New Server: Thank you for your patience. We moved to our new server. Everything should be back to normal EXCEPT for the Gallery. We will have that restored shortly and will make an announcement. If you see something that is not working please report it here: Server Upgrade.

!!

Not Registered?

Welcome!  Please register to view all of the new posts and forum boards - some of which are hidden to guests.  After registering and gaining 10 posts you will be able to sell and buy items on our N'porium.

If you have any problems registering, then please check your spam filter before emailing us.  Hotmail users seem to find their emails in the Junk folder.


Thanks for reading,
The NGF Staff.

Author Topic: Intermittent shorting when DCC fitted  (Read 869 times)

0 Members and 1 Guest are viewing this topic.

Offline longbow

  • Trade Count: (0)
  • Full Member
  • ***
  • N Gauge Society Number: Yes
  • 2mm Association Number: Yes
  • Posts: 540
  • Country: au
    • Awards
Intermittent shorting when DCC fitted
« on: December 14, 2017, 05:38:43 AM »
My latest Dapol Class 22 runs normally with lights under DC but displays an intermittent short when chipped with my standard Zimo MX622N decoder. The problem persists after swapping out the decoder for another Zimo.

I have reinsulated the decoder PCB from the decoder so I don't think the short is arising there.

Any ideas please?


Offline ntpntpntp

  • Trade Count: (0)
  • Full Member
  • ***
  • Posts: 2356
  • Country: gb
    • Awards
Re: Intermittent shorting when DCC fitted
« Reply #1 on: December 14, 2017, 07:36:45 AM »
Is it just the decoder shutting down, or is the DCC system itself tripping?

So if this is a plug-in decoder and there's definitely no possibility of the decoder touching the metalwork anywhere, then it sounds more like possibly a motor fault - drawing too much current? Causing the decoder to shut down?
Nick.   2016 celebrating the 20th anniversary of "Königshafen" exhibition layout!

Offline longbow

  • Trade Count: (0)
  • Full Member
  • ***
  • N Gauge Society Number: Yes
  • 2mm Association Number: Yes
  • Posts: 540
  • Country: au
    • Awards
Re: Intermittent shorting when DCC fitted
« Reply #2 on: December 14, 2017, 08:05:54 AM »
The fault is indicated by the MERG command centre tripping. If it's a motor fault would it still run smoothly under DC?

Offline ntpntpntp

  • Trade Count: (0)
  • Full Member
  • ***
  • Posts: 2356
  • Country: gb
    • Awards
Re: Intermittent shorting when DCC fitted
« Reply #3 on: December 14, 2017, 08:11:45 AM »
The fault is indicated by the MERG command centre tripping. If it's a motor fault would it still run smoothly under DC?

Well, it could still run on DC but draw more current, which a DC controller may or may not notice.

However you've said it's the main command station which is tripping not just the decoder, so I think we can discount that theory.

So when you're running on DC this is presumably on a test track and not the same as your DCC layout?  I've had a loco where a wheel has been shorting to the chassis, but it would only happen at certain places on curves and not on my workbench test track.
Nick.   2016 celebrating the 20th anniversary of "Königshafen" exhibition layout!

Offline longbow

  • Trade Count: (0)
  • Full Member
  • ***
  • N Gauge Society Number: Yes
  • 2mm Association Number: Yes
  • Posts: 540
  • Country: au
    • Awards
Re: Intermittent shorting when DCC fitted
« Reply #4 on: December 14, 2017, 09:27:56 AM »
Yes, on a plain circular test track. The shorting is erratic and does not seem confined to one spot.

Just tried with a Digitrax decoder - lights and no controller alarm but no throttle response at all.
« Last Edit: December 14, 2017, 09:29:28 AM by longbow »

Offline daversmth

  • Trade Count: (0)
  • Full Member
  • ***
  • Posts: 106
  • Country: gb
    • Awards
Re: Intermittent shorting when DCC fitted
« Reply #5 on: December 14, 2017, 09:34:41 AM »
 I had a similar problem.
With dcc decoder fitted to a Farish emu 4ecp and dmu 101, and using a merg dcc controller, both units would occasionaly stop and trigger the current limit on the controller when running.
I sent both units to Bachmann for repair. They replaced the motors in both units. Of course there is no guarantee that the cause of your problem is the same. Just what happened in my case.

It cost me 37 pounds each to do, but i think their prices may have risen since then.

I would be interested to know for future reference where I would acquire a new motor to fit myself, and how much that might be, if anyone can advise?

As a footnote, I have had quite a lot of issues getting my stock to run consistantly on DCC. Mostly for older second hand units that I purchased. In all but one case it was resolved by stripping the bogies and cleaning the wheel pickups. Most of the preowned units pickups were very dirty and DCC requires good train to rail electrical connection.
The one problem not resolved by cleaning was for a dmu 108 that would respond to dcc to set off but then would not respond once running. That went to Bachmann too and they fitted  a new pcb, although i suspect the problem was actually the contacts between the pcb contact arm and the motor, which are integrated into the pcb.

I am no expert, and still very much on the learning curve, but hope my experiences so far may be of use to others.
« Last Edit: December 14, 2017, 09:35:51 AM by daversmth »

Offline longbow

  • Trade Count: (0)
  • Full Member
  • ***
  • N Gauge Society Number: Yes
  • 2mm Association Number: Yes
  • Posts: 540
  • Country: au
    • Awards
Re: Intermittent shorting when DCC fitted
« Reply #6 on: December 14, 2017, 11:15:17 AM »
Thanks. Sounds like I need to start by checking the current draw in DC mode.

I'm not familiar with decoder overload protection - perhaps the events described above are explained by the Digitrax decoder shutting off at a lower load than the Zimo or the controller?   

 

Offline daversmth

  • Trade Count: (0)
  • Full Member
  • ***
  • Posts: 106
  • Country: gb
    • Awards
Re: Intermittent shorting when DCC fitted
« Reply #7 on: December 14, 2017, 11:38:31 AM »
I could only do limited testing on DC, but the  motors that would intermittently draw high current on  DCC seemed to run fine on DC. I have no explanation for that. It was just my observation.
Both controllers had 1.5A cut outs.
« Last Edit: December 14, 2017, 11:40:28 AM by daversmth »

Offline Vonzack

  • Trade Count: (+2)
  • Full Member
  • ***
  • N Gauge Society Number: 20933
  • Posts: 467
  • Country: gb
  • Gender: Male
    • Awards
Re: Intermittent shorting when DCC fitted
« Reply #8 on: December 15, 2017, 10:37:36 AM »
It cost me 37 pounds each to do, but i think their prices may have risen since then.

I would be interested to know for future reference where I would acquire a new motor to fit myself, and how much that might be, if anyone can advise?

Bachmann also sell the motors as spares, I recently got a replacement for a Class 60 for £15. There are other suppliers such as BR Lines and Peters Spares if you Google.

Offline longbow

  • Trade Count: (0)
  • Full Member
  • ***
  • N Gauge Society Number: Yes
  • 2mm Association Number: Yes
  • Posts: 540
  • Country: au
    • Awards
Re: Intermittent shorting when DCC fitted
« Reply #9 on: December 15, 2017, 10:48:58 AM »
A quick check shows my Class 22 drawing about 90mA running on DC at 50% throttle which doesn't seem abnormal. I'll try a stall test tomorrow and see what draw that produces. 
« Last Edit: December 15, 2017, 11:21:55 AM by longbow »

Offline daversmth

  • Trade Count: (0)
  • Full Member
  • ***
  • Posts: 106
  • Country: gb
    • Awards
Re: Intermittent shorting when DCC fitted
« Reply #10 on: December 15, 2017, 12:27:01 PM »
It cost me 37 pounds each to do, but i think their prices may have risen since then.

I would be interested to know for future reference where I would acquire a new motor to fit myself, and how much that might be, if anyone can advise?

Bachmann also sell the motors as spares, I recently got a replacement for a Class 60 for £15. There are other suppliers such as BR Lines and Peters Spares if you Google.

Many thanks for that.
Next time I have a troublesome loco I will acquire the parts and repair it myself. Hopefully ...

Offline Only Me

  • Reader Of The Manual
  • NGF Technician
  • Trade Count: (+16)
  • Full Member
  • ****
  • N Gauge Society Number: 23206
  • Posts: 5728
  • Country: gb
  • Gender: Male
  • Creator of Minature Masterpieces
    • Northants & Cambs Area Group of the NGS
    • Awards
Re: Intermittent shorting when DCC fitted
« Reply #11 on: December 15, 2017, 12:46:29 PM »
I've seen this before, under the pcb is a circuit board, one of the wires will be touching the chassis which under DC wont be an issue but its essentially bypassing part of the dcc socket, so when you put in a decoder it shorts because basically theres a path to the chassis through a wire touching that shouldnt be threre.  More than likely one of the motor wires

I also do repairs  - Pm me if you want it looked at.

Cheers Paul.
« Last Edit: December 15, 2017, 12:48:08 PM by Only Me »



Offline longbow

  • Trade Count: (0)
  • Full Member
  • ***
  • N Gauge Society Number: Yes
  • 2mm Association Number: Yes
  • Posts: 540
  • Country: au
    • Awards
Re: Intermittent shorting when DCC fitted
« Reply #12 on: December 16, 2017, 10:01:06 AM »
Thanks for the inputs. A proper inspection of the electrics for shorts would likely require a fair amount of dismantling so I think it's more sensible to send this one back.

Offline daversmth

  • Trade Count: (0)
  • Full Member
  • ***
  • Posts: 106
  • Country: gb
    • Awards
Re: Intermittent shorting when DCC fitted
« Reply #13 on: January 29, 2018, 05:49:14 PM »
I have a total of  13 locos and dmus.

I have had 2, one dmu, one emu that has exhibited the fault where the merg dcc controller current limiter trips and the loco does not move. Both had new motors fitted to fix this.

I now have a deltic , bought new and little used, that is exhibiting the same behaviour.

So 3 out of 13 have now done this which seems a high proportion.
Just unlucky, or is ths normal or could something be causing it ?

I found that the faulty unit in all cases runs ok on dc, then after doing that it runs ok on dcc for a while before once more exhibiting the fault again.

Not sure what to do with my deltic which is showing this behaviour.

Any advice or opinions appreciated.

Offline daversmth

  • Trade Count: (0)
  • Full Member
  • ***
  • Posts: 106
  • Country: gb
    • Awards
Re: Intermittent shorting when DCC fitted
« Reply #14 on: February 17, 2018, 08:50:18 AM »
So, just to compete the post, Bachmann reppaced the motor under warranty because it had totally died.
It had also blown the dcc decoder due to the high current draw, although the decoder was still able to operate the lights. So I swapped the blown decoder with a fully working one that was  in the trailer car of a dmu that only needed to operate lights and all working again now.

 

Please Support Us!
December Goal: £55.00
Due Date: Dec 31
Total Receipts: £120.00
Above Goal: £65.00
Site Currency: GBP
218% 
December Donations


Advertise Here
anything