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Old 13th August 2008, 19:16   #1
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Arrow Need help with fabricating terminals for a bulb

I'm trying to fabricate this talk light, which has two tube type bulbs, one above and one below a metal plate (pic shows only the top setup). Using GI sheets and sheared brass strips for the terminals.
The power is fed through a wire screwed onto the terminal on the original and the terminal on other side is earthed (through the body), But on this one i need to come up with a way of insulating the left terminal to which the power wire is going to be screwed onto, as both terminals(top and low) get earthed if riveted directly and get connected to each other as they share the same rivet.
I thought of using 2 plastic washers, one above and one below the terminal base, or vinyl ( assuming it wouldn't conduct ) or best use collared washers ( like on Vespa's CB points ) but haven't been able to source them.
Any idea's would be of help!

P.S.- there isn't enough room to use a regular bulb and holder(like in a FIAT's tail light)
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Old 13th August 2008, 23:04   #2
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I am unable to figure out what exactly you are looking for...

You get insulated nuts and bolts with solderable lugs for "TO-3" (acronym for "Transistor Outline - Three") Packaged power transistors. For example the 2N3055. You will get them at any wayside electronic spare part shop. Take a look to see if they will suffice. You also get one mica washer free along with the same. Very cheap.
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Old 14th August 2008, 00:29   #3
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Quote:
Originally Posted by S.H.Shankar View Post
I am unable to figure out what exactly you are looking for...
I guess i my earlier post was unclear. The brass part is going to be riveted to the metal sheet, as both are metals power not only shorts both terminals but also gets earthed directly, i've tried using the washers but the brass part gets displaced and shorts after riveting it too the metal part.
I'll post a picture tomorrow after noon of what im trying to copy, it will probably make it more clear.
I'll check out what you suggested tomorrow too. thanks for that'
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Old 14th August 2008, 10:58   #4
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Don't rivet.

1. First, glue a piece of thin plastic (at least 1mm thick phenolic, ABS, FRP, teflon, ... anything moderately heat resistant; size: larger than the bulb and terminals together) to the base with cyanoacrylate glue (Feviquik or such) or Araldite
2. Drill two holes near the end of the terminals (same as the holes in the pic, but closer to the end. Bend the ends up in way that the terminals look like a J.
3. Cut (split) the contact end of the brass strips in half for almost 80% of the current length. Twist each half away from the center line so that the 2 halves are parallel to each other. Now bend them in such a way that the brass caps of the bulb slip in and are held tight. Clean the strip thoroughly (tamarind helps!) and remove all burrs and spots
4. Mount the bulb in the terminals - the assembly will make the next gluing step easier
5. Now glue the terminals to the plastic part of the base with either cyanoacrylate or Araldite. Allow it to set completely before mounting it anywhere
6. Solder the wires to the terminals or use M3 bolt and nut to fix the wires
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Old 14th August 2008, 19:49   #5
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where exactly are you trying to mount this light. then i can advice you exactly.
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Old 15th August 2008, 00:24   #6
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Attaching a pic of what I'm trying to copy and my tentative setup(the pic above has the exact one though) for one side. Its been pending for years, thought I'd take it up and do something about it.
Also, would getting a dye made for a PVC piece be as expensive as getting one done for a similar rubber piece?

Quote:
Originally Posted by S.H.Shankar View Post
You get insulated nuts and bolts with solderable lugs for "TO-3" Packaged power transistors. For example the 2N3055.
Got a pair of insulated bolts and a silica washer but will the mica washer suffice for 12 V 4 amps current(its pretty thin)
A helpful shop chap suggested i use rubberized (blue color, flexible) silica sheets ( which i cut up into any shape ) and that its works best for insulation. i could possibly stick the material on with feviquick as Mr Deralte suggested onto the brass and use an insulated bolt/rivet along with a mica washer onto the metal plate. would it suffice? but all of it was dead cheap.

Quote:
Originally Posted by DerAlte View Post
Don't rivet.
Sounds good , leaves no chances for it shorting.
The only thing on my mind was the bulbs have too be replaceable(left terminal is rigid and right one is slightly flexible. the bulb is slid in by pushing the right terminal to the side, can a glued terminal take the bit of pressure? and i need to make about 50 of these.
Where could i get an M3 bolt. Need to use a bolt since wire used can can vary in diameter, having a bolt/screw leaves a good option for the user. the original ones are riveted thats how the idea dawned upon me..


Quote:
Originally Posted by DerAlte View Post
3. Cut (split) the contact end of the brass strips in half for almost 80% of the current length. Twist each half away from the center line so that the 2 halves are parallel to each other. Now bend them in such a way that the brass caps of the bulb slip in and are held tight.
Cant visualise this step, can ya explain please. sorry for the trouble.

Quote:
Originally Posted by SirAlec View Post
where exactly are you trying to mount this light. then i can advice you exactly.
It fits onto a metal mudguard, with a bolt. It makes a tail light, top bulb is the brake light and lower one the parking light.

Thanks a lot people'
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Last edited by gendarmee : 15th August 2008 at 00:25.
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Old 20th August 2008, 12:23   #7
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Mica washer is good for much higher voltages and currents. For example the 2N3055 transistor that it is used with is used with up to 60 Volts and 15 Amperes, and there are higher rated transistors serviced with the same washer kits. So no sweat.

I can suggest another excellent material for your base plate, which would be a double sided glass epoxy copper clad sheet, something that would again be available in a good electronics spare part shop. Make sure that you get the "glass epoxy" type, which will be a dull greenish grey in colour as opposed to the cheaper "bakelite" type which will be reddish brown. This sheet comes covered with copper lamination on both sides and is meant for making printed ckt boards. It is available in up to 1'/1' sizes (used to be, now maybe larger sizes are available), you can choose the size you want. You can either etch away copper on both sides (selectively, by masking the areas where you need copper with enamel paint or some such) using Ferric Chloride solution (available at laboratory supplied stores - make sure you do the etching in a plastic container tho as Ferric chloride attacks and dissolves most metals like copper) or you can cut away the copper lamination with a sharp knife and careful work. Then you get a very strong, very durable, heat resistant baseplate, with disignable circuitry on it! Ideal for your application and you can ever solder your lugs to etched copper tracks on both sides. I wonder if an arrangement as shown in the attachment would suffice for you? (Green lugs underneath and the red ones on the upper side) (Pardon the lousy drawing attempted using MS paintbrush!)
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Old 24th August 2008, 10:52   #8
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Another advantage of the glass epoxy material is that once the copper laminate is etched or cut away, the material is an excellent insulator capable of withstanding 100s of Volts per centimeter.
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