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AC/DC Adaptor for external hardware

Discussion in 'General Hardware' started by janetb, Mar 18, 2010.

  1. janetb New Member

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    When my scanner stopped functioning properly and I was told I should buy a new one, it turns out that all it needed was a new power supply/switching adaptor/AC-DC adaptor (different names for the same thing).....! The same has happened now with my external hard drive. Many hardware manufacturers seem to supply their products with cheap adaptors.

    My ext. HD required a 12V-2A adaptor. I have received conflicting views on whether a stronger 12V adaptor (e.g., one which can handle 5A) would be OK--or even better. One technician says it could burn out the HD by over supplying, while the more-reliable-sounding technician says that the HD knows to take only how much it needs and that a stronger one is sturdier, will be working with less stress, and will probably last longer....The 5A one appears to me much better made and has a lot more seals of approval from various international boards.

    1. Is there a danger in using the 5A adaptor?
    2. Would a power surge affect the HD differently with the different adaptors?

    Many thanks for any help,
    Janet
     
  2. AsRock

    AsRock TPU addict

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    To many amps will fry it. Normally you can just look on the AC\DC adapters and see what volts and amps are and get ones as close as possible to what they say. Some AC\DC apapters can be opened and some ( rarethese days ) is a fuse that has failed.
     
  3. xrealm20

    xrealm20 New Member

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    @ Asrock -- that's not entirely accurate --

    Having an adapter that CAN supply 5 amps won't be a problem on a device that just requires two. Think about this - your house normally is wired with 15 amp circuits and you plug in an alarm clock that uses .5 amp. It doesn't cause any problems, because the device will only pull the required amount needed. Or since I know someone will say that's AC current - the PSU in most computers can deliver say 30 amps over 12v rail - and your system draws 10 amps. No harm there.

    Keep in mind that most power supplies are more efficient at about 50% load.

    As long as it's the same voltage and at or over the required amperage draw, any power adapter will be fine.
     
  4. newtekie1

    newtekie1 Semi-Retired Folder

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    The Amp rating is a maximum, not how much is actually sent to the drive. Similar to how an internal power supply is rated. The 12v rail on a power supply might be rated for 18A, but that doesn't mean it sends all 18A to the devices connected to it.

    With external adaptors, you only have to match the voltage and make sure the Amp rating is the same or greater than the adaptor you are replacing.
     
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  5. dr emulator (madmax)

    dr emulator (madmax)

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    i agree just make sure you get a switchmode psu, as the older transformer type are not really suitable for harddrives, as they can give out far to much ac, instead of a smooth dc that a switchmode can

    how do you know what a switchmode psu is ?
    well it will usually say something like ac input 100~240v 50/60hz and will be fairly light in weight
    wheras a transformer type will be quite heavy

    obviously do a bit of research first, cheap stuff is more likely to break
    the more amps it has the more expensive the supply will be :rolleyes:
     
  6. Fourstaff

    Fourstaff Moderator Staff Member

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    Get a quality one, (ie one that gives more amps) they can be useful in more ways than to only power your harddrive.
     
    Last edited: Mar 18, 2010
  7. strick94u

    strick94u New Member

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    ohms law it takes 1 volt to push 1 amp through 1 ohm of resistance
    therefore you could use a 12 volt 100 amp ps and if the resistance is 2 ohms you will only use 2 of those amps.
     
  8. AsRock

    AsRock TPU addict

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    My point is if the device can only handle 2 amps and your allowing the AC\DC adapter to send a max of 5 amps you are puting the item at risk.
     
  9. janetb New Member

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    Well, 4 out of five replies confirmed what I was pretty sure of....:)....! Thanks!

    AsRock
    Thanks for your efforts, but I think you should be careful about giving out incorrect info,...:)....You might want to look into how switch adapters work....The adapter does not send out 5A, rather, it allows the device using it to draw a max of 5A.....

    xrealm20
    I also thought about the example of at home. A 1000W heater can be on the same line as a 60W lightbulb. It needs to be a high-amp line for the heater, but it's fine for the lightbulb as well....:)....
     
  10. janetb New Member

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    PS From 2A to 5A, they were all the same price, in spite of the fact that the 5A one was much more substantial in terms of materials (heavier cable, 3-pin instead of 2-pin)!
     
  11. AsRock

    AsRock TPU addict

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    Ok, i missed the switch part and i do not know any thing about that. But in the past i have used another adapter which was only 250ma higher and it fried the item and both adapters were the same other wise and to be honest this was about 8 years ago and that was with a scanner and it happened when i started to use it...

    A switch adapter is just one with AC\DC changeable right ?.
     
  12. MN12BIRD

    MN12BIRD

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    switching power supply means it uses transistors to switch the AC power on and off REALLY fast to emulate DC power. It has to do with the internal design of a power supply not really like a "switch" in the way you might think of it. Most PC power supplies are switching but I think a few high end ones use some different designs.

    Make sure the type of power is correct. AC or DC. If DC make sure the polarity is correct. Pos to Pos of course! The amperage can be as high as it wants. It needs to be at least what the device drawing the power needs but it can always be more. Just as long as it's not less. Like a few people said the device only pulls what it needs from the supply. The supply can have 80 Amps available and yet a device might only pull .5 Amps when it needs it.

    The fact something fried when you had a PSU with .25 Amps too much might have just been a coincidence.
     
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  13. AsRock

    AsRock TPU addict

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    Cheers but it was a old ass scanner well would be now. Old Trust one ( cheap brand ). Maybe with the old adapter for it pulled the extra power and fried as the circut could not handle it ?. Hence why the original adapter failed as it could not give the power required ?.
     
  14. janetb New Member

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    AsRock

    The main thing these adaptors do is to bring the voltage WAY down--from either 110V (US) or 220V (Europe) down to either 12V or 9V or etc. Scanners and HD's usually (always?) need 12V. If this spec was any higher than required, it would fry the item (usually instantly). Like plugging an American 110V appliance into a European socket (which is 220V). You can't have a higher-than-required voltage. So with these computer external devices, there are several specs you need to check: AC or DC, the voltage, the amperage. The first two must be exact, while the third requires at least the specified amount. [Someone please correct me if I am wrong....]
     
  15. LeeM New Member

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    Everyone seems to be saying voltage should be correct, amp could be higher. What if voltage required is 4.5 and I have an high quality switching 110~220 @ 5v with 2Amp? Please advise: would .5v over would make a difference? I know it is too late to post here at this late date. Still if any of you would care to drop a note, I would appreciate it.
     
  16. Sinzia

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    Depending on the device, it should be ok as long as its not a high-draw (high amperage) device.

    4.5 V is an odd voltage so finding an adapter may be problematic.
     
  17. LeeM New Member

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    Sinzia

    Thank you. It's not a high amp device. All along I have been working on what I was told that if you need a dc adapter, say for 4.5v @ .6a and you have an adapter lying aroundwith same polarity that is 12v @ .3a, it is okay to use it. The logic being 4.5 x 600ma = 9 x 300ma. This forum kind of threw me off. You cleared it up.
     

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