Powerbase problem

[SealionSteve]

Hi

 

I have a Hornby "Percy" loco (I know - but it works reliably and I wouldn't lose much sleep if it died so I use it as a test loco).

 

I fixed a DCC Concepts Powerbase magnet under it (between the wheels with no drive cog) using their recommended screws (just a thought - why not brass screws, since the steel ones they sell you are VERY keen on the magnets!) and the plastic magnet holder supplied as part of the package.

 

Percy then refused to budge when placed on my Powerbase test track. I wondered whether the (steel) screws were shorting, so I removed the magnet and replaced the screws. Percy performed fine.

 

So maybe the magnet was messing with the motor? I "black-tacked" the magnet to the chassis and touched power leads to the wheels. It worked fine.

 

Hmmm. I then glued the magnet in its plastic holder to Percy's base. He worked fine on the Powerbase test track.

 

I realise that it's only a matter of time before the magnet defeats the glue, but what's going on here? At the moment I want to say "It's logic, Jim, but not as we know it". 🤣

 

 

[34theletterbetweenB&D]

Two possibilities:

Screw(s) mechanically locking the mechanism,

Screw(s) interfering with the electrical circuit, could be a short, or causing an open circuit.

 

I'd have it apart to see where the screws went...

[kevinlms]

32 minutes ago, 34theletterbetweenB&D said:

Two possibilities:

Screw(s) mechanically locking the mechanism,

Screw(s) interfering with the electrical circuit, could be a short, or causing an open circuit.

 

I'd have it apart to see where the screws went...

Most people think electrical things stop working because of shorts, but open circuits are far more common. 

[SealionSteve]

Thank you for the suggestions. I could find nothing obvious when looking "under the hood".

 

As I had found that:

 

Scenario 1 screws + magnet in the plastic holder = problem

Scenario 2 screws by themselves (no plastic holder) = no problem

Scenario 3 magnet in plastic holder without screws = no problem

 

I realised that scenario 2 was not entirely eliminating the screws and needed to be modified in case it was the extra thickness of the plastic magnet holder which was causing the screws to be at a different depth into the loco's baseplate (possibly missing something which they were touching before, thereby causing a short or open circuit). So I tried screws and empty plastic holder, kind of hoping it would bring back the problem as then all would make sense. However there was no problem when I tried that 4th scenario. Looks like the villain is the presence of screws plus magnet in this particular loco.

 

I am a bit hazy on the relationship between electricity and magnetism but I know that they are related...can anyone with more know-how than me (probably the majority out there!) confirm or deny that it is possible that there is a current flowing between the screws via the field of the magnet when both are present and that might be causing the problem? Thanks.

Edited July 23, 2023 by SealionSteve
Typo

[gismorail]

I’m currently fitting a Powerbase on an incline on my O gauge layout mainly to give steam locos a helping hand diesels have no issue with the 2 to 2.5 % and rock up it no problem. I have found that a lot of the ideas suggested by DDC concepts are a touch over the top and have not had any need to use the screws . I use plastic card to fit the magnets with a tiny spot of PowerBond   Glue which is so strong and easy to apply. Still to be convinced that the idea is really any good though ….. perhaps useful for removing stray metal bits from the layout  as I have to keep on top of the cleaning the magnets after an operating session 

Edited May 16 by gismorail

[tynewydd]

Quote

Still to be convinced that the idea is really any good though ….. perhaps useful for removing stray metal bits from the layout  as I have to keep on top of the cleaning the magnets after an operating session

As its magnetism, it's power drops as the square of the distance between the magnet and the "plate" - so given a OO code 75 minimum distance from magnet to plate of about 4mm (2mm for the rails with 2mm for sleepers) and a O gauge would be ~8mm the same magnet used for O gauge would be 1/4 the power. Now you can obviously have a 2x larger diameter magnet but you would very roughly need 2x the number of those larger magnets to achieve an equivalent down force and that isn't taking into account the probably increased need for more starting friction for the larger train/loco. Luckily you will have the area for more magnets and may even have 2x the thickness under the loco for magnets or stacking them - magnets increase in power until the thickness approaches the diameter. So it doesn't totally surprise me that it may be harder to get as good a result at larger scales and would need some experimentation.

You can't go closer than the rail head with the base of the magnet because of points and crossings.  But it has occurred to me that for areas of the layout you don't normally see you could think about bringing the "plate" (or another magnetizable thing like a piano wire or even a smaller gauge steel rail (check rails anyone?)) into the four foot and probably increase the  effectiveness very significantly as the distance would be much smaller.

This premium on getting as close as possible to the railhead height also explains why gluing with shims to place the magnet surface at the bottom may be superior to a holder or cage where it is elevated even by a small amount. 

 

----- 

That does not answer the question posed about the screws/holder issue.
Idea #1 - I would expect that the plastic in the holder would be both electrically and magnetically inert. But the magnet is a conductor probably so screws making a short circuit into the loco via the magnet - that's possible.  And the screws on their own might be airgapped, and with the holder no magnet plastic-gapped.  Try a wire between the two screws and see if that makes a short...  
Idea #2 - wild guess territory - could the screws plus magnet be inducing a magnetic field as poles of the powerful magnet that then interferes with the fixed magnet in the motor on such a small loco and so prevent it turning easily?  The steel screws might possibly do this as they interact with magnets, where brass screws would not.  
 

[DCB]

On 16/05/2024 at 16:04, gismorail said:

I.. perhaps useful for removing stray metal bits from the layout  as I have to keep on top of the cleaning the magnets after an operating session 

I have a heavy cast Hornby Dublo brake van chassis as an engineering wagon with magnets under it for ferrous debris collection.  Very useful for finding discarded screws from some elderly Mainline and Bachmann locos.   Triang and Hornby Dublo used the more expensive brass screws unfortunately.  When the debris causes a short I tow it with a Triang Clockwork 2-2-0 or a battery powered Lima class 37.

[DCB]

The O.P may have damaged the motor with his screw and pushed a magnet into the armature and jammed it.  
The magnet needs tp be as close to the powerbase or metal strip as possible,  Triang had a very small gap in their case between magnet and wheel back with their Magnadhesion, which doubled traction on many locos.

I can't think how one could make Powerbase work in 7mm, though you could  increase the magnet size in proportion and use code 75 rail I suppose.
Seems to me putting the metal between rather than under the sleepers of even slices of those plastic magnets sprinkled with ballast between the sleepers would work better.   Steel code 75 rail and steel wheel tyres Triang magnadhesion style would have been my suggestion for magnetic traction improvement.