Electrical Q - Capacitor in a locomotive?

[lehrr]

I've been messing around with a small HO layout for about a month now. Without getting into an argument over the virtues of one track over another, I am set up on Life Like Power Loc, and have a pretty decent dual mainline oval with two dual-spur yards and a long crossover / parking track.

I've accumulated some decent locos and rolling stock. My spectrum and athearn locos have no problem anywhere on the layout.

I have a life-like F7-A loco that I am running with a dummy F7-B and five Athearn heavyweight B&O coaches.

I like to run this guy pretty slow, however on a couple of my turnouts I have a short dead spot, that it gets stuck on when I'm crawling over it.

I got to daydreaming and thought that it might be able to overcome this if there was a small capacitor installed in the loco to supply the split second of voltage necessary when the wheels traverse the plastic frog.

Has anyone ever done something like this? I know that there would be an issue with the reversing voltage encountered when you switch direction from the throttle, however this should be able to be overcome by either a bi-polar capacitor (called something like that, can be charged in either direction) or with dual standard caps with diodes wired inline.

Ideas? Am I off my rocker?

I understand that better locos with 8 wheel pickup would (and do) alleviate this, however I like to tinker and think this could be a cool project.

Thanks!

 

[CBCNSfan]

Hi lehrr, welcome to ModelRailroadForums
To be of any value it would have to be an electrolytic cap. This would be OK for one direction (Polarity sensitive and if reversed Boom!). That brings us to an AC or motor start capacitor and in any case the physical size is something to be concerned about.
I would guess that your F7A has electrical pickup on one truck only. The easiest way to prevent stalling is to add electrical pickups to the other truck that way there is always continuity to the track. I've done this to some train set locos some years back when I first started. I believe that that would be your best bet.

Cheers
Willis

 

[jeffrey-wimberly]

It would take a pretty good size capacitor to do what you're asking. I'm assuming the problem with your loco is that it picks up from 4 wheels on the front truck and the 4 rear wheels are the drive. This is the usual setup on the standard line LL locos. A better bet would be to set up a set of pick-ups on the dummy unit and wire them to the pick-ups in the A unit. That way it would be getting power from 8 wheels spread over a good size area. I do the same thing with my mu'd locos so they have full contact all the time even though they pick up from all the wheels in the first place. The only down side is that if the lead unit derailed (it's only happened once) the lead unit would keep on pulling even though it's wheels were off the track until it jerked the other loco off as well. Kinda like sumo wrestling.

 

[lehrr]

Yeah that is the issue, the life like only has a pickup on one truck, the drive truck has no pickups. What's the easiest way to add pickups to the drive truck or the B loco? Any easy recipes for a scratch built pickup? It's a good looking and running loco with the exception of the dead spots on the frogs.

 

[CBCNSfan]

I just cut strips of brass shim stock to shape, soldered wires to them and then cemented (epoxy) to the plastic gear box (similar to the front truck). Then connected the new wired to the existing wiring. Nothing fancy, but it worked.
I'll take a look later and see if I still have one.
Note, does your drive truck have metal wheels? I recall some of them didn't
Cheers
Willis

Just read Jeffery's post, that's a good idea if the dummy has a pickup for the lights.

 

[Sudasana]

Smart Dummy

There's a short article in the January 2010 issue of Model Railroader on page 68 that looks at wiring up a "smart dummy" B unit. It doesn't have a lot of detail, but it does some have interesting pointers and mentions some specific components that the author used.