Do diodes leak voltage .....DC shuttle line with a DCC loco..weird happenings

beavercreek

beavercreek

Travel, Art, Theatre, Music, Photography, Trains
Country flag
Now I suspect that there are a few fellows who will be able to unravel this little mystery.

I have one of my sections of the layout (the quarry line) as a plain DC shuttle that spirals from one end to the other and back etc with a diode gap at either end for stopping the loco.
It has been working absolutely fine with DC locos and can handle up to 8amps.
So far so good.....

My other layout sections are powered by DCC unit, or DC, depending on what I want to run.

I have just DCC-ed an LGB 0-4-0 D&RGW diesel switcher with a ESU Loksound XL 3.5 board, sound etc (and enabled DC analogue usage in the CVs).
Tested it on the DCC section and everything is tickety-bo...motion, sound, lights, functions etc

As it was one of the locos that usually domiciled on the quarry (DC analogue shuttle line), I then brought it to that line and tested it with straight DC power but strange things .....no sound (I have sorted the sound prob!)........
there is normal motion and lights.....BUT it does not stop after the diode gaps like it did before the installation of the DCC decoder, it just wants to keep on going after the diode gap.

The DC power is from a Train Engineer with PWC switched off ( I tried it 'on' just to see what may happen....confuse the decoder etc... but no difference).
There is up to 22v and plenty of amperage on tap.
I then put a DC analogue loco (same type of loco) onto the quarry line, to see if the diodes had gone west since a few days ago when they were last used.....and the analogue loco stopped happily after the diodes at each end and then reversed after the set time.
So it is definitely something that the decoder on the 0-4-0 is exhibiting whilst crossing the diode gap...

Now I maybe wrong, (more than likely), but I suspect that the decoder is being able to use any 'leakage' of voltage that the diode may allow to power the motor and lights even when it has gone past the diode gap.
If I am correct ....are there diodes with the power and voltage handling, that do not exhibit any leakage?... Schottky type?.......the ones that I have used for years on the DC shuttle are plain old IN4001......

Or do decoders just not work with a diode set-up as found in DC shuttles....

A quandary.... or can I not see the wood for the trees....
 
Re: DC shuttle line with a DCC loco..weird and weirder happenings

I have a couple of decoders that sometimes do the wrong thing when they see DC - ie they might drive in the wrong direction, especially if the volts are turned up too quickly. Could it be the shuttle unit is switching the DC polarity so quick that the decoder doesn't realise it has reversed, and so it carries on in the same direction? However that seems unlikely if the shuttle unit has a delay before ramping up the volts back up?

Does the Loksound have a power buffer fitted? (LokPilot 3.5 comes with one factory fitted, but LokSound doesn't - I think?)
 
Hi Nick .......well....
I am at the test bench as I type.

I have looked closer at the CVs and settings with the ESU Lokprogrammer windows, and there are settings that have been set for the previous loco that the decoder was installed into.
The decoder came from a Marklin loco and the DC function map had no sound functions selected.

I selected function 8 (sound on/off) to be 'alive' in DC analogue mode and also function 4 ( for the cab light which is on aux 4 on the decoder) and low and behold I have sound when under DC power and the cab light on all the time (as opposed to being on or off using function button 4 when operating with DCC)

Unfortunately the ESU sound file of this loco (CAT diesel) does not contain start twin toot, grade crossing toots or reverse three toots so those don't happen in DCC let alone analogue.
I could select to have the bell and horn active in DC but they just continually perform as soon as the threshold DC voltage is applied and cannot be stopped so they are mute....there must be a way for the bell to be set to work for below a certain low voltage and the horn for, perhaps, acceleration but I cannot see this in the programmer screens.
So the sound of the engine start-up, the increse or notch up and down are the only sounds available to analogue DC operation, which is fine

Still the problem of the DCC-ed loco non-stopping after diode gap though...... so one quandary left! :o :-\
 
Mike, have you tried a different DCC loco on the analogue shuttle track?
 
Hi Mark
I didn't have the time to use another DCC loco and I thought that as the one that I had just DCC-ed was working great under DCC power and that it was moving and glowing fine under DC (except for the not stopping after the diode gaps) I presumed that it might be the diodes......wrong!!!!!
I have just taken the chance to put another loco (one that can go around the tight curves of the quarry section ...a Bachmann new type Climax with DCC and sound) and....
It stops after the gaps!

I have checked that the breaking time for the DCC-ed 0-4-0 is at a minimum....... so I am not sure what is keeping it going after the gaps.......... It is not due to the onboard buffer because, if I was not turning the DC power to zero the loco would just keep on going even though theoretically it is not receiving voltage!!

Perhaps the Soundtraxx decoder in the Climax needs more voltage/power to keep going and just stops after the diode gap, whereas the ESU decoder in the 0-4-0 can run on very low power. The starting voltage is set at 7 volts so the diode cannot be passing that much surely.....even the climax sound and lights would be give feedback at that level...........
 
Could it be something related to obscure things like asymmetrical DCC/braking settings in the ESU decoder that could be causing this?
 
Put the loco on the DCC track.. Run it for a minute or so.. Turn OFF track power..
Does the loco take off? - If so, there is some sort of buffer in the decoder, and this loco will not work on your shuttle. It will also take off if sitting on the DCC track, and you hit the stop key.
 
Keith RhB said:
Could it be something related to obscure things like asymmetrical DCC/braking settings in the ESU decoder that could be causing this?
Click to expand...
Keith
Have looked at the CVs and the settings panes and braking is as it should be.
But would that even matter if there is no power to one rail after the diode gap.
The loco just continues ad infinitum, after the diode gap, until the power is zeroed


PhilP said:
Put the loco on the DCC track.. Run it for a minute or so.. Turn OFF track power..
Does the loco take off? - If so, there is some sort of buffer in the decoder, and this loco will not work on your shuttle. It will also take off if sitting on the DCC track, and you hit the stop key.
Click to expand...

Phil
I tis definitely not the buffer on the board (which is only a 2 second one at best) as the loco will carry on going ad infinitum after the gap, and come to the end of the track, unless the power is switched off.
It must definitely be 'seeing' some flow back through the diode as this can be the only way that it would have both rails delivering juice.

What is strange, is that the other DCC loco behaves just like a DC one and stops directly after the gap as it should. So if there was a 'back flow' through the diode, it definitely is not being affected by it!
 
Have you tried using a different power supply for the shuttle section.
TE's are well known to leak voltage. Plus the way the Linear switch works it is possible the PWM is not completely switched out.
 
Tony Walsham said:
Have you tried using a different power supply for the shuttle section.
TE's are well known to leak voltage. Plus the way the Linear switch works it is possible the PWM is not completely switched out.
Click to expand...

Hi Tony
The TE has to be used as it is in situ and is integrated into my 3-layout section wiring for the DCC/DC power options. It is all built in to a cabinet and shelving so no swapsies there...
But....
If it was the TE to blame, then probably the Bachmann Climax (with the Soundtraxx DCC board) would find it a problem too, as the Soundtraxx decoder is notorious for its fussiness with power supply especially DC with PWM (PWC).
But the Climax behaves impeccably and stops after the diode gap, no lights, no sound, no small motor noise...nothing...perfect
The 0-4-0 doesn't even dim the lights after the gap!

I am going to use a multimeter tomorrow to test both the diodes.... and I will test the TE RX base station with PWC on and off ............just in case............
I cannot think of any other reason why
 
Maybe the real problem is that for some reason the shuttle doesn't recognize that loco has entered the diode section because it isn't sensing a short? I don't know how those shuttles work but just thinking out loud here...so maybe the small amount of capacitance back feeds to the shuttle and fools it into thinking nothing has happened so it continues on with the power?
 
The more likely cause could be the (DC) polarity of your motor.

The one in the Climax could be the opposite of the LGB Switcher, especially as they are from different manufacturers?

I would test both locos on a simple DC controller and check if they run in the same direction when you turn the power on.

Or it is a polarity setting in the CVs....
 
Keith
Most DC shuttles are really just timers that reverse the polarity after a set time. The diodes cause a break in voltage supply (so stopping the loco) until the unit reverses the polarity and the loco begins its journey in the other direction as the diode now passes the voltage. So no sensors in the shuttle unit..... It is essentially dumb to what is going on.


Gizzy
I will check the polarity of the motor output from the decoder and change it if it is different from the climax...... But I also reversed the polarity of the TE supply from the controller and that had no effect on the proceedings.... surely the same?
Also the shuttle unit reverses the polarity each time the timer tells it to.
Also, even if the polarity of the 0-4-0 decoder output was different to the climax, the supply being straight DC, then the diode gaps would still stop the loco.....

but I will still give it a go :D
 
Gizzy
I will check the polarity of the motor output from the decoder and change it if it is different from the climax...... But I also reversed the polarity of the TE supply from the controller and that had no effect on the proceedings.... surely the same?

Ah, but the shuttle unit is swapping the polarity too, so in effect this overrides what the TE is doing....

Also the shuttle unit reverses the polarity each time the timer tells it to.

Also, even if the polarity of the 0-4-0 decoder output was different to the climax, the supply being straight DC, then the diode gaps would still stop the loco.

The diodes are 'one way valves'. Think in terms of water flow. if you have a reverse flow then the one way valves won't work

but I will still give it a go

I believe there is no fault with the TE & Shuttle set up as the Climax works. The Switcher did work until you fitted the decoder, so I reckon it is a decoder setting....
 
Mike, can you send me a copy of the CVs (saved into an ESU project) and I will take a look and see if I can find anything that you may have missed.

Mark
 
This thread has really made my head hurt :o :o :o but I think I can make some useful suggestions ;D ;D ;D

[list type=decimal]
[*]Start by constructing a pigeon loft
[*]Order some quill pens
[/list]
 
Well boys...... thank you for the support and the ideas and concerted knowledge....

To confirm what I said about the polarity switching using the TE TX/RX control or the shuttle unit's own timer ....
The TE TX/RX can change the polarity to the shuttle unit. If this is done the loco will either reverse (if in between the diode gaps), or come out to the centre run, across the gap, if already at rest there.
This TE polarity reversing can be done as many times as wished with the TX controller before the shuttle's own timed reverse of the polarity. The shuttle unit is 'transparent' and lets the TE reversed polarity feed straight through to control the loco....but
If the shuttle times out and does its own reverse of polarity then that overrides the TE polarity..but of course the TE can then just reverse it back (if it was so wished)

Doing this TE-controlled polarity switching, with the DCC-ed 0-4-0 on the shuttle line, either stopped the loco from trying to escape but did not reverse it, or if the polarity was switched back again, the loco continued its relentless quest to fall off the end (this also happened at the other end of the shuttle line when tested).

So I tried the Gizzy suggestion
I tried the DCC-ed 0-4-0 on the DCC powered track and it followed the same direction as the other DCC locos...so far so good.
I tried the DCC-ed 0-4-0 on the DC shuttle track with the DCC lclimax and..............it went in the other direction to the other loco. Ah! the motor is oppositely wired from the climax loco.....as Giz had suggested, could be the situation.

So the polarity of the decoder output to the motor, under DC power, was reversed (should not make a halfpenny's worth of difference..but it did ....even though it had been tested every which way but loose).....so, was this the answer......

OPTION....to either
1) open her up and switch over the motor feeds from the decoder or......
2) reverse the polarity using the CVs (CV29)...(yes it would mean that this little loco would have to be controlled in reverse on the DCC track... but a small price to pay)

So I went for the lazy option...reversed the CV polarity setting and tested her....
She now goes in the same direction as the DCC climax when on the DC shuttle and... lordy, lordy..... she obeys the diode gaps.


I am not sure why this motor-feed reversal enabled the loco to 'ignore' the diodes even when it was turned around, polarities of power switched, but it did.
Now like Rhino said for his, it was making my head hurt (and yes, I do know about diodes and how they work Giz ;)).

Polarity........Black polar bear...there's another polar-rarity..............

I am going to find find a dark room and dream of nice things.......

Cheers me dears
 
Rhinochugger said:
This thread has really made my head hurt :o :o :o but I think I can make some useful suggestions ;D ;D ;D

[list type=decimal]
[*]Start by constructing a pigeon loft
[*]Order some quill pens
[/list]
Click to expand...

If you think this makes your head hurt get your head round this http://www.ifwtech.co.uk/g3sek/boards/tetrode/tetrode-manual.pdf I'm building a new power supply for 4cx250b 50/70 mhz amplifier
 
Result!

Trouble is you have 4 areas where polarity has an influence.

1. The TE unit

2. The shuttle

3. The motor

4. The decoder if fitted, which overrides everything else!

That's what made this problem a bit of a head scratcher....
 
sparky230 said:
If you think this makes your head hurt get your head round this http://www.ifwtech.co.uk/g3sek/boards/tetrode/tetrode-manual.pdf I'm building a new power supply for 4cx250b 50/70 mhz amplifier
Click to expand...

Cut my teeth on vacuum devices?

The Helmet Mounted Display on the Apache heliochopter is a CRT....
 
You must log in or register to reply here.
Back
Top Bottom