Topics

BD20

Richard_vanRaay
 

Hi, thanks. I have 18 BD-20's connected to AIU's.
They have been working for about two months. Now one is showing occupancy all the time. The LED on the AIU is always on.
I have changed the bd20 but it still lights on the AIU.
There is only one wire going through the bd20.
When I disconnect the bd20 the led turns off.
I have cleaned the track but am at a loss as to what to try next.
Thanks,
Richard from Tasmania

RONALD ST.LAURENT
 

Richard,

Have you checked all the track in the block to make sure it is isolated?  Sometimes cut track can rejoin.  A small piece of plastic placed in the joint and trimmed properly can be unobtrusive and keep the gap.

Ron

On Thursday, March 21, 2019, 8:17:32 AM EDT, Richard_vanRaay via Groups.Io <richard_vanraay@...> wrote:


Hi, thanks. I have 18 BD-20's connected to AIU's.
They have been working for about two months. Now one is showing occupancy all the time. The LED on the AIU is always on.
I have changed the bd20 but it still lights on the AIU.
There is only one wire going through the bd20.
When I disconnect the bd20 the led turns off.
I have cleaned the track but am at a loss as to what to try next.
Thanks,
Richard from Tasmania


Don Vollrath
 

On Thu, Mar 21, 2019 at 07:17 AM, Richard_vanRaay wrote:
I have changed the bd20 but it still lights on the AIU.
When I disconnect the bd20 the led turns off.
Try a different input channel on the AIU. If that doesn't work... The only thing left is current leakage as seen by the BD20 on/from the track. Verify that the rail gaps are open. Look for debris on the track. Look for current leakage between the rails due to moisture in the ballast. Uninsulated wiring?
DonV

Richard_vanRaay
 

Thanks Ron. I have checked that following your suggestion. That is not the cause.
Cheers.

RONALD ST.LAURENT
 

Hi Richard,

Another thing to check would be continuity with a VOM at each gap.  You should see no continuity, if you do, there's the area of the problem.

Ron

On Thursday, March 21, 2019, 3:58:10 PM EDT, Richard_vanRaay via Groups.Io <richard_vanraay@...> wrote:


Thanks Ron. I have checked that following your suggestion. That is not the cause.
Cheers.

Marcus Ammann
 

Hi Richard

 

If you cannot find any issues with what others have suggested, then desensitized the BD20 as per the Manual at:

 

https://ncedcc.zendesk.com/hc/en-us/article_attachments/200585095/Bd20a.pdf

 

Regards

Marcus

Layout Video https://youtu.be/biFOG0e6IHo

Web Site http://www.members.optusnet.com.au/nswmn/

 

 

From: w4dccqa@groups.io [mailto:w4dccqa@groups.io] On Behalf Of Richard_vanRaay via Groups.Io
Sent: Friday, 22 March 2019 6:54 AM
To: w4dccqa@groups.io
Subject: Re: [w4dccqa] BD20

 

Thanks Ron. I have checked that following your suggestion. That is not the cause.
Cheers.

 

Virus-free. www.avg.com

 

Richard_vanRaay
 

Thanks everybody for your help. I feel really simple but have to admit it was a very simple problem. I had changed some wiring onto a turnout and that bypassed the BD20. 
Thank you all again.
🤗

Don Vollrath
 

Thanks for the feedback Richard. Glad you found the problem. and glad to have helped.
DonV

Jerry Michels
 

Don,

In you rpost you mention current leakage.  I think we see this on our layout when I check certain blocks with a LED tester we use to ensure correct phasing between blocks.  In some locations, If I check for proper phasing between blocks, when I connect opposite rails (e. g. block 1 rail A and block 2 rail B) I get the proper bright LED indication, but if I connect the same rails (rail A to rail B) I get a very faint glow. I take it that this is an indication of current leakage?  We are in a very dry environment, so moist ballast is not a concern, so perhaps debris working it way into gaps may be the problem, or gaps closing with temperature.  Interesting research project.

Thanks,

Jerry Michels
Amarillo Railroad Museum

whmvd
 

Great news, even if I won't claim to understand why it would have shown 'occupied' in that situation. But never mind - enjoy!
Wouter


On Fri, 22 Mar 2019 at 12:30, Richard_vanRaay via Groups.Io <richard_vanraay=yahoo.com@groups.io> wrote:
Thanks everybody for your help. I feel really simple but have to admit it was a very simple problem. I had changed some wiring onto a turnout and that bypassed the BD20. 
Thank you all again.
🤗

Don Vollrath
 

Jerry,
LEDs can be very sensitive and so are your eyes. remember that the DCC signal/power voltage is actually flipping in +/- polarity several thousand times per second and that every wire and electrified rail has a small amount of capacitance to other objects. Charging and discharging that capacitance from that rail or wire to other objects, even if they are supposedly not electrified, will let current flow through a test LED to temporarily electrify the 'other side' with a repetitive amount of current to flow... a few hundred micro-amps perhaps, which can be great enough to dimly light up a sensitive LED so that your eyes can see it. The BD20 on the other hand supposedly requires maybe 8-10 milli-amps of current for track occupancy detection. Long leads of twisted pair wiring and/or the track itself can form enough 'leakage capacitance' and DCC leakage current flow to fool a current sensitive occupancy detector like the BD20. This why it is best to place a BD20 out by the track section to be measured and not use twisted pair wiring placed after the sensor.

Just for giggles notice in some situations just holding the other LED test lead in your hand forms enough of a high frequency antenna and power absorption to light up a sensitive LED.

DonV

DonV.