicitor must I use

The write ups that I have seen on this (I don't do it myself) state that the resistor should be between 100 ohms and 150 ohms.  The capacitor between 0.1 uF and 0.47 uF.   The units should have a rating of 50V or higher.

I purchased a bag full of capacitors(ceramic)with many different numbers on them.Which is which?

Can't help you there without seeing them.

I find no  good results on the internet.

must not have looked too hard.
http://www.wiringfordcc.com/track_2.htm#problem_blown
http://www.members.optusnet.com.au/nswmn2/DCC.htm#Terminators

Is the value that important?(the info for all of them says accuracy +-20% temp.+10 to +85C,withstand 2.5  rated voltage.(15pf 50volts.for some)others 1pf 50v and some more .01uF50v.The resistors are rated 1 watt 100 ohm.Will those do the job?

Well  If I understand what you are writing then +/-20% is pretty sloppy, but yes 50 volt rating should be find.

 
But reviewing - bottom line - if your bus is less than 30' long this is probably not an issue, and you don't need to terminate it.

[rrinker]

 How long is your main bus? If you are talking 50 feet or less, this is COMPLETELY UNECESSARY.

20% tolerance is a 'standard' capacitor, DCC isn't one specific frequency so it's not nearly as critical as, say, tuning a specific radio frequency would be. You can get lower tolerance capacitors from most electronic suppliers - a store catering to electronic hobbyists might not have them. You might have to check the mail order houses and see which of them ship outside the US. Mouser is my preferred vendor because they have no surcharge for small orders - if I only need $5 of parts I can order $5 of parts from them.

                                      --Randy

[heinz]

thank's and I am glad to hear that.my bus is under 30' each side of the control unit and the loks run OK now that I have split the bus in half instead of having one end out of the power supply.one lok though makes a noise,i do'nt think its ringing,more like a snarl,sounds  like a continious  spark,but I can see  nothing.So I thought maybe  the resistor and capicitor would firx it.Volker

[rrinker]

 If it's just one loco, there's a problem with that one, either the motor, or gears, or somethign else. It DOES have a decoder, you aren't running a DC loco as address 00 are you?

 30' each way isn't much at all. I'm sure at the ends you might see some rounding of the signal if you hooked up an oscilliscope, but it should be well within the limits of what a decoder can handle. If you had a severe ringing problem on the bus wires, you'd have issues with controlling mos tif not all of your locos - as it, you change speed or direction or turn the lights on and off and nothing happens, or they take off at max speed even though they were stopped - stuff like that.

                                             --Randy

 

 

[heinz]

Thank's for telling me about the marcus  web site.no my bus is just under 30' each side around.I see Marcus also talks about a TERMINATOR if it RINGS!!thank's  volker(i am running tt scale with dynamis)

[heinz]

the decoder is ok.the does it all the time.i took it appart and foun zip.it's a tt piko taurus,only one year old.the mfrs "Gartner"lists can not tell me what the values of these capacitors are and NEXXTECH who makes them has not replied to my e-mail yet and Radio Shack who sells them does not know.  volker