Fluctuating &strange fan RPM <960, @xxx, >690 etc.

  Ironman556 00:36 07 Jun 03
Locked

I bought an Akasa Nebula with manual speed controller last weekend. Put it in the front panel, all works ok.

Went into the BIOS (GA-6BXE mobo) the other day and noticed that CPU fan was sitting happily at around 4000 rpm, PSU at around 2500 rpm, but the new front panel fan was changing fairly quickly and giving 960, 2500, @(random number), >690 etc. as rpm readings.

It doesn't bother me that I don't know the RPM, my only concern is why I'm getting strange readings. Does it indicate somthing's wrong or should I just ignore it?

Front fan and one of the PSU fans are the same make/model. PIII 500Mhz, 384 MB SDRAM, Win 98SE.

  Ironman556 18:09 09 Jun 03

Seems to have stabilised a bit now.. moves between 650 rpm, 2000 and 3500 rpm still, but no strange symbols.

Just out of interest, can anyone tell me how the RPM is actually measured?

  BillEmm 18:39 09 Jun 03

There should be a temp sensor somewhere on your motherboard which controls this particular fan.

As the temperature increases the voltage (12v supply) to the fan is increased to make the fan run faster and thus increase the air flow - and vice-versa.

On some boards the BIOS has a switch which can be set to a time 'duration' for changing the fan voltage. For example if the value was set to 5 secs then the BIOS would only change the voltage to the fan every 5 secs thus allowing an averaging out rather than having the fan constantly changing in time with the temperature if no, or a small time value, was set.

Hope that make sense?

  Ironman556 23:45 09 Jun 03

Yeah that makes sense. Thanks. I'll tick the thread and ignore the readings in the BIOS now.

  DieSse 03:11 10 Jun 03

The fan speed is reported from a tachometer (rev counter) on the fan itself. This can go wrong even if the fan part is working OK.

  Ironman556 00:21 11 Jun 03

Assuming the tachometer's not working, is the fan stilll ok to use?

  DieSse 09:12 11 Jun 03

Well yes, but if you put some kind of "halt if the fan speed is too low" monitoring (if you can) - then clearly it won't work properly.

  Ironman556 00:17 12 Jun 03

OK. I don't have (or intend to use) anything to control the fan, so that shouldn't be a problem. It's in a PIII 500 system which isn't overclocked (so it's not critical that I know the speed), it was simply a bit of extra cooling. I just wanted to make sure it was ok to use.

Thanks for the responses.

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