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Old 10-09-2009, 11:09 AM   #16
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Would like to use Nichrome wire to make a small heater


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Originally Posted by GerGa View Post
So how could I go about finding out where and in what orientation to connect the diodes? Also how do I choose what diodes - just on allelectronics there are two 1000v diodes, 1 and 3 amp, and also I have not had much luck in finding a zener diode in 35v except here which is 5w but I am not sure what power rating to look for; is that one fine?
Also how could I go about figuring out what kind of fuse or resistor to use and how to hook that up?

And your mention of the 317 and a couple resistors and caps seems like the standard circuit design for a v-regulating circuit that uses the 317 - (just trying to state my understanding)
I'll post a schematic or a description; first let's find the watts/sq. in. and decide if you want the whole steering wheel heated and if you want it heated for the whole time you're driving.

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Old 10-09-2009, 02:50 PM   #17
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Would like to use Nichrome wire to make a small heater


Would I be better off trying to get a grasp for the power need with other things like bulbs or heating pads and resistors with a power source similar to the car? I have an ac/dc adapter adjustable 3-12v, although it does have a 300mA minimum, I could just hook up the 317 variable power supply to that to get lower mA if desired, correct?
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Old 10-09-2009, 05:07 PM   #18
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Would like to use Nichrome wire to make a small heater


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Originally Posted by GerGa View Post
Would I be better off trying to get a grasp for the power need with other things like bulbs or heating pads and resistors with a power source similar to the car? I have an ac/dc adapter adjustable 3-12v, although it does have a 300mA minimum, I could just hook up the 317 variable power supply to that to get lower mA if desired, correct?
The power requirement, whether at 1v or 1000v, will drive the whole design. The heater "doesn't know" what volts and amps are causing it to heat. Using 120vac from your house, and light bulbs or heating pads as loads, is more convenient than zapping your car's elec. system.

And if the power needed to heat your hands over the surface area of the steering wheel is more than 200w or so you might need to beef up your car's alternator.

I can hold onto a 13w CFL for quite a while. The surface area that I am touching is about 5 in. sq. So for my hand I can use about 2 to 3 w per sq. in. And my hand cuts off the free air supply to the bulb so the bulb gets hotter than normal.

For a 100 sq. in. steering wheel surface I might need 200 to 300w, less if I just have hand pads.
. . .Maybe it's time to shop for a new alternator, or use an aux. battery just to run the wheel heater.
The plot thickens and the scope of the design widens to include your car's power system.

Last edited by Yoyizit; 10-09-2009 at 05:20 PM.
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Old 10-09-2009, 08:34 PM   #19
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Would like to use Nichrome wire to make a small heater


My heating pad:
area=160sqr inch
rated power= 45w
measured resistance=90ohm
Turned it on medium which is pretty warm, left it sitting on for more than 5 minutes to stabilize temp, measured volts:around 40-50v

Whole steering wheel:
approx area=140sqr inch

The heating pad does not receive constant varying voltage, it gives intermittent bursts of voltage. my wild guess is 400ms on, 400ms off
So I can't tell exactly the voltage with my analog meter but it was around 40-50v.
My meter only measures to 150mA...
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Old 10-10-2009, 11:18 AM   #20
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Would like to use Nichrome wire to make a small heater


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Originally Posted by GerGa View Post
My heating pad:
area=160sqr inch
rated power= 45w
measured resistance=90ohm
P = V^2/R, so V^2 = PR = 4050 so V = 64v? Don't you use 120v?


Turned it on medium which is pretty warm, left it sitting on for more than 5 minutes to stabilize temp, measured volts:around 40-50v
P = (45^2)/90 = 23w.


Whole steering wheel:
approx area=140sqr inch

The heating pad does not receive constant varying voltage, it gives intermittent bursts of voltage.

Probably a thermostatic control, like on cooktops.


my wild guess is 400ms on, 400ms off
So I can't tell exactly the voltage with my analog meter but it was around 40-50v.
My meter only measures to 150mA...
The measurement of this pad's power consumption might be difficult because of the duty cycle bimetallic temp. control.
http://www.evenheat-kiln.com/controls/inf/inf.htm
You'd need to use a wattmeter for a time interval and then calc. amps.

Since you know the pad's resistance, knowing the amps and duty cycle will tell you the power.
If you have some power resistors you can make a shunt and then use your voltmeter to measure current.

Anyway, with the pad at med, 23w/160sq in = 140 mW/sq. in., so the wheel would need 20W. At 12v this is not even 2A and the resistance of the wheel's heater = 144/20 = ~7 ohms.
So far so good.

At this point you should maybe try to make a small heater for one hand out of nichrome or resistors and mount it on the wheel.
You can power it directly from the battery with the engine off. If you don't fuse this circuit and you short out the battery your wires connecting this circuit will melt very quickly.

The winding pitch will influence the mW per sq. in. This prototype can be much hotter or much colder than the calcs would indicate, so be careful.

Last edited by Yoyizit; 10-10-2009 at 11:45 AM.
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Old 10-10-2009, 02:44 PM   #21
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Would like to use Nichrome wire to make a small heater


Why shouldn't I just get a connector for the ashtray lighter socket? It's still on with the car off, I tested it no load at 13v.
Also how would go about fusing the circuit?

Edit:Also, if your worried about a bad connection there, which I'm sure it does have a bit of resistance, I could just solder in the wires to where the lighter socket is soldered in, and use some high power connectors that I have laying around.

It's not that I don't want to put in a fuse of my own, it's just that much easier to not have to worry about running wires all the way around the engine compartment and in through the dash.

Last edited by GerGa; 10-10-2009 at 07:11 PM.
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Old 10-11-2009, 09:47 AM   #22
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Would like to use Nichrome wire to make a small heater


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Originally Posted by GerGa View Post
Why shouldn't I just get a connector for the ashtray lighter socket? It's still on with the car off, I tested it no load at 13v.
Also how would go about fusing the circuit?

Edit:Also, if your worried about a bad connection there, which I'm sure it does have a bit of resistance, I could just solder in the wires to where the lighter socket is soldered in, and use some high power connectors that I have laying around.

It's not that I don't want to put in a fuse of my own, it's just that much easier to not have to worry about running wires all the way around the engine compartment and in through the dash.
Yes, use that socket. It might be fused at 10A, or not at all.
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Old 10-11-2009, 06:08 PM   #23
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Would like to use Nichrome wire to make a small heater


So I'm not really sure what nichrome to get.
I suppose what I might aim for for testing would would be 20w for 140inch^2.
And we'll say a 7.5 ft length of wire is wound around the wheel. A a 20w total that is 2.66w/ft. I'll pick 8v for head room to go up and down in power. 8v/(2.66w/ft)=~3ohm/ft
So I might look for wire that is around 3ohm/ft.
Are my calcs correct?
thanks
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Old 10-11-2009, 06:47 PM   #24
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Would like to use Nichrome wire to make a small heater


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So I might look for wire that is around 3ohm/ft.
Are my calcs correct?
thanks
I think so, but how will you spread the heat?
Maybe you should use
http://www.google.com/search?client=...UTF-8&oe=UTF-8
of the right resistance per foot or per sq. inch. The manu's rated volts are irrelevant for this application but it does have to withstand the current.
20w @ 8v would be ~4.5 kw @ 120v.

Last edited by Yoyizit; 10-11-2009 at 06:53 PM.
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Old 10-12-2009, 12:27 PM   #25
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Would like to use Nichrome wire to make a small heater


Has anyone mentioned a cars steering wheel rotates? How are you going to wire all this up? Your going to pull the wheel and go through the steering column? Use the lighter outlet and have 5 feet of wire dangling around?

I have a hard time believing someone could actually do this in an "elegant" manner.


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Old 10-12-2009, 02:03 PM   #26
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See above "slip rings" or modify the
http://www.thefind.com/cars/info-ste...l-clock-spring
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Old 10-12-2009, 03:36 PM   #27
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Would like to use Nichrome wire to make a small heater


If outside the steering wheel, the wire could be inside a mechanism that has excess wire wound inside on a wheel, like a measuring tape, and it would be mounted under the steering wheel column. Then the wire might have to be guided somehow to make sure it takes a clean path from the pulley to the wheel, not getting stuck inside the crevace between the wheel and column, etc. I have seen it with a usb cord light for a computer. I am trying to take this one step at a time though.
I found this website where 120v 6watt per foot wire is the most wattage. 120v and 6w is .05ohms/foot. Even though I don't need as many watts that is still wayyy too much current for my volt range.
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Old 10-12-2009, 05:16 PM   #28
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Would like to use Nichrome wire to make a small heater


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Even though I don't need as many watts that is still wayyy too much current for my volt range.
Yeah. We need to do some impedance matching here.
The constraints are the voltage, the power and the length of the heater.
That leaves us with the resistance per foot or per sq. inch and not much else.

Maybe you could make a "braided" network of 1/8 w or 1/4 w resistors, some in parallel and these in series with other paralleled resistors. Hosfelt, Allelectronics, etc. have reasonable prices.
Commonly available values are above 10 ohms but you can use paralleling to get almost any value.
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Old 10-12-2009, 06:01 PM   #29
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Would like to use Nichrome wire to make a small heater


So your saying trials with resistors will give me a starting point for trials with nichrome?
If I wanted to mock up 1 foot of resistors like a 21awg nichrome wire which is .831ohms/ft http://www.heatersplus.com/nichrome.htm , then I would connect a bunch of resistors 1 foot long to make .831ohms of resistance(using whatever combination of series and parallel is needed)? Correct?
I am also fuzzy on how a resistor is going to produce a similar amount of heat, or might there be not too much difference and it mostly comes down to having resistors about the size of wire and similar resistance per length..?
Edit: I tested some resistors and I got them pretty hot, they are 1/4w resistors. I did some calculations and I really see why you said that maybe I should only do part of the wheel, it takes so many ohms to get low enough wattage. With the resistors I guesstimated with an ohm value a reasonable watt value for the whole steering wheel, within my limitations of volts. I came up up with 300ohms per foot at 8ft to give the right power amount for the whole wheel. But, nichrome is much less resistive about 8ohm/ft at 31gauge and 27ohmft at 36gauge;this is way too little(therefore way too hot), and an only an unreasonable amount of wire would up the resistance and down the wattage;within my voltage limitations.
So now to find resistance wire that has very high resistance...
Very high gauge wire and a close wind seems the way to go; best heat distribution for the power I need, but god is the wire so expensive...I really need high resistance
wire..

EDIT #2 - Oh ****. I can use resistors. doh.

Last edited by GerGa; 10-12-2009 at 10:40 PM.
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Old 10-13-2009, 06:24 AM   #30
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