silly design, keyboard without power switch caused battery acid leakage

[DiTBho]

Only this morning I realized the disaster that was silently happening under my nose, things you only realize when it's too late, and my keyboard is dead.

I forgot it in a corner of the lab, inside my locker, they batteries died, the acid leaked, electronic and plastic got corroded.

Easy story, my fault, just ...

... how can a portable AA3-battery-powered device be designed without a power on/off switch?!? how?!?

See, Texas Instruments made a serial - "full size keys for easy touch-typing keyboard, compatible with all variants of TI-83, TI-84, TI-89, TI-92 and Voyage 200 graphing calculators", but then there is no power on/off switch, so there is nothing to prevent acid-leakage with a not-rechargeable battery when not used for long time.

Lesson learned: *YOU* have to remove the batteries, always remove batteries!
Don't forget it. Never forget it. Acid is unforgiving 

[DiTBho]

[madires]

Yep! If you use something rarely better remove the batteries. An alternative is to switch to NiMH cells.

[tooki]

Lesson learned: *YOU* have to remove the batteries, always remove batteries!
Don't forget it. Never forget it. Acid is unforgiving 

Of course, the vast majority of AA batteries use no acids at all: they’re alkaline batteries, whose electrolyte is, well, alkaline.

No less corrosive, of course, but requires exactly the opposite chemistry to neutralize when cleaning the corrosion.

[Peabody]

Do we know that discharging an alkaline battery makes it more likely to leak?  I've certainly had alkalines that leaked even though they were switched off.  Is it being discharged, or is it just age?  Isn't Dave in the middle of a muti-year experiment on this?

[wraper]

Alkaline batteries happily leak even without external discharging. And there is no acid as already said. This Keyboard likely consumes so little power when not in active use that power switch is not needed. Would you suggest a power switch for TV remotes too?

[Peabody]

Anyway, I think the answer is that a physical On/Off switch could be the most expensive component in many devices.  As an alternative, you can put the processor to sleep at some small fraction of a microamp, to be waked up by the first keystroke.  Virtually every remote control works that way.  There's essentially no difference in battery life versus actually switching it off.  In fact, if you have to recharge capacitors when you switch it back on, or blink an LED, the battery might last longer if you just depend on sleep mode.  Of course using a regulator could change that math.

[DiTBho]

Do we know that discharging an alkaline battery makes it more likely to leak?  I've certainly had alkalines that leaked even though they were switched off.  Is it being discharged, or is it just age?

umm, that's what I don't understand about disposable alkaline batteries 

A year ago I bought two packs of four AAA-batteries each (2x4=8 batteries, picture attached) on Amazon, declared as "brand new batteries" with five stars in the feedback section, while talking about - " Estimated battery life when using alkaline batteries " - when I read the TI keyboard manual it said it's about ~ 126 days (~ 4 months) with active use and better than 4 months with moderate use, so I figured there was no problem storing the keyboard in my locker.

Big mistake, now I know ... 

Also, I didn't check that the keyboard didn't have an off button, so the keyboard stayed on standby the whole time and for some reason at some point the batteries started leaking.

Two batteries swelled so much that the plastic gap bent and I had to clean some kind of yellowish sand around them.

Here I used latex gloves because i noticed it was corrosive, and I cleaned everything with trichlorethylene(1) with the help of a toothbrush and protective glasses.

----

Now, from the same batteries-package bought one year ago, four of those AAA-batteries are still powering my pocket CASIO calculator and when yesterday I checked the battery-charge, they are still 90% and there is no acid leaking.


Why is so different results with the same batteries? 

edit: I loaded the wrong pic by mistake, fixed
[ Specified attachment is not available ]

(1) trichlorethylene for removing stains from clothes

[DiTBho]

(
AAA: Alkaline, 1.5 V,  ~1100 mAh
)

[DiTBho]

Alkaline batteries happily leak even without external discharging. And there is no acid as already said

umm, I don't knowm but I had to clean some kind of yellowish sand around them, and the plastic around the yellowish sand is bent and corroded, it changed color, it has mini-holes like holes in cheese

[madires]

Why is so different results with the same batteries? 

https://www.eevblog.com/forum/chat/durahell-batteries/

[DiTBho]

Anyway, I think the answer is that a physical On/Off switch could be the most expensive component in many devices. 

Yup! At least the older TI-92 (prior to the "plus" version) has a physical On / Off switch on the back and you can disconnect the batteries from the motherboard.

TI added the switch to you because you can optionally install an expansion module that adds more flash and ram, but to add the module the electronics must be turned off to avoid damage as the module goes directly into the parallel bus of the CPU.

The new TI-89-titaniom as well as the TI-voyage-200 don't have the physical On / Off switch, and they don't have any expansion module.

My old Japanese PDA made by SHARP in 2005 also has a physical On / Off switch on the back, and you can disconnect the batteries from the motherboard. There is no optional expansion module in this case, the best you can do to expand your PDA is through PCMCIA, which is hot-plug and doesn't requires you to disconnect the batteries.

[DiTBho]

@madires
"DuraHELL batteries"?!?

LOL 

Thanks, at least that makes me smile.
Thanks for the link, it's very informative!

[TMM]

hol' up... you use a keyboard with your TI-83?

 

[DiTBho]

Yup, sold the TI 83, bought a TI 89-titanium, once restored and fixed I will use the keyboard with this one.

[Peabody]

The batteries in your picture are NiMH rechargeables, not alkaline.

[DiTBho]

wrong pic uploaded, right format.
edit: fixed.

[coppercone2]

if you have a device like this, put a strip of wax paper or plastic in the battery cavity like you would get from the store so that until you pull it out its off. A little annoying but we can't be expected to solder a switch and mod every gadget that we use once a year.

[BrokenYugo]

If you are prone to leaving batteries in things alkaline is the worst choice, lithium, nimh, even carbon zinc is much less leak prone and destructive.

[tooki]

if you have a device like this, put a strip of wax paper or plastic in the battery cavity like you would get from the store so that until you pull it out its off. A little annoying but we can't be expected to solder a switch and mod every gadget that we use once a year.

Keystone Electronics sells the pull tabs (and they don't cost much, 12¢ on Digikey), model 119 for AAA and smaller, model 121 for AA and larger.

[DiTBho]

Thanks guys, after a serious cleaning and refreshing of the soldering points

it woooooooooooorkkkkkkksssssssssss again 

the keyboard is back to working. I cannot believe that it works, but it does!
I will follow your valuable battery advice in the future!