Fan Control w. RPM measurement

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Hi Guyzz

I'm going to make a fan control , for moving hot air from my fireplace in the summerhouse living room , to the bedroom.

The fan is a : Papst 8412 N/2GLE (12v dc / 37ma)

As i would like to read the tacho signal , i need a highside driver , and was thinking about using this one (i have some home) , as i see it i can just connect it to the AVR OCR pin , maybe via a 470 ohm just for protection.

http://www.ortodoxism.ro/datashe...

What frequency should i run the pwm at ??

I can see that a high frequency might be better (22khz outside the audible range) , but can a 3 wire fan do that ??

The fet has a 100us turn on , and a 150us turn off time.

I'd prob be using a M8 , and have 2 NTC's (one in each room , no need to move air if the temp is the same) + IR control for the fan

Edit: Saw some hints in here
http://www.analog.com/library/an...

And it also gave me the hint with the pullup on the tacho line :oops: ... At first there was no signal , but after a 10K pullup to 12v "It's Alive" :lol: :lol:

Also some tips about PWM and Tacho readings , as the tacho doesn't get power all the time , when pwm'ing.
But i'm not sure if it's a problem if i use a highside driver , and a pullup on the tacho line.

Any hints/tips are welcome ....

/Bingo

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Quote:
Papst 8412 N/2GLE (12v dc / 37ma)
Papst makes good fans ... but isn't this one a bit small for the purpose ?

Nice high-side driver. But not for PWM-ing, since Ton and Toff are in the 100 us'
And IF it could do the job, it would ruin the tach-signal.

How about this: AVR (is there for IR) generates pwm-signal that drives logic-level N-ch FET. Fan, a small inductor, a small capacitor, and a small schottky in the drain --> voilà: an SMPS. DC on the fan, dogs will be gratefull ;)

Now for the RPM: use a high-pass filter (blocks DC), feed it as inputclock for Timer0, and to do it really decent: clamping diodes to Vcc and Gnd of the AVR.

Nard

PS My brother asked me to build exactly that, also to transport warmth from livingroom to bedrooms. But when I told him that it the fan-duct would also act as an acoustical duct, he ...uh .. withdrew his plan ;)

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tricia, and Ulyana. You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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Remember to save a pin for your CO sensor...

JC

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DocJC wrote:
Remember to save a pin for your CO sensor...

JC

It's a closed furnace

/Bingo

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I know this is an old thread, but I didn't want to open a new one. Could anyone expand on the schematic aspect of what Plons described? I'm guessing the buck type smps and the clamping diodes like Gnd ->|- IN ->|- Vcc.

Thanks

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What i ended up doing was:

Connect the OCRx pin to an nfet , the nfet to a pfet , and then a 10uF cap on the pfet out to gnd , and the fan across that. I basically converted the pwm output to variable DC. Else the tacho would not work.
I connected the tacho pullup to the Atmel VCC , and the signal to an interrupt pin. I had to disable the interrupt for a period after getting the tacho signal (debouncing). And then reenable it approx 15..20 ms later.

I'm quite sure i had 100nF from the tacho line to gnd.

The schematic is "lost" (blushing) ...

/Bingo

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Thanks for the reply. I'm trying with an upside-down buck converter with n-fet on the low side. I hooked it up to the scope and it doesn't really filter too much, I'll have to try it with different components, maybe a different topology.