Hornby Sapphire for Class 90

[zzpjl8]

Hi .

I have several of the excellent Sapphire Decoders which are no longer in production.

Can you use one of these in the Bachmann Clas 90 and operate the Pantograph? I object to the other manufacturer designing their loco requiring only their decoder; given the numerous functionality of the Sapphire, I am hoping the answer is yes!

regards

Nick

[96RAF]

Sapphire has four function outputs each with a protected 200mA limit to max ganged output of 500mA so you need to determine the required panto load and how the panto operation is accessed as it is likely hard wired into the PCB and already ‘allocated’ to a function.

[ColinB]

I don't think so, there are tons of warnings on the Rails website about using the wrong one. Bachmann even developed a special decoder for it. I don't know if the Sapphire is any different from any of their other decoders, but Hornby don't seem to put any protection on their output ports (Functions in DCC speak) which Bachmann and many of the other suppliers do. In the warnings on the Rails website, it actually warns about the wrong decoder damaging the pantograph, so you do begin to wonder if there is some current limit logic in the Bachmann decoder. Normally you would damage the decoder, not the pantograph if you got it wrong.

[Chrissaf]

The Bachmann website indicates that the operation of the Pantograph is achieved via a Servo ... see pasted extract below.

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Now a Servo does not operate with just a DC voltage applied from any normal decoder function. A Servo requires a PWM (Pulse Width Modulated) condition to function. This is possibly what the specified Bachmann decoder is doing.

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Servo Operation.

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A normal standard Servo requires three wires.

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• A ground wire.
• A 6 volt supply wire.
• A control wire.

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The control wire has a square wave signal that has closely defined pulse timing. The pulse width defines the Servo position.

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Without knowing what specific Bachmann decoder is stated as being required (to perform further research) I cannot say if the specified decoder has this special Servo supporting feature built into it or not, but I suspect it may do if Bachmann are indeed saying that the pantograph only works with the specified decoder.

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If the theory above is indeed correct, then the Sapphire does not have Servo support built into it and would not be suitable for Bachmann Class 90 pantograph operation.

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In the warnings on the Rails website, it actually warns about the wrong decoder damaging the pantograph.

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One would assume that the Servo used in the 90 model is very small and delicate. A normal sized Servo used in RC Boats & Aircraft will be much larger and more physically robust. It is possible for a Servo to drive hard in one direction if it is not supplied with the correct timed pulse on the control wire. A delicate Servo therefore has the potential to be permanently damaged if the correct timed control signal is not applied to it.

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EDIT:

Found this on the Bachmann website. It is still not clear whether the 'pre-configuration' that the yellow highlighted text describes, means that the function output is a Servo PWM signal. It is feasible for this to be the case, as there is already PWM firmware code on decoders to control the motor circuit.

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A question that the OP could raise with Bachmann direct.

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FURTHER EDIT:

After further research, Rails of Sheffield also state that they can fit an ESU Loksound decoder that gives full 'pantograph' support into the Bachmann Class 90 loco. The Loksound V4 manual has a whole section on using their loco sound decoders with Servos. That is to say, three wire Servos that operate as I described above. The ESU V4 manual shows up to four RC Servos directly connected to their sound decoder. This gives a higher than 50/50 probability that the Bachmann recommended decoder also has this Servo support natively built into it.

 

[ColinB]

Thanks Chrissaf, I assumed there was something special for Rails to put out that warning. It is nearly worth buying one to see it working.