I installed an NCE DA-SR decoder today, replacing the PC board factory installed for DC.
The wiring to the motor struck me as weird. A black wire went to one motor terminal and a red wire went to the other terminal. But, then, a black wire was jumpered from one terminal to the other. In the center of that wire was a heat shrinked "blob", almost as if there were a resistor under the heat shrink.
When I wired in the decoder, I initially left it off, but the loco would not run. So, I re-installed it, and the loco ran just fine.
I apologize for neither knowing what it is or what to even call it. What is it?
Rich
Alton Junction
Rich,
That is a noise capacitor. Bachmann has used them also.
Jim
I have had Bachmann diesels with caps on the motor leads but removing them did not keep the loco from running. Are you sure the orange and grey decoder leads are firmly soldered to the motor leads?
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.
Jim is correct......more so for electrical noise then mechanical. When running trains on DC near Your CRT TV in the 50's and after, You would see a sort of electrical buzzing line across Your screen, that is electrical noise, when a ceramic disk capacitor is connected across the motor leads that stops the noise. Most people did not care or for that matter not know what it was, those who did know fixed it. Not all engines came with it already installed. My Dad used to yell from the other room at Me to ask if I was running My trains, of course I was..then found a way to correct it.
Something to read:
http://www.studyelectrical.com/2015/02/noise-in-electric-motors-causes-and.html
With todays TV's and such It's really not that necessary. And there are other uses.
Take Care!
Frank
richg1998 I have had Bachmann diesels with caps on the motor leads but removing them did not keep the loco from running. Are you sure the orange and grey decoder leads are firmly soldered to the motor leads? Rich
Thanks to all for answering my question on what that little jumper was called and its purpose. I have installed a fair number of decoders and never saw one before.
To date, Bachmann seems to be the only one with the caps and inductors from all I have read in different forums and the Bachmann forums. Required by the UK and EU where many Bachmann products are sold.
Yes, those plastic tabs have been an issue for some from what I have read.
Good troubleshooting.
So, my only remaining question is, do I need that noise capacitor at all?
richhotrain So, my only remaining question is, do I need that noise capacitor at all? Rich
NO........
zstripe richhotrain So, my only remaining question is, do I need that noise capacitor at all? NO........
richhotrain So, my only remaining question is, do I need that noise capacitor at all?
In fact, you may find that you can tune the motor control much better if you take the capacitor out. The DA-SR doe snot have BEMF, but it is a silent running decoder (which means the PWM motor drive pulses are at a frequency above human hearing range) and the capacitor will have some effect on that signal. Simplistiv view, a capacitor is an open circuit to DC and a short circuit to AC, but the AC frequency that the capacitor appears to be a short depends on the value of the capacitor. Leaving out the math, as the frequency increases from DC to the center frequency of the capacitor, it looks more and more like a short, and as teh frequency climbs higher still it becomes more of an open circuit again. Since in this case the capacitor is wrapped in heat shronk, we can't tell the value (unless for some reason you have a capacitance meter and test it, or rip up the shrink wrap) we can't calculate the effect on the motor signal, but it's a good bet that it does have no small effect since 40KHz high frequency drive is closer to the frequencies they are trying to suppress than DC.
The Bachmann design with capacitors AND inductors forms a fancier filter circuit. Most of the time you can see the components on the Bachmann boards and their values can be determined, which means the effect can actually be calculated. Or, for the best operation, just remove it and don't worry about it. In the case of the Bachmann, the inductors are in series with the motor wires, but without the capacitors they have little effect on the signal. If you DO remove the inductors on a Bachmann board, they need to be replaced with jumper wires to complete the circuit.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Thanks, Randy.
As an aside, Bachmann has started putting the caps and inductors inside some of the locos. You can see them on the parts page. Some inductors look like green resistors but are 4.7 uhry ferrite inductors. Some are wire wound.
The caps have usually been 0.1ufd. Anywhere from one to three caps. On PC boards, surface mount.