I traded godfoot a waterblock for a couple 120mm x 35mm Nidec Beta V fans to run on my radiator. They are from the TA450DC family Model # A31256-10A. They are 3 blade metal framed monsters that are very loud and move serious air (unsure of CFM, but they rock).

The fans are rated at 12V and 490MA.

The fans are way too loud at 12V. I first tried the 7V trick and got a really good balance of noise and airflow, so I can still go that route. However, being a control freak, I wanted even more control. I hauled a 5W 100Ohm rheo out of my parts box and tried it out.

Very strange results! The fan spins full speed with the rheo wide open, as I start to turn the rheo the fan slows as it should, until I get to about 1/16 of a full turn at which point the fan stops momentarily and then begins spinning in the opposite direction. The remainder of the rheo turn seems to have no effect on the backwards spin action of the fan.

I am completely stumped. Any thoughts?

To clarify, I know that this fan should rightfully have at least a 6W rheo (probably a 10W), but I have been running a 6W sunon off one of these rheos for 2 years without a problem.

Is it that part of the rheo travel right before shut-off?

Have you taken any voltage measurements? You've got to have voltage on the ground side for that to happen.

Quote: Originally Posted by Zennzzo Is it that part of the rheo travel right before shut-off?

No, I mean I quite literally barely start turning it when the fan stops and reverses.

Quote: Originally Posted by Hojo Have you taken any voltage measurements? You've got to have voltage on the ground side for that to happen.

The ground is hooked directly to the ground pin in on one of the 475 W Enermax molexes. So that isn't it.

Also, the rheo works fine with another fan.

This is probably because there is a IC (integrated circuit) that regulates the fans RPM. Because you are running this little chip undervoltage, it has the potential to do strange things.

Odds of you ruining it are close to zero, because your not giving it excess voltage, but you're gonna have to live with it I guess.

Do the fans themselves have sensors on them?

Those 120mm Nidec Beta V's should have some sort of impedance protection on them that ironically enough, is deigned to prevent that, I know what you are talking about, see them a lot on older Compaq servers. Do they really have a lot of airflow, like more than a Panaflo H1A?


i gotta go with Hawkeye on this one, but i really think that the impedance control may be messed up. I know the Comair Rotron fans have impedance control on them.

Quote: Originally Posted by BigAkita Do the fans themselves have sensors on them?

Yes, usually HALL effect transistors, uh its too late for me to explain.

Case fans are not just "fans", they have lots of electronics in them to regulate their speed and such.

I can't remember on those particular fans Putwig, but do they have a grounding spot on the frame?
Reason I ask is because the 150mm Comair-Rotron fan sitting next to me here has a spot to screw in a ground screw right on the frame itself.
If they do, you may try grounding them that way.

Edit: I believe in the research I did on them, the CFM is around 150CFM...... but it's been a while.

I didn't see a grounding spot. Just the two terminal connectors 12V and ground. 150CFM sounds about right, they really put out.

Maybe it is the variable voltage confusing the fans IC or IP.

As I said, the simple 7V trick gave a great noise to airflow result .......... I will likely just do that in the end.

Weird though.

u should prob just thro them in the bin and get the new reserator water cooling kit from quiet pc (http://www.quietpc.com/uk/watercooling.php) there the dogs and make very little noise as they r fan free.

^^ To quote Kwigon Jin while tracking through the sea on the Gungon home planet "Theres always a bigger n00b" ^^

Glad you found theres a good medium form the problems. Any particular reson why they were so loud? Never heard of the make/model myself...sounds like somthing industrial grade.

It is extremely unlikely that putwig (one of PR's original H2O gurus) will ever invest in an inferior water-cooling product than what he already has......... not to mention this thread hasn't been touched in about 7 months.
Thanks for reading through the older threads though, at least we know they aren't being ignored.

Quote: Originally Posted by nev_payne Any particular reson why they were so loud? Never heard of the make/model myself...sounds like somthing industrial grade.

They are industrial fans as they came out of a rather large color proofing (thermal transfer type) system from where I used to work. I believe they also have the slotted-style 3 fins that are a bit louder than normal fins.