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I have old Bosch PSR12 driver/drill that all NiCA are dead. I've modified it successfully to work as Corded after removing batteries and connecting 12V 1.5A (220v) adapter. The drill works but when I push for full speed it stops, So I guess the adapter is just not enough. The Battery box has a 12V 1.2aH label on it.

What adapter should I get ? Doesnt 1.2aH equiplivent to 1A ?

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No - aH (More commonly Ah since M. Ampere is a proper name, and hours are just hours) is Amperes*hours and is a quantity of charge. 1.2 Amperes for 1 hour, 2.4 amperes for 30 minutes, 0.6 Amperes for 2 hours - all = 1.2 Ah.

NiCads (when happy) are capable of providing very large currents - so you'll need a 12V adapter with a bit more current capability to be able to run your drill at full speed as a "corded" drill. Cut and try is the best I can suggest - i.e., find a 2.5A or 3A 12V DC supply and see if it will run the drill at full load or not - or else find a large 12VDC battery (such as a car battery) and a DC ammeter and see what the drill actually uses for current when under full load. A car battery charger is often the cheapest high current 12VDC supply available, unless you have an old computer power supply with a high current 12V section. The only trick there is that a 12V (nominal) lead acid battery (as from a car) actually operates at a slightly higher voltage than a 12V NiCad battery pack...

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  • Thanks. eBay offers 100-220V to 12v 6A. Its probably what I need ?
    – Chura
    Commented Jan 22, 2014 at 20:14
  • It would probably be adequate.
    – Ecnerwal
    Commented Jan 22, 2014 at 21:33
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    If going the testing route be sure to actually be drilling something as you test. It will draw more when there is resistance, and usually a LOT more when stalled.
    – Grant
    Commented Jan 22, 2014 at 23:06
  • Even old battery powered screwdrivers like at least a 2amp (5v DC) wall wart for conversion to plugin style.
    – Wayfaring Stranger
    Commented Jan 23, 2014 at 15:06
  • Ofcourse it will be tested with resistence. I've ordered from eBay a 20A 12v adapter. for this price it worth a shot.
    – Chura
    Commented Jan 23, 2014 at 20:07
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I know that a 20A 12v adapter sounds fairly hefty, in comparison to the nominal values of a battery powered drill - but its only about 240W.

A decent mains hammer drill will be rated at 500 - 1000W or even more.

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