Spring contacts for powering ceiling lights in a car shell

[hon30critter]

Hi everyone,

I'm building a couple of cars with detailed and lighted interiors and I want to be able to remove the shells without having to separate any plug connectors that supply power to the ceiling lights. I'm wondering if anyone knows of a source for spring loaded connectors, or if anyone has built spring loaded connectors from scratch. Any suggestions would be greatly appreciated.

Thanks,

Cheers!!

Dave

[tstage]

Are you talking about pogo pins?

[hon30critter]

Hi Tom,

That is exactly the sort of thing that I am thinking of.

I have actually conceived of a design and I am half way through building it. The parts are simple enough. For the male connector I am using some 0.040" styrene for the structure, some styrene tubes with a 1/16" ID, some brass tube with a 1/16" OD, some phosphor bronze 0.032: wire and four small truck springs. My design needs to be quite compact in order for the two halves to be able to fit vertically inside the car. So far, the male half meets that requirement.

The female connector should be simple to build. It will consist of two brass contact pads and the necessary structure to hold them in place, plus the wire connections.

The tricky part will be getting the two halves of the contact lined up properly. One has to be attached firmly to the frame and the other has to be attached firmly to the shell. I'm sure that will be a fun project! Ya, right!!

When all is done I will post some pictures (after I have tested it to make sure it works!).

Cheers everyone!!

Dave

[gmpullman]

Some manufacturers are beginning to use them for the shell to chassis electrical connections. I'm glad of it as stuffing wiring under the shell without crimping or snagging on moving parts can be a pain!

BLI_P4_E6_contact-board by Edmund, on Flickr

This BLI setup actually has ten conductors:

BLI_P4_E6_boiler-contact by Edmund, on Flickr

BLI_P4_E6_boiler-open by Edmund, on Flickr

I wonder if a row of header pins couldn't be adapted? I seem to recall that on some recent Athearn Genesis units used a set of bronze 'fingers' that engage pads on a mating PC board so rather than plungers there are 'feelers' sort of.

Good Luck, Ed

[Overmod]

Part of the 'principle' of many solder-to-board microconnectors is that the frame of the connector is soldered down with pressure applied, and the actual tiny contacts to the circuitry are gold-plated, as are the traces they contact, and any soldering applied to those connections is just to 'protect' them and not for additional electrical continuity.  That is a form of 'spring pressure'...

I'd be tempted to say that a good alternative would be to adapt the pins and sockets of JST connectors, installed in pieces of JST blocks strategically positioned at the corners of the shell.  The engaging tension of 4 of these might in fact be sufficient to hold the shell on the chassis for gentle handling...

[hon30critter]

Hi Ed,

Thanks for the reference. I have come up with my own version of the same thing. This is a bit of a repeat of my previous post. Sorry.

This is the spring loaded part of the connector. It consists of a 0.040" styrene frame which holds two styrene 1/16" ID tubes. Inside the tubes are four truck springs (two on each side). The contacts are made from 1/16" OD brass tubes with a 0.032" piece of phosphor bronze wire soldered inside them. The phosphor bronze wire fits quite nicely through the springs and the springs rest up against the bottom of the 1/16" brass tubes which slide inside the styrene tubes. The contacts have about 1/8" of travel. The soldered on wires prevent the contacts from popping out of the frame.

Here is the initial part of the 'female' part of the connector. It is a small piece of circuit board with a groove between the two contact pads. It will be supported on a styrene frame. I will have to do some carefull measurements in order to get the two parts of the contact system to mate properly, but I have designed a fair bit of tolerance into the system:

Seems to have been a fairly productive night.

Cheers!!

Dave

[Overmod]

hon30critter

It is a small piece of circuit board with a groove between the two contact pads.

Why not a small fin solvent-cemented into that 'groove'.  Just as much separation, but self-guiding in case one of the tubes tries to deflect...

[hon30critter]

Hi Overmod,

The pins are pretty solidly held in the styrene tubes that they slide up and down in. There is very little deflection and they certainly won't be able to make contact with each other.

Having said that, a small fin might help to get the alignment correct when the contacts are being installed.

Cheers!!

Dave

[hon30critter]

I had a little trouble getting the contacts to work. I think it was because the female pads were a bit rough from filing the oxide off. I covered the pads with a layer of solder and resoldered the ends of the male pins and that solved the problem.

Cheers!!

Dave

[Overmod]

hon30critter

I covered the pads with a layer of solder and resoldered the ends of the male pins and that solved the problem.

Just for the record: be sure you flux carefully when using solder as a 'surface-conductive layer', use no-clean flux and carefully clean any residue off anyway to avoid corrosion, and use a type of solder alloy that will not oxidize or corrode over time, but is relatively soft on at least one side for 'conformal' contact.

I'd be at least tempted to try putting tiny pieces of genuine gold leaf over the solder when you 'tin' the contact areas.  Even a thin and intermetallic surface layer would probably have improved defined contact over time, and the cost of the leaf itself would amount to pennies in this application.

[hon30critter]

Hi Overmod,

Thanks for the suggestions.

I'm going to leave them alone for now. The shell comes off very easily so if I run into future connectivity problems, getting at the contacts will not be a problem. I've got too many other projects to complete on this train. It's starting to drag on a bit.

Cheers!!

Dave