Hi, I've just purchased a ROCO LOKMAUS system for my HO layout, and my first go at installing a MRC sound decoder has been a failure. On the test track using a 20ohm resister for protection, the decoder tested Fine, but when placed on the track I think I've fried it. I checked the voltage from the transformer 17.5 volts no load. The voltage at the track is 22 Volts which I think is way too high. I've looked at other sound decoders on the Net that indicate 16V max, MRC as far as I know, don't specify a voltage for the sound decoder . Is my Roco system voltage too high at the track? Any help appreciated thanks.V
Well, you have to be a little careful measuring DCC voltage. Because it is not smooth dc or normal ac sinewave it can mess up the readings on some voltmeters. But that said 22volts does sound over the top. Are you sure you haven't managed to connect the dc power to the track instead of the DCC? (It's just that 22 volts would be about right for that and I'm not a great believer in coincidence )
What kind of a voltmeter do you have? True RMS reading? The DCC voltage is a screwy mess, and can easily mess up a meter. The voltage on the track should be slightly lower than on the transformer - if the output of the "transformer" is DC. While talking about this, remember that when converting AC to DC you will NOT get the same voltage. RMS voltage is a "running average heating power output" of the voltage. Remember - the AC voltage goes up and down. DC voltage = AC voltage X 1.414 - voltage drop of rectifier. Hope this helps. Mark in Utah
The track voltage was checked using an analogue meter by a friend (Aircraft Avionics Engineer) who has a good understanding of AC, at his place of work, I knew my digital meter would not display the correct voltage. Maybe trying a different power supply (14Volts AC) may help. I haven’t been able to find any info on the Net regarding this problem and the Hobby shops in my area don’t seem to have a lot of DCC knowledge. Thanks, any comments are welcome and I appreciate the help. Rod
I'll ask the obvious question...have you put it back on the programming track? What did it do? Assuming you haven't goofed the wiring to the main track (and maybe even if you did) I don't think you should have fried decoder. The 20 Ohm resistor helps limit the current if you have a problem with the decoder installation, hence saving the decoder. But, if there was such a problem, the decoder should not have programmed and read back ok, so the resistor was not having to protect it since all must have been ok. Which makes one suspect a wiring or configuration problem. I think, from a bit of reading and thinking, that trying to make anything out of the voltage on the tracks in a DCC environment is probably going to do little but cause confusion. I just don't think that is where the problem lies, most likely. First, I'd go back to the programming track, then I'd double check, and then check again, all the wiring and any switch settings. I have little DCC experience (just getting started) but quite a bit of debugging electronics experience, so it is probably only half useful advice..... Just thought of another question....what makes you think you fried it?
Hi, Yes It was placed back on the programming track and the controller indicates a short, The first thing I did was check all wiring not once but a number of times. I think the voltage drop across the protective resister saved the decoder initially but without the resister the voltage is too high, well that’s my theory. Could the decode have been faulty from the start? Maybe I should try again, just can’t afford to wast decoders. Thanks for your comments. Rod
How about popping off the shell and seeing what's going on inside the loco. Not much to be lost at this point. Maybe there is a short in the wiring outside the decoder.
Yep did that, all wiring has shrink tube placed on solder joints and all connections checked, no problem inside the loco or outside. I think I will have the transformer checked again and maybe try another power supply. Thanks for the comments. Rod
Greetings, I am working on a 5v control board for my layout, that uses several 5v relays for misc duties. I have two 1.5 relays I would love to use up, but need some help in a simple circuit to down convert to 1.5v. These are really small relays, dont draw a lot of power. Thanks!
I do not know about the decoder but below is a link to buld your own DCC voltmeter. The circuit is provided by NCE. http://jdb.psu.edu/nmra/dcc-v-meter.pdf I have three cheap digital voltmeters that show 13.3 VAC track power from my NCE Power Cab. With nothing on the track, the track voltage is 13.3 VAC. Add one HO diesel with sound and the voltage drops to 13.1 VAC. Add a second loco with sound and the voltage drops to 12.8 VAC. Both locos are just idling. The DC power for the NCE Power Cab is 13.55 VDC. I measured the track voltage with an Oscilloscope and the voltmeters are within a couple tenths of a volt of what the 'Scope shows. The type of meter I use. http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=90899 Don't know what is available in your area. I have compared notes with a couple others using near the same style of meter and we are within a couple of tenths of a volt. The readings compare to the DC power supply voltage. Lex
Hi FireAce The forum likes to hide this option for a new post. Took me a while to figure it out. Click on Forum Tools Click on Post a new message In the subject heading try, Relay Voltage Question. Then your question in the text. That way your thread is mostly for your issue. In this thread, there is an possibility your question could be missed. Hope this helps. lex
