I am building a restive heater, with a fan blowing against nichrome coils. I understand I need to get a decent amount of current to get the resistive wire to heat up. I would like to get a current of about 1A from the Arduino 5V power supply. What is the simplest way of getting a constant current of about 1A through the resistive branch of the circuit?
Using a NPN resistor (PN2222) I was able to achieve a current of about 50mA which is quite short of the desired 1A. I had the 5V from the Arduino UNO to the collector, and a 5V PWM signal to the base. I have an open circuit with the opening of the circuit from emitter with a 220ohm resistor to ground. I arbitrarily had 1k ohm resistor to the base, and a 220 ohm to the collector. I complete the circuit by attaching my digital multimeter to the open circuit.
I am in the elementary steps of this project, and do not have much information beyond what I have provided. I am only testing the current output from the transistor until I have a considerable amount of current through (it does not necessarily have 1A, I just find it to be convenient)
Power is calculated as Voltage x Current, so 5V and 1A is 5W (not much heat). If you put a resistor in series with your Nichrome wire you'll reduce the total power, the voltage will be divided proportionally to the resistance and the part with the most resistance will dissipate the most power.
You can also calculate power as V2/R or I2 x R. (I represents current.)
If you really want constant current, you need some form of constant current driver. Maybe one that's designed for use with LEDs can do the job, they're cheap and easy to find. Then you just switch the constant current driver on the low side with a logic level MOSFET from the Arduino.
You will need a separate power supply for this, no way the Arduino itself can supply the required current.
MorganS:
What is "the Arduino 5V power supply"? If the Arduino is powered from a USB cable, you're limited to 500mA.
If you're powered from 12V on the barrell jack, then you can't get 1A either. 500mA will probably cook the Arduino 5V regulator.
Yeah I do not want to burn up my Arduino in the process.
Whats a good choice for a power supply at this point? I do not need *much heat just enough for a DHT11 sensor to pick up on a noticeable temperature change. This sensor will be located pretty close to the resistive coils. I plan on making a base out of some wood, and mount the resistive wire to screw terminals to prevent the nichrome from burning other electronic components.
WattsThat:
And at least 2 feet of nichrome wire for a typical 1 amp charger. The spec for 26 awg Nichrome60 is 2.67 ohms/ft.
Seems doable for beginner like myself, I have 25ft of wire so I am prepared for mistakes. Thanks!
Part of my assignment requires serial communication, if I am using an alternate power source, i.e. 5v/1A phone charger. How might this affect connecting the Arduino uno to my laptop via USB as well?
DrDiettrich:
You need a power supply that can provide the desired current, and a transistor that can switch that current. A logic level MOSFET will be easy to use.
I was certainly considering use of a MOSFET. I didn't have any laying around for my convenience so I ended burning up a couple low spec transistors which only convinces me more to use a MOSFET .. nothing too major just enough to increase the current across the resistive branch to get more watt dissipation.
Part of my assignment requires serial communication, if I am using an alternate power source, i.e. 5v/1A phone charger. How might this affect connecting the Arduino uno to my laptop via USB as well?
It should not affect communications in any way. Unless it is a crap quality charger.
When you get your n channel, logic level mosfet to turn the heater on and off, the common or negative side of the heater supply 5v charger gets connected to the GND terminal of the Arduino in order to complete the circuit for controlling the mosfet. If the charger used is one of those dollar store specials, it could cause problems with usb comms due to leakage current. More importantly, a cheap-o charger could be a significant safety hazard to you.
The bottom line is that it is highly advisable to avoid bargain chargers simply because they’re not safe. They’re not going to have proper current limiting voltage fold back so any overload could create another hazard, which could be just letting the smoke out or worse, a fire hazard.
which only convinces me more to use a MOSFET .. nothing too major just enough to increase the current across the resistive branch to get more watt dissipation.