HELP! Can you solve my conundrum?

[Cabrider]

Just recently I have a loco that has started to trip out the overload cut-out. My problem is that I have tried everything to find out what's causing it but without success. The loco runs for 3 minutes and trips the controller out. The problem is that no other loco does it, and, here's the problem, it only does it on the outer track and runs perfectly on the inner track. I have renewed sections of track, swapped over the control units and it still trips the other unit, checked the wiring in the loco, and nothing makes any difference! So it's not the control units because both trip out when used on the outer track, not the loco because it runs perfectly on the inner track, and not the track as every other loco runs perfectly. I am at a loss now and can't see what it can be. Anyone any ideas? Answers on a postcard please!!

[WIMorrison]

does it only do it on a curve, or only on a point, or ...

[smokebox]

There could be a lower resistance in the wiring to the outer track allowing slightly more current to flow and causing the overload to trip, possibly not helped by slightly higher current being drawn by that one particular loco due to wear and tear?

[cliff park]

After it has tripped will the loco run straightaway, or do you have to wait for it to 'cool down' before it will run again ?

[sharris]

Does it happen running in both directions?

 

Could it be that something is rubbing against the chassis at a particular curvature that shouldn't be - either causing a partial short circuit or greater friction that is raising the current? 

 

 

[Cabrider]

It only stops on a curve; loco will run straight away after resetting cut-out.

Can't see it being the curvature as outer track is 3rd radius and the inner is 2nd radius and the problem is on 3rd radius track.

Can't see it being the resistance in the wiring as I interchanged controllers which have identical lengths of wiring.

Haven't tried it in both directions - I'll give that a try and see what happens.

I should add I am using the Hornby R8250 controllers which I read are not the best, so if it is the loco drawing too much current  would a different controller such as Gaugemaster make any difference? I also recently fitted a new motor to this loco but it has been running fine until the other day.

 

Thanks for your replies, much appreciated.

 

Incidentally, the loco in question is the Bachmann 76079 as featured in my avatar.

Edited January 6, 2020 by Cabrider
additional information.

[smokebox]

The R8250 controllers are notoriously poor.  Gaugemaster controllers are undoubtedly better but you should really eliminate the fault before buying new controllers.

[kevinlms]

9 hours ago, Cabrider said:

It only stops on a curve; loco will run straight away after resetting cut-out.

Can't see it being the curvature as outer track is 3rd radius and the inner is 2nd radius and the problem is on 3rd radius track.

Can't see it being the resistance in the wiring as I interchanged controllers which have identical lengths of wiring.

Haven't tried it in both directions - I'll give that a try and see what happens.

I should add I am using the Hornby R8250 controllers which I read are not the best, so if it is the loco drawing too much current  would a different controller such as Gaugemaster make any difference? I also recently fitted a new motor to this loco but it has been running fine until the other day.

 

Thanks for your replies, much appreciated.

 

Incidentally, the loco in question is the Bachmann 76079 as featured in my avatar.

What is the ratings of the Hornby R8250, there should be an ##va number on it?

[Cabrider]

I have tried all combinations of running, loco first, tender first, clockwise, anticlockwise, on inner and outer circuits and it only exhibits the cut out problem going forwards loco first in a clockwise direction on the outer circuit and is the only loco to do this.. I have tried again this morning and it runs for exactly 31/2 minutes and then stops. I am now at a loss to know where to look to solve this.

Edited January 7, 2020 by Cabrider

[WIMorrison]

This sounds like a mechanical issue and somewhere an electrical contact is moving going around the curve and allowing both polarities to come together - only you can solve this by carefully looking at the loco and seeing what can possible be allowed to touch this causing short 

[Phil Bullock]

What is the loco please?

[Kier Hardy]

14 hours ago, Cabrider said:

It only stops on a curve; loco will run straight away after resetting cut-out.

Can't see it being the curvature as outer track is 3rd radius and the inner is 2nd radius and the problem is on 3rd radius track.

Can't see it being the resistance in the wiring as I interchanged controllers which have identical lengths of wiring.

Haven't tried it in both directions - I'll give that a try and see what happens.

I should add I am using the Hornby R8250 controllers which I read are not the best, so if it is the loco drawing too much current  would a different controller such as Gaugemaster make any difference? I also recently fitted a new motor to this loco but it has been running fine until the other day.

 

Thanks for your replies, much appreciated.

 

Incidentally, the loco in question is the Bachmann 76079 as featured in my avatar.

 

33 minutes ago, Phil Bullock said:

What is the loco please?

Doh!

 

[34theletterbetweenB&D]

The construction of this Bachmann loco has two main potential areas of weakness when it comes to a short circuit. (Applies to a great number of locos in their range.)

 

If you remove the keeper plate you will see that the pick up wiper strips run in parallel under the axles. If they show any signs of an upward bow, it is possible that they can graze axles. These strips flex as the pick up wiper 'fingers' move on the wheel backs on curves. And there's a  completely invisible location for momentary shorts. Cure, carefully applied insulating tape covering the strips. Careful is the word, you don't want the tape getting wound into the axle gear!

 

The wiring path is a little complex too, and wire insulation could have been damaged. But this isn't curve sensitive, so the  first suggestion is most likely.

 

There are naturally further possibilities, 'tin whisker' or a stray wire core at a connection, but let's start with the most likely. Seen the intermittent internal short on the wiper strips on quite a few Bach steam models...

 

14 hours ago, Cabrider said:

...Can't see it being the resistance in the wiring as I interchanged controllers which have identical lengths of wiring...

But that's only a small part of the circuit. I's the impedance of the entire circuit that matters. However, the primary fault is pretty certainly on the loco, so that's first to tackle

[Cabrider]

I have now narrowed the problem down. The chassis runs perfectly on its own but as soon as the body is fitted, hey presto! it stops after a short while. So I agree with those who say it must be a short somewhere. I resoldered the red wire to the motor as it had a stray wire. I have placed insulating tape over the motor wires and motor top but it still doesn't cure the problem, so it must be somewhere else. If it where the wiper strips surely it happen whether the top was on or not.

[Rowsley17D]

A bit of a low tech solution but have you tried running the loco chassis in the semi-dark to see if you can see a shorting spark and where it comes from? No laughing at the back, please.

[Cabrider]

I am now running the chassis with the body placed on but not fully down. Let's see what happens.

 

UPDATE: Running okay. Have now put insulation tape to cover the DCC ready chip completely. Now test running with body fully pressed home.

 

UPDATE 2: No luck. Ran for 10 minutes and stopped. There is no logical reason for what is happening. It's like your car engine  running with the bonnet up but stopping the minute you close it! I am now ready to admit defeat!

Edited January 7, 2020 by Cabrider
UPDATE

[34theletterbetweenB&D]

6 hours ago, Cabrider said:

I have now narrowed the problem down. The chassis runs perfectly on its own but as soon as the body is fitted, hey presto! it stops after a short while. So I agree with those who say it must be a short somewhere. I resoldered the red wire to the motor as it had a stray wire. I have placed insulating tape over the motor wires and motor top but it still doesn't cure the problem, so it must be somewhere else. If it where the wiper strips surely it happen whether the top was on or not.

Keep in mind that you have an intermittent fault. Here's a possible mechanism. The body clamps a wire with damaged insulation onto the chassis block. That you can test for, with a meter. It's the intermittent contact that creates the short circuit that's the trouble, because that never appears when you have the test meter on the item. That will be happening on the running gear, because it occurs when the mechanism is on a curve.

 

Eliminate one or the other, and problem is solved. Ideally eliminate both, to prevent later problems. I am an impatient type, and usually rip all the wiring out, apply insulation to the wiper strips, rather than attempt to chase down faults.

 

Oh, and another place for intermittent contact leading to shorts on curves - and this one you should see by the 'spark in the dark test' - is on the underside of the metal footplate if a pony truck flange makes contact.

[mossdp]

If the loco is drawing current at very near the limit of what the controller will supply, the controller will heat up of a period of time - maybe several minutes until this trips the overload. This is very occurrence is common with these controllers. They are not suited to anything but locos that draw the lowest currents and pulling trains with coaches and wagons with little rolling resistance.

[Right Away]

It's a long shot, but on reassembling the wheelsets on a Bachmann "Hall", I managed to pinch the thin pick-up wires. Perhaps the problem has existed to some extent on your Std 4 since manufacture, only becoming apparent on a particular radius curve.

 

I would seriously consider dispensing with the DCC socket, if for nothing it will eliminate another potential fault location. 

 

[Barry O]

5 minutes ago, Right Away said:

I would seriously consider dispensing with the DCC socket, if for nothing it will eliminate another potential fault location. 

 

shouldn't make any difference by the sound of it.

 

Do you smell any electrical burning smells?

 

If it runs well with the body off have you checked the temperature of the motor when running it without and with the body on?

 

If it runs OK on the inner loop then pick ups may not be the problem. 

 

If it happens after 10 minutes of running how many circuits of the track has it made by then..some of these locos are not happy with continuous running (I had a similar problem on a Bachmann WD which turned out to be a motor/gearbox/running gear problem)

 

Baz.

 

[Cabrider]

8 hours ago, mossdp said:

If the loco is drawing current at very near the limit of what the controller will supply, the controller will heat up of a period of time - maybe several minutes until this trips the overload. This is very occurrence is common with these controllers. They are not suited to anything but locos that draw the lowest currents and pulling trains with coaches and wagons with little rolling resistance.

Hi Mossdp,

You're spot on! I suspected the controllers from the start before I got sidetracked with looking for other reasons. Like many I have read many comments on the Hornby R8250 Controllers most of which are less than complimentary! You can now add my comments the that chorus. I bit the bullet today a bought a Gaugemaster D controller and guess what? The loco now runs perfectly and has completed a one hour session without fault. So there we have it. I guess it must have been putting a new motor in made it draw more current which was more than the Hornby controllers could stand!

Thanks to everyone for their help in trying to identify the problem  but once again it shows one should trust one's instincts when it comes to fault finding. I done the same thing many times on cars over the years only to find it was something simple and not the complicated reasons I was looking at.