Two N Scale Turbo Trains, 50 Years Apart

[peteski]

That looks good Dwight!



Here is a diagram for an anti flicker circuit. If needed, you can install additional caps in parallel with the one shown in the diagram.  The value of R2 was just an example (for another project thread), and you can use whatever you think works well, and you already have a bridge rectifier. The R1 will always be 150 ohm.  It limits the inrush current to the capacitor.  All the Digikey part numbers were just as an example.

[Tad_T]

Thanks for sharing that @peteski

[Dwight in Toronto]

Thank you Peter - great stuff!

Since I already have three 1.82K resistors on the pc board (soldered in series, end-to-end), could I use the first 1.82K resistor as that shown as R1 in your diagram?  You said “the R1 will always be 150 ohm” - what happens if it were 1.82K instead?

[peteski]

Thank you Peter - great stuff!

Since I already have three 1.82K resistors on the pc board (soldered in series, end-to-end), could I use the first 1.82K resistor as that shown as R1 in your diagram?  You said “the R1 will always be 150 ohm” - what happens if it were 1.82K instead?

That should work, but there might be slight change of LED brightness when the cap charges/discharges. It will probably unnoticeable. I should have stated that 150 ohm is the minimum value I recommend.   If it is, you use those 1.82k resistors stacked in parallel.   If you stack 4 of them touy will end up 270.5 ohms.  That is much closer to 150 ohm than 1082 ohms.

You might wan to try a test run without the no-flicker circuit installed to check what kind of a difference it will  make.

[Dwight in Toronto]

As Peteski was writing out “you might want to try a test run without the no-flicker circuit”, I was trying out a test run on my workbench oval.

It was a ‘good news/bad news’ event. 

First, I was surprised and delighted to see that the bare-bones little circuit (in conjunction with the track power pickup/conveyance scheme) did an admirable job of keeping the LED illuminated with very minimal flickering.  I’d even go so far as to say that it would probably be good enough, with no need to add in the capacitor.

On the downside, even though the copper wheel wipers are imposing very little resistance on the inside face of the rear-most wheels, it’s enough to cause the lead locomotive to struggle and strain its way around the test loop with the full train set.  It’s an obvious, noticeable and unacceptable impediment that was not there before.

I will try to reduce the degree by which the wipers are rubbing on the wheels, which in turn might result in more severe flickering, which would then resurrect the need to splice in the capacitor.

Alternatively, maybe I should just put a battery in the shell with a SPST micro switch in the floor to manually control the rear LED.

All comments are welcome!

[peteski]

I hate using batteries for any sort of  illumination in N scale cars.  Not only it is a pain to do-maintenance (replacement), they often leak caustic electrolyte, causing damage to the battery holder or other items.

I'm confident that  you can adjust the wipers to reduce the rolling resistance.    If you could make the wipers narrower, they would be more flexible.

[Dwight in Toronto]

Peter - I agree entirely about using batteries, for all the reasons you gave.  That would be a last resort!

I had added several pieces of solder to increase the weight of the cab (not the thin rosin-core stuff used for electronics, but the heavier solder used for sweating copper plumbing).  I removed the weights, squeezed the wipers in a bit, and in so doing enabled the powered cab to again pull the full train set.  But as expected, the rear LED was flickering horribly.

Since this entire project has been about experimentation, I soldered in the 1000 UF capacitor:




Thank goodness for all the room in the back half of that shell! 
I’m happy to report that there is no flicker whatsoever.  In fact, when I lifted the cab off the track, I clocked a full 26 seconds until the LED faded out!

So now I just need for my prewired LED order to arrive.

[peteski]

Yeah, 1000µF is a bit of an overkill.

[Dwight in Toronto]

I’m resigned to being patient as I await delivery of a few packets of prewired 0402 LED’s, which will enable me to wrap up this project. 

When nothing had showed up after two weeks, I sent the vendor a status update email. 
Turns out he had run out of the red ones.  So, I guess he’s awaiting shipment from China to replenish his stock.  I should have just ordered from AliExpress or whatever - could probably get 10 times as many for 1/10 the price!

In the meantime, I’ve been running the model pretty much every day.  It’s been performing admirably, in fact, better than I ever expected.  One odd thing - the four powered cab driving wheels seem to get crudded up unusually quickly.  They seem to need cleaning after every 20 minutes or so of running time.  The rear single-axle pickup bogie is using a Kato passenger car wheelset, and it has never once required cleaning.

I don’t know what the Bachmann 50 year old wheels might be made of, but are some wheel materials just worse than others when it comes to grime build-up?

[brill27mcb]

The material and surfaces of the wheels may have something to do with it, but it also might be caused by the half-century old Bachmann motor sparking and causing arcs at the wheel surfaces which can make them pitted and dirty. I have seen this happen in larger scales.

Rich K.

[peteski]

The material and surfaces of the wheels may have something to do with it, but it also might be caused by the half-century old Bachmann motor sparking and causing arcs at the wheel surfaces which can make them pitted and dirty. I have seen this happen in larger scales.

Rich K.

Since there is a DCC decoder between the track connection and a motor (so the electricity has to travel through a bridge rectifier and transistors of the H-Bridge motor driver, any motor brush arcing is basically separated from the track.

I'm not a metallurgy expert but yes, wheel materials used by different model companies do  seem to make a difference.  Most metal model RR wheels are made of brass, and are plated with another metal (nickel-silver, nickel, or something else?). Some older Arnold wheels were actually steel (ferromagnetic) and were likely nickel plated.  Kato wheels seem to be most reliable not requiring frequent. Older Atlas wheels weren't as reliable. I suspect old Atlas wheels are brass with nickel plating.

If you have spare wheelset, you could file the wheel down and see if you can see the golden brass color under the silver-colored plating.  Or check if it is ferromagnetic. Regardless, (unless it wore off) the plated surface is what's making contact with the track.

[Dwight in Toronto]

Thanks for the feedback guys.

I verified with a magnet that the wheels are indeed ferrous.  And for what it’s worth, I took a closeup pic - hard to discern what the plating might be, or if it’s worn in spots.  Probably not helpful in any way, but here she be:

[peteski]

Dwigth, could the magnet be attracted to the axle or the gear, not to the wheels themselves?
But yes, worn plating on the treads could negatively affect their conductivity.