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Topic: Ardunio shortcuts when using Kanthal wire (Read 608 times) previous topic - next topic

PillPollen

Hi!

Super simple. Hooking up a LED to ardunio. Wait 10 sec then lights on.
Everything works perfectly.

Now I do the same but instead of turning on a LED I now want to send current trough the kanthal wire. But then arduino wont even start. The built in LEDs on the arduino boards wont even blink.

Why is this?

MarkT

#1
Jul 28, 2019, 12:25 pm Last Edit: Jul 28, 2019, 12:26 pm by MarkT
[Kanthal wire appears to be some sort of heating element / resistance wire]

Heating elements take huge amounts of power, 10's of watts, completely beyond the power of a microcontroller output to handle, and completely beyond the capability of a USB power supply too come to that.

You need to explain what resistance wire you have, the power you want to control and then it will be possible to discuss possible power supplies and ways to switch the power.

Uno style Arduinos can handle upto 25mA or so output current without too much stress - that's upto
1/8 of a watt of power at most.  Other Arduinos have smaller limits (a few mA).
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wolframore

You have exceeded the current capability of the Arduino by powering a heating element directly through it.

The Arduino is a Microcontroller not a power supply.  The chip can only take 0.2A MAX and the pins are only guaranteed for 0.02A each.

20 ga kanthal has about 0.8 ohms per foot. If you ran 6 inches at 5v you get about 12.5 AMPS enough to kill a lot of things.  (I = V/R)

To do this correctly I would recommend using a relay rated for the current you intend to be pushing as well as power supply that can source it.  That would be the easiest solution. It is possible to switch this with solid state such as a Darlington or a power MOSFET but that would require more work.

Bad Boys Race Our Young Girls But Violet Generally Wins - Get Some Now :) - ELI ICE man

PillPollen

Hi! Thank you for your answers!

Sorry for not being more informative. This is how I have done it.

5v power > arduino > ~3v LED (blink blink) = works
5v power > arduino > 0.1mm Kanthal wire @ ~1cm length = shortcuts

If I take this same 0.1mm wire at about 1cm length and connect it (with jumper wire) to a 9v battery it works without any problem. I have not tried connecting the arduino to the 9v battery because I don't have such connector.

But do you mean that I need to build some sort of I relay? The kanthal wire is meant to light a candle so it does not need to be any super special. Just give the kanthal some electricity and I am fine hehe. But it must come from a microprocessor because of the timing event.

wvmarle

You need some kind of power driver for your kanthal wire (whatever that may actually be - please provide a link to the datasheet of the thing), which in turn is controlled by the Arduino. Common solutions are a MOSFET transistor or relay.
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wolframore

#5
Jul 28, 2019, 06:37 pm Last Edit: Jul 30, 2019, 09:30 pm by wolframore
Shorter the kanthal less resistance and more current would flow thought it.

You need to separate the power from the Arduino using a relay to turn the kathanl on while using a 9v to power the kanthal. Does that make more sense?  Arduino cannot directly power this.
Bad Boys Race Our Young Girls But Violet Generally Wins - Get Some Now :) - ELI ICE man

wvmarle

If that's a standard 9V PP3 battery it may still not work as such a battery can provide only a couple hundred mA on a good day...
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

Grumpy_Mike

Quote
The kanthal wire is meant to light a candle so it does not need to be any super special. Just give the kanthal some electricity and I am fine hehe
Some electricity is way way more than an Arduino can supply from its output pin.

Would you think you could turn the starter motor of a car with two 9V batteries? After all you can get 18V from two 9V batteries which is more than the car battery supplies.

What you need to know is that there is more to electricity than just voltage, there is current as well. You can not get enough current directly so you need a FET to switch an external supply.

TomGeorge

#8
Jul 30, 2019, 11:08 am Last Edit: Jul 30, 2019, 11:08 am by TomGeorge
Hi,
Welcome to the forum.

Please read the first post in any forum entitled how to use this forum.
http://forum.arduino.cc/index.php/topic,148850.0.html .
Then look down to item #7 about how to post your code.
It will be formatted in a scrolling window that makes it easier to read.

Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?

Thanks... Tom... :)
Everything runs on smoke, let the smoke out, it stops running....

PillPollen

Hi! Thank you all for the answers! Regarding a schematic: https://www.arduino.cc/en/uploads/Tutorial/ExampleCircuit_bb.png

But instead of an LED I use a 1cm 0.1mm kanthal wire (hooked to jumper cables).

So you guys suggest a relay. Something that the ardunio will power up and then this something will flow current trough the wire. Now I am not great at electronics, could you pinpoint me in the right direction?

Grumpy_Mike

#10
Jul 30, 2019, 05:41 pm Last Edit: Jul 30, 2019, 05:42 pm by Grumpy_Mike
Quote
So you guys suggest a relay.
No, I said:-
Quote
need a FET to switch an external supply
Quote
Now I am not great at electronics, could you pinpoint me in the right direction?
https://learn.adafruit.com/rgb-led-strips/usage
You need only use one FET and replace the LED strip with your resistance wire.

You still need an independent power supply. We could tell you the voltage if you would be more forthcoming about this wire you have. What is its resistance and how much heat ( in watts ) do you want it to produce?

wolframore

Yes I suggested a relay because it would be simple for a beginner:



  Most of these are rated for 5V @ 5A... Most batteries won't put out that much current but if in doubt you can always get relays with higher current rating:  10A, 20A, 50A... etc.  The 5V is the control voltage which is good for use with Arduino... so get one that says 5V.

 Just replace the light bulb with your kanthal. 
Bad Boys Race Our Young Girls But Violet Generally Wins - Get Some Now :) - ELI ICE man

TomGeorge

Hi,
Do you have a DMM to measure voltages around your project?

Can you please post a picture of your project so we can see your component layout?

There are many gauges for Kanthal Wire, can you post a link to spec/data sheet of the wire you have please?
Can you post a link to where you bought the wire please?

Can you tell us your electronics, programming, arduino, hardware experience?

Thanks.. Tom... :)
Everything runs on smoke, let the smoke out, it stops running....

wolframore

#13
Jul 30, 2019, 09:23 pm Last Edit: Jul 30, 2019, 09:32 pm by wolframore
Resistance of Kanthal is pretty straightfoward... here's a comparison at 0.1mm diameter popular heating wires. 

38 AWG Round Kanthal A1 Wire - 0.10mm diameter, 55.8Ω/ft, 183.1Ω/m

38 AWG Round Nichrome 80 Wire - 0.1mm diameter, 42.23Ω/ft, 138.52Ω/m

38 AWG Round 316L Wire - 0.10mm diameter, 28.5Ω/ft, 93.5Ω/m

just for comparison:

38 AWG Copper wire - 0.10mm diameter, 2.13Ω/m
of course he would be using a heavier GA wire... most likely 22 or 24 or better.  But it's nice to see comparisons.
Bad Boys Race Our Young Girls But Violet Generally Wins - Get Some Now :) - ELI ICE man

MarkT

If I take this same 0.1mm wire at about 1cm length and connect it (with jumper wire) to a 9v battery it works without any problem.
That I seriously doubt.  Tried measuring the battery voltage when you do this?  Suspect you've shorted out the battery too.  Bet the voltage is more like 2V than 9V, and the battery heats up too...
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