8-40CW Surging

[jowalmer]

I purchased one of these (spectrum) in January or February.  It ran good initially but soon after began to surge as it runs down the line.  No problems at full throttle.  Lately it has been getting worse to where, at just under half throttle, it will almost stop under load.  We have 9 locos and this problem is limited to this specific loco.

Track details:  inner and outer oval (10x6) with one yard that has 5 legs.  There are 3 track connections throughout.  I assume that I should have more track connections and will in the future.  I have one of those eraser type track cleaners and assume that the track is clean.  I have not tested the track for power drop offs, however, no other loco has this problem. 

Any input is appreciated as to potential problem and possible fixes.   Thanks.

Jim

[rustyrails]

Jim,
It would be helpful to know if you are running your layout on DC or DCC.  It would also be helpful to know if this locomotive has a decoder installed.
Rusty

[jowalmer]

Oh yeah, that would be helpful too...

Yes, DCC.  The 8-40 came DCC ready from bachmann, I'm not sure what decoder they use.

Jim

[Chris350]

Oh yeah, that would be helpful too...

Yes, DCC.  The 8-40 came DCC ready from bachmann, I'm not sure what decoder they use.

Jim

I hate to sound lie a nitpicker but, DCC ready and DCC On Board (installed) are different animals. Can you clarify that please?  Have you looked "under the hood" as it were?  It will be fairly clear which decoder is installed.  It would also help to know what you use as your controller and how are you programming  your CV values.  OPS mode or Service mode? It sounds like there is a conflict in a CV setting.
  If this is the only loco misbehaving, I bet your electrical is OK.  Does the loco make any unusual noises or sound like it's binding up?

We'll help you get to the bottom of this I'm sure. 
Chris

[jowalmer]

nitpicker is fine.  In my mind i wrote 'equipped' but on paper it came out 'ready.'  This is a DCC loco with a decoder installed by the factory...isn't it?  I always assumed it had a decoder.  I've looked under the hood but didn't look for a decoder.  It is item #83506 and indicates on the website that it has DCC on board.   

Last night I was fiddling some more and yes, it surges at full throttle too.  I kind of feel like either slamming it on cement or crushing it with cement boots.  Ok, now that I've got that out...

I switch between the ez command and NCE Power cab.  Depends on if my 4 year old wants to take the controls.  Outside of the purr of the motor/gears slowing when it shouldn't, I do not here any unusual sounds.  However, a month or so ago it started to squeek.  I consulted this board, went to the lhs and purchased plastic friendly oil.  it was squeeking at the pockets the wheel axles fit into.  I lightly, very lightly oiled the pockets and squeek went away. 

could the problem be dirty wheels?  I'll also try resetting the CVs to ensure there is not CV conflict.  Thanks.

Thanks.

[rustyrails]

You might try disabling the analog (run on DC) feature of your decoder.  You can do that by setting CV29 to 2.  It's probably set to 6 now which enables 28 speed steps and analog mode.  I suggest this because having analog mode enabled is known to cause unpredictable behaviour.   Hope this helps.
Rusty

[jowalmer]

me too.  I'll try it out.

[Chris350]

dirty wheels.. eh maybe, more like the analog conversion on DCC conflict Rusty mentioned.  If it's DCC equipped it could have a circuit board inside with the decoder built into it (I'm speculating because I've never sen the inside of one of these).  You might never see a part you would point at and say "ah ha there's the decoder". One last thing to check, would be whether the wheels are out of gauge.  That might lead to binding on your track work or added friction in the trucks.

[Jim Banner]

The surging suggests either a pickup problem or a decoder problem.  If the headlight is a nice, steady glow with no flicker, then it is not a pickup problem.  Surging as a decoder problem is usually related to the decoder over heating and shutting down to protect itself.  Surging can occur if the decoder is near its maximum temperature and drifts over it, then the protection circuit may start to shut down, slowing the locomotive.  The slowing can decrease heat production enough to let the decoder cool and reset the protection circuit, speeding the locomotive back up.  Decoder overheating is often related to overloading the motor by too much load.  This can be too much train, if weight has been added to the locomotive or it can be drag in the motor, motor bearings, gears, axle bearings or something (wire?) touching a flywheel or drive shaft.  Occasionally, the decoder itself is faulty, for example, it does not turn the output transistors on and off cleanly, leaving the output transistors too long in the transition zone between on and off, which is where they produce the most heat.  Or the protection circuit gets a little paranoid and tries to shut of the decoder at a lower temperature than is normally allowed.  This heat and cool surging is a slower cycle than mechanical binding.  Mechanical binding usually occurs once per turn of the wheels.  Heat can cool surging usually occurs over several turns of the wheels.

If you have an ac ammeter, you can measure the current being drawn by your troubled locomotive and compare it to one that runs okay, under identical conditions.  If the current is significantly higher, then it is time to oil it around - light oil on the motor bearings (but NOT the commutator!!), on the worm gear bearings, on the axle bearings, and on the linkage.  Then gear oil (or very light grease) on the gears.  If the motor current goes down, then you have solved the problem.  (I have seen the bench test current drop by more than 60%, just from lubrication.)  If the current does not go down, you have a bind somewhere, possibly gears forced into too tight a mesh, or you have a faulty motor.  However, if the current draws of your troubled locomotive and your good locomotive are the same, the problem likely lies in the decoder.  If both locomotives have plug in decoders, it is not too hard to swap them and see what happens.  Just don't forget that the address goes with the decoder; it does not stay with the locomotive (that is surprisingly easy to forget in the heat of battle.)  If the decoder is faulty, then it is up to you to decide what to do - ship the locomotive and its original decoder back to Bachmann or install an identical replacement or maybe install an upgrade.

The above description is generic - it applies equally to diesel and steam locomotives.  Just don't oil or grease the parts that aren't there.

Jim

[jowalmer]

One last thing to check, would be whether the wheels are out of gauge.  That might lead to binding on your track work or added friction in the trucks.

I never thought about wheel guage being the problem and will check that out.  I do notice that the surging seems to happen at the same places throughout the layout.

Mr. Banner, I will also check out your suggestions and will focus first on looking at the lights to determine if pickup is a problem.  I will also check to see if I can switch out the decoder.

Thanks.