Odd Battery Voltages

Hi all,

Earlier I needed to do something with my graphing calculator. It only gets used very rarely so I wasn't surprised when it didn't switch on. I immediately suspected the batteries, but they were fine. All the same, I slipped in a brand new set. Still nothing. In the battery compartment they have an arrangement of 4xAAA cells in series to give a 6V supply. However, on checking the voltage from 'head to toe' as it were (from the first '-' to the last '+') I got a reading of minus 3V instead of the plus 6V I'd expected. Checked all the connections and the probes in the right sockets and whatnot: all fine. I'm sure I've had this issue before with a different battery appliance in the dim and distant past but can't recall what the cause was. It's like it's too far in the back of my mind to resurrect any more. :( Can anyone assist, please?

You are not checking from "head to toe".

You might think you are, but you are not.

Gareth.

You were right! However there's still something not right about the continuity of the battery caddy. Unfortunately I can't go any further tonight partially due to the stupid modern prods you get with the absurd amount of shrouding which is making it impossible for me to 'get right in there' as I would like (and these prods don't have the removable shrouds). So it'll have to wait til tomorrow when I can get some more suitable ones. :(

Take the socket from a PC power supply IDE disk power connector without the plastic part. Solder a short piece of piano wire to one of the connector sockets. Fits nicely over typical DVM probes and can fit into small places for probing battery sockets.

I have a few vintage battery power radios that have multiple voltage take-o ffs (taps) at various points within the battery case. One (uses six (6) D-c ells) has the 9V end-to-end, a 3V-from-two tap, and a 1.5V tap for the inte rmittent dial-light. Another using four has taps at 6, 3 and 1.5. It would not surprise me if your calculator had similar conditions.

Clean the contacts. Check for broken or cracked connections. Check each ind ividual cell for the correct voltage (and polarity!!! - ask me why!) prior to installing. I expect this is a mechanical issue in any case.

If you have something like a flashlight to test batteries, that is best as some will give 1.54V, but not enough current to do anything.

Once upon a time, I came across a set of very, very cheap (from China) knoc k-off duracell (small D deliberate) batteries, D-cells in 4-packs. Of the eight batteries, two were "packaged" backwards - the button at the negative end, the flat on the positive end - one in each package. So, I ask.

Peter Wieck Melrose Park, PA

Hi,

If the calculator happens to be a HP 50g, make sure the batteries can supply at least 100 mA without a lot of voltage drop. When initially switching on and checking the memory, it needs that much. Also check if the 3V lithium cell for memory backup is still good. If not, there can be some memory corruption issue, in which case pressing the hard reset key with a pin should clear it.

Dimitrij