Nichrome wire help

Slowbutsure

Feb 18, 2018
21
Hi

So I put some 0.4mm (about 50cm) Nichrome wire across the two terminals of a car battery, thinking it would glow red, get hot etc. However, it mildly warmed and thats all. Am I missing something?

I want to make a kind of heater with Nichrome inside silicone, but I don't understand why its not getting hot. Obviously I know zip about electronics, ohms law and anything like that. And to be honest, I just want to get this working without a big learning curve. Any help appreciated.

kellys_eye

Jun 25, 2010
6,045
Is the battery fully charged?

Far from 'glowing' it should have turned bright white and burned out..... it's about 0.2Ω per foot so 50cm is under 2 feet therefore maximum 0.4Ω at 12V should flow 30A and dissipate 360W!!!

Oct 5, 2014
6,595
Last edited:

Sunnysky

Jul 15, 2016
540
0.4mm 26 AWG 8.992 Ohm/M
50cm = 4.5 Ohms
I=V/R=12.5/4.5=2.78A
P=VI=12.5*2.78A=35W

kellys_eye

Jun 25, 2010
6,045
Hmmm, the list I Googled shows 0.4mm to be 16 gauge..... and 0.4Ω/foot.

D'ho.... my bad (maths) that thought 0.4mm was 0.05in........ sorry.

Externet

Aug 24, 2009
886
Measure the voltage of the battery while the nichrome wire is energized...

Slowbutsure

Feb 18, 2018
21
Thanks for the replies. Im back to the drawing board.

Can anyone tell me what diameter Nichrome wire I need to reasonably heat 4ft of wire using a 12v car battery? Reasonable being anything between 100-250c. I don't need to be precise, and maths is wasted on me

I don't know what size car battery, just a normal size car battery on a 2l car. Hoping for replies along the lines of 0.3mm etc. Rather than formulas. I looked at tables on Wikipedia for Nichrome wire and its all Greek to me.

Thanks!

Bluejets

Oct 5, 2014
6,595
When it comes to cutting foam, you are attacking the problem from the wrong end.
I mentioned my approach above hoping you would see how to go about it.

Above gives all requirements plus, with the dimmer on the transformer primary, an added advantage of good control over required heat for a wide range of cuts, at a low cost. In comparison, low voltage dc control is more expensive and complicated.

You cannot reduce the size of the wire as when heated, and dragged through the foam, the wire will drag in a logarithmic manner and will never give a straight cut. That plus it will never keep up the heat required during the cut.

You started with 500mm of 0.4mm and now you have increased that to more than double so the voltage previously required has also increased.

Slowbutsure

Feb 18, 2018
21
When it comes to cutting foam, you are attacking the problem from the wrong end.
I mentioned my approach above hoping you would see how to go about it.

Above gives all requirements plus, with the dimmer on the transformer primary, an added advantage of good control over required heat for a wide range of cuts, at a low cost. In comparison, low voltage dc control is more expensive and complicated.

You cannot reduce the size of the wire as when heated, and dragged through the foam, the wire will drag in a logarithmic manner and will never give a straight cut. That plus it will never keep up the heat required during the cut.

You started with 500mm of 0.4mm and now you have increased that to more than double so the voltage previously required has also increased.

Thanks, I am not cutting foam. I am making a mini electric blanket to fit around the fuel filter on my car. It's 4ft because its runs up and down a silicone sheet. So I need a step up transformer from 12v to 48v? You think that will work in this application?

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,509
Off topic, but why do you need a mini electric blanket for the fuel filter?

I've seen a few people ask about these and I'm not sure why.

Bluejets

Oct 5, 2014
6,595
Thanks, I am not cutting foam. I am making a mini electric blanket to fit around the fuel filter on my car. It's 4ft because its runs up and down a silicone sheet. So I need a step up transformer from 12v to 48v? You think that will work in this application?

Ah yes...my mistake. I was concentrating on nichrome and became a bit diverted onto what I used it for.

Still, the same calculations will be necessary.
Take the amount of wattage you require first up.
Then decide on length and size of wire that will give that required wattage at your 12v supply.
If the wattage of one circuit is not enough you could parallel two or more.

One thing is the nichrome wire would have to be wound on some heat resistant insulation and in selecting the type it would once again be necessary to know the wattage being applied to approx. the area.

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,509
Having googled for these fuel filter heaters, it appears that they are used in cold weather for diesel vehicles, especially those using biodiesel.

I note that one was mentioned to draw 8.5A at 12V, which suggests a total resistance of 1.4 ohms.

If your 500mm length of nichrome has a resistance of 4.5 ohms, you could either have three lengths of this placed in parallel (resulting in a total resistance of 1.5 ohms) or use a single stand about 170mm in length.

I would recommend the former because the same heat would be generated but over a larger length of wire. This would reduce the risk of uneven heating from a single sorry piece of wire that work probably get extremely hot.

Bluejets

Oct 5, 2014
6,595
Don't know what filter is being used but with a standard diesel filter of 100mm diameter, 500mm of this wire would not even go twice around the circumference so I don't think one would get much heat transfer from that setup.
Even 3 lengths would be pushing it I think.
Then one needs to get good heat transfer with good insulation to boot.
Perhaps all needs a good rethink.

Slowbutsure

Feb 18, 2018
21
Thanks for the thoughts all. Yes, it is for a biodiesel situation. The length I have used is 4ft sandwhiched and glued between two thin sheets of silicone. I never thought of using parallel lengths. It is actually quite tricky to run the nichrome wire up and down and glue it! I poked nails through and then removed the nails when glued. i've got 12v 10 amps going through it but its not enough it seems. So recapping, step up the volts to 48v as a possible answer, or remake it using 4 or 5 shorter lengths. Does it need to be coiled inside? Im wondering about 10 lengths just running from one side to the other? Thanks.

Bluejets

Oct 5, 2014
6,595
0.4mm @ 4' on 12v will give you around 13.68w per length which is approx double what you will get from the same length 0.3mm on the same voltage. You could run whatever number of strings( parallel runs) to get whatever final wattage you require. If the heat conduction into the filter is good, there should be no excess heat buildup in the wire. ( won't glow red as in open air)

Slowbutsure

Feb 18, 2018
21
0.4mm @ 4' on 12v will give you around 13.68w per length which is approx double what you will get from the same length 0.3mm on the same voltage. You could run whatever number of strings( parallel runs) to get whatever final wattage you require. If the heat conduction into the filter is good, there should be no excess heat buildup in the wire. ( won't glow red as in open air)

Thanks. Ive just put it together, so hoping its solved.

Slowbutsure

Feb 18, 2018
21
0.4mm @ 4' on 12v will give you around 13.68w per length which is approx double what you will get from the same length 0.3mm on the same voltage. You could run whatever number of strings( parallel runs) to get whatever final wattage you require. If the heat conduction into the filter is good, there should be no excess heat buildup in the wire. ( won't glow red as in open air)

Success! Thanks all for your help.

Slowbutsure

Feb 18, 2018
21
Ok, next question! I need to control the power going into the wire so that it gets hot enough but doesn't fry the wire. I tried a 100w 1.5R resistor 12v, but then it doesn't get hot enough. (no idea if that was a good idea or not). Would using a 4amp inline fuse do it instead of a resistor? Thanks.

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,509
You limit the temperature of the wire simply by making it longer.

(Unless you want to make it variable)

Bluejets

Oct 5, 2014
6,595
Goes without saying that you should have a fuse but not for control of the heat, rather to protect against faults.

Now is where things start to get more complicated and, as larger currents are involved, more expensive.

To begin with you need to measure the current that the circuit is drawing to get some idea of the size of any switching or voltage drop devices.

This hit and miss method you are using could go on for years which is why theory was invented. One alternative is make it variable.

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