Weird 42S battery problem

[pdicamillo]

When my 42S wouldn't turn on, I put in a set of new 357/303 silver-oxide batteries, and at that time it worked normally. However, a day later, again it wouldn't turn on. I tried again with a new set of 357 batteries from a different manufacturer, and the same thing happened, so there appears to be a problem with the 42S. What's weird is the result I found when I measure the voltages of the batteries in the sets that no longer worked. In both cases, two of the batteries measured around 1.5 volts (normal), but one measured only .5 volts. I'm puzzled as to why all three batteries wouldn't drain uniformly. I thought it might be a bad battery, that's why I tried again with different batteries. Any idea what might be going on here?

[Geoff Quickfall]

so normally the batteries drain uniformally.

Which battery drained starting with 1 (+ve-ve), 2 (+ve-ve), 3 (+ve-ve).

Was it 1, 2 or 3 or was it random, that is 1 and 3 or 1 and 2...?

If it was consistent, both 3, then for some reason the battery at position three is shorting independent of the other two and the on/off switch. Suggests that the contact tab is bridging the +ve and -ve components of the battery at the -ve end of battery 3.

I cannot see anything internally causing a drain of one cell independent of the other two unless:

-as stated above.

-two defective batteries.

Especially with the two remaining cells tested at 1.55 volts. Your battery tester, does it test under load or just voltage?

Geoff

[grsbanks]

Try with LR44 alkaline batteries rather than silver oxide.

The battery chemistry does make a difference.

[Geoff Quickfall]

Interesting, never had a problem with 357 silver oxides. What specifically would cause a battery drain on silver oxides but not alkaline in the same physical container?

Not contradicting, just never heard of this before, or encountered it.

Geoff

[grsbanks]

I'm afraid don't have an explanation, my knowledge doesn't stretch that far. However, I have experienced this with my own HP-42S. Alkaline batteries will last for months, literally, while silver oxide batteries lasted me a couple of days.

[John Keith]

I have use 357 Silver Oxide batteries in my Pioneers and Voyagers since the '80s, never a problem. I do change them out every 2 or 3 years out of an abundance of caution, but they always read close to 1.5V when I remove them.

John

[Geoff Quickfall]

Same here John, do you test them under a load or just the voltage?

I am interested in my question about which position the cell occupied and if it was the same position that died a second time. Probably at the contact end of the anode of the cell and the calculator spring.

Geoff

[pdicamillo]

When I took the batteries out of the calculator to measure them, I didn't keep track of their relative positions. But I'm trying again with 357 batteries, and I'll do that this time. I measure the batteries with a digital multimeter, and this time I measured the voltage across the calculator's battery terminals. When I first put the batteries in it was 4.6 volts. Thirteen hours later it's down to 4.2 volts. I used the calculator for just a few quick, simple calculations. It looks like the calculator will die again soon, and then I'll try the LR44 alkaline batteries.

[jebem]

(03-17-2017 01:37 PM)pdicamillo Wrote:  When I took the batteries out of the calculator to measure them, I didn't keep track of their relative positions. But I'm trying again with 357 batteries, and I'll do that this time. I measure the batteries with a digital multimeter, and this time I measured the voltage across the calculator's battery terminals. When I first put the batteries in it was 4.6 volts. Thirteen hours later it's down to 4.2 volts. I used the calculator for just a few quick, simple calculations. It looks like the calculator will die again soon, and then I'll try the LR44 alkaline batteries.

Assuming that the calculator passes the full self-tests, this suggests one of two possible causes:

1) - The battery batch you are using presents very high internal resistance due to a manufacturing defect or maybe they are out of date.
This results in a very fast voltage drop at the battery terminals especially under load (with the machine in power on state).

2) - Your calculator current consumption is way above the average.
This one is easy to spot as long as your multi-meter is able to measure current in the micro Ampere range.

Here are the normal current consumption on a HP-42S, brand new, barely used:
(Test done using an external 4.5VDC power source. Any 4.5VDC 3R12 lantern battery will do, or else you may use 3 x 1.5VDC AA or AAA batteries in series installed in a battery holder)

Power off state: 9μA average (9 micro Ampere, to be clear)
Power On idle: 0.3mA average
Power On pressing keys: 2.5mA average

If you machine have much higher values, specially when in powered off state, then you need to check possible current drainage causes, starting from previous battery leakage (most common cause IMHO) to a bad bypass capacitor.




I was just checking the 357 / LR44 / SR 44 batteries and th manufacturers claim from 150mAh to 200mAh capacity, depending of the technology and vendor.

Taking the lower value of 150mAh for a LR44 alkaline battery, these are the running values that I found:

- In power off state: 150E-3 / 9E-6 = 16666 hours or 694 days or 1.9 years
- In power On state in idle all the time: 150E-3 / 0.3E-3 = 500 hours or 20.8 days
- In power On state doing calculations all the time: 150E-3 / 2.5E-3 = 60 hours or 2.5 days.

[pdicamillo]

The calculator passes the self-test. I made measurements with LR44 batteries, and they were draining similarly to the 357 batteries. The battery which drains is the one which contacts the negative tab (tab at the left viewed from the back.) I also noticed that with the batteries removed, the drained battery gradually regains its original voltage, eventually matching the other two. But the problem appears to be a very high current when the calculator is off. I measured 5.4ma at either contact tab, and it's consistent over time. I don't remember ever having battery leakage, and there's no sign of it around the battery compartment.

I'm reasonably good at soldering, and I think I could replace a capacitor or some other component that is a likely cause. But I wouldn't know how to find the source of the current drain.

[vk6ti]

Oddly enough I have a 42S that had same problem, although I was too lazy to do any diagnostics, after 3 sets of batteries over 3 days , the problem has disappeared. And I was using the same make of batteries. On mine I did notice it was crashing and draining batteries at same time.

Ray