HP41, N battery (N Cell), charging of HR1

[Uli]

Do you want to know, what happens, if you do not care for the charging current?
1. a big bang
2. a lot of dust
3. you need new cells
4. you need a new charger
5. you need 2 hours to clean your office (no joke)
6. you need flowers for your wife....


(the charger had a temperature control. but it can’t work, if the (too small) cells do not touch the sensor, to have contact with the plus and minus pool).

[Dave Frederickson]

Smart chargers primarily detect end-of-charge using -deltaV. That is the charging voltage will drop a little when the battery is full. For the -deltaV circuitry to properly detect end-of-charge the charge current should be 0.3 to 0.5C where C is the capacity of the battery. If you charge too slowly then end-of-charge is detected by temperature.

So you're in the market for a new smart charger. The favorite BC-700 has been discontinued in favor of the BC-1000 with higher current capability. Another favorite, the Wizard One has also been discontinued and replaced by the MH-C9000PRO which sports exactly the same specs but only has 4 modes of operation compared to the Wizard One's 5.

I haven't found a good source for N-cell NiMH (HR1) batteries. EBL had some 600 mAH cells but they're no longer being sold in the US.

Finally, that was a spectacular explosion!

[Bill (Smithville NJ)]

(10-09-2020 09:12 PM)Dave Frederickson Wrote:  Finally, that was a spectacular explosion!

Reminds me of when I was young and devised a way to recharge my 9v battery for my transistor radio. I had rigged up a transformer and a half wave rectifier. The transformer was out of an old TV so not sure what it's voltage was. But it was a lot!

I found through experimenting that I could connect the 9v battery to the circuit and charge it for about ten seconds. At that point it was boiling hot to the touch. It would run the radio for about another week.

One time I got distracted, and the battery exploded. It sent the metal casing across the room and embedded itself about a half inch into the plaster board wall. It was quite exciting!

This was in 1960 and I was about 11 years old. I found experimenting with electricity a lot of fun. (And I did receive plenty of bad shocks).

73
Bill
WD9EQD
Smithville, NJ

[[kby]]

At least:
1. Your wife,
2. You, and
3. The calculator

…survived. But please don’t sign up for my chemistry lab classes (at least not after we get back to sort if real labs).-kby

[rprosperi]

(10-09-2020 09:12 PM)Dave Frederickson Wrote:  I haven't found a good source for N-cell NiMH (HR1) batteries. EBL had some 600 mAH cells but they're no longer being sold in the US.

These are still available, a friend purchased some here quite recently:

https://ogazent.com/store/batteries-and-...ry-nt50nh/

[Dave Frederickson]

(10-09-2020 10:45 PM)rprosperi Wrote:  

(10-09-2020 09:12 PM)Dave Frederickson Wrote:  I haven't found a good source for N-cell NiMH (HR1) batteries. EBL had some 600 mAH cells but they're no longer being sold in the US.

These are still available, a friend purchased some here quite recently:

https://ogazent.com/store/batteries-and-...ry-nt50nh/

I have some of those batteries, they now have capacities around 380 mAH.

They're also out of stock.

I can, however, recommend their battery adapters.
https://ogazent.com/store/batteries-and-...pter-n-aa/

[rprosperi]

(10-09-2020 11:10 PM)Dave Frederickson Wrote:  I have some of those batteries, they now have capacities around 380 mAH.

I agree they are not the best quality, but often batteries of average quality beats no batteries at all, when wanting to use battery-powered devices...

[Wes Loewer]

I recently got this charger that came with two size N batteries plus I ordered two more batteries of the same brand for my 41.

https://www.amazon.com/ANVOW-Battery-Cha...07ZHF849S/

The batteries claim to be 700 mAh which I doubt. The charger claims to be 200mA which I also doubt. It's a slow, one-at-a-time charger, but there's no chance of overheating. In any case, they suit my needs of charging 4 batteries every year or two.

I thought about testing the batteries in my BC-900, but I didn't want to risk getting them too hot and ruining them. But hey, what are the chances that would happen. ;-)

[BobVA]

(10-10-2020 03:33 PM)Wes Loewer Wrote:  I recently got this charger that came with two size N batteries plus I ordered two more batteries of the same brand for my 41.

Thanks for the link! Please post your results. (I'm particularly interested in the stand-by / self-discharge performance.)

I narrowly escaped a battery leak disaster with my 41 last week and I'd like to find a reliable rechargeable alternative.

[Wes Loewer]

(10-10-2020 10:35 PM)BobVA Wrote:  

(10-10-2020 03:33 PM)Wes Loewer Wrote:  I recently got this charger that came with two size N batteries plus I ordered two more batteries of the same brand for my 41.

Thanks for the link! Please post your results. (I'm particularly interested in the stand-by / self-discharge performance.)

I narrowly escaped a battery leak disaster with my 41 last week and I'd like to find a reliable rechargeable alternative.

The motivation for getting these was also to avoid battery leaks. My only test will be to watch when the battery indicator comes on. I don't use this calculator much, so it might be a while. I suppose I could hurry up the process by putting the calculator into an infinite loop.

For new batteries I usually cycle them through charging and draining on my charger as it sometimes take a few cycles to break them in. I haven't done that with these. Maybe an infinite loop would be a good idea.

[BobVA]

(10-11-2020 12:21 PM)Wes Loewer Wrote:  I don't use this calculator much, so it might be a while.

Same here - the 41's not my daily driver, but I usually have it out every few weeks. Missed that during a recent move and found the batteries dead/starting to leak when I unpacked it. I've got a calendar reminder on my computer now to replace the batteries every six months "dead or alive" :-)

It would be nice to find low self-discharge NiMH LR1 cells, but I haven't had much luck there.

[Wes Loewer]

(10-09-2020 06:56 PM)Uli Wrote:  Do you want to know, what happens, if you do not care for the charging current?

So what was the charging current?

[GVHOVE]

I have been using rechargeable N-type batteries for years in my HP-41

Brand is XCell - X500NH - 500mAh Ni-MH.

In Europe you can order them here : https://akkuplus.de/XCell-X500NH-Lady-N-...0mAh-Ni-MH

My HP-41 is used almost daily (that might change since I have just received my SwissMicros DM41X in the mail) and never had any issues with them.
I do replace them every year or so to avoid leakage.

My charger is a very-hard-to-find, vintage W&W adapter for the HP-41 standard battery compartiment (see pictures). Loads the pack overnight without heating up too much.

   

   

[Dave Frederickson]

(10-11-2020 08:29 PM)GVHOVE Wrote:  My charger is a very-hard-to-find, vintage W&W adapter for the HP-41 standard battery compartiment (see pictures). Loads the pack overnight without heating up too much.

Your charger appears to charge the 4 cells in series. Is that correct?

(10-11-2020 01:23 PM)BobVA Wrote:  It would be nice to find low self-discharge NiMH LR1 cells, but I haven't had much luck there.

That's because an LR1 is an alkaline battery. An NiMH N-cell is an HR1.

It's kinda like a DB-9 connector, which doesn't exist.

Trivia:
9-pin D-sub connectors have a size E shell, so the designation is DE-9. 25-pin D-sub connectors have a B size shell and are designated DB-25. Folks thought "DB" stood for "D-suB" so they incorrectly called the 9-pin connector a DB-9.

[Wes Loewer]

(10-11-2020 08:29 PM)GVHOVE Wrote:  I have been using rechargeable N-type batteries for years in my HP-41
...
I do replace them every year or so to avoid leakage.

"Replace" or "recharge" every year?

The whole reason I got rechargeable N's is so that I would never need to worry about leakage damaging my 41. I don't know that I have ever seen rechargeable batteries leak. I've got rechargeable batteries that are 12 years old in my class set of calculators at school.

[Uli]

(10-11-2020 02:19 PM)Wes Loewer Wrote:  

(10-09-2020 06:56 PM)Uli Wrote:  Do you want to know, what happens, if you do not care for the charging current?

So what was the charging current?

I make a very short test with new HR1, to see what the standard charging current is that the charger use. It’s 500 mA.
With this charger (Miboxer C4-12) I can adjust it in steps to minimum 100 mA. But it is possible to adjust the charger up to 1.0 Amps. I do not know on which level the current was to produce the explosion.

[Erik-M]

The X-cell batteries are also available at conrad in the Netherlands for € 2,12
Lowest price I could find, conrad is usually more expensive.
https://www.conrad.nl/p/oplaadbare-n-bat...uks-255174
I use a SkyRC MC3000 charger because besides all the normal bells and whistles it has a programmable charge current down to 50 mA, a shutdown timer and mAh counter.
And you can connect to a computer to plot a nice charge / discharge graph.
I blew up too many batteries in my life.

[Didier Lachieze]

This is what I 'm using: BC-700 charger + 500mAh batteries + LR1 to AA adapters.

[Dave Frederickson]

(10-12-2020 06:55 PM)Erik-M Wrote:  The X-cell batteries are also available at conrad in the Netherlands for € 2,12
Lowest price I could find, conrad is usually more expensive.
https://www.conrad.nl/p/oplaadbare-n-bat...uks-255174
I use a SkyRC MC3000 charger because besides all the normal bells and whistles it has a programmable charge current down to 50 mA, a shutdown timer and mAh counter.
And you can connect to a computer to plot a nice charge / discharge graph.
I blew up too many batteries in my life.

50 mA is precisely the charging current necessary to apply the IEC "forming charge" to those 500 mAH batteries. It's even printed on the side of the batteries.
http://www.robotreviews.com/chat/viewtop...=4&t=12301

I must say the SkyRC MC3000 is the fanciest charger I've ever seen (Bluetooth, really?) and also the most expensive.

Dave

[Massimo Gnerucci]

(10-12-2020 07:06 PM)Didier Lachieze Wrote:  This is what I 'm using: BC-700 charger + 500mAh batteries + LR1 to AA adapters.

Me too!