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Correct voltage,amps, and control for MINI nichrome heater.

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Dacr0n

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Hey all.. I just have a quick question for the tech heads in here.


I have a small project that I am working on.

I have a little mini heater that I am trying to build.

The heating element is a Nichrome Ribbon turned into a coil.

It is very small.. The resistance of the nichrome unit is only 0.8 Ohms.

I have tried running it on 120 VAC.

I tried hooking a typical light dimmer up to it and slowly bringing on the power until the heater gets hot.. but instead, it just blows the wire.

What do I need to do to make it so that it doesnt keep blowing the heating wire and is in a semi-controllable range.

I am not too knowledgeable about this kind of thing but am trying to learn.

I had an idea to install a power resistor before the element, but Im not sure what size would be good.

My goal is to be able to control the power so that I can get the tiny wire glowing hot and be able to turn it down so it just stays warm. All without it burning it again hopefully.


Would a 1k ohm power resistor work? I would imagine I need a resistor that can handle at least a few amps right? Then have another potentiometer to adjust it to hotter or cooler.



Would using say 30 VAC be easier? I have a hunch that getting a transformer to drop the voltage to somewhere between 12 and 30 volts AC would be good. However, im not sure how many amps I would need the transformer to provide... 2, 10, 15 amps? Like I said its a TINY little heating element but I keep blowing it.


Also... I know most trim pots are for very low amperage... is there a specific name or type that can handle say like 10-15 amps @ 12 Volts AC?


Any ideas?

Thanks in advance!
 
Try applying ohms law V=IxR (I=V/R)

So your 0.8 ohm wire takes 120/0.8 = 150A

Which is 18000W

None of which can be provided by a 120V mains socket.

You need a MUCH longer wire, or a MUCH lower voltage.
 
Well I figured somewhere in the range of 8-12 VAC might work okay.

problem is where can I get 8-12 volts AC with enough amps to make the nichrome heat up/glow

and what is the best way to control it once I find the ideal voltage?

also, hows about running at 12 volts? it will draw 15 amps @ 180 watts

how does that sound?
 
Well I figured somewhere in the range of 8-12 VAC might work okay.

problem is where can I get 8-12 volts AC with enough amps to make the nichrome heat up/glow

You need a simple mains transformer.

and what is the best way to control it once I find the ideal voltage?

also, hows about running at 12 volts? it will draw 15 amps @ 180 watts

how does that sound?

Is 180W what you're wanting?.

Why not try it on a car battery and see how it works.
 
I'm having the same problem you are. I have a 1½ inch piece of nichrome ribbon that i formed into a coil by wrapping it around a piece of 16 awg wire. I have it hooked up to a 5 volt 15 amp computer power supply and it glows red hot in a matter of seconds without exploding.

I haven't figured out how to control the temperature through the heating element, but I'm working on it. Let me know if you figure something out.

I hope this helps you out some.
 
I put up a post yesterday and I got this reply from kchriste:

A MOSFET and PWM is a better solution. If you want a simple manual power control, use a 555 wired for variable duty cycle (PWM). Some examples:

**broken link removed**
**broken link removed**
**broken link removed**

I found the second link worked best for me, so I hope this will help you more. Thanks to kchriste for finding these links.
 
Thanks for the information written above.
I'm just trying to do the same thing.

My question is that I want to regulate Voltage and current. So I was thinking about using a potentiometer and a rheostat. I have a nichrome coil, and a 12VDC computer power supply (I think the wattage is around 400 Watt).

Can I use potentiometer and rheostat in the same circuit to control the power?
Another question is... I have purchased an electric stove like this one:
**broken link removed**

Can I connect the plug to a DC power source? I really will use around 100 Watts of power from a DC power source, instead the 1500 Watt from the AC power source. Do I need to do some modifications to connect it to the DC source or maybe connecting the plug directly will be enough?
 
First a heating element type load does not care if the supply (source) current is AC or DC, it's all the same to the load.

Next, at design time a heating element is designed for a specific wattage given a working voltage and current. For example I have a 120 volt 600 watt heating element lying here. Since the power = the voltage * the current we can say this element when powered by 120 volts (AC or DC) will draw 5 amps. 600 watts / 120 volts = 5 amps. If I measure the cold resistance of this element I read about 19.8 ohms on my DMM. If we do the math we have 120 volts / 5 amps = 24 ohms. That makes sense since when the element heats up the resistance will increase a little. So when cold we have about 19.8 ohms and when it is running at its rated voltage and current (hot) the resistance is 24 ohms. That is typical of a heating element. A change in resistance of 20% to 25% is normal. The resistance is the only real constant subject to minor change.

If I reduce the applied voltage the current will also drop and the load in watts will also reduce. Matter of fact if I reduce the voltage to 60 volts and the element is about 24 ohms the current will drop to 2.5 amps, the power will be about 150 watts or half of what it was at 120 volts. That makes sense doesn't it? In reality this is close as the element likely will not reach 24 ohms but the guess is close. The only way to know the actual wattage would be to monitor the voltage and current and do the math.

Can I connect the plug to a DC power source? I really will use around 100 Watts of power from a DC power source, instead the 1500 Watt from the AC power source. Do I need to do some modifications to connect it to the DC source or maybe connecting the plug directly will be enough?

Yes, you would apply the DC voltage until the current * the voltage = 100. The power in this case is just that, power. Matters not if the source current is AC or DC. Can you use a rheostat? Yes, but you need a rheostat that will handle the maximun current the load can draw. Think high wattage rheostat. Think real high and real expensive.

The ideal situation would be to find a lower resistance and lower voltage heater element. That or an SCR type controller that would handle the load.

Ron
 
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