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BD 20 false positive


Russ Wright
 

I have a block that shows a false positive. The manual suggests a pot method of desensitizing. The p/n suggested seems to be unavailable at digikey. Can anyone provide alternative ideas or possible solutions? Block with problem is 25 feet long with Hand laid wood ties and ballast on Homosote.
Thanks for any ideas.
Russ in Michigan


wirefordcc
 

Hi Russ,

The BD20 instructions also suggest that you can just use a resistor to desensitize the BD20.  The trick is figuring out what resistor you need.  You can do any of the following:
1.  Try different resistors.  The BD20 instructions suggest that you may need something in the 500 - 1000 ohm range.
2.  Get a pot that doesn't fit, but attach some leads to it and adjust it until you get the result you want.  Then measure the value of the pot.
3.  Get or borrow a resistor box.  Adjust it until you find a value that works and then buy the nearest resistor to whatever you dialed up on the box.

Note:  Standard resistor values seem strange.  Don't worry that you can't buy the exact value you figured you needed.  Dial your pot or resistor box to a standard value and see if that works for you.  You may have to go up or down a little.

Allan Gartner
Wiring for DCC


whmvd
 

Russ,

Might be handy to first make sure you're solving the actual issue. First exchange the not working detector with one that's known to work. If the problem stays with the same block, you're right - it's fiddling time. But if it moves with the detector, replace the detector.

Wouter


On Sun, 19 Jul 2020 at 21:27, Russ Wright <russwright5@...> wrote:
I have a block that shows a false positive.  The manual suggests a pot method of desensitizing.  The p/n suggested seems to be unavailable at digikey.  Can anyone provide alternative ideas or possible solutions?  Block with problem is 25 feet long with Hand laid wood ties and ballast on Homosote.
Thanks for any ideas.
Russ in Michigan




Don Vollrath
 

Russ, use only one pass through of the sub bus Sensing wire to that section of track. Make sure you don’t have any twisted wire after the BD20 toward the track section. Make sure there are no other electrical loads attached to the wires to that section of track. Desensitize the BD20 or replace it as others have said.
DonV


wirefordcc
 

Hi Russ,

 

Starting in January, I will be taking over the DCC Corner column in Model Railroader.  I will be including questions and answers.  Can I use your question?  If so, please provide your last name, city, and state.

 

Also, I’d like to hear how you make out.

 

Someone else suggested that you try a different BD20.  You can do that, but if you just want to see if your BD20 is defective, just disconnect the wire going through the red transformer.  The BD20 output should go away.

 

How many loops do you have going through your BD20?  If you have more than one, you may try less.  Also, don’t put things like Frog Juicers after the BD20.  That will cause it to false.  And Don Vollrath recommended that you don't have twisted wires after your BD20.

Allan Gartner
Wiring for DCC