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'Keep-Alive' Circuit For My Porters & Critters
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 Posted: Thu Apr 25th, 2019 07:00 pm
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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 :   :brill:

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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 Posted: Thu Apr 25th, 2019 07:43 pm
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man7sell
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Using some double-backed tape, as a third set of hands, to hold down the super-capacitors.

These super-capacitors have a white-stripe, to show the negative side.

Using small needle nose pliers, bend the contact wire so they meet each other, with a little overlap for soldering.

The end wires are bent at a right angle.





Caps soldered.





3.3K Ohm resistor and 15 Volt Zener-diode will go in parallel to the super-capacitors.

Positive end of the diode, to the positive side of the caps.





I mistakenly ordered 5 Watt resistors that are quite large,
should have gone with 1 Watt ones instead.

Next up is the 68 Ohm resistor and 1N4001 regular-diode.
These will be soldered in parallel with each other.

The negative end then soldered to the positive end of the caps.





Blue wire soldered to the positive end of the circuit.

This will connect to the common positive of the decoder.

The Black to the negative on the decoder.


Waiting for some 3/4" heat shrink tubing, to contain the whole circuit.







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 Posted: Thu Apr 25th, 2019 08:18 pm
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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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 Posted: Thu Apr 25th, 2019 10:27 pm
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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




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 Posted: Thu Apr 25th, 2019 10:38 pm
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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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 Posted: Fri Apr 26th, 2019 03:28 pm
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man7sell
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Using Bachmann HO bobber cabooes as a platform for the keep alive circuits.












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 Posted: Fri Apr 26th, 2019 03:41 pm
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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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 Posted: Fri Apr 26th, 2019 06:16 pm
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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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 Posted: Sat Apr 27th, 2019 02:04 pm
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W C Greene
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...And one radical idea.
Install an r/c receiver and batteries in the Porter,
and then she will "keep-alive" on dirty track, dead track, and across the kitchen table.
Yes, it CAN be done.

Woodie-an old 60's radical thinker anyway





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 Posted: Sat Apr 27th, 2019 05:14 pm
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man7sell
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Love it Woodie   ;)






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