Railpower 1300 testing

[peteski]

The DC throttles were designed rather loosely, because they were made for the old-school models in which the electrical components consisted of a bunch of copper wire wrapped around an iron core (motor) and a tungsten filament in vacuum (light bulb).  Nobody gave much thought to peak voltages or slightly higher voltages since both to those components can easily withstand excessive voltages for prolonged periods.  Only when the more delicate electronics (DCC) were incorporated into models, there seem ot be some compatibility problem.  The main purpose of a DCC decoder is to function under DCC - analog operation was a nice added perk.  Most of those work together just fine, with as it appears a small exception.

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.

Maletrain:  You mentioned some of the modern PWM throttles. We have not tested any of those here (except for a vintage MRC unit which seem to have max voltage within acceptable range).  I suspect that truly modern DC throttles (which use BEMF) have their voltages well within acceptable range.

[Maletrain]

Ben, just a couple of comments, and then we will have to just agree to disagree.

1. You are correct that we can't expect model railroaders to all use oscilloscopes, so that is why it is important to use agreed standards to deal with the things that they cannot measure with a typical RMS voltmeter.
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.

[jagged ben]

...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.

If we're talking about an N scale decoder, and N scale track voltage is industry wide assumed to be max 12V (debatable?), then perhaps the decoder spec should simply state that it's rated for 12V.  Especially if it was designed for 12V with an assumption that the wave peak on the 12V source doesn't typically exceed 18V.  Then no one could blame either the 15VDC Powerpack or the 12VDC decoder for failure; blame would fall squarely on the user, and no one could be accused of mislabeling a product or failing to honor a warranty. 

BTW it's not clear to me that those are the parameters that prompted this thread and discussion.  Unclear to me, or maybe I just missed it, what decoder was putatively damaged by a Railpower 1300. 

And FWIW, in light of this discussion I happened to glance at some decoder packages that just arrived in the mail for me (totally different manufacturer and type of decoder than what prompted this thread), and nowhere on the packaging does it state any voltage rating for the decoder.  So this business of not transparently or adequately labeling products with voltage ratings isn't limited to the manufacturers under previous discussion.   

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.

I agree it would be better if there was a standard for peak voltage on N scale track, but I'm not aware of any.  But that's just all the more reason for decoder manufacturers to be conservative on the ratings they claim for their decoders.  Thus peak being twice nominal instead of 1.5 times.   I have no knowledge that manufacturing tolerances can be expected to be sufficiently tight such that I can agree with your first two sentences. 

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.

To my mind your first sentence just bolsters my argument.  If DC powerpack manufacturers are, or were in the past, incentivized to use high peak voltages, then DCC decoder designers need to be aware of that fact and develop their designs and assigned voltage ratings accordingly.

I'll just add, this thread has been very useful in laying out conceptually what makes a DC powerpack best for both traditional analog and dual mode decoder applications.   I have no problem with a manufacturer putting some advertising copy on their powerpack touting such features.  It might say both "pulse feature delivers excellent slow speed performance" and "limits peak voltage to protect valuable dual mode DCC decoders."    My criticism would be for decoder manufacturers putting a voltage rating on their product that amounts to an overstatement when an ordinary user deploys a longtime-on-the-market powerpack and measures track voltage with an ordinary, not too cheap volt meter.  Common past products amount to a de facto standard.

[jagged ben]

...
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.

...

Good points.  And I apologize if I'm harping on it too much now.  But if all kinds of people have presumably been using the Railpower 1300 with all kinds of dual mode decoders, and only one model manufacturer has issued a complaint about it, then either that particular decoder wasn't as well designed or quality controlled, or perhaps all the other model manufacturers have been sucking up the expense of warranty claims.

[mmagliaro]

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.

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.

Yes, it would be best if BOTH sides (decoder and power pack) had some safety margin.  But in this case, the power pack not only doesn't have a safety margin, it's over the line.  So I suspect that as the source of the problem first.

I agree with Peteski that manufacturers are probably not going to make any changes to legacy products that were designed 25 years ago (like the 1300).  They will keep selling them as long as they sell.  They are, after all, intended to run DC locomotives and they do that.

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.   

[peteski]

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. 

[up1950s]

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. 

FAKE NEWS

[jagged ben]

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.

...

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.) 

[Point353]

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.

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.

[mmagliaro]

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.)

They are two different specs, written in the same NMRA recommendation.  The RMS voltage is the voltage for power.  The DCC command pulses are for the DCC commands.  Both can coexist on the rails at the same time an they don't have to have anything to do with each other.  Imagine a 60Hz full-wave DC with RMS of 24v, always-on, as your power source on the rails.  You'd read 24v if you put a DC meter on the rails.  You could still have the DCC pulses at 22v at a completely different frequency, and that would not affect the RMS voltage you would read on the rails with a voltmeter.

Years ago, people used to build high-frequency AC constant brightness systems that would put high frequency AC on the rails just for lighting up passenger car lighting and loco headlights.  It had nothing to do with the DC voltage for powering the motors.

The decoder should expect to withstand up to 24v RMS for power and command peaks of 22v for commands.  I don't see why the two have to have anything to do with each other.

[peteski]

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.

Remember that DCC Track voltage is type of a square wave. Square wave's peak voltage is the same as RMS voltage.

[peteski]

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.

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?      

[mmagliaro]

Remember that DCC Track voltage is type of a square wave. Square wave's peak voltage is the same as RMS voltage.

I did not realize this!  That means that the NMRA spec's "voltage measured at the track" is, in fact, the peak - the highest voltage, even if instantaneous, that should be on the rails.
So the 1300 is over spec on that voltage.   

This is one of those times I wish I had unlimited income and free time - just to buy 100 decoders and spend a month twiddling around with them and some MRC power packs to see what blows them up.

[Point353]

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?      

Who said anything about "official warnings"?

Given that we still don't have any technical specifics from Rapido, how might you suggest to best address this situation?
What information (and in what format) might be provided to the consumer (who may not have (or need) any technical background) to help ensure that they can select a dual-mode loco and a DC power pack that are compatible with one another?

[u18b]

I've been using "alleged" a lot in this thread. I feel like a news reporter. 

Actually.... I've always considered posts by you to be allegedly from Peteski.

I'm still not convinced you're not a bot.