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DT
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It looks like a good system - except that it ends up being quite expensive and that the points are always reset to one position (when the wire cools). It may not be practicable to leave it on all the time.
 

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Discussion Starter · #4 ·
I was wondering about using a decoder with memory wire and having a return spring holding the points in one direction with the memory wire moving the points in the other.

Thanks
 

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DT
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A stationary decoder sends out a signal (current) for a short period only. This is either a pulse for solenoid point motors or an extended signal for motorised point motors. It wouldn't be long enough by itself to hold the point blades in a switched position. You would need a switching relay of some sort, like in the link above to keep the wire 'hot'.

The link you give in the other topic give some interesting examples of how it can be done. Worth looking at some more...
 

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QUOTE (Doug @ 9 Nov 2006, 15:06) <{POST_SNAPBACK}>A stationary decoder sends out a signal (current) for a short period only.
Some can provide a continuous output. For example the Lenz LS100 can do this (but not the LS150).
For most points there will be one position which is more common and could be the rest position.
As for cost it depends on how you value your time and what you compare it with. The slower speed of the memory wire is also more appropriate than the snap of solenoid devices.
 

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QUOTE (Smokeyone @ 9 Nov 2006, 11:30) <{POST_SNAPBACK}>Does anyone know where I can find out about running dcc with memory wire. Have tracked down a site that shows how to operate points with memory wire but after that I am stuck.

There is a guy using memory wire (via DCC) to raise/lower pantographs ope/close doors & so on. If my memory is correct his name is Andi Dell & the layout is called "Dagworth".

Apparently, the layout is outstanding. I think you may be able to contact hime through the Yahoo group DCCUK.

Hope this helps.
Brian
 

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QUOTE (dbclass50 @ 9 Nov 2006, 18:10) <{POST_SNAPBACK}>There is a guy using memory wire (via DCC) to raise/lower pantographs ope/close doors & so on. If my memory is correct his name is Andi Dell & the layout is called "Dagworth".
Last time I saw Andi's 150 I think he was planning to use a motor for the doors. My own 508 does use memory wire for door operation (see http://www.mergrpc.freeserve.co.uk/class508.htm).
There should be no problem driving pieces of memory wire from an accessory decoder featuring constant outputs, so long as you make sure it can cope with the current (~100 to 150mA each, depending on wire gauge).
 

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Discussion Starter · #12 ·
So if a decoder exists that gives out around 300 mA you could get one decoder to operate two points at the same time such as in a crossover or maybe you would be better off connecting them mechanically and just use a single memory wire !
 

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>So if a decoder exists that gives out around 300 mA
So long as 300mA gives you the amount of movement you need and can deliver enough force. It might be a good idea to get a "test kit" and see how you get on before making a big commitment.

David
 

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QUOTE (Smokeyone @ 19 Nov 2006, 06:14) <{POST_SNAPBACK}>So if a decoder exists that gives out around 300 mA you could get one decoder to operate two points at the same time such as in a crossover or maybe you would be better off connecting them mechanically and just use a single memory wire !
You could connect the two wires in series as the voltage drop on a typical piece of wire isn't high. So just 150ma at twice the voltage.
 

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QUOTE (dwb @ 19 Nov 2006, 09:53) <{POST_SNAPBACK}>So long as 300mA gives you the amount of movement you need and can deliver enough force.
It doesn't work like that. With memory wire 'force' is not proportional to current as such. To operate the wire (i.e. make it contract) you apply just enough current to heat it above the transition temperature for that wire. Anything more is wasted, and if excessive could damage the wire. The 'force' is effectively built into the wire, as all it does is change to a different shape (i.e. about 4% shorter than nominal). If you need to apply more tension to whatever you are moving you need to use a thicker wire which will withstand it. The spec for each wire size mentions the tensile strength and current needed to operate it.
 
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