Zen Buddha Large scale decoders

NMRA Standards say that all non N scale decoders should "... be designed to withstand a DC voltage of at least 27 volts ....".

The NMRA also says that the "typical" voltage for large scale is 18V.
 
Cliff George said:
NMRA Standards say that all non N scale decoders should "... be designed to withstand a DC voltage of at least 27 volts ....".

The NMRA also says that the "typical" voltage for large scale is 18V.
Click to expand...

Ah, OK, my memory was a bit over the mark then - I must have been thinking of a particular item that was rated up to 35v, thus considerably exceeding the NMRA standard minimum.....

Jon.
 
The decoders need to withstand 27 volts. The QSI was one of the first advertised to handle significantly more, and I also believe the Zimo's will do it.

I doubt it's the voltage alone that is causing the problem, but the current draw at stall. Remember two things: stall current is the highest current you will see, and for a short time, at zero rpm, the motor draws stall, like from a dead start. Switching where you are starting and stopping can destroy decoders that don't have a lot of "overhead".

Stall current in a system that runs 2.5 amps can be several times higher.

Many large scale decoders use FETs that are rated 50 or 60 amps just for this reason.

Greg
 
I've been reading the replies with interest (at least I would have been if I understood some of them, not being very technically/electrically minded). The upshot is - would theses decoders be suitable for my PIKO BR80s? No smoke, no sound and probably LED replacement lights fitted.
 
ebay mike said:
I've been reading the replies with interest (at least I would have been if I understood some of them, not being very technically/electrically minded). The upshot is - would theses decoders be suitable for my PIKO BR80s? No smoke, no sound and probably LED replacement lights fitted.
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I am sure that it would be ok in your BR80, the lights are already LED to my knowledge, it has successfully been in operation on a Piko railbus operaing on Massoth 24v and Piko 20v DCC
 
The faulty decoder was sent back to DCC Concepts and I have had a reply.

(My colleague recommends that they are only suitable up to track voltages of 20v (from his previous discussion with RJ).

Continued running above 20v will possibly cause damage to one of the diodes - as evidenced on your returned item.)
This is not the full text of the email, just the pertinent part

So there we have it, not compatible with Large Scale DCC
The problems with the ones both I and my colleague have are being addressed, so if you have one and it shorts take it back to your dealer.
They will be making a new decoder with more safety features and higher voltage rating.built in.
 
Cranford said:
The faulty decoder was sent back to DCC Concepts and I have had a reply.

(My colleague recommends that they are only suitable up to track voltages of 20v (from his previous discussion with RJ).

Continued running above 20v will possibly cause damage to one of the diodes - as evidenced on your returned item.)
This is not the full text of the email, just the pertinent part

So there we have it, not compatible with Large Scale DCC
The problems with the ones both I and my colleague have are being addressed, so if you have one and it shorts take it back to your dealer.
They will be making a new decoder with more safety features and higher voltage rating.built in.
Click to expand...
Thanks Tony. I now have a choice - wait for the improved version or go LGB/Massoth. Anyone got any s/h small decoders going spare?
 
Well, I may be mistaken but I cry "BS"... if they have the 4 input diodes only rated at 20 volts, I'll eat one of those decoders... I will bet anything it's amps that killed it.. I can believe they used cheap diodes, but it's amps in diodes, not the difference between 20 working volts or 30 working volts...

Anyway, unless I can get my hands on one and get the part numbers of the diodes, and more importantly the FETs or whatever drives the motor.

Anyway, shame on them saying that the diodes are only good for 20v, even on O scale they should have a working voltage of 18...

From their manual: (section 4)
Zen Buddha decoders are carefully designed, tested and made with
very close attention to DCC standards & will always work equally well with all
brands of control systems that properly comply with NMRA DCC standards. (bolding from me)

Well, that is not true, the NMRA standard for large scale is over 20 volts, as I have stated, and DCC concepts say don't go over 20 volts.

We had a similar issue with the OEM Soundtraxx "quasinami" in the Bachmann shay, freaks out at 21 volts. (but I guess better than failing)

Greg
 
Sounds like they should have consulted some G scale users and/or done more extensive testing. There is a sentence in their blurb that says "It is virtually un-killable." so well done to Cranford for killing it! :-) But I see they now say "Designed for O and larger scales..." with no specific reference to G scale.

As it happens I run my layout at 18v at - least that's the input DC voltage to the command centre, I don't have the necessary equipment to measure the actual track voltage as it is not sine wave AC - so maybe they would work for me. But I already have enough variety of decoders!
 
idlemarvel said:
As it happens I run my layout at 18v at - least that's the input DC voltage to the command centre, I don't have the necessary equipment to measure the actual track voltage as it is not sine wave AC - so maybe they would work for me. But I already have enough variety of decoders!
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Should be okay as the voltage is likely to be DC superimposed with the digital signal. I doubt it would be more than 18 Volts for the DCC signal. If you can measure DC and AC (RMS) on your multimeter you should an idea on one of those readings?

Otherwise you will need a oscilloscope to measure the DCC, and you would need to trigger the 'scope to get a reading anyhow. Something I've never attempted myself....
 
Yes, something I've always wondered, is there a straightforward conversion from RMS to DCC track voltage? Or is it not that simple?
 
idlemarvel said:
As it happens I run my layout at 18v at - least that's the input DC voltage to the command centre, I don't have the necessary equipment to measure the actual track voltage as it is not sine wave AC - so maybe they would work for me. But I already have enough variety of decoders!
Click to expand...

I agree with Greg, a few extra volts on the track supply shouldn't cause catastrophic failure. However nasty voltage spikes, maybe due to pickups arcing on outdoor track, may destroy low specification diodes.
 
Just a thought in the back of my tiny little mind. Is it not possible with DCC Kit particularly Massoth to select a reduced voltage so that their kit can be used for differing scales?
 
Yes Jon, the voltage is adjustable 14 - 22V with Massoth. But why reduce your voltage because someone makes a cheap job that is not reliable. The higher track voltage is one of the benefits of running DCC - pick up is more reliable.
 
idlemarvel said:
Yes, something I've always wondered, is there a straightforward conversion from RMS to DCC track voltage? Or is it not that simple?
Click to expand...
It's not quite that simple, but probably close enough to determine that your track voltage is not over 18V....
 
Gizzy said:
Should be okay as the voltage is likely to be DC superimposed with the digital signal. I doubt it would be more than 18 Volts for the DCC signal. If you can measure DC and AC (RMS) on your multimeter you should an idea on one of those readings?

Otherwise you will need a oscilloscope to measure the DCC, and you would need to trigger the 'scope to get a reading anyhow. Something I've never attempted myself....
Click to expand...

No, DCC is an AC system about zero volts.. Not a DC voltage with a control signal superimposed on it. - If there was a DC component, then an analogue loco would move as soon as put on the track.

To run an analogue loco on 'Address 0', the mark-space ratio of the DCC signal is altered to give a 'pseudo DC' voltage to drive the motor.
 
So many bits of information, some good, some off in the weeds....

RMS is the way to get "true" DCC voltage.

ALL "AC" systems are about zero volts, i.e. the positive excursions are matched by negative excursions...

"mains" AC is a 60 or 50 Hz sine wave.

DCC is an AC square wave, with no DC component, and the frequency is modulated to derive the "digital data".

To measure your DCC track voltage is:
  1. yes you can look with a scope, that will give you the best idea, because the signal is never perfect, you can see ringing and rise time problems.
  2. use an RMS AC voltmeter... the spec sheet must say RMS, otherwise it won't read right, since most AC voltmeters are set to measure sine wave AC
  3. use a full wave bridge to convert the DCC to DC. Put a little noise filtering on the output, like a .1 cap and a small electrolytic, then you can measure with an ordinary DC meter (this is possible because it is a square wave, so you are flipping the negative excursions back positive. This by the way is one of the reasons DCC is a square wave, very easy to convert to DC to power decoders, etc.
"Address 0" on systems that still suport this, destroy the symmetry between the positive and negative "halves" of the signal, extending either the positive half or negative half makes it look "mostly" like pulsed DC... but still nasty pulsed.

Greg
 
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