# Constant Current

I am needing to supply a constant current of around 1.6A to a nichrome wire using the arduino as a controller. I want to be able to send a command or flip a switch and it go from having no current to a constant 1.6A current for, around, 10 seconds and then shut off.
What do I need to do this?

Depending on the voltage you require there are a number of switching supplies designed to control current to a series of LED's

I would look at eBay for constant current and / or LED driver.

I mention the voltage because the supply you require must be capable of outputting enough voltage to generate the current you need at the maximum resistance of your nichrome wire (i.e. when it is hot)

Why are you not using a constant voltage into the heater element? Since nichrome resistance increases
with temperature, using a constant current could lead to unstable behaviour or thermal run-away, and constant
voltage is much easier to achieve with a single adjustable voltage regulator. Find an adjustable regulator with an enable input?

I can see the value of starting with a Constant Current. Apply a Constant Voltage across a wire, and max current will flow at first, then as the wire heats up, it's resistance goes up, which means, with a Constant Voltage, the current goes down. Thus, the wire will not heat up as fast.

With a Constant Current, the wire heats up faster, then when the Constant Current Source reaches a target voltage, the control mode switches to Constant Voltage. Or, even becomes Constant Current whenever the wire resistance drops below the point where the target voltage is dropped across it.

That's if heating the wire quickly is goal.

A Linear device that would do this nicely is the L200CV. It can be "programmed" to run at a constant voltage, and switch to a Constant Current mode when the load resistance drops below a certain point. But, it's Linear, so not very efficient. It will need ample heatsinking at those currents.

Switch Mode Voltage Regulators with Current Limiting would do the trick.

I would hunt around on eBay using a search term such as: "Switch Mode Voltage Regulators with Current Limiting Adjustment"

Like, maybe, this one: Adjustable Automatic Step-up&Down Power Supply Voltage Regulator 5-30V~0.5-30V 3A

I’m guessing you don’t really need “constant current”… That would be unusual for a heater… Look up the Ohm’s-per-foot (or Ohms-per-meter) for whatever wire gauge you have. Then calculate the resistance for whatever length you have.

Once you know the resistance use [u]Ohm’s Law[/u] to calculate the voltage required to get 1.6A through the resistance. (V = Current x Resistance)

DVDdoug:
I'm guessing you don't really need "constant current"... That would be unusual for a heater... Look up the Ohm's-per-foot (or Ohms-per-meter) for whatever wire gauge you have. Then calculate the resistance for whatever length you have.

Once you know the resistance use [u]Ohm's Law[/u] to calculate the voltage required to get 1.6A through the resistance. (V = Current x Resistance)

What about when the wire heats up...and the resistance goes up? Wouldn't the math be better if it targeted the resistance of the wire at a particular temperature?