Fan speed monitoring

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I have a solid state relay controlling my pool pump and as the datasheet and the warning on the heatsink says, it gets HOT!

I have the unit bolted to the inside of the steel enclosure it is in and that box also gets rather warm to the touch.

I am going to put a small DC fan and ventilation on the enclosure to get some forced air cooling. It is a three lead variety, 12vdc with the yellow wire giving me a sinewave of various frequencies based on the fan speed.
I would like to have an AVR send status of the fan to my host pc.

Question(s) are/is:

Would it be easier to convert the sine wave to square wave with a zero crossing detector and feed that into the timer/counter of the avr, then the AVR send some value to the pc for conversion to fan speed.

OR

Should I look for a 'simple' fan control IC that can do the monitoring for me and output a digital value to the AVR instead?

If the IC has some degree of programability where I can change the fan speed if I wanted to, or speed alarm points even better.

Suggestions welcome

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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Do you want to monitor the speed just as a failsafe - is it running? Or, do you want to control the speed?

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Good questions,

Originally just is it running. Simple, just convert the sine wave to a DC component and use the AVR's comparator.

Then my inner freak kicked in and I thought about measuring the fan speed, and if I was doing that with a dedicated IC, I guessed that controlling the speed was a feature of the IC.

Primarily just run/fail. The PC software can be tailored to do just about anything so the controlling is more eye candy for me than anything else. This is a home project.

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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You can use comparator and input capture. Do a timer reset on one edge and capture on the other., If the timer overflows, then its not turning. Appropriate timer scale is important.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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I'll keep this in mind, thanks Jim.

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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Is the tach output really a sine wave? Most three or four wire fans have an open collector output that gives two pulses per revolution.

There's actually a standard for such fans, but the server appears to be down at the moment: http://www.ti.com/tool/cc-debugger

While looking for the document above, I stumbled across and app note from TI on doing fan control with an MSP430: http://www.ti.com/lit/an/slaa259...‎

When I was looking at doing fan control for a work project I did find that there are some analog fan control ICs that provide automatic temperature-based control, but I don't recall seeing any that had failure detection. There are also SMBus fan controllers that offered a lot more programmability and had fault outputs, but I didn't have any luck finding those for sale in small quantities. I'll be curious to hear if you can turn up anything better, but an AVR is probably your best option here.

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Yeah, for now I am just going to turn the fan on with the control signal. I will make something to turn on an LED while the fan is spinning to indicate that it is running and mount that to the front of the enclosure.

I'll post a photo when I am done

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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While you are at it, you might as well add an NTC or as DS1820 and a red flashing LED for an over temp alert.

JC

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Maybe at sometime. Right now I am just going to get the fan running. The monitoring stuff was my inner freak kicking in.

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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Hi Jim,

I would just use a retriggerable monostable. Too slow a frequency and the output will oscillate.

Cheers,

Ross

Ross McKenzie ValuSoft Melbourne Australia

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have fan failure as DEFCON 2
have overtemp as DEFCON 1

whilst having a fan might help with temperature, it does not necessarily prevent overtemp. Thus it is good to have a failsafe.

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or, make or buy a water cooled heat sink, cooled by the pool water, and put that on the SSR :)

on the other hand, you'll probably find enough cheap fan controllers on eBay, which are used to cool down PC's.

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Well, I drilled the holes for the fan, mounted it, and connected it all up and it does indeed cool everything down.

Problem is the little fan spins so fast, and the metal cabinet makes for a speaker enclosure that you can hear it upstairs!

I am going to have to get a simple fan control IC after all, or try out Smileymicros fan control project in his book with a few modifications ;)

First I shall go search for a dedicated ic.

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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jgmdesign wrote:
Problem is the little fan spins so fast, and the metal cabinet makes for a speaker enclosure that you can hear it upstairs!

Have you considered some of those noise isolating fan mounts like:

http://www.quietpc.com/afm03b-group

- S

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Jim,

Is this fan going to be bringing in air from the outside environment? If not, all you are going to do is move a lot of hot air around within the box - there has to be a way to carry the heat out of the box.

If you are going to add inlet and outlet ports allowing outside air to circulate through the box, what are the environment particulars. If outside, you will need to protect or shelter the entire box from inclement weather.

It seems to me that you might need an external heat sink with the SSR mounted directly to the heat sink, in order to get the heat out of the box entirely. Get a finned heat sink with the fins placed vertically and let convection cool the fins. Then if the fins get too hot, turn the fan on and have the air blow over the fins.

By using a heat sink, you keep the water resistance of the box in tact. Simply cut out a rectangle slightly larger than the SSR, mount the heat sink squarely over the cut-out, applying a sealant between the heat sink and the box. From here, simply mount the SSR directly to the heat sink, using thermal grease for enhanced heat transfer.

Again, using this method, if you do need a fan for cooling, it will only be when the heat can't be extracted from the inside of the box by the heat sink fins by convection.

Always let nature do the hard work for you.

I've been there and done that, many, many times on Asphalt plants - some of the harshest environments on electronics.

By the way, did you know that the average intelligence of a given Asphalt worker is such that, if you gave him a steel ball, he would more than likely break that steel ball with a rubber mallet?

You can avoid reality, for a while.  But you can't avoid the consequences of reality! - C.W. Livingston

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Enclosure is a poorly made NEMA 1 steel enclosure mounted right next to my brand new breaker panel witl a three inch piece of 3/4 inch conduit between the two for the high voltage wires. The location of this is the basement of my home. There is a hole at the bottom of the enclosure where he fan is mounted for air intake and three holes at the top for warm air exhaust.

I thought about the rubber mounting rings. But I still like the idea of the motor control as well. Looks like I will be calling Digikey.

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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Looks like the winner right now is the TC664 from the evil empire.

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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But the good old 555 should be able to detect underspeed/stall? My bench supply even uses it to regulate fanspeed based on temperature.

Or two comparators, one to convert the sine to a square, feeds a simple RC network and a comparator to turn on a LED or whatever. By using the open collector feature of most comparators you can create a quick discharge and slow charge of the cap. You probably even could use a BJT or two.

For some reason I find it more fun to use old-school stuff on these simple things. Throwing in an MCU is so old and boring nowadays :)

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I agree. At the same time though I don't have the time to play like I used to.

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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Colin O'Flynn did a really nice fan flowrate failure detector a while back. It was in Circuit Cellar, though I don't recall which issue, and circuitcellar.com doesn't appear to be loading for me right now. He, uh, did use an, uh ..... pic for his project.

I have the whole project in PDF format, but I don't know what the rules are about uploading here. I'll provide the report file which give good detail, and if the Atmel gods approve, I can upload the rest of the pdf files (schematic, code etc.)

It's basically using an NTC to measure air temp changes, so airflow. Much better than rpm.

Attachment(s): 

Dean 94TT
"Life is just one damn thing after another" Elbert Hubbard (1856 - 1915)