Need help with hand held heat gun project

Capt. Quirk

I am trying to control a hand held heat gun (110vac, 1500watt) with an SX or Propeller. I want to replace the 3 position switch that turns the heat gun on low, high, or off with something that I can control electronically.

Currently when the switch is toggled to the low power position, it passes power through a 3 amp diode, and then splits into 2 parts. One part supplies the motor, and continues to a heating coil unit. The second part goes directly to a 2nd heating coil.

When the switch is toggled high power, it just by-passes the 3 amp diode. Then supplies full power to the part 1 motor and coil assembly, and the 2nd heating coil unit.

I would like to supply some sort of NCO square-wave to better control the heating coil temperature output, and separate the small dc fan motor from the heating coils. There are a few diodes on the motor, that I assume is rectifying the ac to dc for the motor.

In order to control the fan and heating coils, can I control it using only 110ac? Or do I need to rectify the AC and control it with DC power? Either way, what shall I use to control the power to the motor and heating coils? Mosfets? I alredy have thermocoupes to measure the temps.

I am going to use this with either a toaster oven shell or just a Pyrex glass bowl to solder surface mount ic's.

Thanks

Bill M.

Franklin

For the heater take a look at "lamp dimmer" circuits. You will probably have to beef them up a bit to handle 1500W though.

Phil Pilgrim (PhiPi)

Make sure that the motor is controlled solely by a hand-operated button, not started or stopped by the Prop. Also make sure that the heating coil cannot be powered unless the motor is running. This pair of caveats serves two purposes:

1. It keeps the heat gun from burning out due to overheating, and

2. It prevents the unit from turning on automatically -- perhaps when you're not present -- and starting a fire.

-Phil

kwinn

@Capt. Quirk.
The simplest method is to control the ratio of the number of AC cycles that are on and off. In the past I have used a '4017 to count AC cycles and turn a triac on with the "0" output pin, and off with the "1 to 9" output pin. This was a form of PWM with a 6Hz frequency that provided 10 levels of heat. Using a micro to do this provides a lot more flexibility, although using a prop is a bit of overkill.

Capt. Quirk

@ Franklin: That was a good idea. I found a 1500 watt circuit in a AppNote. Only about $5.00 in parts

@ Phil: Based on your advice, I am planning to incorporate the original heat gun's rocker switch to create a baseline motor rpm, and then a second button that will activate an SX to run the heat and cool down profile. After the profile has ended, the SX will idle or sleep until the rocker switch is used to turn off the fan. Thank You.

@ Kwinn: I found several 4017 circuits and an AppNote TB094 (that used a small Pic). I am definitely headed towards a Propeller controlled circuit. I know it's overkill, but it's just another project to help me learn the chip. After I am through with the SX, I am hoping to learn more about the Propellers counters, and use it to keep track of the AC frequency and control the heat levels.

For now, I am planning on using the 1500 watt circuit, with the temperature output controlled with a 200k potentiometer by a R/C servo for now. An SX will control the fan rpm and temperature via the 200k potentiometer. For simplicity I am planning on using a type K thermocouple with a max6675 CJC chip.

The plan is to make a KISS surface mount oven, where the most expensive part will be either the microcontroller or the LCD, and enter it in the Schmartz Board contest they announced today.

kwinn

For controlling a heat gun a prop is be overkill imho, but for an smt oven controller it is a great choice. Learning about the prop while doing this is a bonus. Good luck with it.