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Diode Matrix - which diode to use?

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  • Member since
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Diode Matrix - which diode to use?
Posted by Reformed Grownup on Monday, April 7, 2008 11:27 AM

I am putting the finishing touches on my homemade CDU, and I'm about to turn my attention to a diode matrix to control my yard switches. I've searched the 'net and I've found several different pages discussing how to build them, but none of them are clear as to what diode to use in the matrix. From the pictures that accompany some of the web pages I have the feeling there is no hard and fast rule about which diode is "right".

So I pose the question to the brain trust here...does it matter? Do I need to go to RS and drop $1 on 2 diodes, or can I use the cheapies that are 25 for a couple bucks? What do you/have you used? What would you recommend?

Electronics are not my forte, so forgive me is this seems a simple question and i seem oblivious (I usually am Smile,Wink, & Grin [swg])

Some additional info that may or may not be of interest  - I'm powering things with an old Life-Like transformer  (12ish Volts I imagine), using CDU to throw the switches (duh), small yard - 7 switches

 

Thanks for any and all input.

Richard
  • Member since
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  • From: Winnipeg Canada
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Posted by Blind Bruce on Monday, April 7, 2008 12:43 PM

First of all, what's a CDU? And secondly what type of switch machines do you have?

The twin coil switch motors have what is known as a high voltage kick back so your diodes need a higher reverse voltage. A 1A 600 PIV diode is hheap and should work for you. A 1n4004 has a higher PIV than a 1N4001 and both are in the 25 for a buck category.

73

Bruce in the Peg

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Posted by NeO6874 on Monday, April 7, 2008 1:14 PM

CDU = Capacitive Discharge Unit.

 

I've not seen a diode matrix used (though I've only quickly glanced at the schematics once or twice), though I guess it could be a simple rectifier to get DC out of the AC terminals on your old powerpack...?

-Dan

Builder of Bowser steam! Railimages Site

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Posted by Grog on Monday, April 7, 2008 1:48 PM

I have used both the CDU and the diode matrix although it has been about 10 years. The diode matrix is the ultimate yard control for Atlas type switch motors (momentary contact switch) and the CDU is a must so that the motors do not melt down (if the button stays on). A single button push and any of my 8 yard tracks was selected regardless of previous position. I know that cheap diodes are available and can be used but my notes are not handy. If someone does not have this info I will dig but we have moved since then and they might be hard to find.

 I found them...The diodes I used are 1N5404. They are a 3 amp diode. I am no electronics guru but I do understand the need for a high current diode. Lets say 5 switch motors are thrown at the same time...could be a problem for smaller diodes, I guess. The CDU takes some of the high amp danger out of the equation but imagine 10 switch machines getting thrown at the same time with no CDU. I would imagine 3 amps could easily be reached.

  • Member since
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  • From: Eastern Shore Virginia
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Posted by gandydancer19 on Monday, April 7, 2008 2:49 PM
The 1N4004 is a good choice.  And I have used them in the past with my home made CDU and diode matrix.

Elmer.

The above is my opinion, from an active and experienced Model Railroader in N scale and HO since 1961.

(Modeling Freelance, Eastern US, HO scale, in 1962, with NCE DCC for locomotive control and a stand alone LocoNet for block detection and signals.) http://waynes-trains.com/ at home, and N scale at the Club.

  • Member since
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  • From: Northeast OH
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Posted by NeO6874 on Monday, April 7, 2008 4:07 PM

OHH, now I get it. I was thinking the diode bridges for use in locos and noth the crisscross of wires connected with diodes to set routes Dunce [D)]

-Dan

Builder of Bowser steam! Railimages Site

  • Member since
    November 2007
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Posted by BlueHillsCPR on Monday, April 7, 2008 4:13 PM
 NeO6874 wrote:

OHH, now I get it. I was thinking the diode bridges for use in locos and noth the crisscross of wires connected with diodes to set routes Dunce [D)]

That would be a Bridge Rectifier as opposed to the Diode Matrix. Smile [:)]

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