I am driving myself mad, as this thread has kicked off a memory of reading about US diesel electric locos where they hook up a second loco that has no engine and no cab and its traction motors are supplied solely from the 1st loco. There is a specific name for the slave locos, but I can't remember it!

Ah, it's just clicked - they are "slugs."

These posts are brilliant. Thanks everyone. However, I am considering something that is a cross between a Flux Capacitor and a Viktor Schauberger vortex implosion perpetual motion generator and stick it in a baggage vehicle behind the loco. That should do the trick.

Some US heavy shunting combos were known as "Cow and calf" (https://www.american-rails.com/cow-calf.html). I think you can buy models of them from some US dealers and I saw some years ago in a Walthers N-scale catalogue.

One of the worst things you an do to an electric traction motor is to run it at high mechanical load and low speed. One way to get around this is to (effectively):

- take two heavy duty diesel-electric shunters
- couple them together more-or-less permanently
- remove the diesel motor and generator from one, and replace them with a big block of concrete for traction
- run the electric traction motors on both units from the diesel engine and generator on the still complete loco

There were also "slugs" which was a slightly different approach to the same problem.

Neil

According to https://en.m.wikipedia.org/wiki/Slug_(railroad) some diesel-electrics can generate more power than they can use at low speeds (before wheel-slip sets in) and a slug is used to provide extra adhesion/traction, using that excess power.

The BR class 13 is effectively a cow-and-calf lash-up



https://en.wikipedia.org/wiki/British_Rail_Class_13

Quote from: stevewalker on September 19, 2019, 11:18:38 AM
According to https://en.m.wikipedia.org/wiki/Slug_(railroad) some diesel-electrics can generate more power than they can use at low speeds (before wheel-slip sets in) and a slug is used to provide extra adhesion/traction, using that excess power.

Looks like I was wrong on this.  I'll delete my previous post. 

But note that the electricity generated by the alternator attached to the engine and used by the traction motors will be somewhere in the hundreds of volts, so the connectors and cable feeding it across to the slug only have to tolerate that voltage.  Feeding 25000V via a cable would be a very different matter. Some trains such as Pendolinos have a 25kV cable along the set at roof level, but this is permanently connected and can only be removed in the depot. 

QuoteBut note that the electricity generated by the alternator attached to the engine and used by the traction motors will be somewhere in the hundreds of volts, so the connectors and cable feeding it across to the slug only have to tolerate that voltage.  Feeding 25000V via a cable would be a very different matter.

At low voltage the current will be greater,so  thicker conductors  and  less insulation will be needed compared to the same load run at a higher voltage were a more  insulation will be required,but the conductors will be thinner.

Quote from: edwin_m on September 19, 2019, 05:00:07 PM

Quote from: stevewalker on September 19, 2019, 11:18:38 AM
According to https://en.m.wikipedia.org/wiki/Slug_(railroad) some diesel-electrics can generate more power than they can use at low speeds (before wheel-slip sets in) and a slug is used to provide extra adhesion/traction, using that excess power.

Looks like I was wrong on this.  I'll delete my previous post. 

I only knew because I happened to read it a few months ago.