Resitance Wire

[iceblue]

Hi. Is there anybody who can give me some information on resistance wire? I cant seem to find much useful info anywhere. I have two types of resistance wire, both of which are usually used on 220V AC. The one is the flat type used in toasters, and the other it the round one found in hair dryers, ceramic hobs, etc.

What I would like to know is if this can be used on a 12V DC supply? Also, can it be connected to a constant supply or would it have to be regulated somehow to prevent it overheating. Any other info would also be helpful.

I did find one manufacturer who had a certain type of resistance wire which could be used on 220V AC or 12V DC but it did not say whether it was only that type or all types which could.

 

[dknguyen]

It's rated for 220VAC, so its resistance is such that 220VAC will push enough current through it to heat it up, but not enough to overheat or melt it. If you connected 12VDC to it, nothing bad would happen, but nothing useful would probably happen because the resistance is too high for 12VDC to push enough current through to heat it up. You'd have to shorten it voltage proportions it is rated for or use thicker (lower resistance) heating wire.

It shouldn't need to be regulated since it's just wire- as long as the supply doesn't fry because the wire is too low resistance for the supply voltage.

It's just wire with extra high resistance.

 

[Boncuk]

Resistance wire

Hi iceblue,

restance wire is sold in electronic shops with a good assortment.

The wire is called "Konstantan" (english: constantan?) and is manufactured in different calibrated diameters for equal resistance vs. length.

You can of course use toaster or spiral type wires as a resistor, but they are manufactured to produce heat and at their nominal power they will glow which is pretty unwanted in an electronic circuit.

Your application describtion is pretty vague. Please post a little schematic for clarity.

Boncuk

 

[Boncuk]

... but nothing useful would probably happen because the resistance is too high for ...

The "high" resistance of a toaster wire is about 60Ohm at 220VAC; better to use a small piece than a bunch of stranded copper wires.

There is one disadvantage to the use of heater wires: They can't be soldered

Hans

 

[Centretek]

Resistance wire or 'Nichrome' wire is not rated for any particular voltage. It's just wire with a higher resistance than copper. The wire used on an older single bar radiator has a resistance of roughly 0.8 ohms per inch.
I use a length stretched between two 2 inch screws on a sheet of ply, and fed with 12 volts, to slice polystyrene foam into sheets (like a hot knife through butter).
It should be so hot that it glows but makes a beautiful clean cut.
A fret saw can also be adapted to carry nichrome wire to cut free form shapes from polystyrene foam. You just have to adjust the supply voltage to the resistance of the length of wire you wish to use.

 

[Boncuk]

I use a length stretched between two 2 inch screws on a sheet of ply, and fed with 12 volts, to slice polystyrene foam into sheets (like a hot knife through butter).
It should be so hot that it glows but makes a beautiful clean cut.

Ever tried the high-E-string of a guitar? It doesn't need to glow, but makes super accurate cuts. You can put the pieces together like a puzzle with almost no gap.

Boncuk

 

[Sceadwian]

All the hot wires I've used don't glow, that'd be a fire hazard. At 220V you'd need to cut the heating element into 18 sections and drive them in parallel from a 12 volt source to get the same heating capacity, and that's going to draw an absolutely insane DC current. Assuming line power is an option for what you have in mind you're better off using a triac to run the heating element, you can use phase control for the temperature if you want easily as well.

 

[Hero999]

If you want to use batteries then you could use an inverter or better still connect 18 in series but use a MOSFET and PWM for temperature control rather than a traic.

Altrhough 220VDC isn't as dangerous as 220V AC you still need to be very careful, especilly as there's no way of isolating all those batteries connected in series.

 

[Sceadwian]

18 12 volt batteries in series? 12 volt batteries already have 6 cells, the pack resistance is going to be horrible, and charging it properly would be a nightmare. 220VDC is more dangerous than AC, AC current will tend to cause a neutral muscle paralysis because it reverses direction. DC will cause muscles to hard clamp more readily.

 

[Hero999]

But 220VAC has a peak voltage of 311V and it only takes one fith of the current to kill at AC than it does at DC.
ESD Journal - Electrical Hazard


The idea that DC is more dangerous than AC is a myth, all electrical standards I've read state a much higher touch voltage for DC than AC.

Tha pack resistance won't make any difference to the current because the voltage is also increased as each cell is added and the current required for the same power is reduced as the voltage is increased.

 

[Sceadwian]

I stand corrected, looks like the increased risk from AC is related to bio-electrical interference from the 50-60hz signal. Basically it causes the heart or breathing rhythms to be interfered with easier than DC.

 

[iceblue]

Thanks for the many responses. Ok, here's one idea I had in mind. My car doesn't have heated windscreen washer jets so I was thinking of using the resistance wire to heat up the water. I would probably have to wrap the wire around a thin copper pipe so I'm not sure how I would insulate the windings. Any suggestions? Also it would be connected to the rear demister switch so will only operate when the rear demister is on.

I know I could also just divert the washer hoses along the radiator or engine but I dont like that idea as it would take a while before the water warms up sufficently.

By the way, I live in South Africa where it seldom drops below zero, so I'm not doing this to prevent water from freezing in the jets but rather to warm the water just slightly so that I dont get that thin film of 'mist' forming on the outside of the window when it is very cold.

 

[Hero999]

Does your demister work?

If not you can but small fan heaters that plug into the cigarette lighter socket.

 

[iceblue]

The demister works fine, but that only helps on the inside of the window. But either way, this was only one idea I had in mind. i may not do this at all as it may be more trouble than its worth. The main thing I wanted was some info on how to use resistance. So thanks to everyone for the help.

 

[crutschow]

I would probably have to wrap the wire around a thin copper pipe so I'm not sure how I would insulate the windings. Any suggestions?

You could use a high temperature tape such as one made of fiberglass.

 

[crutschow]

Another thought. I've seen 12V immersion water heaters that plug into the lighter socket with an element that you hang over the edge of a cup into the water (see **broken link removed**). Perhaps you could adapt one of those to your needs.

 

[Torben]

I'd second Carl's suggestion of using the heating tape. It's commonly used to keep water pipes from freezing in the winter, but it would probably work quite well to heat the wiper fluid for you. Most hardware stores should carry it.


Torben

 

[mneary]

I don't think that the initial temperature of the fluid will influence its behavior once it's exposed to moving air as a mist.

More important are freezing (melting) point, volatility, surface tension, and the temperature of the glass. A detergent or alcohol helps a lot.

 

[bryan1]

One good use I found for nichrome wire was for my dumpload on my RE based charge controller. I grabbed several 2Kw 240 volt immersion heaters from a scrap yard and simply cut some of the wire and put them in parrallel so I had a 4.9 ohm load resistance so when my charge controller hits 27.5 volts around 5.6 amps of current is drawn. I know you can buy replacement demister tape so that may be your wasiest option.

Cheers Bryan

 

[iceblue]

Thanks for all the input. Not sure whether I'm still going to do the heated washer jets thing but i certainly got a lot of useful info that I will be able to use for other projects. May just put together one of those polystyrene cutters for the time being, since I actually need one.