Bachmann CEP/BEP multiple working issues

[mikesndbs]

Hi

 

Got a CEP and BEP and even a pair of EPBs that run well on their own, they run at close to the same rate also.

But when coupled together there is an odd surging effect when they slow down then speed up again.

Not layout specific nor controller, anyone know what the issue is please?

[DCB]

As no one else seems to have a theory, I wonder if it is traction tyres gripping and amplifying slight variations in the speed change.  I used to have Manor and KIng classes (Now out of use) with Hornby Tender drives which did something similar when double heading 

Last year I had to fit non traction tyre wheels to a new Hornby (?)  156 sprinter to stop it de railing  when starting and stopping as the grip was so harsh.   My 1960s Triang DMU with brass wheels and  a Lima DMU from the 1990s run at very different speeds but happily runs a 6 car set because the Triang slips and the Lima has spur gears so  does not stop or start abruptly,  so I suspect Traction Tyres.
 

[RFS]

52 minutes ago, DCB said:

As no one else seems to have a theory, I wonder if it is traction tyres gripping and amplifying slight variations in the speed change. 
 

 

These models do not have traction tyres. 

 

What happens if you run the units together but not coupled, ie with some daylight between or on adjacent tracks? 

[Taigatrommel]

None of the mentioned models from Bachmann have traction tyres.  Having a quick look at your YouTube channel, there are fairly tight curves.  These could be creating resistance that affects the different units within a train at different moments.

[NIK]

Hi,

 

I've not looked into this in detail but I think I remember talk about the back EMF feedback features of decoders reacting with one another when in a consist.

 

I think the solution that was mentioned was to turn off the back EMF feedback feature on all 'locos' except the leading one.

 

I think that's a bit of a challenge for model Southern Region practise in particular where splitting/combining  of units can occur quite frequently in stations and fiddle yards.

 

I don't think there are any DCC decoders that offer say the option to automatically turn off the back EMF feedback to all of the advanced consist bar the front unit.

 

Regards

 

Nick 

[RFS]

3 minutes ago, NIK said:

Hi,

 

I've not looked into this in detail but I think I remember talk about the back EMF feedback features of decoders reacting with one another 

 

Regards

 

Nick 

The issue has been raised in the non-DCC forum so l have assumed it's DC.

[mikesndbs]

Hi guys. Yes confirmed DC and not my layout it's a freinds with straight track.

[DCB]

Just to confirm these do not have DCC decoders?    If so removing them and fitting blankers might be a first step.

[SRman]

I run mine on DCC, where BEMF can be a problem, although in my case, none of my CEP, MLV, EPB or HAP units "fight" each other in multiple. One thing that might help though would be to use more rigid couplings between units. I use Kadee #20s at the cab ends of all my Bachmann units.

 

 

 

 

Edited March 15 by SRman

[mikesndbs]

Brilliant info guys thanks. These are being run under DC, but I guess bemf can still be a thing. Is there any cure for it, can't use flyback diodes due to needing to go in both directions 

[NIK]

Hi Mike,

 

Sorry, I didn't spot it was a non DCC topic but carrying on from what DCB said did you buy any of the units second-hand in which case there is a slight chance they may have DCC decoders fitted but running in DC compatibility mode.

 

You said it was not controller specific but were all the controllers tried of the feedback type?.

There is just a chance that feedback controllers may struggle with multiple units.

 

Also I find it very difficult to judge slight changes in speed of a model train - maybe coupling together units is showing variations in electrical pickup.

 

Do the units have Kadee buckeye couplers at the cab ends - that may reduce the effect of surging.

 

Regards

 

Nik (EMU and DEMU mad)

[RFS]

I have a lot of EMUs too and run many different combinations without problems using DCC. I've found that to prevent buffeting between units you need a rigid coupling. I used to use Kadees, but these are not rigid and I now use Hunt magnetic couplings which have cured this problem. 

 

I would also check the driven bogies of these units. It is a known fault that the gear pin can fall out meaning only one axle is driven. To check if this has happend, try turning each wheel with your fingers: if the pin is in situ you won't be able to do this and all is well. 

[mikesndbs]

Here is a video of them running 

 

[34theletterbetweenB&D]

11 hours ago, mikesndbs said:

...confirmed DC and not my layout it's a friend's with straight track.

Another potential cause is inequity in current supply along the layout from a bunch of factors:

Skinny wiriing cores,

Insufficent track feeds, 

Reliance on rail connectors and point blade contact for conduction,

Worn switches not making and maintaining positive contact.

 

I had the last one on my original DC switched section layout, some years after going DCC, some of the section switches were simply worn out - that's what comes of enthusiastic operation!

 

Lovely looking layout, hope the problem can be quickly overcome.

[franciswilliamwebb]

1 hour ago, mikesndbs said:

Here is a video of them running 

 

Streuth, that is bad!

 

If it were me I'd start testing with an oval of set-track on the floor using a basic Bachmann DC train set controller and then work up from there.

[DCB]

My Lima / Triang DMU combo runs just fine on my On Track controller and  a H+M Power master very like the OP has as well as an H+M Safety Minor.  However I do get surging with my Triang  Halls when descending  my 1 in 30 gradient with a heavy train.  It's the worm drive binding up,  being non reversible,  if  the motor runs rough it does not happen so as a work round  I drive down on half wave on a H+M Safety Minor which is a Variable Transformer like the Powermaster.    So having checked the YouTube video carefully I see your Powermaster has half wave so run it on half wave, probably need max power and see what happens  
Does it surge on half wave?     Worth a try.

Edited March 16 by DCB

[mikesndbs]

1 hour ago, DCB said:

My Lima / Triang DMU combo runs just fine on my On Track controller and  a H+M Power master very like the OP has as well as an H+M Safety Minor.  However I do get surging with my Triang  Halls when descending  my 1 in 30 gradient with a heavy train.  It's the worm drive binding up,  being non reversible,  if  the motor runs rough it does not happen so as a work round  I drive down on half wave on a H+M Safety Minor which is a Variable Transformer like the Powermaster but which has half wave , I am not sure if the OP Powermaster has half wave  or if it has high/ low resistance,  my safety Minor has both.
Does it surge on half wave?     Worth a try.

 

Less so apparently but I guess that's because of the longer gaps between pulses. Not good for these modern motors however 

[DCB]

The On Track and H&M are both variable voltage, not sure about the other.  They might run more happily albeit not as controllably.

Incidentally

We used to put a 1N400 (?) diode in circuit for forward direction (cab first) and two for reverse (Blunt end) with HST Power cars to ensure the back one didn't surge against the front.    Obviously this would only work with fixed sets and only two power units, but the 0.7 ish / 1.4 ish  volt drop made a difference. 

 

It really sounds like worm drives winding up,  as one pushes or pulls the other.