Oppie wrote:
"ian field" wrote in message
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"Oppie" wrote in message
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"ian field" wrote in message
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Does anyone know the fancy/technical name for a model railway track
cleaner that's based on flyback pulses from a blocking oscillator to
break down oxide and crud on the rails?
Googling "model railway+track cleaner" produced a few examples of
commercial units but none were referred to by the technical name, I need
some schematic examples to base a similar gadget to clean switch
contacts in a 12V system that occasionally get corroded.
TIA.
Will this help you?
http://freespace.virgin.net/c.gardner/semg/relco.htm
also http://www.merg.org.uk/resources/faq.htm
Track cleaner A device for cleaning track so that dirt or other
deposits do not impede the flow of electric current. A number of methods
exist to accomplish this. MERG Technical Bulletin A4/1 features the Relco
Track Cleaner which superimposes a high frequency, high voltage signal
over the traction current. This burns through track deposits when
traction is interrupted. Mechanical abrasive rubber-type products are
also available such as the Peco PL41 Rail Cleaner and the MERG kit 83,
PCB and Track Cleaner. These must be rubbed over the track to clean it. A
variety of solvents applied with a clean cloth are also suitable as are a
number of wagon-mounted abrasive blocks. A popular MERG method is to
polish the rail tops with the rough surface of common hardboard.
July 2006
That's one of the pages I found googling and it doesn't mention the
technical name for an electronic track cleaner - I'll have to phone the
local model shop and ask them.
From what I can make of it, the device monitors the load and when it drops
out, superimposes HF pulses on top of the DC feed. Sounds similar to the arc
lamp ignitors I work with - a 20 turn winding in series with the DC feed to
the lamp (track) and a 2 turn primary fed by a spark gap connected to a
600V charged capacitor. Spark gap breaks over and dumps capacitor into
primary. Nice sparks on the secondary!
Can't imagine this is too kind to any electronics installed in the layout
but then again, probably doesn't need the 14kv that my lamps need.
When I was a kid I built myself something similar for a Fleischmann
model railroad. Those are DC operated. I don't have the circuitry or
schematic anymore but basically I ran the pulses all the time. They got
shorted out as long as the locomotive made contact and the spike voltage
only ran up when dirt got in between.
I built a simple pulse generator with Ge transistors (and blew quite a
few in the process), a few Hertz, then hung a reversed transformer from
an old tube radio in series with the variable transformer output. Since
I had also built the regulator myself it compensated for the DC drop
across the added transformer winding. Well, to some extent because I had
no clue about loop stability and all that back then. Guess I lucked out.
Of course, at that age I was blissfully unaware of EMC and all that
stuff. So don't do this at home ;-)
--
Regards, Joerg
http://www.analogconsultants.com