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Nichrome heater experiments

by nuncoop
Tags: experiment, heater, nichrome
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nuncoop
#1
May11-09, 02:56 PM
P: 28
Ok, I'm rather new to electronics as I've only taken a highschool-level electronics class and that was several years ago. Right now I'm trying to put together a low power heater consisting of a length of nickel chromium wire and a DC or stepper motor. What I'd like to do eventually is be able to heat the nichrome wire up to a comfortable temperature (around 50 degrees Celsius) by attaching it to the motor in series and spinning the rotor manually. Here is what I have to work with:

- ~ 3.25 feet of nichrome wire at 35 AWG (This is an estimate as the diameter didn't come on the package)
- a small motor out of a wind-up flashlight. I cannot find the rating for it but it does have "A6V5" printed on the side (6 amps, 5 volts?)

I have already tested a length of 4" nichrome with the small motor, but when I cranked it there didn't appear to be any heating of the wire. My questions are: Is there any way to make a stepper motor more efficient and output more power when the rotor is cranked? How much power do I need in order to heat a 3.25' length of nichrome wire to 50 degrees Celsius?

Any input is appreciated, as I am a complete beginner.
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Tizzo
#2
May11-09, 05:46 PM
P: 5
You'll only need about 0.2 amps to get 50deg C.

If it's 3.25 ft and 35 AWG you're probably looking at about 63ohms resistance. You'll need 12.6V to get your 0.2amps. That's 2.52 Watts.

Maybe you can hook the motor up to a multimeter and figure out how much current and voltage you can get out of it.
Phrak
#3
May12-09, 08:45 PM
P: 4,512
Something doesn't add up. If you crank out 30 Watts into a near dead short (your 4 inches of nichrome.) you should feel the resistance on the crank. A crank telephone ringer puts out about that much, where a 30 Watt load is about as much as you can manage with the little crank handle.

Try alternately shorting and opening a couple pigtail leads on the crank thing, so you know you're getting current.

vk6kro
#4
May12-09, 09:00 PM
Sci Advisor
P: 4,032
Nichrome heater experiments

You can't do much with existing motors to increase their efficiency.

Phrak mentioned the old crank telephone ringer, and you can improve those. I put 3 Neodymium magnets on the magnets of one of those and, after that, you could hardly turn it if the output was shorted. It generated over 100 volts though, open circuit.

No idea where you'd get one of those now.

With your existing setup, maybe try to get light from a LED and then from a torch bulb before you try to heat up Nichrome wire. Your motor might have too much internal resistance to supply the current you need as a generator.
Phrak
#5
May12-09, 10:17 PM
P: 4,512
Quote Quote by vk6kro View Post
You can't do much with existing motors to increase their efficiency.

Phrak mentioned the old crank telephone ringer, and you can improve those. I put 3 Neodymium magnets on the magnets of one of those and, after that, you could hardly turn it if the output was shorted. It generated over 100 volts though, open circuit.

No idea where you'd get one of those now.

With your existing setup, maybe try to get light from a LED and then from a torch bulb before you try to heat up Nichrome wire. Your motor might have too much internal resistance to supply the current you need as a generator.
We had one when I was a kid. It was stuck on a nice board with a lightbulb as a science demonstration gizmo. So we rigged it up to the doorbell button for a Holloween prank. There was a sign, "push doorbell", to direct our victims. A yelp at the door told us of our success. We got some irate candy seekers until my dad shut down our operation.
vk6kro
#6
May12-09, 10:42 PM
Sci Advisor
P: 4,032
:)

You'd get sued for millions if you did that now. Can't have any fun any more.

Ours had a nice wooden box with a lid that lifted upwards. It was maybe 1930's vintage.
The three horseshoe magnets were pretty useless and needed remagnetizing, but they perked up considerably with Neodymium magnets placed carefully on the upper poles.
Phrak
#7
May12-09, 11:09 PM
P: 4,512
Quote Quote by vk6kro View Post
:)

You'd get sued for millions if you did that now. Can't have any fun any more.

Ours had a nice wooden box with a lid that lifted upwards. It was maybe 1930's vintage.
The three horseshoe magnets were pretty useless and needed remagnetizing, but they perked up considerably with Neodymium magnets placed carefully on the upper poles.
Very nice. It's good to hear you left the original equipment intact. I'm fairly sure those old horseshoe magnets loose their strength over time. You might even take them to get re-gaussed if you can find someone. I think the magnetos on old hit and miss engines (circa ~1930) do the same.
nuncoop
#8
May15-09, 04:23 PM
P: 28
Quote Quote by Phrak View Post
Something doesn't add up. If you crank out 30 Watts into a near dead short (your 4 inches of nichrome.) you should feel the resistance on the crank. A crank telephone ringer puts out about that much, where a 30 Watt load is about as much as you can manage with the little crank handle.

Try alternately shorting and opening a couple pigtail leads on the crank thing, so you know you're getting current.
When I hooked the motor up to a digital multimeter I could definitely feel the resistance. The reading on the multimeter was roughly 17 volts as I was cranking it. I then attached the leads to the nichrome wire about 1 inch apart, and although there was a significant amount of resistance, the wire did not seem to heat up at all. I'm very confused at this point.
nuncoop
#9
May15-09, 04:31 PM
P: 28
Quote Quote by vk6kro View Post
You can't do much with existing motors to increase their efficiency.

Phrak mentioned the old crank telephone ringer, and you can improve those. I put 3 Neodymium magnets on the magnets of one of those and, after that, you could hardly turn it if the output was shorted. It generated over 100 volts though, open circuit.

No idea where you'd get one of those now.

With your existing setup, maybe try to get light from a LED and then from a torch bulb before you try to heat up Nichrome wire. Your motor might have too much internal resistance to supply the current you need as a generator.
I might have phrased that wrong. Ideally I'd like to use a motor like the one's found in hard disk drives, as they are compact enough for the application I will be using them in. I know that as you increase the rpm, the wattage and voltage you get out of the motor increases. What I wanted to know was if increasing the steps in a stepper motor increases these values as well, without having to raise the rpm. I am using a DC motor right now but I have a stepper handing if the DC motor doesn't work.
vk6kro
#10
May15-09, 07:27 PM
Sci Advisor
P: 4,032
You shouldn't have felt much resistance when measuring on the voltage scale of the multimeter. This draws very little current.

What you could do, is put the multimeter on the 10 amp range and wind the shaft of the motor. See what current it can produce into a short circuit. Start slowly if you are worried about overloading the meter.

This will give you an idea of the internal resistance of the motor. This resistance will always limit your available current.

If you have an electric drill with variable speed, you can check the current at various speeds.
Just grip the shaft of the motor in the jaws of the chuck and measure the short circuit current or the output voltage.

You can calculate the internal resistance. It is equal to (open circuit voltage) divided by (short circuit current).
nuncoop
#11
May18-09, 07:34 PM
P: 28
Thanks guys for all the suggestions and advice! I'll keep working on it and post more questions if I have any.


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