Thanks, Randy. I heated up a side of the capacitor with the soldering iron and pulled it off the jumper (on both of my U30Cs). Now they run like a charm and only draw about 0.15 amps each. I emailed MRC today and asked them what frequency the PWM operates at in the 9950s. Their response was that they do not use pulse, that their DC power is 'linear'. I might just go and purchase an oscilloscope to look for myself. Brian
Nothing to resolder, just remove the capcitor. It's wired across the rail pickups, or maybe the motor wires. Nothing needs to be there.
If you are going to install a decoder, you would be removing the jumper anyway, so it wouldn't matter. But to run it on a PWN DC system you need to pop the capacitor off. Or swap in someone else's 8 pin dummy plug - they are all the same. I wasn't aware they did this on other locos, I know this was done with the Gensets.
--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 (everyone) for the helpful insights. I am learning a lot in the process. I think I can remove that capacitor on the jumper and resolder a connection. Here is an image I found of the jumper--the capacitor is easy to see: http://www.gp30.com/atlas/u30b-05.jpg
Has to be a capacitor - a resistor is a resistor, DC or DCC. A cap though, effectively open to DC but a short at DCC frequency.
If the 9950 uses PWM drive - that will 'look' like DCC in the voltage on the rails and will short through the capacitor. Perhaps evidence that the Tech II's did not use PWM as some have stated - I never thought they did.
SOme locos, Bachmann especially, have capacitors on the motor terminals. They have no effect on DC, but can cause issues with PWM DC, and also cause problems with the PWM output of a decoder, as well as interfere with BEMF if the decoder hasit. Those should always be removed.
Are you referring to the component mounted ON the 8-pin jumper board used for DC operation ? If so, that component is a very light resistor. The shorted resistance has no effect on DC, but it creates enough of a short to trip a DCC system. The idea behind it is to prevent you from running that engine set for DC on a DCC system using address 00 - which really isn't a good idea anyway.
You can remove that compoent with no ill effects.
Mark.
¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ
I've honed in on the culprit: a multilayer ceramic capacitor on the jumper in the PC board atop the motor. This jumper (Atlas part 994120) has one small capacitor on one side. Using the old MRC 2400 Tech II powerpack, everything works fine. Locomotive runs great, lights work, all using 0.2 amps. However, using my newer MRC 9950, this capacitor gets incredibly hot. The locomotive runs, the lights work, but this tiny little capacitor is hot enough to burn my finger. I wonder if the MRC 9950 has PWM at a frequency that is causing an electrical series resistance (ESR) effect in this capacitor, causing it to heat up. Wish I had an oscilloscope to look at this. Do I really need this capacitor? Will the lights flicker without it?
It's taken a year, but I've finally finished my signalling/control panel project and am ready to solve my Atlas Silver Series U30C high amperage issue. I have encountered a new wrinkle that may shed some light on the problem, and I'd like your input about it before I take these U30Cs apart:
In the past year I've built a 3 ft-long test track, powered by an old MRC 2400 Tech II powerpack. I have an ammeter and voltmeter connected so I can see the current and voltage on this track. When I put either of my two U30Cs on this test track, they run like a charm at about 0.2 amps. They're very quiet and have no problem moving slowly, or quickly. They're smooth running, and their amperage draw is normal.
My layout (not the test track) is powered by MRC 9950 powerpacks, which have amperage and voltage displays built-in. I run DC, no sound. My Atheran, Bowser, Atlas Silver Series GP40, and Intermountain locomotives run great and draw 0.2 to 0.5 amps. But on the layout the Atlas U30Cs draw 1.2 amps each (!), and when they move I can hear a faint sound of arcing where the wheels meet the rails.
I can't figure out why these U30Cs draw 0.2 amps on the test track, and 1.2 amps on the layout. I don't have electronic schematics of the MRC 9950 or MRC 2400 Tech II. I don't know how they are different in their DC design. Is the MRC 9950 actually doing some PWM to control speed? Does this point toward some specific modification on these U30Cs that I should be looking for? They were new locomotives when purchased in 2017 (well, I thought they were.) But maybe they've been modified.
Thanks.
Thanks for all of your input, everyone. I'm in the midst of signal system wiring, but as soon as I get tired of that I will start some U30C "surgery" using your ideas.
Sounds like there is something rubbing on the drive shafts or flywheels. Or the drive wheels have something binding them.
I have quite a few of those on my roster and when running with a train pull 200 to 250 ma. Something is definitely amiss.
Try disconnecting the truck wires and motor wires from the board and connect the trucks directly to the motor (bypassing the board) and re-test your current draw.
If it's still high, there are probably some bad windings in the motor and should be replaced. If it's down to where it should be for current draw, the problem is the circuit board. Either get a replacement board, or make something of your own design - there's not much to it.
Or, maybe something is binding, or causing a resistance, like maybe old grease in the trucks and gears?
Do you have to keep turning up the throttle on your DC power pack to get them to move?
Just throwing some ideas out there!
Mike.
My You Tube
I recently purchased a pair of new Atlas U30C Silver locomotives at a train show. The locomotives are operated as DC units on my DC-powered layout (they have no decoders or speakers installed.) Unlike my other locomotives, these two U30Cs draw a very high amperage: each one draws 1 to 1.5 amps, depending on train length, grade, etc. Both headlights operate no matter what direction the locomotive is moving.
I removed the shell from one of them and operated it for a short time, looking for a short or anything unusual. When I touched the PC board I nearly burned my finger from the heat being generated. That was quite a surprise. I am guessing that the PC board is not intended to handle 1 to 1.5 amps, and that is why it is so hot to the touch.
These locomotives are rather heavy and are both good pullers, but I cannot understand why their amperage draw is so much greater than my other locomotives, including some of my old Blue Box Athearns. Perhaps the motors are on their last legs? Or the PC boards are flawed? Any ideas would be appreciated. Thanks.