Source for N-Cell NiMh Batteries and Charging adapters



#2

I was asked to post on here a while ago and never got around to it. I know several people here have searched for NiMh N-Cell batteries and there really are not many suppliers of these batteries.

You can find batteries and charging adapters here for the N cell batteries.

Website HERE!


#3

That's great! Thanks for posting!

Does the fact that the NiMH N cells are supplied pre-charged imply that they are low self-discharge cells?


#4

Re your closing question, I cannot say. I did however, prior to using them "recharge" all rechargeable AA and AAA batterys I have.

Thinking on this subject, I find myself curious as to how many recharges these batterys will take.

#5

Quote:
That's great! Thanks for posting!

Does the fact that the NiMH N cells are supplied pre-charged imply that they are low self-discharge cells?


No. They are just charged right before shipping so they are ready to use when they are received.

#6

Re rechargeable AA, and AAA batteries, 2000 mAh for the former, 1000mAh for the latter, I found them at Office Max in my area, Pittsburgh, PA. I expect that other electronics/computer stores would have them too. As to charger, Trader Horn carries or carried there items, and I expect that other outlets do also.

#7

Thanks & have just ordered some to try on my HP41C calculators.

I did however notice the voltage on these re-chargeable batteries is specified as 1.2 V instead of the 1.5 V rating of the N size Alkalines. Has anyone found any issues arising from the lower voltage when used in the calculators?

Thanks,

Michael


#8

The 1.2 volt rechargeables work just fine in the HP-41. HP even sold a replacment battery pack which used 2/3N size NiCd cells. For heavy users of the card reader, it was a blessing. While the smaller cells held less energy than alkalines, their much lower internal resistance allowed the '41 to get far more from them. The card reader motor takes so much current that the low battery detect circuit would fire during a card read or write when alkaline cells were still 90% full(!), much to the dismay of '41 owners back then.

The disadvantages to NiCd cells were higher initial cost, the nuisance of recharging, high self-discharge rate and very abrupt end-of-charge. That last meant that you could be using the '41 just fine and have the low battery indication appear and the card reader stop almost simultaneously, right in the middle of a card write or read.

Of course, today's far higher capacity NiMH and NiCd cells will do even better than what we had in 1979.


#9

Thanks Jim.

Cheers,

Michael

#10

Quote:
I did however notice the voltage on these re-chargeable batteries is specified as 1.2 V instead of the 1.5 V rating of the N size Alkalines. Has anyone found any issues arising from the lower voltage when used in the calculators?
Yes, my 41cx's low-battery annunciator is on at 1.2V. If you're not using the card reader, I see no reason for rechargeables. Before I got my double extended memmory module, a set of alkalines lasted me about two years with regular use. How long would the rechargeables last? Five years? Ten years? Because of their much higher initial cost, they would not pay for themselves, and they would require frequent recharging (especially since the low-battery indicator would no longer be helpful).

#11

1,2 V is just the nominal voltage of NiMH and NiCd cells. This does not mean the voltage is lower than what's offered by a single-use Alkaline battery with "1,5 V" printed on it.

The point here is the fact that NiCds and NiMHs keep their voltage relatively constant - whether they are almost full or nearly depleted, they offer their 1,2...1,25 Volts. As opposed to Alkalines who deliver 1,5 V when new and near 1 V when nearly empty.

According to my results the battery indicator of the 41C and 41CV comes on at roughly 4 V for the whole pack, i.e. 1,0 V per cell. That's the voltage where NiCds and NiMHs can be considered empty. I never observed the low-bat-indicator while using the HP NiCd battery pack with its average 1,2 V per cell unless the pack was nearly empty. Of course that's 4 V under load, not the open ciruit voltage of the cells that can be measured after they have been removed from the calculator.

Since the card reader (and the wand) draw substantially more current from the batteries than a standard 41C/CV/CX, the use of rechargeable batteries is almost mandatory when one of these items is used. Otherwise alkalines are fine as well.

Dieter


#12

My 41cx shows the low-battery "BATT" indicator when the alkaline batteries are at 4.8V no-load which won't be much different from the 2mA on-but-idling load of the calculator. New alkalines are nearly 1.6V no-load. I could of course get a lot more life out of alkalines if I could run them down to .9V per cell, but then I would lose the indicator and later maybe some data too, or get leakage if they were left in the calculator for months. I've gotten two years out of a set of alkalines, changing them as soon and the BATT annunciator came on at 1.2V.

#13

I ordered four of these and received them today. Mechanically, they seem to be well made. Electrically, they pose a problem. Charging an N-cell in an AA charger requires either the charge current to be limited to 10% of the cell's capacity (for N-cells this ranges from 15-20 for Ni-Cd cells to 40-50 milliamps for Ni-Mh cells), or the implementation of a delta-V charging limiter.

Properly designed N-cell charging adapters (I own two types, one sold by Educalc in the '80s for the HP-41, and a set sold by Radio Shack) have a specifically selected resistor in series with the cell to drop the current from what is appropriate for charging AA cells, down to the level necessary to safely charge the lower capacity N-cells. Most AA NiCd chargers will charge at a rate around 50 milliamps, and most AA NiMh chargers charge at a rate of around 150 to 200 milliamps. These N-Cell adaptors HAVE NO CURRENT LIMITING RESISTOR. When using these N-Cell adapters, the current is not limited as to what is appropriate for N cells, and overcharging is quite possible at the charging rate provided for AA cells. Overcharging at relatively high charging currents will severely shorten the life of any rechargeable cell.

Using these adaptors approriately requires knowledge of the charge condition of the cells, their capacity, the charging current for the AA charger, and then closely monitoring and limiting the time of the charge to manually prevent overcharging.

An electrical engineer should have been engaged in the design of these adaptors.

Edited: 13 Dec 2012, 7:55 p.m.


#14

Dan, you are absolutely right with you warning. For those who are looking for more details and specific recommendations, a look at a thread from June 2011 may offer some useful information. You will find it here.

In a few words: simple N-AA-adapters are fine if a decent processor-controlled charger with sufficiently low charging current is used. For instance the one mentioned in message #10.

Dieter


#15

Here's a suitable charger


#16

Seems to be quite the same as the one I suggested in my linked post. The BC-700 has a lot of different names. ;-)

Dieter

Edited: 16 Dec 2012, 10:27 a.m.


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