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Old 07-12-2012, 07:57 AM   #16
rksylves
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Join Date: 07-28-09
Location: Melbourne, Florida
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Yes, I did.

I use temperature probes purchased from Maverick that they use on their ET-73 units. They had no porblem supplying the temperature curves for the probes.

I also use a simple 12v, 10 cfm fan that's probably too big as I've never seen it go over about 50% powered.

The software reads the temperature in the cooker (via the probes) and compares it against the set temperature. It then determines the percentage of the error between the two. It then will turn on the fan via the PWM output by that error percentage. As the error decreases, the fan slows down. That way there's almost no overshoot.

I used a FET to control the fan. The PWM output is connected to the gate. There's a 1K ohm resistor connected between the drain & +12v. There's a 100uF 25v cap between the source and ground. The fan connects across the cap with a connector.

The idea is that the PWM output turns the FET on & off based on the calculated error percentage. When the FET is on, the cap charges and powers the fan. The lower the duty cycle the lower the average voltage for the fan, hence it slows down. The cap will 'average' the PWM pulses to create sort of a variable DC for the fan.

Pretty simple really.

Photobucket seems to be having some issues at the moment. As soon as they fix it, I'll post some photos of it in use and some internals.

Russ
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