HP92266 N cell charger

[TASP]

Received the Interstate Batteries NiMH rechargable N cells, and figured they were worth a try in the 'official' HP92266 charger.

As received, the cells had a voltage ~ 1.25 volts. I'm not sure what % charge that translates to. I was able to load 3 cells normally, and then cant #4 so I could put my milliampmeter in series with the pack.

At the start, the current was close enough to 16 mA. Overnight charging (and then some) and a removed cell after a 1/2 hour or so wait, shows a voltage of 1.4 volts.

I then put the cell back in the charger and measured the charging current at 14 mA.

Assuming, an average of 15 mA for a full charging time, the math for a 500 mAH capacity comes out to 33 hours.

Meh, that ain't bad. Back in the 80s, I just left a set of NiCADs in it all the time. I've checked around, and NiMH cells in emergency lights, and other standby applications seem to survive trickle charging OK, so if I did leave a set in the charger for a year, it probably isn't a disaster.

As it is, I'll charge sets (I have 3, so far) for 48 hours, and then bag them and and put them in the kitchen battery drawer, ready for another stint in a 41.

Nice after all these years in storage the charger still works. And since I am finding the collecting aspect of this HP calculator world to be fun, having the HP N charger up and working in this modern era with new battery chemistry just makes it all the better.

[Dave Frederickson]

(03-22-2015 05:37 PM)TASP Wrote:  Received the Interstate Batteries NiMH rechargable N cells, and figured they were worth a try in the 'official' HP92266 charger.

I had bad luck with cells purchased from Interstate through Amazon. The actual capacity of 500mAH N cells ranged from 289 to 388mAH. Interstate admitted their stock had gone bad, but would not replace them free of charge. The Ogaz batteries were better.

(03-22-2015 05:37 PM)TASP Wrote:  Assuming, an average of 15 mA for a full charging time, the math for a 500 mAH capacity comes out to 33 hours.

That equation only works for discharge. I think 50 hrs is a better estimate for charging. I recommend the BC-700 smart charger with N cell adapters from Ogaz.

Dave

[Bill (Smithville NJ)]

(03-22-2015 06:18 PM)Dave Frederickson Wrote:  That equation only works for discharge. I think 50 hrs is a better estimate for charging. I recommend the BC-700 smart charger with N cell adapters from Ogaz.

Dave

I agree on the 50 hours. Following equation:

1.5 x Battery Capacity/Charge Current

1.5 x 500/15 = 50 hours.

When I used to charge a lot of NiMh battery packs for amateur radio, I used a timer to cut the charger off after the correct number hours.

If you have a charger with higher capacity for fast charging, just watch for any heat buildup. I have a Fast-Charge charger which has a built in fan to cool the batteries during the charge cycle.

Bill

[TASP]

As noted in my post, I'll leave them parked in the charger for 48 hours.

My cell phone has exhibited disturbing psychotic behavior when left on it's charger over night, so I am in the habit of charging it in the kitchen when I getting lunch ready. I'll just have the N charger adjacent, and keep an eye on it.

I've had variable luck at Interstate. Sometimes their branded stuff works great and sometimes I'm really disappointed. FWIW, their rechargeable N cells were cheaper than the last set of alkaline batteries I bought at Ace Hardware.

Except for my 41s, I don't think there is anything in the house that takes N cells.

[rprosperi]

(03-22-2015 05:37 PM)TASP Wrote:  Received the Interstate Batteries NiMH rechargable N cells, and figured they were worth a try in the 'official' HP92266 charger.

Can you post a photo of the HP92266 charger? I don't recall a charger for N cells from HP, and am curious to see it. Also, what power adapter does it use, or is the plug integral to the charger?

[TASP]

Yes, I will try for a picture. I am getting a routine down that seems to work moderately well for getting pictures uploaded.

(I'm not terribly tech savvy with computers and image hosting sites. Erf !! Why can't I just copy and paste everything like I used too ?!?!?!?!?!?!?!?)

[Dave Frederickson]

Pics are available at EnterHP.

[Sylvain Cote]

(03-22-2015 06:54 PM)rprosperi Wrote:  Can you post a photo of the HP92266 charger? I don't recall a charger for N cells from HP, and am curious to see it. Also, what power adapter does it use, or is the plug integral to the charger?

Robert,

You can find the specification and pictures here.

Sylvain

[TASP]

Yeppers.

That is exactly what I have. Back in the 80s, I seem to recall using the Radio Shack brand N cell nicads.

Now that I think about it, those batteries otta be here somewhere. Apparently they are in the missing box, along with the 1 year of PPC Journal, and the 41 desk stand. And a stack of hardbound HP catalogs.

Bocote wood, EduCALC. Think it was the $20 one.

[rprosperi]

(03-22-2015 07:05 PM)Dave Frederickson Wrote:  Pics are available at EnterHP.

(03-22-2015 07:12 PM)Sylvain Cote Wrote:  You can find the specification and pictures here.

Sylvain

Wow, and both are sites I've not seen before, so not only instant answers, but new info sites to check out as well.

Thank you both!

[Dieter]

(03-22-2015 05:37 PM)TASP Wrote:  As received, the cells had a voltage ~ 1.25 volts. I'm not sure what % charge that translates to.

It translates to nothing. The voltage of NiCd and NiMH batteries is very similar from near-full to almost-empty. It also depends on ambient temperature and other factors. That's why you cannot reliably determine the charge status of a NiCd/NiMH battery. Well, at least not by determining the voltage.

(03-22-2015 05:37 PM)TASP Wrote:  Assuming, an average of 15 mA for a full charging time, the math for a 500 mAH capacity comes out to 33 hours.

First of all, 15 mA was the charging current of the standard HP82120A NiCd-pack when connected to the dedicated AC adapter (82066A, 82059A etc.). This was fine for the low capacity NiCd cells of the day, but it leads to very long charging times if you want to fully charge a contemporary NiMH cell. Actually you have to multiply the 500/15 by a factor of approx. 1,25 (the charging process is not 100% efficient - there is a loss of approx. 20% which leads to a factor 1/0,8 or 1,25). This yields about 40 hours. Or a bit more since low charging currents are a bit less efficient than higher currents.

(03-22-2015 05:37 PM)TASP Wrote:  Meh, that ain't bad. Back in the 80s, I just left a set of NiCADs in it all the time. I've checked around, and NiMH cells in emergency lights, and other standby applications seem to survive trickle charging OK, so if I did leave a set in the charger for a year, it probably isn't a disaster.

If NiCd/NiMH batteries may be used at all with such excessive charging times depends on their construction. There are special battery types that can handle this kind of charging better than others that can be easily destroyed. In the NiCd days the usual limit for trickle charge was about 0,03 CA, which in this case translates to 0,03 x 500 mA = 15 mA. But I can't say anything about the batteries you use. Anyway, since 40 hours are required for a full charge, this charging time should not cause major problems, provided the battery was empty before.

(03-22-2015 05:37 PM)TASP Wrote:  As it is, I'll charge sets (I have 3, so far) for 48 hours, and then bag them and and put them in the kitchen battery drawer, ready for another stint in a 41.

NiCd batteries, and especially today's NiMHs, suffer from self discharge. After a month the capacity may be down to 70%, after a year you can consider a previously fully charged NiMH empty. So it's not a good idea to charge these batteries and then store them in a drawer for an undetermined time.

There is a solution to this problem: NiMHs with low self discharge, e.g. Sanyo/Panasonic Eneloop batteries. But AFAIK these are not available in small sizes like the N-type you need.

Get a decent charger with moderate charging current and processor control (e.g. the mentioned BC700) and charge your batteries as you need them. This can be done in 2 or 3 hours. And after just 30 minutes you already have charged the same capacity as the one you used to get with the HP battery pack in 1980. ;-)

Dieter