Getting power to the turntable deck

[ejstubbs]

I am considering using sprung phosphor bronze strips on the underside of my turntable deck as pickups to power the track on the deck.  The plan would be to have contact "pads" powered from the tracks that the turntable connects to.  I'm wondering what would be the best material to use for those contact pads: phosphor bronze again, or nickel silver, or copper?  Would any combinations be a definite no-no?

Edited April 5, 2018 by ejstubbs

[cliff park]

OK, I'll put my two pennorth in to start it off. Assuming these pads will be soldered to springy fingers to rub on phosphor bronze strips, the criteria I see would be wearing of strip and corrosion. If the pads are too hard they will erode the strips, too soft and they will wear away. This could happen surprisingly quickly. A classic solution is to have each finger split at the end into even smaller fingers, so spreading the load and wear. This could work quite well with phosphor bronze, easy to cut and shape, and definitely springy, and should be self cleaning if used reasonably regularly. Also easy to solder to.

[ejstubbs]

Maybe I didn't explain it very well.  The idea is that the phosphor bronze strips will be wired to the rails on the turntable deck.  They will pick up power from contact pads in the turntable well.  The contact pads will be wired to the rails of the tracks that run to the turntable, and will be positioned so that the phosphor bronze wiper strips will only make contact when the turntable is positioned at or close to the relevant outlet track.

 

The idea is that the turntable deck track will be unpowered when the deck is not aligned with an outlet.  When it is live the polarity of the track on the deck will match the outlet track.

 

The design is still fairly nebulous at the moment but I wanted to see if there was any combination of wiper strip & contact pad materials that would be better or worse than others.  Corrosion is certainly a risk better avoided.  As far as wear goes, I'm anticipating that it should be fairly straightforward to replace the contact pads in the turntable well if they get worn, less so the wiper strips.

[DCB]

That's basically how Triang did it in 1950 something,   PB on brass should work quite well as long as your table only revolves one way I haven't actually built a good system yet but my best one has sprung horizontal pickups bearing on a vertical downwards extension of the left hand rail at each end though this only changes polarity and mid point rather than isolating the deck.

 

The usual problem is the drag of the contacts either makes the deck wobble and shudder or simply stop, or the contacts don't really make good enough contact.  My latest attempt has all the electrics on a lower level and the deck just has two wires disappearing down the hollow pivot and no locking or contacts visible.   Hope to make some serious progress tomorrow evening.

[ejstubbs]

My latest attempt has all the electrics on a lower level and the deck just has two wires disappearing down the hollow pivot and no locking or contacts visible.   Hope to make some serious progress tomorrow evening.

 

That's the approach I was originally thinking of, before I started to muse about PB contact strips.  As you say, it's much cleaner, with no electrical gubbins cluttering up the turntable well.  In theory it should be simple enough: a DPDT centre off switch to control which of the outlet tracks provides power to the deck, and to provide isolation of the deck, and a DPDT on-on switch to set the polarity of the deck to match the outlet track.  That does mean, though, that there are three combinations of switch positions which would result in things not working properly - too easy for the operator to make a mistake, at least for my addled brain.

 

It's just occurred to me that it ought to be possible to use magnets and reed switches to detect where the table is.  And by using two magnets, one on each 'leg' of the deck, and putting them in different positions on each 'leg' then I think it should be possible to activate four separate reed switches and thus select the correct power source & polarity for all the likely options.  The reed switches would then fire DPDT relays to connect the right outlet track's power to the deck at the correct polarity.  Hmm, some more pondering required... (Any more than two outlet roads would start to get rather complicated, though, I can't help thinking.)

Edited April 5, 2018 by ejstubbs

[RAF96]

My diy TT is unpowered for rotation but DCC power to the bed (and indicator leds) is by way of a 1/4” stereo jack and socket with a DPDT switch to flip the bed ‘polarity’ as required.

 

The leds are red/green bipolar and tell me which way the polarity is ‘pointing’.

 

You can find the associated wiring diagram in my gallery on this site.

 

The table gets little use so being man-draulic without indexing is not a problem for me.

 

Rob

[ejstubbs]

Very interesting, but I don't use DCC (which is why I posted this in the Electrics (non-DCC) forum).

[RAF96]

It doesn’t have to be DCC, the methodology is perfectly capable of working on DC, but for the interest of anyone who wondered if it was bi-use I qualified mine as DCC.

Rob

Edited April 5, 2018 by RAFHAAA96

[Theakerr]

A while back Ken Patterson on Whats Neat demonstrated using an old large guitar style plug in jack and base that his turntable rotated on.  Minimum of two channels and easy to put a polarity changeover switch on.  I understand you appear to be committed but I thought I would post this for info.

[ejstubbs]

OK, the 6mm jack plug approach is clever, but it doesn't get around the problem that I am trying to solve which is not just polarity switching but also making sure that the power is coming from the correct outlet track from the turntable.  I'm trying to eliminate as much need for switch setting - and hence room for operator (ie my) error - as possible from the task of running a loco on to the turntable, turning it and then running it off the turntable on to a different track in a different power section.  With DCC only polarity would be an issue, but using DC power sections in the way I want to adds a bit more operational complexity - which I now believe I can eliminate by using straightforward electrical componentry.

 

Providing the power connection to the rails isn't the biggest issue - the table doesn't need to be able to turn more than about 210°, so ordinary power feed wires with a bit of slack in them should be fine.  I'm going to use a 50mm lazy susan bearing for the deck, which has a hole through the middle plenty big enough to allow the wires to pass through.

 

Arguably the title of the thread is perhaps inadequate - but there is a limit to how much information you can sensibly fit in there and it still be comprehensible.  It's also getting late, and I've had a difficult day at work, so I'm afraid I'm in no real position to set about crafting a better title just now!

[AndyID]

Trying to make this work with sliding contacts is possible but it's going to take a lot of mucking around to get it to work reliably. I think you have the right idea of using reeds and magnets to detect the position and then using relays to switch the track circuits. That might seem a bit complicated but there are plenty of people here who can help you with the circuit diagram.

 

An alternative to reed switches, if there is space, might be to use microswitches acting on a cam under the baseboard.

 

Andy

[RAF96]

The problem with the jack plug pivot method is motorising the bed has to be done by way of belt or table rim gear drive as spindle drive is not easily achieved.

One advantage is the bed just lifts out for any necessary work to be done.

 

Edit...

If you are saying each outlet road possibly leads to a different power section then I can see the need to power the bed (when swung) from the indexed outlet road as opposed to having all the outlet roads connected to the inroad and only having the bed polarity to fret over. In your case a limited swing arc and multi-power sections is of no advantage apart from being able to use direct wiring rather than split scraper rings, etc.

Rob

Edited April 6, 2018 by RAFHAAA96

[Junctionmad]

some nice slip rings on aliexress for a few quid , perhaps the day of  hacking  things out of PB is over !!

 

https://www.aliexpress.com/item/1PC-Hole-Slip-Ring-2-4-6-8-12-Channel-1-5-2-10A-Hollow-Slipring/32848760332.html?spm=2114.search0104.3.101.38cc5198bOw4cT&ws_ab_test=searchweb0_0,searchweb201602_3_10152_10065_10151_10344_10068_10342_10343_10340_5722611_10341_10698_10697_10696_5722911_5722811_10084_5722711_10083_10618_10304_10307_10302_5711211_10059_10534_308_100031_10103_441_10624_10623_10622_10621_10620_5723011_5711311_5722511,searchweb201603_25,ppcSwitch_5&algo_expid=fd161325-f0ee-4af6-835e-43f35c7c8ab8-15&algo_pvid=fd161325-f0ee-4af6-835e-43f35c7c8ab8&transAbTest=ae803_1&priceBeautifyAB=0

[NinOz]

How about some pogo pins instead of the PB strips.

Example:

https://www.aliexpress.com/item/10pcs-Spring-loaded-pogo-pin-connector-3-Pin-Pitch-2-54mm-Surface-Mount-PCB-SMT-brass/32722259285.html

 

CFJ

[doilum]

Out of the box thinking.

A circle of PCB around rhe pivot.

This is divided into a series of segments.

Some segments remain unpowered.

Other segments are fed by the out put rail as described above.

Current is collected by plunger pickups, or better still, by spring loaded carbon brushes.

This would be my definite route if given the challenge of modelling Top Shed in gauge 3. There are however mechanical wizards reading this who would have a go in Z!!