HP 33E Battery Contact Polarity?



#10

Hi,

I have an HP 33E but the rechargeable battery pack is long gone. I've heard that one can use standard AA batteries if you wire them in series. Is that correct? If so, which battery contact is the positive contact? I don't want to plug the batteries in backards and fry it!

Thanks,

-Danny Eskenazi


#11

You may wish to think that one over.

My experience is admittedly VERY limited, but my HP-31E, in which I've used AA alkaline batteries, has developed the "2 Disease", while my HP-34E with a rebuilt Ni-Cd pack has not.

I've asked here once before whether the slightly higher voltage of the Alkaline batteries might account for the dreaded "2 Disease", but I don't know that anyone ever refuted that suspicion. (I certainly could be mistaken.)

Does anyone else have an opinion on this?


Edited: 9 May 2007, 5:18 p.m.

#12

Looking at the bottom of the calculator with battery cover off and top end of the calc away from you, he bottom left contact is positive. The upper left contact is negative. I tape two NiMH cells together and use an aluminum foil jumper to complete the circuit on the right hand side.

I wouldn't bother with alkalines. The NiMH cells will take a charge within the calculator (takes a while, mind you), and last quite a long time when they are fully charged.

Be careful when inserting and removing such a makeshift pack. The fit is snugger since the positive pole buttons are not recessed and make the batteries a little longer. My 33C has the positive contact broken off, but enough of a stub remains to complete the connection fine. The 34C has contacts intact but I am careful.

Mixing up polarity won't fry the unit but in continuous memory models it will discharge the capacitors and erase programs. I have done that a couple of times :)

Les


#13

I wish to confirm eveything Les has said. I now use NiMH's in my HP-31E.

tm


#14

Be aware that the 30 series units do not offer any internal reverse polarity protection. A shorted transistor or other damage in the power supply is possible.

#15

Les,

Another thought. Since the NiMH cells work so well with my 31E, do you think it's ok to use then in my 25C battery pack? I'm now using NiCads.

tm


#16

NiMh cells in Woodstocks is fine so long as you charge them externally in a proper NiMh charger. Very long run times per charge and no danger of frying your 25C are both very good reasons to do it.

I NEVER charge batteries in a good machine. It just isn't worth the risk.


#17

Randy,

I hear you loud and clear.

tm


#18

All, thanks for the advice! Sounds like I'll buy a pair of NiMh batteries and an external charger.

Best Regards,

-Danny


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