HP 21 battery charger



#3

Has anyone an idea where I could get a HP 21 battery charger ?


#4

If you can not find an original one, you may use a transformer that delivers 8 volt AC, at open circuit (I mean, with no load), and 200 mA. Polarity is not critical when working with AC. IT IS ABSOLUTELY NECESSARY THET RECHARGEABLE BATTERIES IN GOOD CONDITION ARE CONNECTED IN THE CALCULATOR WHEN USING THE AC ADAPTER. The batteries will filter the half-wave rectified AC and also work as a regulator/voltage limiter. USING THE AC ADAPTER WITHOUT RECHARGEABLE BATTERIES WILL RESULT IN EXCESS AND UNFILTERED VOLTAGE SUPPLY THAT WILL DAMAGE YOUR CALCULATOR. Other option is to substitute the rechargeable batteries with regular alkalines. That will power your calculator OK, but IT IS NOT POSSIBLE TO USE THE AC ADAPTER WITH ALKALINES. And always check proper battery polarity.


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