Edelux / SP PV8 - Co-ax into a lego-brick UNTIDY.

[Somnolent]

This is probably one for Kim...

Friend of mine has decided to go dyno on his recently aquired audax bike and we've built him a new front wheel around a SP PV8 dynamo which has a lego-brick style connector:

For his light he's chosen a SON Edelux - which, it turns out has a fine co-ax cable, which makes for a very untidy entry into the lego brick.
Spade terminals to fit a SON dynamo could have been heat-shrinked (and appropriate bits come with the Edelux) or if it was a B&M light it would have come with twin core cable that can fit nicely into the lego-brick.

My thought is to cut the co-ax short and hide some sort of connector to twin-core behind the fork leg - but what kind of connector?  Tamiya would be a bit bulky.  M/F spades and shrink wrap?
Or is there some other solution that I'm missing? 
 
 

[Brucey]

I would suggest that you splice a short length of figure 8 cable onto the end of the co-ax. Solder the joints, and use heat-shrink to insulate/weatherproof them. Tether the jointed part of the cable to the fork leg directly, e.g. using tape or zip ties.

I would recommend that you do this about 4" above the hub, where the cable is to be tethered to the fork leg anyway. Leave enough slack in the cables  (eg doubled up in the base of the steerer, or under the fork crown) so that the connection into the lego brick can be remade if needs be.

To deter corrosion, a smear of Vaseline or waxoyl (which can be run in with a hairdryer) in the lego brick will help enormously.

cheers

[grams]

Cut back an inch or two of the outer sheath, then twist together the outer braid and slide it into  a short section of skinny heat shrink. Bingo, you now have two separate wires ready for your lego brick.

(you may like to add a short section of larger heat shrink to cover the join)

[Kim]

Cut back an inch or two of the outer sheath, then twist together the outer braid and slide it into  a short section of skinny heat shrink. Bingo, you now have two separate wires ready for your lego brick.

(you may like to add a short section of larger heat shrink to cover the join)

Would be my suggestion (you can re-use the outer sheath instead of heatshrink, but you do need some heatshrink over the split).  It's how I've terminated Schmidt coax into the lego brick on The Red Baron.  Neat enough, and not adding an extra point of failure.

[Brucey]

that is fine but there are two things about it that I am not so keen on

1) such wires are exceptionally difficult to rework with limited tools etc should the need arise (which doubtless will be in the dark, by the side of the road... )

2) typically the centre core of skinny co-ax is itself, er, skinny, and may not make such a good/reliable connection in the lego brick.

BTW when splicing wires as I suggested, it is usually best to stagger the two joints lengthwise by about 20mm or so; this means that there is less danger of a short (because each solder joint lies alongside an insulated section of the other conductor), and it is often possible to use a single piece of heat shrink to insulate the splice. If done well, you would hardly know that the joint was there.

FWIW I have a length of chunkier figure 8 cable spliced in this way to some skinnier stuff (that emerges from the headlight shell) on my most-used bike; the chunkier stuff just happens to work well in the connector block, and the original skinnier cable was never quite long enough anyway.

cheers

[Kim]

that is fine but there are two things about it that I am not so keen on

1) such wires are exceptionally difficult to rework with limited tools etc should the need arise (which doubtless will be in the dark, by the side of the road... )

This is true, and a reasonable argument for having a short length of bellwire and some insulating tape in your toolkit.  Bonus points for it being pre-terminated in a spare lego brick (or, more importantly given the lower roadside fettleability, spade connectors).

2) typically the centre core of skinny co-ax is itself, er, skinny, and may not make such a good/reliable connection in the lego brick.

Nahh, the Schmidt stuff's about right.  At least as much copper in the central conductor as the usual B&M style bell-wire, possibly a bit more in the outer.  It's not 'skinny coax' in the headphone cable sense, and it's mechanically ideal for use on a bike.  Just a bit of work to terminate.

BTW when splicing wires as I suggested, it is usually best to stagger the two joints lengthwise by about 20mm or so; this means that there is less danger of a short (because each solder joint lies alongside an insulated section of the other conductor), and it is often possible to use a single piece of heat shrink to insulate the splice. If done well, you would hardly know that the joint was there.

Agreed.  Bonus points for using adhesive-lined heatshrink in this sort of application.

[Brucey]

it seems to me that it may be best to have the piece of wire that goes into the lego brick insulated with a soft plastic (PVC ?)  rather than a hard one; this means that the insulation will be easy to strip should the need arise when tools are limited.

Also, provided there is enough slack/length in the wire, you can temporarily remake the dynamo connections without disassembling the lego brick itself (which is usually a bit fiddly); just jam the complete plug (having removed any loose bits of wire from it) over the connector whilst the bared wires are draped over it.

In an ideal world it would not be necessary to contemplate such eventualities, but stuff happens...

FWIW I find it baffling that so many hub dynamos are arranged so that the connections require either a variable force or a high force to connect/disconnect the wires.  It seems obvious to me that folk will occasionally drop the front wheel out without remembering to disconnect the wires first, and that the wires/connections will simply be pulled off.  3/16" (5mm) blades require a high enough force that wires are at very real risk of damage if they are simply yanked off.  If such connectors are re-set to a lower force, they lose their ability to self-clean, which is necessary because they are almost invariably made of dissimilar materials, which in combination with nasty crevices, is bound to encourage corrosion.

Years ago I built a very simple arrangement for hub dynamo connection where there were two small (open ended) sockets attached to the hub, into which some simple terminals (in matched material, soldered to the wires) were inserted. The fit of the terminals in the sockets was such that crevices were largely avoided.

 The terminals themselves were slightly springy, such that if they should ever work themselves slack they could be easily re-set (eg using a fingernail) so that they were snug again. The insertion force was low, such that pulling on the wires would result in a disconnection with very low risk of damage. The contacts were self-cleaning as the terminals were inserted/removed.  Although it never actually happened, if the terminals should ever drop off the wires, the sockets were sized such that it would be easy to stuff  a bared wire end into the socket and make a temporary connection that way. 

I created this arrangement in a short time in my shed and it worked fine for over 50000 miles (and several decades) on a bike that basically lived outdoors.  Why you can't buy anything with similar properties is quite beyond me...

cheers

[Kim]

To be fair, the lego brick disconnects from the hub easily^[1] if you forget to unplug it (but not so easily it doesn't stay put in normal use), and if you've terminated the cable properly (stripped conductor of the right length), mostly without damaging the connection.  And it's made of two bits of plastic that can be re-used indefinitely.

The main flaw in the design is that it's a bit fiddly, and it treats the cable as sacrificial.  I'd say it was a decent effort, and certainly works better in practice than spade connectors (which work admirably well as long as you never remove the wheel).  A bit more strain-relief would be nice.


_{[1] Rotational alignment of the hub in the drop-outs matters, of course.}

[Brucey]

I quite like the (pragmatic, simple) lego connector bricks too but the force varies quite a lot with the wires used. However because the materials are dissimilar, and there is a bad crevice, corrosion is likely unless steps are taken.

Also I am not sure why the connector is offset in most cases (moreso in the later shimano designs that don't have an earth return connection than in older ones which do). It seems to me that the effect of the offset is to make sure the connector is tugged at an angle if the wheel is dropped out with the connector in place; this ensures that one wire will see a very hard tug AFAICT. If the connector were inline, it might make for a slightly less neat installation in some cases but the wires would see a better shared force when yanked off.

BTW I usually run with the QR lever on the RH side of a hub generator, so that I am less likely to forget to disconnect the wires when removing the wheel.

cheers

[tatanab]

Why you can't buy anything with similar properties is quite beyond me.

https://www.sjscycles.co.uk/dynamos/sinewave-cycles-gold-plated-quick-release-connectors/  or  https://www.sjscycles.co.uk/lighting-spares/supernova-qr-gold-connector-set-with-integrated-shrink-wrap/

[andrew_s]

I forget to disconnect my Edelux & SON hub fairly often, and have had no problem with the spade connectors failing to come off, because I've generally poked them with a small screwdriver to slacken them off if they seemed unduly tight.
I've seen no sign of corrosion, though I do keep my bikes indoors.

That's since 1998, with B+M Lumotecs with DIY spades, Schmidt E6 with preinstalled spades, and Edelux with preinstalled spades.

[Polar Bear]

I've lost count of the number of times that I failed to remove the female spade connectors from the Schmidt.  Never once has it proved problematic. 

[Kim]

Other than in a crash (which is a failure mode worth considering - with a bit of bodgery the bike was ridable, even if my body wasn't), I've not actually managed to damage the connection to a dynamo spade connector, but I do usually remember to disconnect them, and apparently have enough mechanical sympathy not to yank the wheel when I forget.  What I do tend to do is bash my knuckle on the spokes while applying sufficient wiggling force to unplug them from the dynamo.  This isn't a problem with the lego brick, which doesn't require any wiggling.

I've not had corrosion problems with either, but like andrew_s, my bikes live indoors.

I'm perfectly happy to use both types of dynamo and both types of cable (with a preference for the durability and aesthetics of the coax), but I'm no stranger to soldering, crimping and heatshrink.


Gold plated banana plugs certainly make for a nice inline connection, but I'm not sure what problem they're supposed to solve compared to the usual 2.8mm spades.

[Brucey]

Why you can't buy anything with similar properties is quite beyond me.

https://www.sjscycles.co.uk/dynamos/sinewave-cycles-gold-plated-quick-release-connectors/  or  https://www.sjscycles.co.uk/lighting-spares/supernova-qr-gold-connector-set-with-integrated-shrink-wrap/

quite nice, rather pricey, but

- not easily tweakable should there be wear or other loss of contact load
- uncertain self-cleaning effect
- materials below the gold plating are not specified, and the connector interface is full of crevices, so corrosion performance uncertain in our glorious climate
- not easily repairable by the roadside (small is neat but if the socket were slightly bigger then you could make a temporary repair connection more easily)
- no strain relief other than that afforded by the heat shrink

What I find strange is that no-one has made a hub generator that has simple (open-ended) connection sockets in it; these are much easier to deal with than most of the arrangements that have been made. For example  you could have sockets in the generator that would accept little plugs (similar or better yet with fewer crevices) directly.

cheers

[tatanab]

- not easily tweakable should there be wear or other loss of contact load
- uncertain self-cleaning effect
- materials below the gold plating are not specified, and the connector interface is full of crevices, so corrosion performance uncertain in our glorious climate
- not easily repairable by the roadside (small is neat but if the socket were slightly bigger then you could make a temporary repair connection more easily)
- no strain relief other than that afforded by the heat shrink

True, but none of it is a killer.  I've had some in use on my dirty old hack for 4 years with no issues.  Size - the size of the socket cavity is about 16AWG so easily takes a bit of wire bent over for a quick repair.  For better self cleaning and material specification you could use contacts from mil spec connectors, even gold plated D sub  20 gauge contacts which I was using for this and similar purposes about 30 years ago.  It has been 10 years since I last had a ready supply, but anybody in the electronics type industry knows that these are easily available.

[Bolt]

I cut all all of my front dyno lamp leads short and terminate with 2mm gold plated banana plugs to mate with a corresponding figure 8 "fly lead" with banana sockets to run from the headtube or fork crown down to the dynamo.  This makes it very easy to swap lamps between bikes and makes for a tidy and reliable arrangement.