D
Zen Buddha Large scale decoders
- Thread starter Cranford
- Start date
Wow, that's really rated low... also pretty funny, most people have stopped using Schottky diodes... too expensive for the amps, and voltage drop. FETs are cheaper, lower voltage drop. (history, first units used regular diodes, too much heat and voltage lost, then people use schottky with lower voltage drop, but expensive, last, since manufacturers used FETs for the H bridge power to the motor, just add 4 more and strap as diodes, now fewer different parts used, saves manufacturing costs too)
Schottky is not needed at these frequencies... old school design.
Definitely if you have a 5 amp unit, you use diodes rated higher... so this does indeed explain the diode going out. Also confirms what I said, these are 60v diodes, no way 20 volts killed them, it was overcurrent and a marginal design.
Greg
p.s. good call on the 1.4v loss, thanks for catching that!
Schottky is not needed at these frequencies... old school design.
Definitely if you have a 5 amp unit, you use diodes rated higher... so this does indeed explain the diode going out. Also confirms what I said, these are 60v diodes, no way 20 volts killed them, it was overcurrent and a marginal design.
Greg
p.s. good call on the 1.4v loss, thanks for catching that!
Last edited:
Hi All, am back again on this subject, as readers will notice it is 11 months since the start of this problem, I have been in contact monthly with DCC concepts and the problem still has not been resolved, the latest being on the subject of voltage at he decoder, now you have all indicated readings of input and track voltage for G scale locos but apparently we have been reading the wrong voltage, it still doesn't distract from the fact that it is not high enough for us. I asked how to read this voltage, below is the answer I received, if anyone can put it in plain English I would be grateful, they are however still working on manufacturing one that will cope with higher volts.
Hi Tony,
DCC voltage is a square wave and is reliably measured using an oscilloscope.
AC meters will give different readings depending upon their sampling rate.
However, there are meters, such as the RRamp meter that are specifically designed for DCC.
We are currently developing our own version. The prototype was in my hands for about an hour.......
There's plenty to read about via the DCCwiki pages.
DCC Power - DCCWiki
DCC Power - DCCWiki
A booster takes DC power from the power supply, and the DCC command information from the Command station, and creates a digital waveform, which is applied as track power.The length of time that the voltage changes provides a method for encoding data. DCC uses a binary encoding system. To represent a one, the time is short (nominally 58µs for a half cycle).
dccwiki.com
Hi Tony,
DCC voltage is a square wave and is reliably measured using an oscilloscope.
AC meters will give different readings depending upon their sampling rate.
However, there are meters, such as the RRamp meter that are specifically designed for DCC.
We are currently developing our own version. The prototype was in my hands for about an hour.......
There's plenty to read about via the DCCwiki pages.
DCC Power - DCCWiki
DCC Power - DCCWiki
A booster takes DC power from the power supply, and the DCC command information from the Command station, and creates a digital waveform, which is applied as track power.The length of time that the voltage changes provides a method for encoding data. DCC uses a binary encoding system. To represent a one, the time is short (nominally 58µs for a half cycle).
dccwiki.com
Tony, this may not answer your question but I hope it is still of some help.
Accurately measuring an AC voltage often isn't straightforward.
I sometimes demonstrate this by using a multimeter to measure the mains voltage. Typically here in the U.K. the reading will be around 230V. I then repeat with the same meter but set to read DC volts, giving a reading of around zero!
In my opinion the issue of voltage measurement with these decoders is a bit academic. Earlier posts seem to suggests that some of the components used don't have a sufficient factor of safety for a G scale product that's reliable on all commercial G scale systems.
Accurately measuring an AC voltage often isn't straightforward.
I sometimes demonstrate this by using a multimeter to measure the mains voltage. Typically here in the U.K. the reading will be around 230V. I then repeat with the same meter but set to read DC volts, giving a reading of around zero!
In my opinion the issue of voltage measurement with these decoders is a bit academic. Earlier posts seem to suggests that some of the components used don't have a sufficient factor of safety for a G scale product that's reliable on all commercial G scale systems.
I would say that measuring DCC volts with an AC voltmeter gives you a good enough answer to know whether it is up to the job of handling g scale locos or not, without having to invest in special equipment.
The simple circuit shown in post #41 will accurately measure your DCC track voltage.
I re-read the entire thread.
1. The current handling of the input diodes on the decoder is marginal.
2. this is not a voltage issue for the diodes, as stated again in post 41, the PIV (peak inverse voltage) rating is 60 volts.
3. the "overvoltage" issues claimed by the manufacturer are somewhere else in the product, but you need the part number for the output transistors.
4. from all the reasons you have been given, I would not use the products for G scale because:
My guess is either low-rated output transistors, or poor internal regulation from track voltage to the voltages needed for the microprocessor.
Greg
I re-read the entire thread.
1. The current handling of the input diodes on the decoder is marginal.
2. this is not a voltage issue for the diodes, as stated again in post 41, the PIV (peak inverse voltage) rating is 60 volts.
3. the "overvoltage" issues claimed by the manufacturer are somewhere else in the product, but you need the part number for the output transistors.
4. from all the reasons you have been given, I would not use the products for G scale because:
- clearly some component somewhere cannot take either G scale voltages or current
- the first explanations about diodes were BS (hope that means the same there as it does here)
- the current rating is not sufficient is my guess, underrated output transistors is my guess
- the fact you keep getting unhelpful answers and no resolution from the manufacturer
My guess is either low-rated output transistors, or poor internal regulation from track voltage to the voltages needed for the microprocessor.
Greg
In general I'd agree.
However sometimes it's worth purchasing adequate equipment that may no longer be the very latest thing.
For example
NCE D408SR Large scale 4 Amp DCC decoder
is possibly even cheaper than the Zen Budda with the benefit of being tried and tested with a better reputation.
Thanks for your response Neil, can I ask, have you successfully used the NCE decoder, it appears to have only solder connection instead of screw.
Tony
In short yes, but I haven't mastered the instructions on all of the outputs.
The 4A D408SR board has two sockets and two appropriate pre-wired plugs are supplied with it.
Can I presume that the prewired plugs are track feed in and power lead to the motors. What provision is there for lighting?
Have looked up the Pdf file for it, not clear on what you say about plugs but now I think one plug has 4 leads and the other 8 leads is that correct?
Sort of, the four wire plug has a pair of track wires and a pair of motor wires.
The other has nine wires, two commons and seven outputs.
pretty standard over here, track pickups and motor on one connector or group of wires, and function "outputs" and common on another.
it's an inexpensive decoder, and screw terminals cost money...
there are 2 sockets supplied with matching wired plugs
Greg
it's an inexpensive decoder, and screw terminals cost money...
there are 2 sockets supplied with matching wired plugs
Greg
google is your friend 
the manual is on the NCE site...
I've used many of them. Good workhorses, and really inexpensive.
Greg
the manual is on the NCE site...
I've used many of them. Good workhorses, and really inexpensive.
Greg
I have one of those in an old REA U25B diesel. The decoder came as part of the 10 amp NCE set I bought, and the first DCC install I ever did.
Curiously it seems to be the only decoder in my fleet that sometimes doesn't work out correctly which direction to run *when on DC*. It's fine on DCC.
Curiously it seems to be the only decoder in my fleet that sometimes doesn't work out correctly which direction to run *when on DC*. It's fine on DCC.
you mean it's direction on the same polarity of DC is not consistent? Wow, never seen that.
Greg
Greg