please advice an EE idiot on using chargers

[Steve Simpkin]

(07-30-2022 10:30 AM)teenix Wrote:  Best not to use chargers connected to any Woodstock calculator.

The Classics and 67 should be ok as long as the charger itself is ok. If it is faulty then it may cause problems.

Probably the best rule of thumb is charge all batteries externally to the calculator.

cheers
Tony

Agree with Tony. When in doubt, consult the warning in the Owner's Handbook for your model regarding use of the AC charger and (good) batteries.

Per the HP-25 Owner's handbook (Page 102), "Attempting to operate the HP-25 from the ac line with the battery pack removed may result in damage to your calculator." A similar warning is in the manuals for the Woodstock series (HP-2x), Spice series (HP-3x), HP-65 and HP-67. Because of the risk of batteries that could fail open or have a poor connection, it is also not worth the risk to charge batteries in the calculator for any of these models. Models without Continuous Memory are not likely to be damaged if their power switch is Off, but why take the risk. Models with Continuous Memory have the batteries connected to the CMOS memory chips at all times so they can be damaged even with the power switch set to Off.

The Classic series models have a different AC charger design that has a regulated supply for the calculator and a separate unregulated supply to charge the batteries. Classic models without a card reader (HP-35, HP-45, HP-55, HP-70, HP-80) can be safely operated without the batteries installed. The HP-65 and HP-67 are a special case because the card motor and sense amplifier are connected to the batteries. Per their manuals, don't operate those two "Classic" models without good batteries in place.