Ok, the hunt is on... Nimh charger solution for N-cell batteries in the USA



#36

Found a nice source for Nimh batteries in the US, but now need to either find some AA to N cell adapters or a dedicated N-cell recharger.

Hoping someone has some links. :-)


#37

I've been looking too. Couldn't find a thing. Charged some old nicad N's with an AA charger with a bolt as a spacer.

I was thinking of making a nice set, but figured there HAS to be some out there somewhere.


#38

This unit come with an adapter for N cell batteries: Mimio

However, it only comes with ONE adapter for 2 N cell batteries. At least that is how mine came.

Cheers.

#39

I must say, I prefer the AA-N-adapter idea. Here is a picture of a homebrew adapter, made of a piece of aluminium tube:

Please note: the shown (disposable) Duracell batteries are not rechargeable and are only there to demonstrate the different sizes. ;-)

However, if N-batteries are charged in AA-chargers, there are a few precautions that have to be considered:

  • The key issue is the so called relative charging current. In numbers, that's simply the actual charging current divided by the battery's capacity. For instance, 100 mA for a 500 mAh N-size battery are 0,2 C. Regular NiMH batteries usually are charged with rates between 0,1 and 0,5 C. For a 500-mAh-battery this translates to a charging current of 50...250 mA.
  • The charging time is roughly 1.2 divided by the relative charging current. For instance, 100 mA and a 500 mAh battery give 0,2 C, so the charging time for a completely empty battery is about 1,2 / 0,2 = six hours.
  • Faster charging means more stress for the NiMH-battery, unless it is not specifically built for it, and definitely requires some kind of charge control. In other words: a special charger that is able to detect when the battery has been completely charged and then turns the charger off.
  • The essential point here is the much, much higher capacity of AA-sized batteries compared to the N-versions we use here. Their capacity is roughly five times as high as in the N case, which means that the relative charging current is five times as high as well. In other words: if an AA-N-adapter is used to charge an N-battery in an AA-charger with, say, 700 mA current, this would mean a rate of 1,4 C or less than 1 hour. Which is more than a battery like the GP50NH will take without the risk of damage.
  • So, the solution is simple: yes, use an AA-N-adapter to charge our N-batteries in a regular AA-charger, but be sure to use one with sufficiently low charging current. One may think of a good old simple-charger from the Eighties when regular NiCd AA-cells had the same capacity as N-NiMH-cells today. For instance, I got this old Panasonic charger for 4x AA with 50 mA charging current, which is perfectly fine for this case, giving a relaxed charging time of 12 hours. Some of today's higher end chargers may be set to currents as low as 100..200 mA while providing exact charge control (current, voltage, temperature, battery-full-detection). This would be perfect.

Dieter

#40

I don't have one of these. However it claims to be adjustable so that it can accommodate just about any size battery, including N.


#41

Looks like a nice solution. Only wish it could handle 4 batteries at a time.

#42

I could not find a spec about charging current. I like to charge the N-cell with the specs Dieter mentioned here and here as beeing safe.


#43

If you buy this charger, measure the current and figure out the charging time yourself. However, this charger seems to be smart enough to deal with lithium cells so it might "know" when to turn off charging for ni-cads as well and you won't have to worry about it. Modern nicads can be charged at much fast rates than older ones without damage.


#44

Yes, but over here in Europe we don't get NiCd anymore. I bought 8 NiMh and what I understood they should be charged with lower current. Anyway, I will have it sorted out before the CL board arrives (Yuppie :-)


#45

Quote:
Yes, but over here in Europe we don't get NiCd anymore. I bought 8 NiMh and what I understood they should be charged with lower current.

Actually you can often charge NiMH with even higher (absolute) currents than NiCds. The point here is that NiMH N-cells (500 mAh) have 2 - 3 times the capacity of the latest NiCds (200 mAh). Now, if your charger provides 200 mA charging current, that's a whopping 1 C for the NiCd, but only moderate 0.4 C for the NiMH version. Which is very nicely balanced between speed (3 hours) and safety.

So, 150 or 200 mA seems to be just right for current N-size 500 mAh NiMHs. But where is a decent, sufficiently sophisticated charger that can handle low charging currents for N cells as well as higher currents for more common AA and AAA sizes? Here's a suggestion:

At least in Germany the Conrad IPC-series chargers have quite a good reputation. There are various models, even sold under various brand names. For our purposes the IPC-1L is just fine. It is a full-featured AA/AAA charger that can be set to different charging currents. It offers four independently controlled battery slots with four displays to inform about voltage, charging current, charged capacity, elapsed time, discharge current and much more. Of course the whole charging process is monitored and processor-controlled. Yes, it can even make a geek happy. ;-) So, first it is a really fine charger for regular AA and AAA cells.

The IPC-1L now can be set to three different charging currents: 200, 500 and 700 mA. The lowest is the default setting - perfect for our N-cells, charging an empty cell within 3 hours. Get a set of four AA-N-adapters, and you're done.

I assume similar other chargers are available in other countries around the world. The key combination is a decent processor controlled charger that can be set to a low charging current.

Dieter


#46

Quote:
Get a set of four AA-N-adapters, and you're done.
For example : N, LR1 to AA adapter.

#47

Now if only we could find those in the US! I have spent hours searching the web for a US source for a N-Cell adapter with absolutely no luck.


#48

You can use these from DX. N and AAA cells are the about the same diameter so all you need is a small compression spring to take up the extra space. Any hardware store will have a selection of them.

Although I haven't tried these adpaters I have tried
these adapters and the N cells fit perfectly. N cells measure about 1mm greater in diameter then AAA cells.

(BTW, I highly recommend the Next Generation RF remote control system. It's not only nifty in the way they replace a cell with combination cell/RF transmitter, but it works extremely well.)

-Katie


Edited: 10 June 2011, 3:40 p.m.


#49

Thanks Katie. I am going to give those a try.

#50

If AA-N-adapters are really absolutely unobtainable, there are several solutions:

In the early Eighties a German supplier offered a set with N-batteries and a dedicated charger for the HP-41. The device essentially looked like a modified AA- or AAA-charger. As far as I can remember, the gap between charger contacts and battery was filled by something like a spring-loaded metal strip.

Generally, one can think of all possible kinds of spacers. A friend of mine simply used four screws in his charger. This kind of solution also has another advantage: the charger's contacts for AAA-cells may be used, which means that many, if not most chargers can be used because charging currents like 150 or 200 mA are quite common for AAA batteries.

And finally: make your own adapter - it's not rocket science. Get some aluminium tube with 12 mm inner diameter, maybe 1/2" (GP states 11,65 mm for their GP50NH) and press in another short (solid) piece with 12 mm outer diameter. Maybe you want to add a small spring (usually not required).

And finally, if everything else fails - maybe you have a friend or relative in good old Europe. 8-)

Or try a different approach: get a simple battery holder for four N-cells and connect it to a simple constant current charger. If you don't have one, make your own.

Dieter


#51

All good suggestions and all suggestions that I have considered. I was going to go with the cylinder in a cylinder approach since my search for a commercial product was not leading to much success but I think I am going to try Katie's suggestion first.

Cheers.

#52

Dieter, thank you for the clarification on this and for proposing a product.

I appreciate this very much.


Roger (not a geek on charging :-)

#53

I was able to find some specs on the Lenmar site and they claim automatic charge termination. There are actually 2 versions of this charger, the more expensive one having an LCD display for monitoring charge. I am considering giving this unit a try.

Cheers.

Edited: 9 June 2011, 12:58 p.m. after one or more responses were posted


#54

I ordered two of the BCUNI3 with the LCD Display along with some NiMH N Size cells. I'll let you know how it works.

Gerry


#55

Thx


#56

Hey, Gene.

I found that Amazon sells the BCUNI3 and I ordered the NiMH N Size cells from Batteries in a Flash. http://www.batteriesinaflash.com/assembly-cells/nimh/n-series/n-size-rechargeable-battery-400mah-nimh-1-2v-flat-top-cell

I've been wanting to do this for a while but I couldn't find an charger that would support N cells. Now I'll see how this works.

Gerry


#57

Sounds like you ordered flat top cells. The site Katie mentioned says: "Note: Charger will not work with Flat Top style batteries, only Button Top style batteries."

Dieter


#58

Here is a link I posted in another thread for button top cells: GP50NH

#59

The BCUNI3 data sheet states a current of 1000 mA and mentions no lower currents. Don't you think this is quite a bit ..."too much" for a tiny 500 mA N-cell? Let alone a 200 mA NiCd - in that case the battery is toasted with no less than 5 C.

The data sheet also says that -dU detection is used here. Well, at least 5C will give a significant voltage drop that should be easy to detect. #-)

Dieter


#60

More like 2C on a 500mAH NiMh cell. Still high but maybe tolerable with newer cells. After all there are a number of manufacturers that are putting out cells designed to be charged at 4C (Admittedly larger capacity to begin with).

I have a very nice Maha AA/AAA charger that is completely configurable as to charge rate. I think that the best solution for me, when I find the time, may be to assemble some kind of adapter.

Cheers


#61

M. Joury wrote:

Quote:
More like 2C on a 500mAH NiMh cell. Still high but maybe tolerable with newer cells.

A look at the data sheet gives the relevant facts: GP batteries allow fast charge rates of 0,5 to 1 C (or 250 to 500 mA) if the charging process is controlled and terminated as the voltage has dropped by at most 5 mV.
Quote:
After all there are a number of manufacturers that are putting out cells designed to be charged at 4C (Admittedly larger capacity to begin with).

Yes, especially Sub-C or similar sizes for high-drain applications like RC models or power tools. That's a completely different story. I don't think you run your model railway on 25000 Volts just because British Rail does so. ;-)
Quote:
I have a very nice Maha AA/AAA charger that is completely configurable as to charge rate.

Sounds quite similar to the proposed IPC-1L / BC700 charger. I see the charging current can also be set to 200 mA, which in my humble opinion is just right for the tiny 500 mAh N-cells we use.

Dieter


Edited: 10 June 2011, 9:15 a.m.


#62

Quote:
Yes, especially Sub-C or similar sizes for high-drain applications like RC models or power tools. That's a completely different story. I don't think you run your model railway on 25000 Volts just because British Rail does so. ;-)

Actually I was referring to AA batteries for general use. Rayovac had a 2000mAH version that would rapid charge in 15 minutes and I believe that Energizer has something equivalent.

The Rayovac cells are some of the best I have ever used and are very interesting in that they have internal circuitry to cut off the charge. They are designed to be used in a special Rayovac charger but can be charged by regular AA chargers as well. When charged with regular chargers you will often get an error at the end of the charge when the charger reports an open circuit because the cell itself has opened the circuit internally to stop charging.

All we need is the same sort of capability in an N-Cell...

Cheers.


#63

These special "15-minutes-batteries" have been available for a few years now, over here a similar solution was offered by Varta. The point is that this 4C charge required a special combination of charger and batteries, that - as you mentioned - were equipped with some kind of internal electronics that prevents possible damage. In the meantime they offer a special new charger which is claimed to charge regular (!) NiMH AA-cells in 15-20 minutes - with 7500 mA.

There is something these 15-minute-batteries and special rapid-charge batteries have in common: apart from their different chemistry it's their sheer size resp. volume, or the ratio surface : volume. In a tiny N-cell there simply is no room for electronics (unless you do want to significantly cut down the useable capacity), and high charge rates will heat up the cell much more than a bigger AA or Sub-C size battery. That's why we probably will never see rapid-charge N-cells. And, honestly, who would buy them except nerds like us ?-)

Dieter


#64

Yes. You are correct on all counts. I did note in my original post that the 4C cells are of a larger size and capacity than the N cells that we are discussing but as chemistries get better so do charge rates. We are seeing this across the board with different technologies. For example (and much more recently than the 4C AA's I was referring to) LiPo batteries are now being produced that can accept a 5C charge rate, an accomplishment unheard of just 2 years ago. This is purely a chemistry change as the same chargers are being utilized to charge these newer packs.

And yes, the 4C AA technology has been around for quite some time. I have been using those Rayovac cells for 10 years and am very disappointed that they were recently taken off the market (at least by Rayovac).

The charger that you mention that uses a charge current of 7.5A is interesting. It would seem to me that the batteries would heat up very quickly and without internal protection might be at risk of damage. After all those Rayovac's were EXTREMELY hot when they came off the charger after a 15 minute charge cycle.

Cheers.

#65

I have an old Buddy-L Supercharger (circa 1993).
The Salvation Army store sold it to me for $0.25 USD about 11 years ago. It recharges disposable alkaline cells as well as NiCd's and adjusts to various lengths.

It fell out of the market because it would stop before complete recharging, so users need to run a cell through several cycles.

(I just wish it also recharged 9 volt batteries)

Ren

dona nobis pacem


#66

Hi Ren,

Quote:
(I just wish it also recharged 9 volt batteries)

In the mid-60's, my transistor radio would eat 9v batteries very quick. So I came up with a very quick charger - remember these were standard carbon based 9v batteries. I took a transformer out of an old TV, used a rectifier tube, and had a very high voltage (unknown amperage) charger. I found that about 9 seconds would shove enough power into the battery to run the radio for a few more hours. The battery would be too hot to touch after charging.

Once I miss-timed it and the heat caused the metal covering on the battery to shoot off the end and it ended up embedded in the wall of my room. Thank goodness my parents never figured out what I was doing with all that 'old' electrical junk I had. Forturnately, I only receive a few shocks with my expermenting and survived the experiences. Great fun at the time.

Bill

Edited: 9 June 2011, 2:03 p.m.


#67

Hey Bill,

You reminded me of when I was a kid and at Christmas time my Dad would hang the lights around the house. He would cut off the male and female plugs and hardwire all the strands together so there were a lot of AC plug pigtails floating around the garage. I got curious about what would happen if I stripped the wires of a male plug, twisted them together and plugged it in.

Well, in my room there was a big flash of light, then it was dark and my father was cussing up a storm somewhere outside. I pulled what was left of the plug out of the socket (it felt really cool in the dark), wiped all the soot off of the wall and hid the evidence. He never knew about that one.

Or I could tell you about the time I was up early in the morning, bored, so I took the bulb out of a lamp and turned it off and on an bunch of times (rotary switch) and didn't know if the lamp was on or off. So I stuck my finger in the socket to find out. Oh man did that hurt. It was fun though in a brain-damaged sort of way.

Gerry


#68

It's a wonder we all survived our youth! I suspect nearly all of us here did something like Bill or Gerry did, at some point in the formative stages of our lives.

I remember me and my chemistry being banned to the basement after a couple of odiferous Sunday morning "experiments." And, the cherry red glow of the rectifier tube in my first 300 V DC power supply (the filter capacitor got hooked up in reverse polarity - my Dad actually gets credit for that one!). Also, try loading your squirt gun with salt water and squirting the wall sockets to see what happens!


#69

I remember sticking a bobbie pin in an AC socket and being pinned in the corner of the room watching a shower of sparks pass in front of me. I suppose that's why people kid-proof the electrical outlets these days. It's no fun being a kid any more.


#70

Yep, we did survive. I'd forgotten about the Chemistry Sets we all had - most likely made by Gilbert. Do they still make Chemstry sets for children?

Gilbert had a lot of what would seem very questionable sets for kids:

Metal Casting Set
The Glass Blowing Set
The Machine Gun

And my favorite:
Gilbert U-238 Atomic Energy Lab

which came with three radiation sources and
the very educational comic book
“Learn How Dagwood Split the Atom” .

Following is link to great site of all the Gilbert sets:

My Life with Gilbert Science Sets

Bill


Edited: 10 June 2011, 7:26 a.m.


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