Stay alive or extra pickups, or both?

[Bob G]

I've just built a Worsley Works SR Motor Luggage Van using an old Graham Farish power bogie.

Now I'm a DC Dinosaur, but I have seen the benefit of fitting Tramfabrik's stay alive systems in coach lighting systems in Maunsell Coaches.
So I had the idea of fitting a couple of spare stay alive Tramfabrik capacitors across the motor connections to the power bogie rather than building a second set of power pickups on a Poole Mk 1 coach bogie with China metal wheels at the non-driving end of the MLV. My experience of building such a trailer pick up bogie previously is the friction is too high, which is why I thought a set of stay alive capacitors would do the same sort of job as Bulleid's booster locos used to use when they jumped the third rail feeds.
The tramfabrik ones are quite massive capacitors, at 220uF.

Any suggestions, and do I need a diode matrix to make sure the charge that I can build up works in both directions?

If anyone can produce a wiring diagram I'd be very happy

Cheers
Bob
   

[chrism]

Any suggestions, and do I need a diode matrix to make sure the charge that I can build up works in both directions?

If anyone can produce a wiring diagram I'd be very happy

My initial thought is that you'd need two diode matrices;
One to make sure the caps get charged whichever direction you're running and without discharging them back to the track instead when changing direction.
A second to make sure they discharge to the motor for the direction you're running. I suspect that you'd also need some form of logic control for this because you'd need to reverse the feed to the motor when running in reverse.

Unless someone knows better I suspect it'd be simpler to add more pickups.

[Moria]

I am not an electronics engineer, so I could easily be wrong, but here is my understanding of what you are asking..  I am sure that people will be along to correct me if I am wrong though

My understanding of Stay alive is that it is a DCC technology that assists the DCC chip in maintaining it's settings during a ( brief) power out, and a little bit of power to continue the drive during that period as well as being cleverly controlled by the electronics on a DCC chip, both in regards to charging the cap and discharging the cap using common standards developed that all DCC manufacturers are following.

On DC, you are using the term stay alive to actually mean a capacitor that acts as a flywheel, which is not the same thing.

Doing the math, for a flywheel capacitor, you would probably need a capacitor of approx 20V 0.5F (to give you about 1 to 2 seconds)  which is not small, and I expect would not fit inside N gauge stock even though they are getting smaller.  The tramfabrik ones for 1F are only 2.7v so put one of those on a DC circuit and there will be smoke, maybe even a bang inside your lovely new model

You would also have it permanently in place rather than as required in DCC, so turning off the controller wouldn't actually stop the loco because the capacitor would still discharge, so you would have to learn where to turn the controller off when approaching signals or buffers, because the controller is no longer on/off..  its on/ capacitor.

Finally, if your controller is a PMW style one, which applies full power but in limited amounts of time, then your loco will charge from that first full pulse and suddenly take off at nearly full speed even though your controller is set to minimum as your capacitor will be overriding the controller and potentially damaging your controller or loco with feedback through the rails from the cap.

Stay Alive, as it is designed, needs some special electronics between the capacitor and the motor..  ( something like a DCC chip ) to make it work..  so I would fit extra pickups for DC.

Graham

[Bealman]

Seems pretty unanimous.....

Extra pick ups!

The alternative seems complicated to me.

[Bob G]

I guess I had not thought it through! Extra pickups it is then!

[Steven B]

I can only echo what Moira wrote.

If you want the benefit of a keep/stay alive then you'll need to power your motor via a dcc decoder as per the NGS Hunslet.

Steven B

[ntpntpntp]

For DC locos,  fit as many pickups as practical and an effective flywheel (ie. reasonable mass) on the motor.  A flywheel really does make a difference.

@Moria's explained why electronic stay-alive isn't really a viable option for DC.

[Nigel Cliffe]

For DC locos,  fit as many pickups as practical and an effective flywheel (ie. reasonable mass) on the motor.  A flywheel really does make a difference.

Flywheels only work when motors are spinning at a modest speed or higher. 

They work in one of two ways - if properly in balance they keep the motor spinning by inertia;  if out of balance then they add vibration which might shake the wheels back into contact.

In the past I've been asked to sort out the running of a DCC fitted loco - the problem was the out-of-balance flywheel. 


- Nigel

[geofff]

Bob

I don't understand the question, nor the answers - but would like to see a picture of the model.

Regards



Geoff

[Bob G]

Bob

I don't understand the question, nor the answers - but would like to see a picture of the model.

Regards



Geoff

Well you will get to see it shortly, but obviously it is in bits at the moment!
I'm modelling S68001 as it was in all over green with no yellow panel from 1959 - 1970.
It will have horns rather than a whistle making it really 1964 - 1970.

Bob

[njee20]

It's a shame Bachmann never downsized the MLV.