Decouple fans and hard disks supplies

Hello respected engineers! I've built myself a frame where I've put six hard disks for a RAID5 system, and six 8x8 cm fans to cool them down (they live in a quite hot environment!). The PSU is a 500W one however I was concerned that the fans may pollute the hard disks' supply too much.. since they're motors after all! I've accidentally put a finger into a fan (what a pain!), and this stopped the fan for a moment and also caused hard disk errors, and thus convinced me even more that I need to decouple the fans' motors supply from the hard disks supply.

But how? I'm just a hobbyst when it comes to electronics, so I may even intuite correctly, but I won't be really sure of my thoughts. Right now, they are that I need some big inductors (with as low DC resistance as possible), some (big?) capacitors and maybe also a big rectifier as well.

The best scheme I've thought so far is to link all 6 fans together in parallel, then apply power through a circuit like this:

6 fans--*-ind-*-ind-*-ind-*-ind-*-ind-*-ind---diode------*-----PSU +12V | | | | | | | cap cap cap cap cap cap 6 HDs---PSU +5V | | | | | | | Gnd ----*-----*-----*-----*-----*-----*------------------*-----Gnd

of course in the above scheme I don't even need them to be six, it's simply the more the better, I just happened to have six of them on my bench (more or less a coincidence).

But now the big question: what's the right size of the caps, also to not overload the PSU at start? Will the diode really help the hard disks to not get some bad bad bad back EMF? Notice also that the wire that feeds the fans is AFTER all the wires that feed the hard disks (otherwise the voltage drop caused by the fans would have affected the hard disks). Yes, at least I know this. ;)

Is my scheme ok? What can I do to improve it? I really care about the hard disks and the data they contain!

Thank you very much, Mike

If you look at the label on the fans, it will show that the power consumption is only about 2W and that it only takes 200mA or so. That low power is why you went "ouch" instead of went looking for your finger..

Half a dozen of those aren't going to affect a 500W supply. They don't need further decoupling. If you did get data errors at the same time, it is more likely because you jarred the case or some other leads in your haste to remove your person from the vicinity of the fan.

They also don't generate *external* back emf. The electronics in the fan (yes there is some, unlike "conventional" motors) makes sure of that.

If you really care about your data, have a proven* backup strategy. *ie including trying recovering the backups periodically...

You are quite right that excessive temperatures is one of the big killers of disk drives - up there with mechanical jarring caused by such things as attempted finger amputation. The answer to a hot environment however, is to make things hotter, not simply shift the hot air around faster..

Can I suggest sheets of thick aluminium as a starting point? I use aluminium floor plates, cut to size - the same length as a drive but a couple of inches wider. Bolt the drive to a plate, leaving a 2" wide strip along one edge. Bolt one, or two, standard processor HSF assemblies to the strip - but fit a suitable Peltier device between strip and heatsink. I use 65W ones. Alternate the side you bolt the drive on, so you have a staggered set in the complete assembly.

The Peltier device will pump the heat from the drive and plate into the heatsink. Typically the plate will be well *below* ambient temperature. The HSF will be well *above* ambient, so will transfer heat into the airflow very nicely. The Peltier device, of course, also has to be connected to a DC voltage source (eg 12v). It is, strangely enough, that the HSF is much hotter than ambient that makes the whole system so effective...