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Author Topic: Testing a 220VA Wall Socket?  (Read 399 times)
Pepe Lapiu
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February 27, 2019, 09:47:52 PM
Last edit: February 28, 2019, 12:37:39 AM by frodocooper
Merited by Artemis3 (1)
 #41

Not that... It depends how strong your fan is. if it moves the others by airflow alone, they generate electricity. A generator is the same thing as an electric motor, more or less. If you pass current, it makes the axis rotate. If you rotate the axis fast enough, it generates current. You don't want current flowing back into your controller board/psu.

Good to know. I'll just make sure no fans are driving other fans by adjusting the speeds appropriately.

Problem is you need feed back rpms to the controller so it doesn't complain, at least until Braiins OS is ported to the S15.

That's not really a problem. Faking an RPM signal is easy. Or I can always pluck out one fan's petals and leave it running just as an RPM reporting fan.

And the reason why they use fans in push/pull is because that's the most efficient way of moving air around a case. Every fan you buy has a CFM rating. But that rating is in open air with no restrictions.  Once you add restrictions like ducks, elbows, fan grills, filters, and congested cases, the actual CFM goes way down from the rated one.

For example with water cooling it was once believed that radiators with multiple thin fins and thicker radiators would do a better job at cooling the system. Problem is, when the fins are too close and the radiator is too thick, the fans struggle at pushing air throught them. One remedy was to install thicker fans, faster fans, or have them going in push/pull configuration. And still, lab testing showed that thinner radiators with wide spacing between the fins actually performed better.

In other words, the more restrictions you have, the less effective and the more noisy your fans are. That's why it's beeter to have a set of fans pushing air in and an other set pulling air out. And tgat's why I think removing the grill on the exhaust side will help the airflow and help reduce the noise.

When you buy a fan, don't look just at the RPM and CFM rating. They only tell part of the picture. The static pressure is actually more important than the CFM rating. Static pressure is the fan's ability to push air throught restrictions. Kind of like water pressure versus water flow. Sadly, very few fan makers post the static pressure numbers.

But essentially, when you have two fans in push/pull, that basically doubles the static pressure while the RPM remains the same. So a lot more air gets moved.
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