Hi all,
I've finally got a TSU-750 installed in my C-25, with all-wheel pickup and keep-alive capacitors.
There are three capacitors hooked up in the keep-alive circuit, with a total value of 420uF. When I went to test/program this loco on my programming track (JMRI with a Digitrax PR3), the loco responded but JMRI told me there was no loco on the track. I'm guessing that it isn't handling the inrush current of the capacitors.
I remember seeing here that a 100 ohm capacitor in parallel with a diode would add a bit of extra resistance and allow programmers to read some decoders with large keep-alives. The thing is, this site suggests using this in conjunction with a 1000uF capacitor, and I was wondering if I should adjust the value of the resistor to allow for the smaller capacitance?
Thanks in advance,
tbdanny
The Location: Forests of the Pacific Northwest, OregonThe Year: 1948The Scale: On30The Blog: http://bvlcorr.tumblr.com
Not really. The current is based on idealizing the components so the capacitors are a dead short for the charging period, total current is essentially via the 100 ohm resistor. Value of the caps doesn't really matter. A larger resistor will mean less inush but slower charging, smaller resistor is higher inrush but faster charging. If anything try slightly larger, not smaller, the charge time factor is determined by R x C, so if C is smaller, you need a larger R to keep the time the same.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Some folks have also said that you may need a 1K ohm (1000 ohm) resistor across the rails for some DCC systems to be able to detect a locomotive and read some sound decoders.
Also, many, if not all, sound decoders require extra power to the programming track. Not all DCC systems have the programming power required. Thus the need for a programming tack booster. This is not the same as a regular DCC booster.
I have also heard that the PR3 needs 14 volts for sound decoders as 12 volts is not enough. You may want to talk to someone who uses Digitrax to confirm or deny this.
Elmer.
The above is my opinion, from an active and experienced Model Railroader in N scale and HO since 1961.
(Modeling Freelance, Eastern US, HO scale, in 1962, with NCE DCC for locomotive control and a stand alone LocoNet for block detection and signals.) http://waynes-trains.com/ at home, and N scale at the Club.
Changing the resistor value only changes the rate at which the capacitor charges. You may have to temporarily disconnect your capacitor from the circuit to do your programming.
Have you tried programming the engine on the main ? This can sometimes overcome shortages of programming track power in these cases.
Mark.
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