How Do I get the wire to heat up?

[onotoman]

Hi Guys,

I'm out of my depth with a 'project' and I wonder if someone can help?

I have an old miners lamp and it is meant to be sealed once assembled (to prevent the flame igniting any gas in the mine)

The way the wick is lit is by an electric current being passed across a 'Platinum Wire' and heating it sufficiently to light the fuel. The wire is very close to the wick - needless to say, the platinum wire is missing.

One of the terminals is connected to the body of the lamp and the other is connected to a ring around the base of the glass in the lamp. I've ensured that all insulating washers are present.

I have obtained the following information:

An owner of another of these lamps told me that fuse wire can be used in place of the platimun wire.

The Electrical Lamp Lighters used at the Pits where the lamps were used put out 4 Volts

So, I Put some 5 Amp fuse wire across the terminals and set my Bench Power Supply to 4V and put some fuel in the lamp. BUT I just cannot get the wire to heat sufficiently.

Would the platinum wire have been much thinner?
Would 1 Amp Fuse wire do the job?

I even tried connecting the Croc Clips of the Power Supply directly to each end of the 5 amp fuse wire but still no joy.

Any advice greatly appreciated - I'm good with mechanics but my Electrical knowledge is very limited (as you can tell)

Best Wishes

 

[rob_croxford]

perhaps your PSU does not supply enough current. Try lowering the rating of the fuse wire. Either that or meaure the amount of current supplied and choose a fuse wire that is just above this value.

 

[onotoman]

Hi Rob,

Thanks a lot - of course! 5 Amp Fuse Wire won't heat if there's just over 2 amps passing though it. Do you know where I may be able to buy 2 amp fuse wire. The 'consumer' packs just seem to have 5 amp, 15 amp and 30 amp.

perhaps your PSU does not supply enough current. Try lowering the rating of the fuse wire. Either that or meaure the amount of current supplied and choose a fuse wire that is just above this value.

 

[rob_croxford]

I imagine RS or Farnell will have some however i wouldnt expect places like maplins or somewhere to have it. A simple google search should throw up some results.

Either that or boost the current.

best regards

 

[davenn]

Another thing to keep in mind too ...
Platinum wire is used for a very good reason. it has an extremely hi melting point
your fuse wire, once you find the right value is probably going to do just that "fuse" ... burnout and go pop, never to be used again

A platinum wire is going to be able to achieve the hi temp needed without melting and going pop

cheers
Dave

 

[rob_croxford]

I completely agree with Dave's point. If you intend to use this lamp on a regular basis fuse wire is deffinatly the wrong choice of fillament (so to speak).

http://www.pgmetalshop.com/platinum-pt/platinum-pt-wire-microwire-fine.html

This site offers Platinum wire in a range of different thicknesses. Perhaps this would be a better choice for prolonged usage.

 

[daddles]

Platinum wire is used for a very good reason. it has an extremely hi melting point

While platinum has a melting point a bit more than iron, it's not really considered a refractory material like molybdenum, tantalum, or tungsten. I suspect the real reason is the platinum is more resistant to oxidation at the required temperatures and, thus, lasts longer. But something like tungsten, which has a melting point about 1700 K beyond platinum's, would probably oxidize too readily (if you got it too hot). However, since you probably only need to go to a red or orange heat (say, in the 800-1000 deg C range), it might work for this application. Platinum has become pretty expensive too. You might be able to use an incandescent light's filament for some tungsten, but you'll have some mechanical problems securing it and it won't be as robust as a straight piece of wire.

Another wire to consider trying is Nichrome. One place to find some would be to find an old toaster and salvage some wire from the heating element. In a pinch, you can also try some Chromel wire from a type K thermocouple, as it has a composition somewhat similar to Nichrome. The real reason I'm proposing these two is that it's likely they're easier to get your hands on and cheaper than platinum.

 

[duke37]

Platinum is used because it is resistant to oxidation and acts as a catayst. It promotes reaction between gas and air and is of course used in car catalytic convertors.
Thin fuse wire is used in glass fuses but you will need to extract it which may be difficult.
Some battery gas lighters use platinum wire. It does not even get red hot.

 

[daddles]

Good point, duke37 -- that's likely the reason for the platinum. When a stream of pure hydrogen contacts a platinum mesh, it will ignite (a friend and I built a Döbereiner lighter once).

 

[(*steve*)]

I would also consider nichrome wire. (The correct platinum wire replacement would be best, but melting platinum might get expensive after a while!

You need to test using the normal power supply (some form of battery I presume) as its internal resistance no doubt plays some (not inconsiderable) part.

 

[poor mystic]

I see platinum wire, 28 gauge, 2 inches length, through amazon for $28. A whole lot less hassle!