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man7sell
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The age old problem, of small locos loosing power, over turnouts and dirty track.
Can't afford to go buy that many commercial circuits,
for 3 Porters, 2 mechanicals, and whatever will come in the future.
So here goes ...
First the circuit : 
The basis for holding the charge will be five 1 Farad super-capacitors.
Rated at 2.7 Volts each, in series, will hold a total of ... 13.5 Volts.
You could use six, for a total of 16.2 Volts.
Or use 3 Volt rated super-capacitors, five in series would be 15 Volts.
To protect the super-capacitors from over voltage,
a 15 Volt Zener-diode is used in parallel with the super-capacitors.
Also a 3.3K Ohm resistor to control discharge, when the loco is removed from the power,
again in parallel with the super-capacitors.
A regular 1N4001 diode, bypasses the 68 Ohm inrush limiting/charging resistor,
for discharge to the decoder, on the blue common positive wire.
Lastly to address programming the decoder,
the keep alive-circuit needs to be either disconnected (connector or inline switch),
or a 100uH 0.5 Amp choke in the negative side of the circuit.
All of this will be installed in a tender.
Photos of the build to come.
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Rail Systems Built Inch by Inch
Capt. Paul Mansell
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Helmut
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You should use a 13 Volt Zener-diode, instead of 15 Volt, if you want to enjoy your circuit for a longer time.
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Regards, H.
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man7sell
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H,
Two schools of thought on that.
As the capacitors will charge to 13.5 Volts,
a 13 Volt Zener-diode would be dumping extra voltage all the time the capacitors are charged,
so the Zener-diode would not last as long.
Having a 15 Volt Zener-diode will just act as an over voltage protection for the capacitors.
But thanks for the input.
Paul
____________________
Rail Systems Built Inch by Inch
Capt. Paul Mansell
m (-_-) m
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man7sell
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I'm building some 'keep-alive' circuits for my critters.
The circuit will be housed in a separate tender with pickups on the wheels.
http://freerails.com/view_topic.php?id=8419&forum_id=54
So I have a couple of questions:
1. Where would be a good place to connect the 'keep-alive' to the decoders on a sound 0-4-0 Porter?
2. What sort of pickups are available, or ones maybe you have built, for the tenders?
Paul
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Rail Systems Built Inch by Inch
Capt. Paul Mansell
m (-_-) m
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slateworks
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Paul,
being an electronics numpty I can't help with the electrical connection question as it could vary from decoder to decoder,
but the literature with your decoder might show a diagram with connection tabs named.
As far as pickups are concerned, I used flexible 0.14mm/0.005" thick phosphor bronze strip, on my Porter tenders.
Only one side was needed, as the chassis of these trucks is live to the other side, where wire was connected directly.
I've seen it suggested elsewhere that making the pickup contact to the rear face of the wheel,
rather than the rim, causes less drag, but the above set-up works fine for me.
Commercially available pickups are available but relatively expensive for what they are,
and there's no guarantee they'll fit - easier to make your own.
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Doug
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Helmut
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The keep-alives must always be connected to the decoder's internal rectifier's 'plus' and 'minus'.
Some decoders with a 'Susi' Interface already provide this.
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Regards, H.
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man7sell
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Well anyway, I did manage to hook up my first capacitor 'keep-alive',
and did a test run on a 0-4-2 sound DCC Porter, and it ran seamlessly.
Have to download a video.
Also need to set the CV, I think 10, to '0' for the DC use,
because when I turn off power, the loco wants to go about 8" down the track on it's own.
Toots its whistle too. 
____________________
Rail Systems Built Inch by Inch
Capt. Paul Mansell
m (-_-) m
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man7sell
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Hookup to a DCC sound 0-4-2 is easier, and here is on with my hi tech camera mount.
____________________
Rail Systems Built Inch by Inch
Capt. Paul Mansell
m (-_-) m
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man7sell
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Forgot to set the DC mode off.
This is what happens when you remove power from the track.
Funny 
https://youtu.be/1yyVVMhrb6Q
Paul
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Rail Systems Built Inch by Inch
Capt. Paul Mansell
m (-_-) m
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Helmut
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Quite logical.
When CV29 bit2 is set,
the decoder checks the input for DC-level,
when there is no DCC signal.
As the DC input is zero,
the motor power signal is set to zero accordingly,
and stops the loco.
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Regards, H.
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Stan S
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Have you ever added a Keep-Alive to a non-sound Bachmann Porter?
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“ When art critics get together they talk about Form and Structure and Meaning.
When artists get together they talk about where you can buy cheap turpentine ”
(Pablo Picasso)
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man7sell
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Sorry it's been a while. Non sound Porter is waiting for its keep alive, so that is a good question (Great questions I know the answer)
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Rail Systems Built Inch by Inch
Capt. Paul Mansell
m (-_-) m
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