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Manual USB Battery Charger for NIMH aa aaa Batteries

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Machnumber2

New Member
Hello,
Does anyone know of a USB battery charger for nimh aa or aaa batteries that will allow you to manually control the current flow and time of charge on the computer screen? I wold like to charge my batteries specifically at 270 ma for 16 hours. I currently have a best of the best of the best (from men in black) Maha Powerex charger but it is not fully charging my 24 2 month old duracell 2650 mah aa batteries. Yes I have the the manual completly and explored every option on the charger. The closest I can get is the break in feature but that takes 48 hours.

How about a cheap timed charger that allows you to select the current and time?

Thank you for reading my post, I welcome any ideas.
 

audioguru

Well-Known Member
Most Helpful Member
Why do you think your Duracells are not being fully charged?
270mA for 16 hours will over-charge them and shorten their life.

The Powerex "breakin" is 265mA for 16 hours. Then a discharge then another over-charge.
Why does a battery charger need an expensive LCD display? To make lots of profit for the manufacturer.
 

Machnumber2

New Member
"Why do you think your Duracells are not being fully charged?
270mA for 16 hours will over-charge them and shorten their life."

Why do you think they would be overcharged?


"It is better to keep your mouth closed and let people think you are a fool than to open it and remove all doubt"
Mark Twain
 

audioguru

Well-Known Member
Most Helpful Member
Energizer's website has a Ni-MH battery Applications Manual. It shows that their Ni-MH cells are fully charged at slightly more than their capacity then over-charging causes increased internal pressure and temperature.

They recommend sensing the voltage peak or sensing the temperature rise to determine that the battery is fully charged then turn off the charger or use a trickle charge current that is only C/40.
 

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Machnumber2

New Member
1. These are Duracell batteries

2. The amount of energy put into the battery can exceed the amount stored by 150%, therefore the amount of energy you put into the battery does not mean that is what its capacity is. In other words, if you push 1500 mah of energy into a battery, it may only store 1000 mah of it, the rest is lost to heat and other forms. I believe Energizer was simply saying that thier battery could have slightly more charge than is advertised, like having say 1050 mah stored when its capacity is 1000 mah.
 

audioguru

Well-Known Member
Most Helpful Member
You might be looking at the spec's of old Ni-Cad cells that needed 40% more time to be fully charged.
Energizer also still has an old Ni-Cad Applications Manual on their website that talks about it.

Duracell's website talks about nearly nothing, not even listing all their batteries.

In "the good old days" Energizer and Duracell were owned by two competing razor blade companies.
Now Energizer Holdings sells energizer batteries, women's bras and things and Schick razor blades and things. Duracell is owned by Proctor and Gamble who make and sell soap.
 

Machnumber2

New Member
Ok.

It says right on the battery "Standard charge 270 ma for 16 hours" so I think its safe to say it would not be overcharged.

The Maha charger is terminating the charge process to early. The only way for me to defeat this is to use the break in feature setting the battery capacity to 2700 mah-I get a fully charged battery that way but it takes 48 hours. How do I know if the battery is fully charged or now? The Maha charger features a discharge setting that measures this and I have confirmed the battery capacity several times using several methods.

270 ma for 16 hours = 4320 mah

Battery capacity = 2650

4320/2650 *100 = 163%, in other words you need to put in significantly more engery to the battery than will be stored.

Back to the original question though, if you know of a USB charger that allows you to manually control the charge rate and time would you please let me know.
 

Berserk87

New Member
"It is better to keep your mouth closed and let people think you are a fool than to open it and remove all doubt"
Mark Twain

way to insult the only guy trying to help you.


why dont you just make a dc-dc converter that does 5V @ 270mA? you could also use a attiny and a transistor to set a timer.
if your knowledge of electronics is good enough.
 
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Machnumber2

New Member
It was way to blunt sounding, sorry.
I have little knowledge of electronics other than a few semesters of required electrical engineering courses in college years ago. All I can remember from that basically is that v=volt, I=current and R=resistance.

I really dont want to make something or reinvent the wheel althought that sounds fun. You would think a USB with its 5 volts could be easily configured with software to vary the voltage from 0 to 5 and then somehow control the current to keep it constant with a screen on the PC letting you see whats up and control the settings.
 

audioguru

Well-Known Member
Most Helpful Member
Energizer and I think it is wrong to over-charge a 2650mA/hr battery with 4320mAh.
 

kchriste

New Member
Forum Supporter
The USB port on a computer is not capable of varying the voltage without additional hardware such as a USB client and microcontroller.
If you have lots of money and don't want to reinvent the wheel, then get a battery analyzer which can check your battery capacity and charge them at just about any rate you want:
**broken link removed**
The poor man's solution is to connect the batteries to a wallwart via a current limiting resistor, put the batteries down your shorts, and plug it in. When the batteries get uncomfortably warm they are over charging. Sleeping tends to over charge the batteries more. :D
 

audioguru

Well-Known Member
Most Helpful Member
The poor man's solution is to connect the batteries to a wallwart via a current limiting resistor, put the batteries down your shorts, and plug it in. When the batteries get uncomfortably warm they are over charging. Sleeping tends to over charge the batteries more. :D
Excellent idea that is recommended by Energizer Battery Company.
 

Machnumber2

New Member
I have a battery analyzer. Money is very much an issue. How often to you put electronic things down your pants? At least its low voltage DC so hopefully safe for you.

The current limiting resister is an interesting idea. I am not going to do it but that might work pretty well with a timer.
 

audioguru

Well-Known Member
Most Helpful Member
I bought Energizer Ni-MH battery cells with a charger. the charger is simply a timer. It charges dead cells that it came with but it seriously overcharges cells that are already charged and lower capacity cells.

A proper charger senses that the cells are fully charged then turns off. It refuses to overcharge cells that are already charged.
 

Machnumber2

New Member
Yes thats correct. A timed charger will also fully charge a battery when a smart charger sometimes will not. Sometimes the smart charger terminates the charge too early as is the case with my Maha charger. The charge curves for different brands and capacities of nimh batteries may not all be exactly the same, so a smart charger has to use a once size fits all approach to estimate when the battery is fully charged. In order to fully charge the batteries I have, they need to start off dead, then recieve 270ma for 16hours using a timed charger. Its possible that another brand of smart charger would do a better job, but I am not going to buy another one and chance it.
 

audioguru

Well-Known Member
Most Helpful Member
A good charger design senses the voltage peak that occurs when a Ni-MH battery is fully charged. The peak is very small so sometimes the circuit misses it. So a timer and a temperature sensor are used as backups.
 

Machnumber2

New Member
Guro...and your point is...?

Chipee...You see I think the maxim ic you mentioned is a chip right? That seems like it would be too much work and study for me.

When I googled it, I did come accross several message boards discussing early termination problems with smart chargers. The preferred method does appear to be a timed charge from a dead battery at the recommended current and hours.
 

audioguru

Well-Known Member
Most Helpful Member
Guro...and your point is...?
A good charger circuit does it properly.

Chipee...You see I think the maxim ic you mentioned is a chip right? That seems like it would be too much work and study for me.
The Maxim charger ICs are simple and their datasheet explains clearly how to use them.
If English is a problem then learn it.
 

Machnumber2

New Member
I think so too. I think the Maha Powerex charger is top of the line or close to it. But I got this thing about 3 years ago. Maybe the batteries nowadays have more capacity, so the curve is different and therefore it changes the charge termination behaviuor. The charger maybe would work fine for a 2000 mah battery instead of a 2650...

Letter ending I was going to use -
...so maybe its just the battery who knows.

Letter ending I am using after I read your "english" remark.
... so you see numbnuts it could be that the charger is optimized for lower capacity batteries. Frankly its been one moronic idea/suggestion after the next here and then I ask if there is anything already made and a guy with a double digit IQ suggests using a computer chip and building a charger. Good god.

Aaahh that was fun. Please print out this post on your printer, roll it up cram it.

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