Hey Jeff, Bring your scopemeter over next weekend, and we can take some pictures of the traces in different situations? It will be fun, and we can answer these questions with oscilliscope traces to prove one way or the other what is really happening.
Jeff, in my haste I have missed the word "time", but that was what I have meant :teeth: ie: you are indeed right, these are very poor explanations, which refer to "average" /"equivalent" voltage , so 12 V switched on 50% and off 50% time is referred to as 6V this could have mislead, sorry Chris
..which is why seeing Robert's oscilloscope pictures is going to be of interest. The motor does NOT see a "referred" voltage - it see a real voltage, and hopefully Robert can show us what is happening and what the voltage really amounts to. Of course this may just open a big can of worms, but modeling in the "I think it works this way" is not the way to go.
Don; i'm just getting caught up with this thread, and thought i would slip in this little bit of info. Here is the link i used to help understand what i was measuring and dealing with when my power cab arrived a few weeks ago. http://www.members.optusnet.com.au/nswmn/meters.htm Robert's comment about a "true RMS" meter is important as only a meter with this can get close enough to read DCC power. I had a hard time understanding the whole principal of the AC/DC inner workings of DCC, but have final resolved all of them. I d eleted the thread to the "diode voltage reducer" that i'm sure you have read about. The diode numder that Robert posted (i think it was an NS #) can be crossreferenced with Radio Shack, where i bought a bag of 50 for under $2bucks. I'm sure he will post the number again for you if you ask. Robert, Chris and the other folks here are great, and i'm sure will help you figure it out. I'll just follow along and read the post from here on out, as I am still learning too. Good luck, and have fun. Tony B..
Wow that site is the "nuts" Has some really good information. The DCC Pocket Tester looks as if it might just answer all the questions we have been asking. How did you find this site?
it has already been discussed on the Trainboard :thumbs_up: see: http://www.trainboard.com/grapevine/showthread.php?t=82441 see messages #46, #51, #68 specifically and all the others as well !! Chris
Rob, I did this some time back and posted the temperature difference between DCC and DC on a marklin 3 pole motor and also showed the math behind this in the Z scale Yahoo group. The bottom line was you WILL NOT burn out the motor with DCC under normal operating conditions. I am saying normal because you could burn motors with DCC or DC any day by stalling it long enough with enough current through it. Anyway I have borrowed a few good equipments from my work and we could do the math on paper and calculate the DCC currents then prove it by testing it. I also will build some hardware to run the motors at 50V+ with the same Decoder to show Voltage does not matter. (Inductor is a current device) By pulsing the voltage you are controlling the current. I will get a new 5Pole Marklin and a GP motor for this test . I hate to disagree with many of you folks but this is like riding on one's fear of burning motors with voltage and it has gone on for too long. Will document and post all details of calculations and test results after the test. Rob, Jeff is traveling till Tuesday of next week so how about this Friday? We could do it on your MRC and I will test it on my Digitrax too. Kim
Don, I had posted it in the Z_scale Yahoo groups many years back, I tried searching for it and gave up, Anyway when I first started on DCC I found the locos running hotter than when run on DC. Which is true if you run a loco at slow speed on DC say at 3V and run the same loco with DCC and ~ the same speed it ran at 3V DC, the motor will run hotter, which is where all the fear of motor burning up comes. The temperature is still well within the operating region of the motor. I had a test setup with temperature probes on two motors and checked the temperature difference running at different speeds. Anyway will post all details on test setup, math and results on Friday. Kim
OK, Friday we will put this issue to rest once and for all! :shade: Now I just have to get throught the longest day of the year... The last day of work before the Christmas Holiday! It already feels like I have been here several hours!
You know, I think today is the longest day of the year(in Australia). Doesn't this post apply to all scales? Maybe not in absolute terms, but relatively speaking, the results should be applicable. We might reference this in the DCC or Inspection Pit forums. In any case, it is very interesting to me. Thanks.
Chriss, I used to think just like you, but knowing some of the advantages of dcc, I am not going back. Despite all the problems and frustrations of learning something you dont know, I love it.
No problem Don, its the least i could do to pay you back for hooking me up with that decoder a few months back. I kept this sites address stored so i would have it for referance in the future. I found the amp test very interesting, and have used this to determine if a new loco is dragging to much and needs a little tweeking. I still have not bought a Tony's DCC meter, as i can get pretty close with my Fluke true RMS meter (close enough). i built one of the diode voltage reducers that R Ray described, and have left it in line on my track current just for a safty measure. Im opperating at 9.87 volts at the track according to my Fluke. i know this is not exact, but close. With the diode reducer removed i run at 13.12 volts on the stock power cab. I too am very interested in the tests that R Ray and ? (sorry i suck with names) hopefully this will put the voltage issue to rest once and for all. My NCE dealer freind claims that you can not over-volt a loco because of the pulsing of the power, however there was so much chatter here and on Z Central about voltage, that i followed R Ray's lead and built the diode reducer. So i look forward to the mad professors latest tests and findings. Leaving things to the experts.... Tony B....
Some simple summaries: Motors burn out from three things: 1) bearing failure 2) overloading 3) over voltage [think of someone putting 220 VAC on a 120 VAC appliance] Can't help with the bearings but lets look at the overload and over voltage: If a loco is overloaded, it will eventually likely overheat. The more the voltage the greater the problem. But still not likely to be the reason (who really overloads e.g. really long trains for hours). For Marklin's brush type motor, brush wear and armature contamination from them are a reason but I have usually found that most of my Marklin motor failure is from lube failure (can't run them for days without re-lubing). Pretty much ditto from any other drive train. The motors used in the GP's and SD's don't have the brush problem and I have not seen heat in any way from them. Over voltage: this is not really possible with DC or the locos would run Lionel style at warp speed. But DCC is different. It pulses at somewhat higher voltage (10 volts at the lowest, 15 or even a bit higher on some out-of-box systems). Still, this is really not enough to arc the windings and no one runs the loco at the max Speed step 12/28 or 128 (programmable) or it would run just like a DC loco on an HO or O power pack - way too fast. So run without fear from motor overvoltage, really.
This is a scope signal at speed step 1 of 28, showing the duty cycle pulsing the motor. The RMS Track Voltage is set to 8.75 volts and the actual voltage that the motor is seeing is pulses of 6.7 volts for about 1.3ms each. Duty cycle is about 9% Kim has a lot more scope caps, and will write up the difinitive results, but from the testing, the voltage does stay high, and it's the duty cycle that varies with speed step increases. Of note is that it looks like you probably won't burn out a motor if you over voltage it with DCC, because we ran the voltage up to 16 VRMS at the rails, and ran the motor at speed step 28 for several minutes while observing 120ma current draw, which is the same current draw with the track voltage set to 8.75 VRMS. Kim was also demonstrating that we can run the motor on pulses of 45 volts, without damage to the motor as long as the duty cycle was low. We did smoke a decoder during testing, but the motor still ran fine, although running very fast at speed step 4. Kim will post more
Thanks Robert & Kim. This is the first definitive real life info we have seen on this whole subject. Sorry you lost a decoder. Hope it wasn't one of those DZ123M0 although I see a few comments where they may be in the food chain again. Keep us up on the info to come. ...don
Robert/Kim Is there any significance that the pulses appear to be in groups of 2 and then groups of 3 and in other scans the blips seem to almost be randomly placed in time. ...don
