nichrome wire

[libraryman]

Hi, i have some nichrome wire handy that i want to use for a dew heater design, unfortunately it is too heavy /thick (27 thou) for 12 volts it gets dam hot!!  and would require too much length.

I use an old computer power supply that will give me 3.3 volts output and that is just fine for the length of wire i need.

Question: is it o.k. to use such a low voltage for Nichrome wire and would amperage be an issue?

i don't do electrics so i need a little advise

Ray

[nightvision]

Should be OK, I use it lot for foam cutting, lower voltage = lower current.

[libraryman]

cheers Tony

Ray

[StuartJPP]

As above, 3.3 Volts will work however this isn't to say that it still won't be too hot for the length of wire you are using.

This is a very rough estimate...

27 thou ≈ 0.6858mm ≈ 22swg which is approx 3 Ohms per meter.

At 12V and 1 meter you will be dissipating 48 Watts (12*12 / 3)...which is quite a lot. At 3.3V and 1 meter you will be dissipating 3.63 Watts, much more realistic and shouldn't be any problem for your old PC power supply.

[libraryman]

Hi Stuart, thanks, as a precaution i have ordered some 30 swg nichrome wire, it's going to be used to keep the dew of my coma corrector so i do not need much heat, the other issue i have is room so it has to be quite narrow in section.

as it happens i have 12 volts 5 volts & 3.3 volts from that particular supply so i should be able to work something out

Ray

[skybadger]

Hi Ray, can I ask: where are you ordering from ? I could do with some of that too.

Cheers Mike

[1parsec]

I bought some nichrome wire from this Ebay store.  They sell shorts lengths so not to expensive to test different diameters

http://stores.ebay.co.uk/a-Typical?_trksid=p2047675.l2563

[libraryman]

The bay is where i sourced mine as well.

Ray

pic-projects

[Gina]

Me too.

[IanL]

Sorry, bit late in spotting this one, but all the calculations you need are explained in detail here, including deciding whether to use a single length of wire or multiple lengths in parallel depending on voltage, resistance of wire, etc:

http://www.blackwaterskies.co.uk/2013/05/making-your-own-nichrome-dew-heater.html

There is also a google docs spreadsheet to work out all the calculations for you.  It is (reasonably) foolproof even if you did sleep at the back of class during physics lessons:

https://docs.google.com/spreadsheet/ccc?key=0AlThwu5Ko_kLdEl3WjQybVRUdmIyZUVkN1czc2wwa0E&usp=sharing#gid=0

(Read the article above for instructions on making your own copy of the spreadsheet, as you can't directly edit the copy above).

[libraryman]

Brilliant !!

Ta Ray

[Rhys Hardwick]

That's great, I've been thinking of making so nichrome heaters rather than using resistors, and that spreadsheet will be very helpful.

How flexible is the wire? Can I use it for a variable diameter heater for eyepieces?

[IanL]

How flexible is the wire? Can I use it for a variable diameter heater for eyepieces?

The wire is very flexible and very strong, even the very fine gauges of wire (almost hair-thin) are incredibly strong and won't break no matter how tightly you wind it.  You can literally pull a length over the edge of a sharp knife and you wouldn't be able to cut it using your hands alone (you have to use snips or scissors to cut it).  The two main problems with nichrome are:

- It is incredibly 'whippy' and will always want to spring back in to a coil.  I've set out a few ideas as to how to control it - heating whilst under tension helps to straighten it out a bit, but even so you will have to fiddle around sticking it down to whatever tape you are using to make the heater band.

- You can't solder directly to nichrome.  It doesn't 'wet' and the solder will just run right off it.  In industrial applications they would crimp the nichrome to copper to make connections, but that isn't easy to do at home.  The best approach (described in the article) is to make two interlocking 'nooses' of copper and nichrome wire and then twist it all together.  You can then solder the copper wire to itself trapping the nichrome inside a ball of solder, which makes for a good connection and a mechanically sound joint.

Good luck.

[Rhys Hardwick]

That's great information Ian, cheers. I'll test out my current heaters, and if needed make some out of this

[nightvision]

Have a look at fishing trace crimps, they are`small metal tubes about 2 -10mm  long, just crush them to clamp together wires, I use them for joing wires to nichrome.

http://www.ebay.co.uk/bhp/trace-crimps