Fan Control w. RPM measurement

Log in or register to post comments
Go To Last Post
7 posts / 0 new
Author
Message
Bingo600
Bingo600's picture
Level: Raving Lunatic
Joined: Sun. Apr 25, 2004
Posts: 4086 View posts
Location: Denmark
#1
Posted by Bingo600: Mon. Mar 24, 2008 - 10:05 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

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

Tags:

Learning and Information, General Electronics
Top
Plons
Plons's picture
Level: Raving Lunatic
Joined: Tue. Nov 1, 2005
Posts: 7037 View posts
Location: Hilversum - the Netherlands
Posted by Plons: Mon. Mar 24, 2008 - 11:06 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

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

Top
DocJC
DocJC's picture
Level: 10k+ Postman
Joined: Tue. Dec 11, 2007
Posts: 13284 View posts
Location: Cleveland, OH
Posted by DocJC: Tue. Mar 25, 2008 - 03:04 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

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

JC

Top
Bingo600
Bingo600's picture
Level: Raving Lunatic
Joined: Sun. Apr 25, 2004
Posts: 4086 View posts
Location: Denmark
Posted by Bingo600: Tue. Mar 25, 2008 - 03:43 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

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

JC

It's a closed furnace

/Bingo

Top
frakk2136
frakk2136's picture
Level: Wannabe
Joined: Thu. Jun 4, 2009
Posts: 77 View posts
Posted by frakk2136: Mon. Aug 24, 2009 - 08:32 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

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

Top
Bingo600
Bingo600's picture
Level: Raving Lunatic
Joined: Sun. Apr 25, 2004
Posts: 4086 View posts
Location: Denmark
Posted by Bingo600: Wed. Aug 26, 2009 - 02:41 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

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

Top
frakk2136
frakk2136's picture
Level: Wannabe
Joined: Thu. Jun 4, 2009
Posts: 77 View posts
Posted by frakk2136: Fri. Aug 28, 2009 - 06:31 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

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.

Top