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...2.The difference between 21 volts and 25 volts is a 19% increase above 21. If that were a 19% increase above the specified voltage, then maybe that would be "within margins" for designs. But, isn't 18 volts peak more the expected value for 12 volts RMS? So, isn't 25 volts really 108% above the spec and 39% above the "reasonable expectation" for peak voltage? The whole pulse thing throws out any basis for expectations of peak to RMS.
3. It isn't just "a substantial fraction of those decoders should survive some amount of operation at 25V in any case", but rather all of the decoders should survive, provided they are subjected only to conditions that their designers made provisions for in the design. If the designers made provisions for 25V peak, then the designers would put in margins associated with component parameter tolerances, so that some would survive beyond 25 volts, but a few would probably fail at 25 volts. But, what is the standard for peak voltage on N scale track? We don't want that to be close to the values of limiting voltage for the components that we use.
4. It seems pretty clear that straight DC motors can be made to perform best with voltage pulses that can damage sensitive electronics. So, it seems that, to get the best DC performance and the smallest DCC decoders, we are going to have to recognize some incompatibility. If there are to be "dual mode" decoders, then there must be some understanding of the envelope of parameters that they must be required to deal with and not fail, otherwise, customers and the industry will suffer. Open standards work to solve this type of problem. The alternatives are either a constant series of incompatibilities revealed by customers losing expensive items, or customers becoming captive to single vendors because only MRC locos should run on MRC throttles, only Bachmann locos should run on Bachmann throttles, etc. etc. etc. Neither of those alternative options seems like a good idea.
...I have my doubts that DC throttle manufacturers will redesign their vintage product to be more DCC friendly. DC seems to be on the way out anyway. And for most part the DCC decoder manufacturers make their decoders play well with the DC throttles. What we have here is a rare exception of an alleged (I have not personally experienced this problem or seen any damaged decoders). If this was a wide-spread issue, we would be hearing all about it from lots of sources. So among all the different DC throttles out there, and all the DCC decoders we have a single alleged incompatibility. That doesn't strike me as a cause for alarm or a wide-spread problem....
Ok, let me rephrase.If a powerpack is delivering 25V peaks on a waveform that has an RMS voltage well under 21V, and that powerpack is being used to run a dual-mode decoder with a stated rating of 21V, and the decoder gets damaged, then I squarely blame the decoder manufacturer for overstating the voltage rating of the decoder. I do not blame the powerpack manufacturer for putting 15VDC on their powerpack if the RMS voltage stays below that, and it is a regular waveform with a peak amplitude less than twice the nominal max voltage. To be clear, in the context of previous posts in this thread, I'm talking about 25V peaks in a repeating waveform, without transient irregular 'spikes' that go higher. And unless I missed it, no evidence has been presented in this thread that the powerpack in question is delivering such spikes. It's delivering a regular waveform with an average voltage that matches the spec on the outside. That's my opinion. My reasoning is that model railroaders, and consumers in general, cannot be expected to test their equipment with oscilloscopes before operation, but testing with a quality volt meter is a reasonable expectation. Also, the difference between 21V and 25V is not large enough that it shouldn't be accounted for in safety factors and manufacturing tolerance, anyway. That is, if the decoder package says 21V then I would expect that a substantial fraction of those decoders should survive some amount of operation at 25V in any case. Not that I would make a warranty claim if I knew that a decoder had been so operated, but they should give themselves some headroom on their rating. Tolerating waveform peaks up to twice the average voltage is an admittedly arbitrary number in this context, but eminently reasonable given common waveforms one finds in powerlines and electronics of all sorts.
I would still love to see the specs (like max voltage rating) of the Rapido decoders which were allegedly damaged by the 1300. I've been using "alleged" a lot in this thread. I feel like a news reporter.
The NMRA recommendation is not on the decoders. It is a recommendation for what is allowed to be on the track voltage.It says that voltage measured at the track shall not exceed 24v (for N Scale). And it says that the DCC command peaks shall not exceed 22v. 24v "at the track" means "rms" to me, because that is what you would measure if you put a voltmeter on the rails. Therefore, the 1300 is well within this recommendation because its RMS maximum is nowhere near 24v. But the command peaks are exactly that, peaks. Could a 60 Hz sine wave peaking at 25v harm a decoder because it's over that line? Maybe. The onus is on the power pack manufacturer to stay under that 22v limit, in my view....
It's simply a matter of a legacy product, the 1300, being used in an environment that MRC could never have predicted. My beef with them is not that they make the 1300, but rather, that they showed no inclination to investigate the problem to see if Rapido has a legitimate beef. Instead, they took a "HOW DARE YOU!" attitude. This is not a new problem. That message has been posted to Rapido's web site for over a year. Either MRC doesn't care to investigate, or they did and they don't want to share what they found.
Now wait a minute...24V RMS track voltage is clearly not the same exact standard as DCC command peaks at 22V. Because if the peaks are 22V then the RMS voltage can't be higher.The way I read it, if you are running a DCC decoder on a DCC system, you should be able to expect that the peaks won't exceed 22V. The same evidently cannot be said for running analog. In other words, if you're running a 'dual mode' decoder on an analog throttle, you'd better expect to see up to 24VDC RMS. Which means the peaks could well be higher.(I agree that neither manufacturer has handled the publicity aspect of this very well, but I was trying to keep my comments general, as to what I expect as a consumer.)
Now wait a minute...24V RMS track voltage is clearly not the same exact standard as DCC command peaks at 22V. Because if the peaks are 22V then the RMS voltage can't be higher.The way I read it, if you are running a DCC decoder on a DCC system, you should be able to expect that the peaks won't exceed 22V. The same evidently cannot be said for running analog. In other words, if you're running a 'dual mode' decoder on an analog throttle, you'd better expect to see up to 24VDC RMS. Which means the peaks could well be higher.
Seems to me that, if Rapido is going to offer locos with dual-mode DCC decoders that they assert will also run on DC, then it's incumbent on Rapido to verify that their decoders are compatible with DC power packs and, if necessary, furnish a listing of those compatible power packs. If that is not feasible, then they should provide a specification for the maximum (peak) input voltage that their decoder can tolerate without damage. Likewise the power pack manufacturers should be able to specify the maximum (peak) output voltage that their power packs can produce.
Remember that DCC Track voltage is type of a square wave. Square wave's peak voltage is the same as RMS voltage.
I thing that this is blown way out of proportion. We have alleged incompatibility of one DC throttle with one DCC decoder. We now need official warnings to be included with the products?
I've been using "alleged" a lot in this thread. I feel like a news reporter.
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Topic: Railpower 1300 testing (Read 41058 times)
