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Topic: heating coil module 12v (Read 1 time) previous topic - next topic

raschemmel

Quote
A thermistor sensor, 10k ohm.
What is the operating temperature range for the heater ?
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

Alaaj

Great write-up by DVDoug!

I would add one thing:  Ways of driving the Power Resistor(s) or NiChrome wire [hereafter referred to as the Heater or Heating Element], since in most cases an Arduino output will NOT be able to source or sink the required current AND/OR if the voltage supplied to the Heating Element is greater than +5.

OK, one other thing: How about using a thermistor to implement a control loop.  Use the Arduino to turn on the heating element until, via the thermistor, a target temperature is reached.  In which case, turn the heating element off.  And, as DVDoug suggested, have two "set points", one slightly higher than the other such that, the heater is left on until the temperature reaches the first set point, then turn it off until the temperature falls to the second set point.  The difference between the two temperature set points, is called the "deadband" and causes a hysteresis effect.  The smaller the deadband, the more often the heating element will cycle.

In the attached schematic, a MOSFET drives the Heater, and the Thermistor is the upper part of a voltage divider, and the voltage at H3 varies with temperature.  Since you didn't divulge the target temperature (in the box), you will need to select an appropriate thermistor, OR if it's a temperature so high that no thermistor will suffice, then consider a thermocouple or other means of determining the temperature.

The values and Jameco part numbers are merely suggestions. Choose a "Logic Level" MOSFET that can easily handle the current required to drive the heater.  The suggested RFP12N10L is a 100V device that can handle up to 12Amps (though, a heat sink may be required at currents that high).  I selected it because it's low cost (only 79 cents), yet has some beef to it.

 R1 is to limit current in cases where the MOSFET's input capacitance is high enough to cause an inrush current that might damage the Arduino output.  1/4 Watt is fine.

actually yes that's what I was thinking about, considering the maximum degree(38), minimum degree(36), and the difference between the actual air temperature (a) and the setpoint temperature. (s)

where above the max, off, level 0% or a-s>= 1 degree
below the min on, the highest level 100%  s-a>= 1 degree
if  a-s< 1 degree  on, level 25%
if  s-a< 1 degree  on, level 75%
if a=s on, lever 50% which should be the default at start.

and yes, I am using thermistor 10k ohm as a temperature sensor,
will the NI-chrom wire going to work in this case ?

thank you.

Alaaj

What is the operating temperature range for the heater ?
between 36 and 38 degrees

Alaaj

Uhmm, no. If at full load it's 50W it's 25W @ 50% duty.

Instantaneous power is given by:
P(t) = U(t) x I(t)

Average power is:


For a 50% duty cycle that's the same as T = 1, Ton = 0,5 and Toff = 0,5. Filling that in gives:


And that's why we use RMS (although mostly for sinusoidal AC). So you could still use:
Pavg = URMS x IRMS

For the above PWM for example with 5V and 10A:



And 3,54V x 7,07A = 25W again :)

I thought it's 30 watts at 5 volts, Thank you for your explanation!!
could you please explain me the RMS? how can I apply it?
Thank you

 
Is that an INDUCTION heater designed to heat ferrous objects like steel bars or bearings by magnetic eddy currents? If so, it won't heat air.
Induction Heater
Ummm I don't know if its only for objects,

raschemmel

Quote
between 36 and 38 degrees
Why aren't you using a DS18B20 sensor ?
They are much easier and more accurate than a thermistor.
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

outsider

#20
Mar 25, 2018, 01:32 pm Last Edit: Mar 25, 2018, 01:53 pm by outsider
25 X 25 is a square, you need another dimension for a box, and that is _______? Will the heater be on the bottom? Side(s)? Is the box top open? I'm thinking of those rubber mat heaters or Kapton strips of around 50 to 75 W and duty cycle switching with a 30 second or so cycle time.
EDIT:  I was thinking in inches, make that 20 to 30 W.

TomGeorge

#21
Mar 25, 2018, 02:51 pm Last Edit: Mar 25, 2018, 02:52 pm by TomGeorge
Hi,

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

What are you aiming to heat?

Thanks.. Tom... :)

Everything runs on smoke, let the smoke out, it stops running....

ted

#22
Mar 25, 2018, 07:50 pm Last Edit: Mar 25, 2018, 07:55 pm by ted
http://www.ef-uk.net/data/thermostat.htm
+ car cigar lighter + styrofoam

TomGeorge

#23
Mar 25, 2018, 10:39 pm Last Edit: Mar 25, 2018, 10:40 pm by TomGeorge
Hi,
My heater turned up this morning.
If I get a chance at work over lunch I'll see what it can do.

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

ReverseEMF

When you consider that a DC motor's power output is normally controlled via PWM there is absolutely no difference in replacing the motor with a power resistor.  
Except that a DC Motor will respond a heck of a lot faster than a power resistor -- so it's not exactly the same ;)
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septillion

Depends on what you're measuring ;) Or what you drive with the motor if we talk speed ;)
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