HP 45


I would like to make my HP45 operable. The calculator is OK, but I need a replacement battery. Can anyone point me in the right direction? I appreciate any assistance the group can provide.



Hello Rolf,
Those battery packs are always on E-bay. here is a link to one of the offerings.... http://cgi.ebay.com/NEW-BATTERY-PACK-FOR-HP-35-45-55-65-67-80-CALCULATOR_W0QQitemZ5855556744QQcategoryZ11713QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Best regards, Hal



If you bother about buying on ebay or if you don't want to spend too much money, there is the alternative of making a pack by yourself. Recently I got a 45 and a 67 with both packs gone. Since the 67 is still in workable condition (except for the rubber wheel of the card-reader) I wanted to have a replacement pack for it and decided that the easiest option is to make one myself. I took 3 NiCd cells and connected them in series, some good tape holding the entire thing (including contact-plates) together. With some appropriate wiring and 2 additional plates with the right aspect-ratio and bend into a V-shape along their longest side (all fixed to the "pack" with tape) it makes a working battery-unit. The NiCd cells are somewhat too short to fill the entire battery-compartment but with some "filler" (could be anything suitable even some folded paper) the pack's contacts remain in place. Be sure however that the pack's internal contacts as well as the contacts connecting it directly to the calc's terminals are ok. Although the 45's manual does not indicate that a pack has to be in the calculator when it is run on the AC line (the 67's handbook explicitely does to prevent calculator dammage) I would NOT recommend operating the 45 without a pack inside (which is in fact what you do when the (internal) wiring of the pack is faulty).


I would NOT recommend operating the 45 without a pack inside

The 35 and 45 can safely be used on AC power without a battery! The power adapter has three pins from which one is ground, one feeds the battery pack and the third powers the calculator. As long as the power plug is connected to the calculator the battery is actually disconnected from the internals of the device.

This is not the case for later models where (as in older TIs) the battery pack is used to regulate and limit the external power. As far as I know, calculators with a card reader (65, 67, 97) need a battery a avoid damage to the card reader electronics!



From what I remember of the schematics :

Classic models without a card reader (35, 45, 55, 70, 80) can be safely used on the adapter with no battery in place. When the adapter is plugged in, the battery is disconnected from the calculator.

Classic models with a card reader (65, 67) can damage the card reader sense amplifier chip if connected to the adapter with no battery fitted. This is particularly true of the 65 (the chip was re-designed in the 67).

Woodstock, spice and sting models without continuous memory should not be connected to an adapter with no battery in place. It is unlikely to cause damage, but I wouldn't risk it.

Woodstock, spice and sting models with continuous memory MUST NOT BE CONNECTED TO AN ADAPTER WITHOUT A BATTERY IN PLACE. Sorry for shouting, but this is the most common way to ruin the (HP custom) RAM chip and possibly other parts.

Topcat models without continuous memory (91, 92, 97, 97S) will not be damaged if connected to an adapter with no battery, but the printer and/or card reader may not work properly. There is a circuit built into these machines to limit the supply voltage under these conditions.

Topcat models with continuous memory (95C) must not be connected to the adapter without a battery in place. The same protection circuit as in the other topcats is there, but it only works with the power switch 'on'. There is a very real risk of damaging the always-powered RAM chip if connected to an adapter with the machine turned off.


One thing I forgot to add (for the legal people out there)

The information was offered in good faith, but obviously I am not responsible if you damage a calculator by following it.

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