I need a couple of power switches which can simultaneously switch on AC 230V and DC 12V power. I guess that would make it a DPST switch. I would assume that using a normal DPST switch (rated at say, AC 240V) wouldn't be classified as safe enough for this, and that I would need something specifically made for this purpose?
NoSp wrote in news: snipped-for-privacy@50g2000hsm.googlegroups.com:
Choose for current as well as voltage, low voltage stuff might have very high currents that can destroy switch contacts. Consider things that can make strong surges too, like capacitors or inductors on the equipment side of the DC switch. You might have to choose a higher current switch than you'd normally expect.
Lostgallifreyan wrote in news:Xns999BA884F1103zoodlewurdle@140.99.99.130:
Also, if isolation of the high and low voltage systems is critical (it usually is), maybe consider a high-volt low current switch for the mains, driving a mains voltage relay coil with heavier contacts for low volt DC.
innews: snipped-for-privacy@50g2000hsm.googlegroups.com:
That sounds like overkill for my purpose. I'm building an external enclosure for two hard drives which are totally independent of each other (they just happen to share the same enclosure and power supply) and I'd like to be able to switch them on/ off independantly. So instead of having a mains switch (for the power supply) as well as switches for each drive's power (I suppose cutting off one of the power lines will do) I'm thinking that two switches will do where one half of each switch is wired up to the AC whilst the other half is for supplying DC power to the drive itself. This way I can turn on the power supply and the drive I want all at once.
innews: snipped-for-privacy@50g2000hsm.googlegroups.com:
That isn't a good idea. The switches aren't designed for that application, and flashover between circuits can destroy the drives. Why not use a power switch, and another switch to select the drive? On second thought, selecting a drive by powering the other down can damage the drives, the controller, or both.
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I was afraid of something like that :-(
The idea is to prevent unnecessary tear, wear and noise from the drive I'm not using, which is why I thought I could solve this simply by routing each drive's power line from the Firewire/SATA bridge board (say +12V or whatever the drives use) to its own switch would solve this.
NoSp wrote in news: snipped-for-privacy@o80g2000hse.googlegroups.com:
Not overkill at all. That's exactly the kind of DC load I had in mind, hard drives have LARGE startup current surges. You'll probably want a decoupling or smoothing capacitor on the line too, which will increase that surge.
The simplest way is a mains 10 amp switch, the kind you might find in many junk boxes. Get one that has a high dielectric strength of at least a few KV for its insulators. Don't worry about using a big switch, it's better that you do, it's by far the easiest way you'll get decent separation between your 12V and mains lines. Get a double pole changeover type, wire mains in to common terminal of one pole, mains out to both the other terminals. 12V in to common terminal of the other pole, one drive to each of the other terminals. And slather the connectors after soldering, with plenty of VERY insulating goop, ideally an epoxy to make sure that only brute force with a hard object can make an easy electrical path reappear between your low and high volt lines.
Lostgallifreyan wrote in news:Xns999C5075F8648zoodlewurdle@140.99.99.130:
Forgot to say, it needs to be the centre-off type, or you won't be able to switch off the mains, or switch off both drives with the arrangement I described.
Why not just tell the drives to spin down?
That way you can locate them where you can't get at the switch.
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Lostgallifreyan wrote in news:Xns999C5116699C0zoodlewurdle@140.99.99.130:
Why not two switches, one for mains, one to switch power to either drive?
Gary Tait wrote in news:Xns999C5F22BBEA0wonkynillmailnil@142.77.1.194:
Because the OP asked for one.
innews:Xns999C5F22BBEA0wonkynillmailnil@142.77.1.194:
I actually asked about two switches. but not in the above configuration, but rather in a way that I can individually choose between powering up drive A, drive B or both. I've also been wondering if there was a way to NOT spinup the drives when power is applied, but instead have the computer (a Mac G4 running MacOS 10.4) send a "spinup" signal at will. Alas I've asked around but nobody seems to know about any such solution.
How do those professional rack mounted hard drive enclosures work with several drives? Do they just have a single power switch and spin up all drives?
NoSp wrote in news: snipped-for-privacy@w3g2000hsg.googlegroups.com:
"I need a couple of power switches which can simultaneously switch on AC 230V and DC 12V power. I guess that would make it a DPST switch."
Sounds like one switch to me... And you were right first time, you just overlooked the need for centre-off, and for high current contacts for the DC line, you DO need that to switch on a hard drive motor, unless you want to risk data loss and annoying early replacement. Don't forget the high dielectric strength and the thorough insulation of terminals...
Not sure about the spin switching, but that's a different thing entirely, that will be down to the signals your drives accept (firmware controlled), and the system that sends the signals. If you can find out what a PC sends as a wakeup signal to a suspended drive, you can emulate that signal on whatever system you want, probably.
innews: snipped-for-privacy@w3g2000hsg.googlegroups.com:
I didn't know about the high power surge of hard drive motors, so I learnt something new :-) As for the switch issue; a centre off switch won't do as I sometimes might want to use both hard drives. I could of course solve the whole issue with three switches: a) AC switch for power supply b) DC switch for powering drive A c) DC switch for powering drive B
... but not a very elegant and "pro" solution, which is what I'm aiming for. That's why I thought up this idea with just two switches (one for each drive, but simultaneously switching power to the power supply). To avoid any further misunderstanding, here's an illustration I've made:
I'm open for other solutions of course.
I've asked about this in Mac related forums in the past, but have received no replies. I know from experience that I can easily *spin down* a hard drive connected to my Mac (by dragging the drive icon on the desktop to the trash/eject icon), so I'm sure there's a command for "waking up" a drive as well. However, if software that takes advantage of this is available or not is a totally different question, and I'm no programmer :-(
NoSp wrote in news: snipped-for-privacy@q5g2000prf.googlegroups.com:
True, I forgot that bit. You could use two switches, DPST, but not centre off, but all that stuff I said about strong dielectrics and insulators on all terminals will apply, and route wires carefully so heat can't melt something to allow mains and DC to meet. The scheme you drew is the easiest to expand to more drives, too.
One drawback with it is that the power will switch on the moment you switch ANY switch, so unless you're fast the boot sequence will be done before all drives you might want enabled are powered up for that session. That single fact might make you want to revise the whole deal.
The drive on standby thing might be easier than it looks, but it's hard to know, software can easily be arbitrarily complex, way beyond need. In Windows, if a drive was active but shuts itself down with its own firmware controls, just trying to access it in Windows (which has no idea it has shut down) will wake it up with no problems, just an annoying moment of waiting. As your Mac OS can ask a drive to shut down, it might have just as easy a way to ask it to wake up. It seems very odd, if that is not so.
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