on 3/11/03 9:08 AM, Mark Jay Mirsky at [EMAIL PROTECTED] wrote: > Dear Ken, > > Your explanation is lucid but I am still puzzled. I understand the > importance of the device having the correct voltage. What exactly then does > the power adapter mean on a Syjet when it reads output "5v-1.0A 12V 0.75A" > ? Does the power adapter chose the voltage automatically?
Standard computer power connections (ie the four-pin power supply connectors inside your computer case going to each hard drive) utilize two different voltages: 12V and 5V. I'm not sure internally how the drive uses each of these voltages - perhaps someone else on the list knows. Inside the firewire drive/case that you have, the external 12V power supply voltage gets split/stepped down inside the case to provide the standard 12V/5V configuration to the internal drive. > On the Radio > Shack or Belkin devices that are sold as replacements, the user chooses > settings. In particular the amperage settings but there is no setting for > 2a, only 1.5 or 5 amps. How would you set it? And if your explanation that > the hard drive device draws the amperage that it needs, is correct, then > why did a previous response to my question warn that a device advertised as > supplying up to 5 or (I assume) 5 amp adapter by Radio Shack might indeed > damage the hard drive. The device will draw only the current that it needs. If your adapter is only rated for 1 amp and your device requires 2 amps, there are two possible scenarios: 1) The device >may< work, but work erratically, especially when it's doing something that requires the full two amps, or more likely: 2) The power supply would overheat, and possibly burn out (or blow an internal fuse in the power supply adapter). On the other hand, if the adapter is rated for 5 amps and your device requires 2 amps, it will only draw the 2 amps as it is needed; your power supply would simply have overhead that wouldn't be used. > When I look at the printer power adapters I become > even more confused, for there they list 30 volt outputs and 400mA to the > device. I understand from the careful reply of a member of the list that > printers use more voltage, but does the 400 mA here mean that the amperage > is much less for the printer than for say a old Zip drive power supply > which draws 1 amp? Keep in mind that total power = voltage x current. In the above example, the printer adapter is 30V x .4 amps, which is 12 watts. The Zip drive power supply, which is 12V by 1 amp also happens to work out to 12 watts, so both units can put out the same amount of total power, just a different ratio of volts/amps. To sum up, make sure you match the voltage of the original power supply. As for current, try to match the original or go to a higher amperage and you'll be OK. > The Macpower adapter sold by Other World Computer lists > +12V--2A as its output. When the Does anyone have a real experience of > these replacement power supplies? I recently purchased a Mercury Elite Firewire/USB drive from OWC and this is the same spec as the power supply that came with it. This would probably be your best bet. Good luck. -- Gregg -- SuperMacs is sponsored by <http://lowendmac.com/> and... Small Dog Electronics http://www.smalldog.com | Refurbished Drives | Service & Replacement Parts [EMAIL PROTECTED] | & CDRWs on Sale! | Support Low End Mac <http://lowendmac.com/lists/support.html> SuperMacs list info: <http://lowendmac.com/supermacs/list.shtml> --> AOL users, remove "mailto:"; Send list messages to: <mailto:[EMAIL PROTECTED]> To unsubscribe, email: <mailto:[EMAIL PROTECTED]> For digest mode, email: <mailto:[EMAIL PROTECTED]> Subscription questions: <mailto:[EMAIL PROTECTED]> Archive: <http://www.mail-archive.com/supermacs%40mail.maclaunch.com/> --------------------------------------------------------------- >The Think Different Store http://www.ThinkDifferentStore.com ---------------------------------------------------------------
