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Thermostat with pic and pwm fan

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Melkor

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Hello there.
I have this project of mine to buld a thermostat using a pic 12F683.
The purpose of this project is to ventilate and cool a cabinet where I have my router, switch and UPS.
The cabinet is roughly 40x40x40 cm and I have a 12 v 12 cm fan 0,36 A.
My problem is, how do I power this setup? I need to have a dual supply, 12v and 5v.
I was thinkin several option:
Two china made adapters, to power 5v and 12v. I really would prefer not going that way, More wasted heat and we all know the quality of those.
I have some adpaters from old phones that give 5v. I could then charge pump it to near 12v. I rather like this one but I have no idea how to build it.
Hacking the UPS and take the 12v directly from the battery to power the fan but then how do I power the pic? A 7805 is out of the question because of the wasted heat at that voltage difference. A switching regulator is a better option but I don't have any.

Any advice, ideas?
 
I've been doing heating, air conditioning, and electronics for 40 years, and I've never needed a microprocessor to run a cooling fan. What is it about this job that requires so much brain power?
 
It's an excuse to learn how to program PICs :)
I know it could be done with discrete components but my goal is to evolve my PIC knowledge to robot building, and I needed this done (40º C inside the house, I'm affraid to know how high it gets inside the cabinet).
 
Oh.

A 7805 will waste 2.5 watts to run the fan. Is that really out of the question compared to the waste power that's already in the box?

www.roman black.com makes some fantastic voltage converters in switching style. Go look there!
 
Why do you want all that complex technology? Just put gaps at the top and bottom of the cabinet, the heat created by the router and what not will create a natural convection inside the cabinet hot air will go out of the top gap and cool room air will come in from the bottom. My cabinet is only slightly smaller than yours, I have a router a wireless access point and a cable modem in it, all of them get scorching hot (not exactly state of the art) The air temperature inside the cabinet isn't even 10 degrees F over ambient. Just for reference the actual metal case of my router is 120 F under normal conditions. The only thing ventilating my cabinet is a slot above and bellow the front door that are each 25mm long and about 3mm high.
 
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Since the 12V runs the fan (if not, get a 12V fan), I would start with a 12V supply. Use a LM7805 regulator to get the 5V to run the PIC (only need a few mA).
 
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Why do you want all that complex technology? Just put gaps at the top and bottom of the cabinet, the heat created by the router and what not will create a natural convection inside the cabinet hot air will go out of the top gap and cool room air will come in from the bottom. My cabinet is only slightly smaller than yours, I have a router a wireless access point and a cable modem in it, all of them get scorching hot (not exactly state of the art) The air temperature inside the cabinet isn't even 10 degrees F over ambient. Just for reference the actual metal case of my router is 120 F under normal conditions. The only thing ventilating my cabinet is a slot above and bellow the front door that are each 25mm long and about 3mm high.

Well, that's how it's been working until now but starting a few weeks ago when it started to get warmer I've been having some strange disconnects.
 
Have you measured the cabinets air temperature?
 
I just put a thermometer in, it's reading 55 ºC (about 130 F) with outside ambient temperature at 35º
 
Can you provide the full dimensions of your enclosure and the size of the air vents and their location? The air temperature in the cabinet should not be that high. What all do you have in this cabinet?
 
I have the project for the cabinet somewhere, maybe tomorrow I'll post it.
Inside I have a DSL router, Wireless Access Point with the antenna outside, a 800VA UPS and a 24 Port 10/100 Switch.
The cabinet has holes in the lower part, drilled with a 6mm drill and some 5 mm slits on the upper part.
 
Since the 12V runs the fan (if not, get a 12V fan), I would start with a 12V supply. Use a LM7805 regulator to get the 5V to run the PIC (only need a few mA).

Look back at Mike's post. I have an old Tandy (Radio Shack) AC adapter sitting here with a 12 Volt 1 Amp output. I use it to drive a 7805 to power my little PIC programming board. A PIC only draws a few mA. The 12 Volts has more than enough power to easily drive a few 120 mm fans. Additionally a standard 12 volt fan as found in a PC does not need a regulated 12 Volts. Run your fan(s) off the wall wart and power the PIC off a 7805. That is what I would think about doing.

Ron
 
How many 6mm holes, and how long and how many 5mm slits are there, and where are they in relation to one another?
 
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