omarc

So, if I'm not mistaken, we can sum up by saying that slowing down DC controlled fans does not involve any significant reduction in energy consumption, while PWM speed reduction actually involves a reduction, which can be considered approximately proportional to the reduction in speed. Is that correct?

Thanks for your answer. In fact I was concerned primarily in estimating "power usage in terms of energy expended". In other words, I wanted to understand whether keeping the fans at low revs leads also to a (more or less) proportional reduction in actual expended energy. I seem to remember that in certain applications the reduction in speed (or light intensity) is obtained by applying a variable resistor that absorbs some energy preventing it from reaching the the motor (or the bulb), so that the actual total energy consumption remains the same, with the result that one thinks of saving energy and instead he does not save any. I wanted to understand whether such a "fake energy saving" takes place also in PC case fans.

I think I finally learned and understood that case fan speeds are usually controlled by varying the voltage (3pin fans) or by means of PWM (4pin fans). I also know, if my old school memories don't deceive me, that the expected maximum power drawn by a DC fan can be estimated by multiplying its design voltage by its design amperage (ex: 12 V x 0.3 A = 3.6 Watts). What I'm still trying to clearly figure out concerns the wattage a fan actually draws when operating at speeds below maximum. Is it correct, for example, to assume that a fan which draws 3.6W at maximum speed will draw 1.8W when running at half speed?

Now I have the information I needed. Thanks.

Thanks for your answers. I understand that an "old" device can obviously have worse performance than a brand new one, but this does not mean, I think (and hope), that an old device, just because it is old, can not perform its task properly. Especially when the device is a "first class" one which has not been working full time. Anyway, apart from such evaluations, my question is strictly related to the unit's technical specifications: can the HX650W be used with the latest ATX motherboards or is it mandatory to buy a new one?

Why? Are its voltages or connectors incompatible with current MBs?

While planning about upgrading my PC's basic hardware (MB+CPU+RAM), I am wondering about my 11 years old Corsair HX650W being or not being compatible with the latest LGA1200 motherboards. I searched for information but was not able to find any; which is actually understandable, given the age (of the PSU and also... mine). So I'm trying to ask here. Thanks in advance for any help. :]