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Discussion Starter · #1 ·
Well with typical Bank holiday weather here in the UK, it's time to take the layout out for a bit of family entertainment.
All our locos are fitted with DCC chips but one, a hornby Eurostar runs for a while comes to an abrupt stop and leaps into action after a second or so.

I thought the dcc decoder might be at fault, so I replaced it with another hornby decoder but the same thing happens.
I've noticed that the dcc circuit board gets very hot, I've got the orange pin inserted into the arrowed hole.
And I've oiled the worm gears and cleaned the wheels.

Is there anything else I can try. All the other locos run fine.

Fabben
 

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It could be that the motor is drawing too much current.

Most people here would suggest that you replace the decoder with another make such as the TCS M1, ESU or Bachmann.
 

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Discussion Starter · #5 ·
Thanks for the advice, a 1amp TCS decoder has just been ordered.

I looked up the hornby 8215 and it allows a continous 500ma.
Which begs the question "does Hornby produce locos which can't be handled by their decorders?"

Fabben
 

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There shouldn't be problems with a Hornby DCC ready loco and a Hornby NMRA compliant decoder. Try to eliminate all other possible causes before blaming the decoder. Does it stop in the same place every time, or just randomly? What controller are you using btw?
 

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QUOTE (poliss @ 27 May 2008, 08:56) <{POST_SNAPBACK}>There shouldn't be problems with a Hornby DCC ready loco and a Hornby NMRA compliant decoder. Try to eliminate all other possible causes before blaming the decoder. Does it stop in the same place every time, or just randomly? What controller are you using btw?

***No there shouldn't be but there very often are problems with Hornby DCC ready loco's and decoders.

Poliss you are modelling in N scale and if this modeller was too - and not using the H decoder - then perhaps I'm make the same comment.

but

This is not an issue related in any way to whether the decoder is compliant or not: Compliance is primarily a software issue and in this case the issue is Power handling which is a factor of the low power hardware that the decoder is made of.

Hornby decoders are low powered at 500mA which is usually the top rating for an ultra micro N/Z scale decoder and so they do have a tendency to run warm and are very easily damaged - to the point the comment was once coined "they don't need feedback, they give off smoke signals". This is a shame as the difference between a 1/2 amp and 1 amp decoder size wise is zero and component cost-wise is about 10p!

Hornby loco's generally draw well less than 200Ma when running, however the odd combination will be higher than that. Heat is cumulative so under load for a while the low powered decoder will heat up considerably. There is about zero tolerance in the hornby decoder so it is not uncommon for the combination of larger hornby locos + hornby decoders to let the smoke out.

Its good advice to use a 1 amp of higher decoder on 4mm scale loco's where possible or decoder death can be expected more often than is really acceptable. My recommendation for a cost effective high power and really competent decoder that will do the job every time is either TCS DP2x (wireless direct plug in to even the tightes of them), or TCS MC2 or M1 which both have option of bare wires or 8 pin plug. Yes they are a wee bit more exxy but they perform better every time!

Oh... and Fabben - ingore the Hornby diagramme and DO remove the capacitor. It will always affect the best slow speed performance as any component, especially a capacitor, masks the real motor back EMF from the decoder.

Regards

Richard
DCCconcepts
 

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Discussion Starter · #10 ·
can the output from a dcc chip go into some transistor circuit to increase the power handling.
I'm not saying that it's a practical idea - I'm just curious if it could be done?

Fabben
 

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QUOTE (fabben @ 28 May 2008, 08:32) <{POST_SNAPBACK}>can the output from a dcc chip go into some transistor circuit to increase the power handling.
I'm not saying that it's a practical idea - I'm just curious if it could be done?

Fabben

*** Nope Fabben, it wouldn't help at all.

Think of pipes and water pressure: The direct analog to pressure here is heat generation as the decoder parts are stressed.... and burnout when over heated.

Back to the water pressure analogy:

Pressure is made up of the interaction of the diameter & strength of the pipe (the current rating of the parts) and the amount of water forced through it... (the speed = voltage and the amount = amps - together creating the pressure (current)).

Your limit for safe flow is the rating & diameter of the smallest bit of the pipe... ie: If you have a small pipe and add a bit of larger pipe after it, the whole of the water still has to go through the restricted bit first...... so there's no "relief" for it by adding the new bit!

Clearly trying to move more water through will simply increase pressure in the original small pipe, as the increased load would have to go through the original parts that are already stressed as well as the added circuit. Trying to add more would simply burst the small pipe.

So... the answer is bigger pipe to start with - or in the case of where this started which is with a decoder, better power handling in the parts chosen.

Richard
DCCconcepts
 

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QUOTE (fabben @ 28 May 2008, 00:32) <{POST_SNAPBACK}>can the output from a dcc chip go into some transistor circuit to increase the power handling.
I'm not saying that it's a practical idea - I'm just curious if it could be done?

Fabben
I daresay it would be possible to rig up some sort of amplifier circuit - after all that's moreorless what the output stages of the decoder are. But absolutely certain that it would be cheaper, less space consuming and much less hassle to get a higher-powered decoder in the first place.
 

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QUOTE (Edwin @ 28 May 2008, 15:19) <{POST_SNAPBACK}>I daresay it would be possible to rig up some sort of amplifier circuit - after all that's moreorless what the output stages of the decoder are. But absolutely certain that it would be cheaper, less space consuming and much less hassle to get a higher-powered decoder in the first place.

*** Hi Edwin

The output stages are regulation and control not power amplification.

The maximum "power" potential is always available at the rails - the decoder really just controls what is allowed to get to the motor in response to its demands. As I said above, anything that demands more power can't be simply tacked on at the output stage of the decoder - it would esepcially require its own separate power supply and some added control circuitry as well otherwise it would simply demand more power through the input (original decoder) part to feed it and would therefore increase the load causing earlier than previous failure.

As noted, doing it would neither be space or cost effective as you are then using double the expensive parts of a normal decoder. Far better to use a quality product in the first place!

regards

Richard
 

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Discussion Starter · #14 ·
It's taken a while, but I got a TCS DP2X chip and finally managed to put this into the EuroStar.
Which you may remember was tripping out because the previous Hornby chip was under powered.

I have a Hornby Select - and I use it to program the loco.
It responds for around 10 seconds or so and then has a mind of it's own.

Is this a limitation of my DCC controller, which is quite basic.
Or does the TCS need programming at the CV level?

Fabben
 

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QUOTE (fabben @ 9 Jul 2008, 22:19) <{POST_SNAPBACK}>It's taken a while, but I got a TCS DP2X chip and finally managed to put this into the EuroStar.
Which you may remember was tripping out because the previous Hornby chip was under powered.

I have a Hornby Select - and I use it to program the loco.
It responds for around 10 seconds or so and then has a mind of it's own.

Is this a limitation of my DCC controller, which is quite basic.
Or does the TCS need programming at the CV level?

Fabben

I'm afraid its a problem with the Select - its waveform is so far off true DCC spec (its a wild sawtooth and not a square wave) that its confusing the decoder

Richard
DCCconcepts
 
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