Railpower 1300 testing

[Point353]

I see where you are going with this. Looks like you are familiar with electronic design. I missed that myself. 
I would still change the speed control pot to 15k, and install a resistor between the top lead of the pot and the positive of the bridge rectifier. With the high gain of the Darlington transistor, you could also add a resistor between the wiper lead of the pot and the Zener diode's cathode.

Removing the 10K resistor from the original MRC design results in a schematic comparable to that of the Kato power pack.
Max indicated that he ran a simulation, per my earlier suggestion, with a resistor between the top lead of the (original 20K) pot and the positive output of the bridge rectifier (and without the zener diode). He found that, with a 2.2K resistor, the pulses were reduced to 20V and the maximum DC out was about 12V at full load. I'd still like to see the results (simulated 'scope traces) of that configuration. However he dismissed it, preferring the pulse action of the original MRC circuit - along with the added zener diode.

[peteski]

Removing the 10K resistor from the original MRC design results in a schematic comparable to that of the Kato power pack.
Max indicated that he ran a simulation, per my earlier suggestion, with a resistor between the top lead of the (original 20K) pot and the positive output of the bridge rectifier (and without the zener diode). He found that, with a 2.2K resistor, the pulses were reduced to 20V and the maximum DC out was about 12V at full load. I'd still like to see the results (simulated 'scope traces) of that configuration. However he dismissed it, preferring the pulse action of the original MRC circuit - along with the added zener diode.

The transistor is a voltage follower. Whatever voltage is on the base will be also on the emitter (output). In the original 1300, the speed adjustment pot's slider goes through the full range of voltages (from zero to full voltage coming from the rectifier).  To limit the maximum voltage you would add a resistor between the top lead of the pot and the positive side of the rectifier.  That is what I mentioned few times already.  This can be done with the 10k AC-injection-resistor in the circuit, or without it.  But if used, the value of that AC-injecting-resistor should also be changed.

I wonder why we are mulling over all of this?  The 1300 is what it is.

[Point353]

I wonder why we are mulling over all of this?  The 1300 is what it is.

The instigation was the accusations made by Rapido.
The lack of specific details led to an investigation here to see if the alleged "spikes" could be observed and, if so, the source identified.
No evidence of any signals in the output that would meet the conventional definition of "spikes" has been observed.
However, the maximum amplitude of the voltage peaks at the output of the 1300 could conceivably be deemed questionable.
Several means have been identified to limit the peak output voltage.
Without more information from Rapido, regarding the failure mode of the decoders they are using, we can't be certain if the issue is that the output of the power pack is a bit too high or that the withstanding voltage capability of the decoders is a bit too low - or some combination of both.

 
 

[peteski]

The instigation was the accusations made by Rapido.
The lack of specific details led to an investigation here to see if the alleged "spikes" could be observed and, if so, the source identified.
No evidence of any signals in the output that would meet the conventional definition of "spikes" has been observed.
However, the maximum amplitude of the voltage peaks at the output of the 1300 could conceivably be deemed questionable.
Several means have been identified to limit the peak output voltage.
Without more information from Rapido, regarding the failure mode of the decoders they are using, we can't be certain if the issue is that the output of the power pack is a bit too high or that the withstanding voltage capability of the decoders is a bit too low - or some combination of both.

But you are modifying the MRC design. The problem is with unmodified 1300.

[Point353]

But you are modifying the MRC design. The problem is with unmodified 1300.

Right - based on the presumption that the peak output of the 1300 is somehow too high.
Yet, we haven't seen the presence of any "spikes", which is what Rapido has asserted.
However, all this is pure speculation without more info from Rapido. 
At the minimum, Rapido needs to quantify the maximum DC input voltage that their dual-mode decoders can tolerate - in particular whether or not they meet the NMRA specs of 24V for an N scale decoder and 27V for HO.
It might turn out that the MRC pack is fine and the decoders used by Rapido are deficient.

[peteski]

Right - based on the presumption that the peak output of the 1300 is somehow too high.
Yet, we haven't seen the presence of any "spikes", which is what Rapido has asserted.
However, all this is pure speculation without more info from Rapido. 
At the minimum, Rapido needs to quantify the maximum DC input voltage that their dual-mode decoders can tolerate - in particular whether or not they meet the NMRA specs of 24V for an N scale decoder and 27V for HO.
It might turn out that the MRC pack is fine and the decoders used by Rapido are deficient.

I highly suspect that the word "spikes" is being misused by non-electronics-savvy people (like explained earlier in this thread).

If Rapido uses ESU decoders, then those likely have the same specs as other ESU decoders. I also mentioned those voltages earlier in this thread. See https://www.therailwire.net/forum/index.php?topic=44170.msg569478#msg569478

LokSound micro has a Operating Voltage range 5-21V while all the other LokSound decoders work on 5-40V.

[Point353]

I highly suspect that the word "spikes" is being misused by non-electronics-savvy people (like explained earlier in this thread).

If Rapido uses ESU decoders, then those likely have the same specs as other ESU decoders. I also mentioned those voltages earlier in this thread. See https://www.therailwire.net/forum/index.php?topic=44170.msg569478#msg569478

LokSound micro has a Operating Voltage range 5-21V while all the other LokSound decoders work on 5-40V.

However, it's still not known which one Rapido is using. It could even be a special OEM version with different specs.

[mmagliaro]

Could you run a simulation that shows how much current flows through the zener diode when the throttle (R2) is at the full setting?

I had done this, but didn't post it.  With a 500 mA load (about 24 ohm), full throttle, 12.1v through the load, the zener conducts only about 6 mA.  With 20v across it, that would be only 120 mW.  So a 1W zener is still plenty capable.

And by the way, the NMRA spec says, "when measured at the track".  So I think that means AVERAGE DC voltage of 24v, not the peak, in which case, the 1300 would be well within the spec, unless that NMRA spec meant the "maximum" measured at the track which might mean the peak.  After all, if you had an electrolytic capacitor on the input to the decoder to smooth its own power supply, that would indeed cause the input voltage it sees from the track to be much close to the peak than to the average.

[peteski]

Going back to the spike theory, as Point353 observed, the 1300 is basically like the beloved and safe Kato throttle, with a higher-voltage transformer, and with added single resistor for the pulse functionality. None of the 1300s components should to be prone to generating true voltage spikes during normal operation.

I agree with Max that if this throttle is killing DCC decoders, the most likely cause is its higher than standard output voltage.

[Maletrain]

Picking-up on the comment about Loksound "micros" being rated up to only 21 V instead of the 40 V of other Loksounds, doesn't this suggest that design to higher voltage ratings increases size of the decoder?  I don't know if it is just due to a smaller integral capacitor or if all of the internal components need to be larger to achieve the higher voltage rating.  But, in our quest to put sound (and who knows what else) into smaller locos in smaller scales, it seems like the whole area of electrical power specifications and requirements needs to be re-thought.  Some specification for peak voltage on the tracks seems warranted, so that it cannot be conflated with max RMS voltage and allow unlimited peaks.  Maybe there should even be different standards for decoders that serve different purposes, such as "micro" vs "dual mode".  If every decoder has to be "idiot proof", they are probably going to be bigger than what fits into some of our desired applications.

[mmagliaro]

Picking-up on the comment about Loksound "micros" being rated up to only 21 V instead of the 40 V of other Loksounds, doesn't this suggest that design to higher voltage ratings increases size of the decoder?  I don't know if it is just due to a smaller integral capacitor or if all of the internal components need to be larger to achieve the higher voltage rating.  But, in our quest to put sound (and who knows what else) into smaller locos in smaller scales, it seems like the whole area of electrical power specifications and requirements needs to be re-thought.  Some specification for peak voltage on the tracks seems warranted, so that it cannot be conflated with max RMS voltage and allow unlimited peaks.  Maybe there should even be different standards for decoders that serve different purposes, such as "micro" vs "dual mode".  If every decoder has to be "idiot proof", they are probably going to be bigger than what fits into some of our desired applications.

In general, components with a higher voltage rating are larger.  This is true even for "large" discrete components.  Look at the size of a 16v 100 uF axial lead capacitor vs a 25v vs a 50v.   
Honestly, I think the 24v rating in the DCC spec was quite generous and allowed for a safety margin.  There's no reason that any power supply should be putting peak voltages that high on the rails when our motors run on 12v.
Even a "sloppy" simple sine wave power supply doesn't need to have peaks higher than 18v to achieve a 12v average.

So I wouldn't want to see the spec changed to allow higher track voltage and requiring higher decoder input tolerance.

[peteski]

Picking-up on the comment about Loksound "micros" being rated up to only 21 V instead of the 40 V of other Loksounds, doesn't this suggest that design to higher voltage ratings increases size of the decoder?  I don't know if it is just due to a smaller integral capacitor or if all of the internal components need to be larger to achieve the higher voltage rating.  But, in our quest to put sound (and who knows what else) into smaller locos in smaller scales, it seems like the whole area of electrical power specifications and requirements needs to be re-thought.  Some specification for peak voltage on the tracks seems warranted, so that it cannot be conflated with max RMS voltage and allow unlimited peaks.  Maybe there should even be different standards for decoders that serve different purposes, such as "micro" vs "dual mode".  If every decoder has to be "idiot proof", they are probably going to be bigger than what fits into some of our desired applications.

It is not that bad.  The (only) alleged problem might occur when decoders are used on DC with DC throttles that use pulsing DC (unfiltered output from a full-wave rectifier).  That is when the decoder's built-in filter capacitors will smooth out the pulsing DC to be closer to the peak voltage (rather than RMS voltage).

When decoders are used in their intended (DCC) environment, they are much safer.  DCC signal is a square wave which is highly unlikely to get neat the maximum rated voltage. Its peak and RMS values are the same.

Let's not overthink this or have knee jerk reaction to a problem that none of us heard of until the Rapido's MRC 1300 warning was somehow brought to our attention.  If you run your trains with DCC you have nothing to worry about.  How many people buy DCC equipment to exclisively run them in DC and also have a MRC 1300 throttle?  I think a very small number of modelers.

To me Rapido's problem is more an exception than a rule. And we don't even know if anything was proven scientifically by Rapido.  HAve they actually done some scientific tasts?  Do they know what component is failing?  What are their decoders specs for max safe operating voltage?

Even this thread, while informative and enligtening, doesn't prove that 1300 blows up decoders. ALl we know it is that 1300 seems to have slightly higher output voltage than few other DC throttles.  But we haven't even tested it powering a DCC-sound-equipped loco to see how much lower the output voltage is under more than 50mA of load.

[up1950s]

How many people buy DCC equipment to exclisively run them in DC and also have a MRC 1300 throttle?  I think a very small number of modelers.

Now people are at times forced to buy DCC because DC versions are not available . That 1300 screwed the hell out of many thrilled to run their new equipment , and at least one manufacturer . The 1300 manufacturer replied with an unconcerned , it's not our fault comment . Thanks to Rapido and now Max we know the truth about that defectively designed and damage causing Railpower 1300 , further we know that they don't take the consumers or the products that their product consumes with the proper concern and respect they deserve. Shame on them .

[Point353]

Now people are at times forced to buy DCC because DC versions are not available . That 1300 screwed the hell out of many thrilled to run their new equipment , and at least one manufacturer . The 1300 manufacturer replied with an unconcerned , it's not our fault comment . Thanks to Rapido and now Max we know the truth about that defectively designed and damage causing Railpower 1300 , further we know that they don't take the consumers or the products that their product consumes with the proper concern and respect they deserve. Shame on them .

Can you cite a standard or specification that the MRC DC power packs (either 1300 or 1370) are required to meet but are not so doing?

Again, for reference, the NMRA standard for a DC power supply simply states that "Full throttle voltage available at railhead shall not be less than 12 volts direct current at maximum anticipated load." 

[peteski]

Is the 1300 a current MRC product? If not, when was it discontinued?

The other question begging be asked is how many model railroaders do you personally know which were affected by the alleged problem with 1300 and Rapido decoders?  None, one, ten, 30, 100?