HP 34C - which way round are the batterys fitted?

[Jon Duke]

Hi, the message title says it all really. I'm seeing if I can get my father's old HP 34C working. The batteries were badly corroded and thinking that there would be marks telling me which way round to fit new ones, I pulled out the old ones, only to find that there are no marks that I can see on either the body of the calculator or the case.

I do also have the charger. Is there a max charge time and is it OK to run it while connected to the charger? Thanks for any help.

[Katie Wasserman]

Look here

Charging time varies depending on which battery type you used as the replacement. Newer cells generally have higher capacity than older ones and require more charging time. It's always best to not overcharge as the heat from overcharging will reduce battery lifetime. Charging for 10-12 hours should be enough to fully charge most cells and not too long to damage them. It's ok to run the calculator while the batteries are charging but charging times will be longer.

Edited: 29 Mar 2010, 10:02 a.m.

[Jon Duke]

Hi Katie. Thanks for your reply regarding charging the calculator. Would you know which way round the batteries go?

[Jon Duke]

Sorry Katie!!!! I only just spotted the picture! 10**6 thanks

[db (martinez, ca.)]

Jon;

Here i am in the unnatural position of wanting to add something to Katie's post, the weird thing being that she taught me over half of the little i know about charging batteries.
Here goes: IMHO it is dangerous to charge the batteries INSIDE your model of hp calculator. A high percentage of them are dead because the batteries weren't making good contact, maybe because of slight corrosion or dust, and the irreplaceable ROMs got fried with too much DC. This also happens to the Woodstocks. Let this be known as the too much cheesecake too soon syndrome.
I avoid the problem by charging the batts outside of the calculator or running slightly used AA alkaline 1.5v cells in place of the 1.25v rechargeables. The last is an easy solution if your calc has broken spring contacts like a couple of mine do.

QUESTION: Has anyone tried to coat the batt contacts with something like that conductive anti-oxidizing goop which is used on aluminum high voltage wiring?
db

[Jon Duke]

Hi DB, thanks for your words. What you say sounds like a good safe approach. It's something I hadn't considered. Re things to stop corrosion, I favour silicone grease, what plumbers use to ease plastic plumbing pipes over O rings in connectors. Over here the phone companies dip wires in it before clamping them in roadside distribution boxes, so it ought to be good. It is very inert indeed. The only thing to watch out for is that it does not go down well in places where paint is being applied, like car bodyshops: it causes wet paint to roll back from any trace. HTH.

[Michael de Estrada]

Jon,

Let me add to what has already been said. You may have noticed that the original battery pack uses AA flat top cells, which do not have the extended tip at the positive terminal. This makes the battery shorter, such that it compresses the battery contacts less. Using regular high-top cells can result in eventual breaking of the battery contacts due to over-compression, which bends the contacts past their yield point. I've also seen them break off from their mounting rivets. To this end, I always use flat top NiCad AA cells in all of my HP Spices, which I purchase from Batteries Plus for $2.50 each. You should be able to find them at any store that reubuilds battery packs.

Michael