# Electronics DIY electric lighter

S

#### stephenkohnle53

I have been building a electric lighter without soldering since I don't know how to solder, so I am going to ask my brother to show me how on the weekend. Until then I've been using alligator clips, 9 volt batteries (preferably one) and graphite from pencils as a resistor. Unfortunately the mechanical pencil resistors break easily and now I'm using pencil resistors and I am now struggling to find what length of resistor I need. I do have a voltmeter but I think it is damaged since it can't measure voltage accurately or measure resistance at all. Can one of you show me how to calculate the resistance needed and how to calculate the length needed. I am using an HB pencil and I want to simply light paper on fire.

#### .Scott

Homework Helper
First, good luck trying to solder to the graphite. It isn't going to work. You will need to use some kind of clip. Also, the melting point of regular solder (361F) is well below the kindling point of paper (454F). So you may need to crimp the wire to the clip.

Bear in mind that all of these temperatures are well above what it takes to give yourself a burn. Given enough time, you can burn yourself with temperatures as low as 110F. Google skin burn temperature.

What you are looking for is an intense spot of heat. So you will be using a short piece of graphite - that you can select by experimentation. I'd settle with experimentation since you can't measure resistance anyway, and even if you could, you would need to model the resistance drop in the battery.

Not only does the short piece of graphite provide the small heat source, it also reduces the resistance, thus increasing the current (amperage), and likely creating more heat.

Be careful with the battery. It will also warm up.

The kindling point of paper is 454 Fahrenheit. You will need more than that - say 600. Plus blowing softly on the paper while burning it will improve your odds of a flame.

S

#### stephenkohnle53

I meant I am going to solder other connections in the circuit not the graphite. Also I have been experimenting and no matter how far or short distance I move the clips the graphite will not heat up. BTW currently the longest distance I have tried is about half the length of a pencil, shortest is half a centimeter. Could the graphite be too high resistance considering HB has high resistance as far as pencil graphite goes

#### .Scott

Homework Helper
I meant I am going to solder other connections in the circuit not the graphite. Also I have been experimenting and no matter how far or short distance I move the clips the graphite will not heat up. BTW currently the longest distance I have tried is about half the length of a pencil, shortest is half a centimeter. Could the graphite be too high resistance considering HB has high resistance as far as pencil graphite goes
I suspect the problem is that the 9-volt battery cannot provide the current needed. Although I do not know the resistance of HB.

There is another method - but it requires good current and about 40 volts with a regular Number 2 pencil. You use two pieces of pencil to form an electric arc. But use UV eye and skin coverings if you experiment with this - it will generate x-rays and potent UV. My source for this method comes from a time when I needed a UV source to erase a UV-erasable PROM. That arc erased it in less than 30 seconds, many times faster than using the (unavailable) UV bulbs.

S

#### stephenkohnle53

I dont think I will do that for this purpose but I may try that another time. As for now this article explains the resistance http://www.troelsgravesen.dk/graphite.htm
But since my voltmeter does not work, do you have any idea how I could calculate the resistance and length of resistor needed using that article. According to a video I watched a while ago I need 1 amp of current thus needing 9 ohms of resistance if I cut down a full pencil of HB from 175 millimeters to 82.89 millimeters would that work assuming my resistance and amperage is correct? I got that by dividing the 19 ohms of resistance the HB lead has by 9 to get 2.111111111 then divided 175mm by 2.111111111111.

#### .Scott

Homework Helper
But since my voltmeter does not work, do you have any idea how I could calculate the resistance and length of resistor needed using that article. According to a video I watched a while ago I need 1 amp of current thus needing 9 ohms of resistance if I cut down a full pencil of HB from 175 millimeters to 82.89 millimeters would that work assuming my resistance and amperage is correct? I got that by dividing the 19 ohms of resistance the HB lead has by 9 to get 2.111111111 then divided 175mm by 2.111111111111.
You need to look at the data sheet for the battery you are trying to use.
https://d2ei442zrkqy2u.cloudfront.net/wp-content/uploads/2016/03/QU1604_US_UL1.pdfI get 82.89 as well. But...
You seem to be thinking that you can draw 1 amp from the battery at 9 volts. That would be 5 watts.
In looking at the data sheet, notice that the maximum power case shown (top right on page 2) is 1000mW, 1 watt. Under those conditions, the battery voltage drops rapidly and the battery dies in about 2 hours. If you have been experimenting with the same 9 volt battery for more than a few minutes, that battery is probably well on its way down that voltage curve.
So, for starters, you will need at least 5 fresh batteries wired in parallel. And in this case,10 batteries will last almost 3 times longer than 5.

According to that curve on the data sheet, your voltage is going to drop into the range of 8 to 8.5 very quickly. So you may want to adjust your resistance target accordingly.
Also notice that the internal resistance of the battery is 1.7 ohms. So if you are targeting a 8.3 ohm resister, about 17% of the heat will be expended by the batteries, not the pencil.

Looking at one of your links - that #2 pencil I was mentioning before is the same as your HB.

#### Tom.G

How To Test a 9Volt Battery Without a Meter:

To test the voltage of a 9V battery without a meter handy, I use my tongue. Use the upper surface of the tongue, near the tip, and briefly touch the battery contacts. If it gives a good tingle, it is fairly good. If you sort of wish you hadn't done that (it can hurt just a little bit), the battery is brand new. You will get a sort of metallic taste. If you get a chemical taste, the battery is leaking (wipe off your tongue on a shirt sleeve to get rid of the taste.) (I know, sounds gross.)

p.s. Most people cringe at the thought of the above process, especially those with little electrical or scientific background. I've been doing it for decades with no known side effects other than an occassional 'Well! That one is new."

#### sophiecentaur

Gold Member
There is a big problem here because you need a low voltage and high current - because the resistance of your graphite piece is inconveniently low.
Google "resistance of a pencil lead" and you will find several different answers (depending o the dimensions and actual material.
If you want local heat then there is no point in using a full length lead, of course, so you would choose around 1cm (?perhaps?) which would have a resistance of around 1Ω (give or take). If you can put 1A through it, the power dissipated will be (V2/R) 1Watt and it will need 1V. You are needing something like at least 5W, briefly.
I reckon that you will not get enough from a primary cell (even a good alkaline) to do that but a Nimh cell (rechargeable) will give around >5A for a short time. Two cells in series, connected up with short lengths very thick wire. 10mm2 cable would be fat enough and you would need good screw connectors and a good battery holder with clean contacts. The graphite will break easily and you will need to hold it in a strong base to take the stress, with copper wire wrapped round the ends of the graphite for a good contact and avoiding over tightening the screws. A lot of trial and error to avoid breaking the graphite.
If you want to use rechargeables you will need to be careful and use a proper charger. (They do explode if mis-treated) but they could do what you need.
But frankly, if you don't have a working meter of any kind, you could waste a lot of time and money.
Alternatively, why not go for nichrome resistance wire?

#### NTL2009

... The graphite will break easily and you will need to hold it in a strong base to take the stress, with copper wire wrapped round the ends of the graphite for a good contact and avoiding over tightening the screws. ...
And this copper wire will conduct a lot of heat away from the graphite, copper being a very good conductor of heat as well.

This is one source of inefficiency in filament light bulbs. The supports for the filament draw heat away, and that section of filament isn't hot enough to produce visible light. IIRC, this is one reason why "rough service" bulbs have lower lumen/watt - they have additional support for the filament. Also, 220V lamps require a longer filament (all else being equal) than a 110V lamp, and often an added support, so filament bulbs on 220V are generally a bit less efficient than those for 110 V. I believe ~ 48V was the 'sweet spot' for most filament designs.

#### AlexCaledin

How about taking a 110V bulb, breaking the glass carefully (leaving the filament intact), and powering it with a 9V battery? Maybe it will be glowing red a little, hot just enough to kindle paper.

...tried a small 26V 0.12A bulb (without breaking glass), it starts glowing at 2V or so.

Last edited:

#### sophiecentaur

Gold Member
How about taking a 110V bulb, breaking the glass carefully (leaving the filament intact), and powering it with a 9V battery? Maybe it will be glowing red a little, hot just enough to kindle paper.

...tried a small 26V 0.12A bulb (without breaking glass), it starts glowing at 2V or so.
I have seen that method on the films as a detonator system for explosives,

S

#### stephenkohnle53

I think I may try the lightbulb idea, btw I was able to get the graphite to work but it keeps breaking so I think I will try that. BTW the reason I did not try nichrome is I do not have any and id rather not spend money on it. I may try to get some by taking apart something with nichrome, I work at goodwill and I have seen many things that should have some, assuming they are undamaged and although the nichrome might be damaged I might as well try since I get 30% off and they are only a dollar. As for the battery testing I think the voltmeter is working, currently it appears to only be able to accurately measure voltage though.

#### jim hardy

Gold Member
2018 Award
Dearly Missed
I did not try nichrome is I do not have any and id rather not spend money on it.
Fishing leader or music wire - broken guitar string perhaps.

I have seen many things that should have some,
Toaster or hair dryer from discard pile.

#### Asymptotic

Fishing leader or music wire - broken guitar string perhaps.
Maybe not the string itself - a high E in a light gauge set is typically 9 mil stainless steel (or nickel-plated steel, or a nickel alloy). On the other hand, the overwinding on an electric guitar G or D string is thin enough.

When it comes to cheap, how about using threads from a steel wool pad? Learned in the Boy Scouts how to start a fire using steel wool and a 6V lantern battery ....

#### sophiecentaur

Gold Member
Yes. Brilliant bit of remembering. Just dipping a crocodile clip into a bunch of steel wool is about the best demo of electrical heating that can be done on a kitchen table top.

S

#### stephenkohnle53

Alright what voltage of a bulb should I use and how many 9 volt batteries and could I get a 12v bulb and power it with 6v or 9v from a battery. I was thinking I could use a 6v lantern battery with a 12v bulb since I do not need it to be bright and if I get nichrome from a hair dryer could I use the 9 volts I have to power it. Also I have several flashlights and lamps at home could I use their bulbs and battery.

S

#### stephenkohnle53

I read that leds do not generate any heat, so do IR leds generate enough

#### Asymptotic

I read that leds do not generate any heat ...
That's not correct. LEDs are more efficient than incandescent and other light sources (about 80 lumen/watt, versus 15 lm/W for incandescents), but they do generate heat.

... so do IR leds generate enough
To serve as an electric lighter? Probably not. Look up the specs for a high output IR LED.

One thing I'm sure will work is 31 AWG nichrome wire (this is the size used for model rocket engine igniters).

S

#### stephenkohnle53

By the way I made the lighter from a hair dryer, I was going to take apart the hair dryer and use the nicrhome for the lighter but I decided to see how it would work without the blower and it gets so hot without it that it gets bright yellow in 1 maybe 2 seconds. So now I am using that as the lighter but I want to lower the current between 9 amps and 4.5 amps but I am unsure of what amperage I should use so I want to get a variable potentiometer, any ideas on where I can get one for cheap? Maybe from scrap electronics?

Edit: I want to change the current so that I can turn it on for more than a few seconds without the wire melting, it was able to get bright white in about 3 seconds
Edit 2: I know it needs to be between 4.5 and 9 amps since it has a switch that changes the amperage to either 9 amps or 4.5 amps. 9 is what i have been using because 4.5 does heat it up but not enough to change color nor light paper.

#### Asymptotic

I want to lower the current between 9 amps and 4.5 amps but I am unsure of what amperage I should use so I want to get a variable potentiometer, any ideas on where I can get one for cheap? Maybe from scrap electronics?
A potentiometer alone won't work, and I'm betting the full/half heater power switch puts a power diode in series with the heater (so that quick n' dirty way of chopping power in half has already been used). A reasonably cheap way to go about it is use a PWM or an SCR phase-fired controller similar to this Yeeco 4000 watt/120 volt controller (also available for 220V input) on Amazon.

#### sophiecentaur

Gold Member
By the way I made the lighter from a hair dryer,
Haha. Well done but DANGEROUS if you were using mains voltage. Not surprising that it got too hot with no air flow. The 9V battery idea is a lot better and safer. You could use part of the length of the element and choose the length to suit the temperature that you want. If you choose a length that's the same fraction of the original length (e.g. 9/240 or 9/120, whichever) then the voltage drop across the section of wire will be the same as when it's in the dryer. It will still be too hot but use perhaps twice that calculated length and it will still glow with no air current over it. Vary it until you get what you want. It won't be very critical.
BUT please avoid using mains voltage. You will only risk burning your fingers and not zapping yourself to death!
You will need an alternative way of drying your hair, though.

S

#### stephenkohnle53

Don't worry about my hair, I have an extra hair dryer. But I do see your point about hurting myself. I should have thought that through more, it is ironic considering recently I made a thread about me not being safe or careful. Yeah I'll try that, considering that certainly is safer

"DIY electric lighter"

### Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving