How to Charge an 8 AA NiMH Battery Holder?

[jakfish]

Hello, All,

To power a M1 MBook netbook computer, I've built an 8 AA NiMH battery holder with a female socket lead, onto which I've connected the right-sized male plug to charge the M1.

If possible, I'd like to charge the batteries in the holder rather than take them out and put them in a separate charger. My dilemma is much better explained by this link, where a gentleman successfully built exactly this for his M1:

http://www.pocketables.com/forum/showthread.php?t=2415&page=3

I live in the USA and I can not track down a charger/hardware that can make this work. Because the battery holder has a female socket, I obviously have a choice of plugs to work with.

Any suggestions? Many thanks,
Jake

 

[Martaine2005]

Hi jakfish,
I presume the batteries are in series 9.6V?
Any radio controlled transmitter charger will work. Providing it is 9.6V.
Then cut off the end if the polarity is reversed. From memory Futaba were the odd ones out.
But just solder the required size jack with correct polarity.

Martin

 

[jakfish]

Hello, Martin,

Thank you for the quick response. Yes, the total voltage is 8 x 1.2 = 9.6v

But as the pictures show with successful charging of battery pack (in link listed above), there's a need for a double-female coupler.

I'm pondering this:

http://www.amazon.com/ACS-Traveller...=8-42&keywords="ANSMANN"+battery+charger+nimh

But I'm uncertain if: a) it'll work b) how to connect it to the battery pack. I either have two male leads or two female sockets.

Thanks again for posting,
Jake

 

[Martaine2005]

Hi Jake,
I couldn't actually open the linked pictures.
The double connector is probably because your battery is in the middle.
So charger/adapter to battery and unit being powered.
Something like this?

 

[jakfish]

Hi, Martin,

Thanks again for the fast post.. Re: the link above. This is the key picture.

I can't see the ends of your suggested couplers. Do they match this? (Here's hoping my pasted pic shows up in my post.)

Jake

 

[Martaine2005]

Hi Jake,
That pic is just a coupler connection because both the charger and battery already have the same connector.
You can omit the central "connector" by replacing the battery and charger connectors to male and female of your choice.
Example.

 

[jakfish]

That's what I want! Thank you, thank you. Could you please give me the exact terminology of these things? I'm at a loss when I google/shop. Secondly, in your opinion, would your suggested charger work with this arrangement? Even though it says such ominous things such as "For JR Transmitters Only"?

Again, much indebted,
Jake

 

[Martaine2005]

Hi Jake,
These connectors are called DC connectors. The pic I linked have screw terminals for easy termination. I prefer soldered joints. But if you don't have a soldering iron, these are ideal.
You must pay attention to polarity!!! Red to red and Black to black etc...
The charger I also linked was just an example. It would work perfectly well with ANY 9.6v Nimh or Nicad.

Martin.

 

[jakfish]

Hi, Martin,

Thank you for steering me through this. I ended up buying the DC connectors you suggested, but decided to get this charger:

http://www.amazon.com/gp/product/B001AVUAVC?psc=1&redirect=true&ref_=oh_aui_detailpage_o00_s00

The Tenergy adapter seemed to have more charging monitors and safety switches for the hard-of-thinking like myself, and I'll cut the Tamiya end and fasten on your suggested DC connector and match its female end to the 2.1mm male adapter I bought for the battery holder.

I'll post back when it all comes and thanks again,
Jake

 

[jakfish]

A follow-up note: success. After following Martin's splicing instructions, I set up the Tenergy multi-voltage adapter (with its new female dc connector fastened in place of the Tamiya harness), it flashed its red charge light upon connection to the 8 aa nimh battery holder, and two hours later (at 0.9A, for partially drained cells), it showed a solid green light connoting a full charge.

I have read that nimh's should only be charged at 0.9A as opposed to fast charging at 1.8A. Martin, do you hold with that? One Tenergy safety feature is an auto shut-off after five hours--I do not think five hours, at .9A, is sufficient time to charge 8 aa's with their 2000mAh capacity if they were substantially drained.

I'd be interested to hear other folks' opinions.

Thanks again for providing such a helpful forum,
Jake

 

[Bluejets]

5 hours at 0.9A = 4,500mAh.(roughly) so your assumption is incorrect.
As far as rate of charge , it depends on the cells involved and manufacturers specs.

 

[jakfish]

Hmm, neither math nor electronics are my strong points, but if I have 8 AA nimh batteries at 2000mAh each, isn't that 16,000mAh, more or less? Or perhaps my previous post mentioning 2000mAh wasn't clear enough--2000mAh is for each battery, not the holder.

I apologize for any confusion.

Jake

 

[CDRIVE]

Hmm, neither math nor electronics are my strong points, but if I have 8 AA nimh batteries at 2000mAh each, isn't that 16,000mAh, more or less? Or perhaps my previous post mentioning 2000mAh wasn't clear enough--2000mAh is for each battery, not the holder.

I apologize for any confusion.

Jake

Your cells are wired in series. Because of this the 2,000mAh rating is not additive. Only the cell voltages are additive with series connected cells.

Chris

 

[Martaine2005]

Hi Jake,
Yes, Bluejets and Uncle Chris are both correct. (as usual)
Regarding the cells, each one 'should' have it's Maximum and standard charge rates printed on them..
Example: Standard 230 mAh 12/14 Hrs - Maximum 1150 mAh 2.5 Hrs.
Also as Chris pointed out, only the voltages can be added together in a series configuration.
Parallel connected batteries are the opposite. Add the mA/Amps but voltage stays the same as the one battery. Example with your batteries:
1.2v x 8 = 9.6 @ 2000 mAh.. Series..
2k x 8 = 16000 mAh @ 1.2v.. Parallel..
Real world use is often very different due to many variables.. Cells, charger, wiring, temperature, age, etc etc.

Martin

 

[jakfish]

You folks are very patient and I appreciate you walking me through this with such clear explanations. Between 1800mAh and 5000mAh packs, Tenergy recommends 1.8A charging. 2000mAh is at the high end of 0.9A specs and low end of 0.9A. If it'll do it in five hours, I'll stick to 0.9A. The gentleman who built the M1 pack (cited in the first post) appears to use fast charging--but he's long gone from the forums.

Much obliged again,
Jake

 

[Martaine2005]

Hi Jake,
Tenergy make batteries and chargers!
Chargers seem to last years...However, if batteries lasted years...No more Tenergy!!!
It's never a good idea to fast charge batteries, let alone only fast charge them. They will eventually die sooner than charging over night without the battery getting hot.
Yes I am being cynical, but there must be some truth in it somewhere!
Trust the battery specs rather than a third party charger.
Just my 2 cents!

Martin

 

[jakfish]

That makes a lot of sense. I'll try it at a slow charge and post back if a slow charge doesn't appear to work. Fingers crossed for an overnight charge.

Jake

 

[Martaine2005]

I am positive the batteries will like you for it!
Nothing wrong with fast charging occasionally, but people don't let the cell cool properly before use.
So they are using a 'still cooking' battery..

Martin

 

[cjdelphi]

Fast charging is not good for cells...

When charging batteries, heat generated is simply wasted energy thanks to the internal resistance at play...

Lower currents keeps heat down, cheaper to charge, and less stress means they last longer and hold more charge...

But, a 1000ma battery rating might only be 500ma requiring only have the time to charge, so a slow charge while monitoring battery voltage is a safe bet, I prefer to charge 1 cell at a time though .

 

[jakfish]

I have learned a great deal about electronics through this thread. Here's a question that always generates a lot of answers: does a lithium ion battery suffer significant deprecation simply by the plugging in of an a/c adapter? For instance, my M1 has a 2400mAh l-ion battery. If the battery sits in the machine all night and I plug in the a/c adapter the next morning, there's a very brief charge.

I've read that just the act of connecting a/c to a battery constitutes a cycle, the same as a full discharge/recharge. Other articles say that's not true. And other articles feel the wear on the battery is somewhere in between.

The nice thing about this battery holder is that it's easily Velcro-ed to the M1 bottom, allowing it to stay connected, as if the M1 is always connected to an a/c adapter, a workaround to this dilemma.

But I'm curious to hear your veteran opinions.

Jake