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HP Forum Archive 07

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NiCad AAA rechargeable for the 49G
Message #1 Posted by Vieira, Luiz C. (Brazil) on 10 Jan 2002, 12:36 p.m.

Hi;

I'm test-driving a set of rechargeable AAA batteries, 250mAh, P-4SPA Panasonic, in my 48SX, but I intend using them with the 49G. Can I borough from any of you some previous experience on this? I am trying the rechargeable ones cause I needed to replaced the alkaline set for three times in less than one year. Of course, I upgraded the O.S. more than four times in the same period, among many data transfer operations between the calc and other calcs or computer. I did not take measurements to confirm, but I was told by two owners that data transfer is the most power-consumption operation. I thought O.S. upgrading was the most, cause of the 49`s flash-memory.

I have also seen some information at the Museum about power consumption in the 48G (posts or archive? I don't remember...), but I am not sure that the differences between alkalines AND NiCad`s were taken into account., say, 1.25V instead of 1.5V (each cell), different Volt X Current and Volt X Time curves, etc.

Anyway, the 48SX is running O.K. with a freshly charged set for about a week, normal operation (2~3 hours daily usage), what is no longer a reference. If there is something about it, I'd like to know.

Thanks and best regards.

      
Re: NiCad AAA rechargeable for the 49G
Message #2 Posted by Tom (UK) on 10 Jan 2002, 1:05 p.m.,
in response to message #1 by Vieira, Luiz C. (Brazil)

I can't answer your power consumption questions but have the following experiences with NiCads:

The voltage colapses very quicky when they run out - so you get hardly any warning when they are about to die. The low battery warning on the HP48/49 is set for 1.5V batteries so when it comes on there may be lots of life left in the NiCads - but the point at which they fail may not be indicated. It would probably be best to recharge them regularly (say once a week) to ensure you don't get caught out. Perhap you should carry round some alkalines as spares to use at a moments notice (and when the NiCads are recharging)

NiCad capacity is much lower than alkalines so expect to have to recharge them more often.

NiCads loose about 1% of charge per day so if the calculator is not used for some time don't be surprised if they are discharged.

It may be best to only start changing the FLASH memory when you have freshly charged NiCads just in case they fail while you are updating the memory.

Have you considered using NMH batteries as they have a higher capacity and may have a better discharge profile.

You can obtain alkaline battery chargers but these only work if the batteries to be recharged are NOT fully used, I think they work best if there is still 30% charge left - how you work this out for a calculator is anyone's guess...

I'd be interested to see how you get on with your battery solution, hope the above is of use.

      
Re: NiCad AAA rechargeable for the 49G
Message #3 Posted by W. Bruce Maguire II on 10 Jan 2002, 1:24 p.m.,
in response to message #1 by Vieira, Luiz C. (Brazil)

I'm test-driving a set of rechargeable AAA batteries, 250mAh, P-4SPA Panasonic, in my 48SX

Just to add to what Tom wrote, if you are going to go the rechargeable route, I would suggest NiMH. Target carries Energizer-brand NiMH AAAs with a capacity of 700mAh. I have tested them, and indeed, they seem to exceed that capacity!

But, NiMH, like NiCd, batteries lose about 1% of their capacity per day! So, for applications that need (or you want) to last quite a while between battery changes, there is really no substitue for alkalines. Lithiums would be a good choice, but I have only been able to find lithiums in AAs and 9V (again, Energizer brand).

Bruce.

p.s. For all the battery/power enthusiasts out there: www.cheapbatteries.com carries the 9V lithiums. They are GREAT for smoke detectors! You can install the lithiums, and FORGET ABOUT THEM for at least 5 years!

            
Re: NiCad AAA rechargeable for the 49G
Message #4 Posted by Yani on 10 Jan 2002, 6:13 p.m.,
in response to message #3 by W. Bruce Maguire II

In addition to the good advice from Tom and Bruce...

NiMH also have the additional benefit that they do not have as severe a memory effect as do NiCd batteries.

It works this way. When you recharge a partially discharged NiCd the terminal voltage more rapidly drops so that it appears to have less capacity and the low voltage opperation point of your device is more quickly reached.

There is a common misconception that partial discharge reduces the capacity of the cells. This is not the case. The capacity remains, it is only the voltage discharge curve that is effected.

This is why it is advisable to fully discharge NiCd cells every so often to eliminate this memory effect.

I always use NiMH now for this very reason. Also the price/capacity of NiMH are so close to that of NiCd that it is worth while now to use MiMH instead of NiCd.

For my 41Cs I keep one spare set of fully charged batteries on trickle charge. Mind you with copious use of the card reader it takes more like one month not four to six months between replacements.

      
Acknowledged! and other doubt...
Message #5 Posted by Vieira, Luiz C. (Brazil) on 10 Jan 2002, 10:45 p.m.,
in response to message #1 by Vieira, Luiz C. (Brazil)

This is just to acknowledge your valuable posts, guys. Thanks a lot!

Anyway, to all those who want to add more info, I, and guess also all others taking advantage on these good posts, am inviting to go beyond. I believe many will use these precious info and others to come.

By the way, NMH or NiMH? I was told once which chemicals are used in these batteries, and I forgot. Please, what do NMH stand for?

Best regards.

(I'll keep the NiCad's for now in the 48SX to get to their performance, but I'll begin chasing the NiMH AAA's right in the morning!)

            
Re: Acknowledged! and other doubt...
Message #6 Posted by Yani on 11 Jan 2002, 6:22 a.m.,
in response to message #5 by Vieira, Luiz C. (Brazil)

Nickel Metal Hydride hence NiMH.

      
Re: Plug-in power for hi-consumption operations?
Message #7 Posted by Paul Brogger on 11 Jan 2002, 11:14 a.m.,
in response to message #1 by Vieira, Luiz C. (Brazil)

I wonder how hard it would be to rig a small normalizing jack to interrupt the battery power when a 4.5V DC power source was plugged in?

Maybe as a compromise, one could then power the calculator from the wall during desk-bound, power-consuming operations, and use the batteries the rest of the time?

            
Re: Plug-in power for hi-consumption operations?
Message #8 Posted by Vieira, Luiz C. (Brazil) on 12 Jan 2002, 12:07 p.m.,
in response to message #7 by Paul Brogger

I cannot feel as being more acquainted with the idea. In fact, for hi-consumption ops (nowadays, it's refered to as more than 150mA... Goodbye, Vaccum Tubes, goodbye bipolar transistors... See you in Hi-amps equipment), and for system upgrading (HP49), that would be more than desirable...

Why didn't HewPack offered that? Maybe God knows... (not the one that posts here; the other One)

That's something not just to wonder about, but to research about. Thanks for the valuable tip, Paul.

Best regards.


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