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Battery pack of HP 25 calculator
08-06-2018, 09:04 AM
Post: #8
RE: Battery pack of HP 25 calculator
(08-06-2018 07:42 AM)Graan Wrote:  I have bought a HP 25C and when looking at the battery contacts in the calculator I dont see how it will be a good connection to the batteries. It was 2 NiMH batteries (GP cells 1300 mAh) inserted when I got the calculator. The connectors from HP 25C are 2 pcb studs with traces with some slodering. What I can see there is no good contact direct to the batteries.

Since this hasn't become absolutely clear here: There are the contacts inside the battery pack that connect to the plus and minus ends of the batteries, and there wre the two contacts at the bottom of the battery pack that connects to two tabs inside the calculator.

I assume you are talking about the connection between the two batteries and the battery holder.

This indeed can be a bit tricky, depending especially on the shape of the cells' plus pole. In a 29C I had no problem with usual button-top Sanyo/Panasonic Eneloops, while others recommend flat top cells. If your GP batteries don't provide good contact inside the battery holder you may try a different type. In any case I'd recommend NiMH cells (and a decent external charger with "intelligent" charge control). You may also remove a bit of the pastic inside the holder so that the batteries make better contact.

(08-06-2018 07:42 AM)Graan Wrote:  I connected the HP 25C to a power supply and it works fine, but when inserting the batteries the calculator does not seem to work properly.

What is "does not work properly" supposed to mean? Does it work or not?

(08-06-2018 07:42 AM)Graan Wrote:  The batteries are charged. Measuerd 1.3 V on battery.

That's the open circuit voltage. Which doesn't say much about the battery condition, not even the charge status. You have to apply a load to get a useable result. For instance you could connect a 10 Ohm resistor (1/4 W or more) to each of the two batteries and measure the voltage once again.

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RE: Battery pack of HP 25 calculator - Dieter - 08-06-2018 09:04 AM

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