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Recommanded NiMh battery cells for HP82162A
09-25-2017, 09:50 AM (This post was last modified: 09-25-2017 09:53 AM by Sadsilence.)
Post: #18
RE: Recommanded NiMh battery cells for HP82162A
(09-24-2017 07:13 PM)Dieter Wrote:  
(09-24-2017 05:56 PM)Sadsilence Wrote:  for HP82143A etc. packs I am using following cells with very good results:

I hope you have access to a device for welding solder tabs to these cells. Never solder directly to any kind of battery contact.
But you already said it:

(09-24-2017 05:56 PM)Sadsilence Wrote:  I feel there is also a version with solder tails around. Sorry, no link.

Yes, there is. Here is a version with solder tabs. NiMH cells with low self discharge ("ready to use") and solder tabs generally seem hard to get.

(09-24-2017 05:56 PM)Sadsilence Wrote:  Those are LSD cells,

Since not everyone seems to be familiar with this term: this stands for NiMH batteries with extremely Low Self Discharge. This means you can charge them now, put them in a drawer and when you want to use them on Halloween next year (!) they are ready to power your flashlight. Or your calculator. ;-)

(09-24-2017 05:56 PM)Sadsilence Wrote:  Of course, contrary to akkuplus (which I can recommend, too) you have to assemble, weld or solder packs by yourself.

That's the essential point. ;-)


Hello Dieter,

thanks for additional hints.

Indeed, I have such a welding machine for solder tabs and still looking for 1/3 AAA NiMH LSD cells for my HP82120A packs ;-).

Details of charge curcuit within HP41 rechargeable battery pack are perfectly explained here.

There is a 1/3 AAA NiMH C=170 mAh datasheet from GP, that states an overcharge time of one year for 0.1C charging current (=17mA) does no harm to the cell. Normally, as already mentioned, from overcharging point with high current any energy put into cell is transformed into heat which finally destroys cell's chemistry. A charge current of 17 mA at 1.2V (or 1.4V-1.5V when fully loaded) cell voltage puts so little energy into cell that heating up is neglectable and little heat can easily be dissipated over cell surface.

Looking at HP82120A curcuit actual charging current Ic depends on voltage of cells.
Formula is ( 12V - 0.7V - battery voltage )/ 365 Ohm.

Empty pack @ 4*1V = 4V -> Ic = 12V - 0.7V - 4V / 365 Ohm = 20 mA
Loaded pack @ 4*1.4V = 5.6V -> Ic = 12V - 0.7V - 5.6V / 365 = 15.6 mA

That perfectly matches 17 mA standard charge current of mentioned 170 mAh 1/3 AAA cells.

To get a completely empty battery fully loaded you need around 16 hours (typical formula is 15-16h @ charge current C/10 as there are energy transforming losses). Even if you charge not completely discharged battery for 24 hours there will be no damage. By the way that is exactly the way I charge my rebuilt HP82120A batteries.

Theoratically you can speed up things by replacing 365 Ohm current limiting resistor of charging curcuit with one of lower value. For instance AC wall plug adapter can deliver up to 200 mA or voltage regulator can handle 100 mA or even more. Despite there is more than one reason NOT do it:

1. You can really destroy NiMH cells then.
2. Current limiting resistor gets too hot as power dissipation increases quadratic with current through resistor. Even an 100 Ohm resistor, allowing a current of 60...75 mA is cooked when using a default 0.25W type. Using a high current resistor is no solution due to limited space and capsuled enviroment of battery. There is no way to get heat outside.
3. Voltage limiting Z-Diode cannot deal such high currents in error case and will be blown, too.
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RE: Recommanded NiMh battery cells for HP82162A - Sadsilence - 09-25-2017 09:50 AM

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