Current preset circuit.

Thread Starter

rahul411

Joined Feb 19, 2018
260
I forgot to read the valuable comments on this thread as i didn't received any notification in mail and got busy with the studies yesterday. Sorry for that.
The situation i have is the power source ( suppose 12V, constant voltage) will be connected to some kind of circuitry which will then connect to heater. But the thing is the heater coil will be variable, meaning at the output i have some coils which i want to heat but if the current is not limited the heater coil will get heated too fast and might melt down. So i want to have a control over current to avoid destruction of heater coil. Coils of different resistance is there.

Also i want to know which is better, to vary the current or the voltage to limit the power to the heater?
 

MrChips

Joined Oct 2, 2009
24,161
I forgot to read the valuable comments on this thread as i didn't received any notification in mail and got busy with the studies yesterday. Sorry for that.
The situation i have is the power source ( suppose 12V, constant voltage) will be connected to some kind of circuitry which will then connect to heater. But the thing is the heater coil will be variable, meaning at the output i have some coils which i want to heat but if the current is not limited the heater coil will get heated too fast and might melt down. So i want to have a control over current to avoid destruction of heater coil. Coils of different resistance is there.

Also i want to know which is better, to vary the current or the voltage to limit the power to the heater?
It doesn't matter whether you vary the current or voltage. The two are interrelated by Ohm's Law.

What you need is a thermostat. If you want to avoid catastrophic failure caused by over temperature, use a thermal cutoff switch:

upload_2019-8-19_11-36-0.jpeg

 

AnalogKid

Joined Aug 1, 2013
9,351
I would start with simply varying the output voltage of the supply and see if the results are satisfactory.

IF the load always is nothing more than a resistive heater, then another option is a pulse width modulation (PWM) circuit between the supply and the heater. Same end result as a linear voltage regulator with way less wasted heat. Low cost on ebay, there are many to choose from because of their use in various DIY automotive modifications.

ak
 

Thread Starter

rahul411

Joined Feb 19, 2018
260
I would start with simply varying the output voltage of the supply and see if the results are satisfactory.

IF the load always is nothing more than a resistive heater, then another option is a pulse width modulation (PWM) circuit between the supply and the heater. Same end result as a linear voltage regulator with way less wasted heat. Low cost on ebay, there are many to choose from because of their use in various DIY automotive modifications.

ak
can pwm be used for inductive type loads to heat?
 

AnalogKid

Joined Aug 1, 2013
9,351
Depends. All inductors have resistance, so the question is which is dominant in the inductor's total impedance. Does it have a part number/vendor, or is it a custom/hand would part? Do you inow it's inductance and resistance?

ak
 

Thread Starter

rahul411

Joined Feb 19, 2018
260
Depends. All inductors have resistance, so the question is which is dominant in the inductor's total impedance. Does it have a part number/vendor, or is it a custom/hand would part? Do you inow it's inductance and resistance?

ak
Custom hand wound one, but I'm not sure about the inductance part but resistance will be between 3 to 20 ohms.
 

TeeKay6

Joined Apr 20, 2019
572
Copper wire
You can control the heat produced by a coil (or any length) of any metallic wire by controlling the amount of current flowing in the wire. You can control the amount of current either directly (current limiting) or by controlling the voltage applied across the wire (end to end). Devices & circuits are available to limit current, regulate (hold constant) voltage, or both. Usually, controlling voltage is easier to understand. To create a design you need to know what is the resistance of the heating wire and how much current is needed to heat the wire to the temperature that you desire. Don't forget that the same heating current flows through the wires that connect your power source to the heating element; those wires need to have low resistance (large diameter) compared to the heating element so that most of the heat developed is in the heater, not the connecting wires.

Voltage controllers can operate via PWM and other schemes. Yes, the controller of a soldering station can obviously control the heat of a soldering iron...or a suitable heating element that replaces the soldering iron.
 
Top