Scalefour Forum

Are there any recommended wires for current collectors? I have tended to use 0.35 phosphor bronze in the past, but with steel wheels am wondering if steel on steel might be a better option?

Steve

OK, I'm going to say it, the best wire for collectors is no wire. Use split frames/axles - all the problems with collectors go away. However, this may not help in your quest to find a reliable wiper system.

Phosphor bronze works fine with steel wheels and has the advantage of being springy so you can regulate the pressure on whichever part of the wheel the wire bears on. PB is softer than steel so wear first but for steel to be springy it has to be hard and would tend to wear the tyre. Pickups are easier and cheaper to replace than wheel tyres.

HTH

David

I thought this a very good question when I saw it and there's been a lack of anything definitive on the subject. I use phos. bronze wire on the corner of the flange because Guy Williams said he tried a number of configurations and this worked the best and I haven't seen anything since to rival his results.

The split frame method does work very well and I built my first P4 loco this way but it's the matters arising that sink it - followers of Dave Holt's thread on his Black 5 might wonder what he might do with the ends of all his pipes if they were live. Anyway for whatever reason I chose pick-ups instead for future construction and haven't seen any reason to change. However, the superior performance of the split axle system does suggest that the wheel picks up from the track well enough and any problems on a normal loco are probably related to the curs-ed pick-ups.

A search produced a number of leads and it would seem that we might sensibly just copy the contact materials used in switches. The trouble is that steel (our tyre) is never used for these. I recall Alan Goodwillie is an advocate of gold pick-ups which makes much sense (although gold plated flanges might look rather startling) but tin and nickel also come to mind - materials that might be suitable for plating the wheel tyres. One issue to be considered with switch contacts is deterioration during storage which usually leads to silver falling from favour because it reacts badly with airborne sulphur. I know dissimilar metals react and here I fail to understand the full chemistry - it looked so easy at O level. I've come across half reactions and oxidants so perhaps someone might rescue me here and comment on what phos bronze/steel and other combinations including nickel are doing to each other to form an insulating layer while sat in a siding. Carbon based materials were also mentioned as contact materials and I wondered if this might rescue the plunger pick-up. It works for motor brushes.

The remarkable realisation - it's obvious really - is that contact resistance reduces as pressure increases, hence Guy's attempt to get a point contact to reduce surface area. We've always talked of minimum pressure and this was repeated the last time pick-ups came up on this forum but shouldn't we be applying a greater force? I'm a very long way from stalling the motor and can't say I've noticed things getting hot so far. Warm, perhaps. Perhaps this is why the split axle system works - there's the full loco weight keeping things in contact.

DaveB

Carbon based materials were also mentioned as contact materials and I wondered if this might rescue the plunger pick-up. It works for motor brushes.

The original P4/Studiolith plunger pickus used carbon but they did not seem to find favour, did anyone try them?

There is a thread from 2011 at https://www.scalefour.org/forum/viewtopic.php?f=19&t=1247&p=8650 that contains some interesting thoughts on the subject.

I'm interested in the idea of using gold as the pick-up material bearing on the wheel rim, and have gone so far as to buy a small quantity of gold wire (18 carat, from memory) to test its feasibility. Purchase of a short length of gold wire for such a purpose didn't break the bank, but there are other problems to be faced, such as the fact that gold will chemically combine with the elements in solder and may leave you with an embrittled joint. Gold's resistance to oxidation does, however, hold out the promise of making a high pressure contact between pick-up and wheel unnecessary.

In my researches I came across this article: https://link.springer.com/content/pdf/10.1007%2FBF03215140.pdf which seemed to make some interesting and pertinent points.

I was sold on the idea of split axle current collection long ago, but I do agree with Dave Bradwell that it creates a different range of problems as regards creation of an insulation gap in all the places where it is required. An obvious place where this problem rears its head is tender brake rigging (I use all tender wheels for current collection), as I have yet to find a non-conductive material of adequate strength for use as the cross shafts. One solution is to fit insulating bushes into the frame holes carrying the upper mounts for the brake hangers, but I am currently experimenting with insulation of the (brass/ph.b) wheel bearings from the hornways. One of the advantages of this approach is that frames and their spacers can be soldered together, or, as in my experimental case, a fold-up set of etched frames can be used. Furthermore, insulation of bearings from frames avoids the potential problem of the running plate or some other part of the upperworks bridging the insulation gap - yup, been bitten by that one too.

I prefer 0.3mm hard brass wire mostly, bearing on the edge of the flange as Dave has said. Wound in a few coils this stays springy with minimal contact pressure.

Philip

I'm with Mr Venton. Split axles/frames; a bit tricky to set up but trouble free thereafter.

Richard

Gold is used successfully in space applications but for a sliding contact it has to be hard as otherwise it will ablate, especially against steel. Personally I wouldn't recommend it.

PBM.

I seem to recall that Mike Sharman reckoned there was some adverse reaction between phosphor bronze current collectors and steel tyres, but I regret to say that I cannot recall exactly what caused the problem.

I have successfully used hard brass wire bearing on the edge of the steel wheel flange, and have heard this recommended by others.

martin goodall wrote:I seem to recall that Mike Sharman reckoned there was some adverse reaction between phosphor bronze current collectors and steel tyres, but I regret to say that I cannot recall exactly what caused the problem.

I have successfully used hard brass wire bearing on the edge of the steel wheel flange, and have heard this recommended by others.

He did, though I have never been able to work out a good science based reason why he thought that it was a significant problem. Different metals in electrical contract can suffer from Galvanic corrosion, but only in the presence of a electrolyte. So ships floating in salty water have a real problem, but its not typically a significant problem in dry air. (Your quote Martin notes the role of lubricants presumable as these may be conductive?). Also when considering Galvanic corrosion the chemical characteristics of Brass and Phosphor Bronze are not significantly different.

Gold contacts (normally on both contact surfaces, note) are certainly popular for good reasons in modern electronics but I'm not at all sure they have much in common with a steel tyre and pickup wire setups. Typically we have overcome a certain unreliability of electrical contact, of which wheel to rail contact is likely to be the most problematic, by the liberal provision of pickups. I suspect this is very much more to the point than the use of exotic metals for our pickups.

The popularity of Phosphor Bronze for pickups is, I think, due to that fact that it is a relativity good conductor, is not given to corrosion in air and it has desirable mechanical properties in terms of springiness and resistance to damage. I've used it since the 70s and never noted any particular problems.

Perhaps Mike Sharman knew something from his RAF days?

I generally use PB (strip preferably) with a small brass pad as the contact point. I've also used brass wire and can't say I have noticed a difference.

I have used 0.35mm phosphor bronze. If possible, where there is space like on a tank engine, I wipe the top of the wheel but if not, then I wipe the back of the tyre. I like the top wipers because they are protected more from damage. I put in one or two 360o bend(s) to make it more springy and also bend the end so that the wire bears on the back of the tyre rather than the edge where the very end of the pick-up can get caught.

In the (distant) past, I made a complete loop at the end where the wire bore on the back of the tyre and filled it with solder. It was something I read that was supposed to help but can't say I found any reason to continue with it.

There was a discussion involving pickups and top wipers back in 2011 and the early part of this thread in 2017.

Hi All,
In answer to Keith's query, I did fit Studiolith plunger pickups to an 0-6-0t back in the 70's, they worked very well but were tricky to fit.
They consisted of a nickel canister and an anodised aluminium stepped collar, the anodising forming the insulation, so they had to be glued to the frames, and the canister glued to the collar I used Araldite, but then you had to solder the wiring to the canister. Once you had this assembled you had to insert a spring and the carbon rod and hold those in place whilst the wheels were fitted, a bit tricky. I did try to develop the principle using tube instead of the canister, but then Studiolith ceased.

steve howe wrote:Are there any recommended wires for current collectors? I have tended to use 0.35 phosphor bronze in the past, but with steel wheels am wondering if steel on steel might be a better option?

Steve

I have used pb without probs for years.. the date on this :- http://www.clag.org.uk/tedpick01.html was a bit of a shock. The design uses the principle that a long enough lead, through a coil if space requires, causes any harmonics through the spring to be of a low enough frequency to allow the contact point to follow any movement of the wheel due to wobble or suspension. Despite the softness of the spring, the very small contact area provides a relatively high contact force over a range of movement.
The tip, bent through 90° approximately 1.5mm from the point rubbing on the tread allows that portion to vibrate at certain speeds, flicking off any accumulating dirt or 'gunge'. Carefully positioned and adjusted, it keeps the treads shiny and they rarely need cleaning, if ever.
The link above shows them hiding behind the cosmetics of a diesel bogie, but in some steam cases where the wheels are all on show, this is an option:- http://www.clag.org.uk/coronation0-4-0.html (scroll to the bottom of the page) Here the top pivots of the brake hangers are fitted into poly tube bushes, and the brake pull rods serve as pickup busses.

'Course I now agree that no pickups at all are best - battery power and radio control is the way to go in this millennium!

Ted.