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DC power adaptor votages

peter999
peter999 Posts: 7,102 Forumite
Part of the Furniture 1,000 Posts Combo Breaker
edited 13 December 2010 pm31 8:35PM in Techie Stuff
I'm looking for a cheap small 12V Dc power supply to replace the faulty one my cordless drill charger.

I've been looking in 2nd hand/charity shops etc.

Dc power adaptors that use these standard Dc power plugs you get on small electrical items: http://www.maplin.co.uk/Module.aspx?ModuleNo=43084

I bought a 2nd hand one, that is labelled 13V == (solid line, with dashed line underneath), which I think means it is 13V Dc output.


I measured the voltage on the Dc output plug, it reads 20V Dc.
I'm wondering whether this is possible or if item is faulty.

Can you have no load voltage at 20V Dc ?

peter999


Ps: I checked my 6V DC mobile phone chargers, they read what they are labelled as, 6V Dc at output.
I checked a 3V Dc adaptor, it gives 2V Ac on output (not sure what that's about) !
.

Comments

  • I'd say that's quite possible with an unregulated adaptor. Try measuring the voltage with a load on it - say a 5w car bulb if you have one.
  • fwor
    fwor Posts: 6,845 Forumite
    Part of the Furniture 1,000 Posts Name Dropper
    As kwikbreaks says, it's almost certainly unregulated. Even if you use a regulated one, I would not rate your chances of success.

    Typically a cordless drill charger incorporates circuitry to monitor the state of charge of the battery pack and adjust the charging current accordingly - a generic 12V power supply won't.

    Incidentally, the most common (in my experience) cause of failure in drill battery pack (particularly NiCd pack) chargers is that the cells degrade due to internal crystal growth, and gradually pass more and more current, causing the charger to overheat. Replacing the charger does not solve the problem in this case.
  • peter999
    peter999 Posts: 7,102 Forumite
    Part of the Furniture 1,000 Posts Combo Breaker
    fwor wrote: »
    Typically a cordless drill charger incorporates circuitry to monitor the state of charge of the battery pack and adjust the charging current accordingly - a generic 12V power supply won't.

    Incidentally, the most common (in my experience) cause of failure in drill battery pack (particularly NiCd pack) chargers is that the cells degrade due to internal crystal growth, and gradually pass more and more current, causing the charger to overheat. Replacing the charger does not solve the problem in this case.
    I don't think there is anything special about the original charger.

    It labelled as 12V == 220mA (solid with dotted line underneath)

    The charger battery base has a diode inside, so I assume actual adaptor output is AC voltage & it is rectified to DC.

    The adaptor should then regulate to 220mA max current.
  • paddyrg
    paddyrg Posts: 13,543 Forumite
    It's almost certainly as it is unloaded, unregulated chargers are way cheaper than regulated ones :-)
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