[earleybird]

If , like me , you have muddled on, recharging AA rechargables of various types with various chargers using indeterminate charging times hoping that the charger will sort the charge rate and times automatically then the following information might be of interest.

Ni-Mh Batteries
There is a simple formula you can apply to determine how long your batteries need charging for to achieve a full charge.

First make a note of your battery power rating . (Mine are 2800mAh)

Then look at your charger and find the charge rate .It will probably say something like 'Sec: AA-2.8/5.6V -- 750mA '

Sec (Secondary output ie charging output)
AA (battery type )
2.8 (max 2800mAh ie 2800 milliamps per hour output)
5.6v (5.6volts the maximum voltage supplied ie 4x batteries at 1.4volts)
750mA ( the maximum charging output )

The bit we are interested in is the mA rating which could be anything from 150mA (very slow charging rate ) to 750mA (untra fast charging rate)

In my case I take the battery rating (2800) and devide it by the charger output rate (750) and the answer is the number of hours it will take my charger to fully charge my batteries.
2800/750 = 3.7 hours

You might find that like me you have been seriously undercharging your batteries. I had recently been using an old 150mA charger which works out thus
2800/150 = 18 hours gulp

Right then any questions ?

[Scousemouse]

Thanks Earleybird, that looks very useful.

My AAs often come out the charger, "F*&% M* H**$-fire that is hot"
Which I suspect implies I am overcooking them.. Could this be dangerous? or does the charger ease off when they are charged to the full?

Peter

[earleybird]

Originally Posted by Scousemouse

Thanks Earleybird, that looks very useful.

My AAs often come out the charger, "F*&% M* H**$-fire that is hot"
Which I suspect implies I am overcooking them.. Could this be dangerous? or does the charger ease off when they are charged to the full?

Peter

it depends on the charger. Fast charging will make the batteries very hot but most recent chargers have a small electronic circuit incorporating a 'chip' which detects how much your batteries are charged and either reduces the charge rate to a trickle or stops charging. These chargers are generally called smart chargers.
Some chargers have a small electronic circuit board which simply incorporates a timer which although preventing over-charging is crude and not strictly speaking a 'smart'charger.

If you are using Ni-Mh batteries then you should make sure that you are using a Ni-Mh type charger not an Ni-Cd charger.
If you want fast charging then use a charger with at least 500mA output or use batteries with a lower rating ie 1600 or 1800mAh .

Ni-Mh batteries do not have a 'memory' so do not need periodic conditioning. Ni-Cd batties do develop 'memory' over time and its recommended that they are discharged and fully recharged every 10x charges or so.

[Overread]

What happens if your charger has no fixed charging rate? Maha C9000 (or Powerrex C9000) has multiple charging amounds (and discharging rates too). I'm never quite sure what is the best setting save that slower is generally better for the batteries.

Overall though the cheap rechargers are a waste of time and damaging to the long life of the batteries - my cheap energizer charger would push the batteries out very hot and had no cutoff - so very easy to "overcharge" and have the batteries sit there just cycling in the holder. It charged them very fast, but fast, hot recharges with no cut off took their toll and my batteries started lasting me less and less time.

So as well as getting enloops I also spent some cash on an overall better charger so that I could at least have something thatwould not damage the new batteries as well. Plus a good charger saves me spending £5 or more on regular batteries in shops each time my rechargables die and I don't have time to recharge them.

[earleybird]

it is a common fallacy that slower charging rates are better for batteries.

Its actually better for Ni-Mh batteries to charge them fast. These batteries are made to do just that.You need at least a 500mA charger output rate

If you are using the Powerex c9000 the formula still works just use the selected charging output
I can thoroughly recommend these batteries which are at a great price too.
http://www.amazon.co.uk/gp/product/B...ef=oss_product

[Overread]

I've got my three sets of
http://www.amazon.co.uk/Sanyo-Eneloo...2488168&sr=1-1
so for batteries I am well sorted for the while :) The fact that they last so well between uses is fantastic!

Although I do have the 7dayshop 4AA battery holders as well - good for keeping the batteries in sets for the flash whilst also not getting lost like exastic bands tend to

[nick scarle]

I have a Uniross X-Press 300 charger which takes AA or AAA batteries.
The label reads:
AA (2.8V ... 285-320mA 0.896VA)
AAA (2.8V ... 115-130mA 0.364VA)

Any ideas why the charging rates should be so different depending on the type of battery?

Nick

[earleybird]

Originally Posted by nick scarle

I have a Uniross X-Press 300 charger which takes AA or AAA batteries.
The label reads:
AA (2.8V ... 285-320mA 0.896VA)
AAA (2.8V ... 115-130mA 0.364VA)

Any ideas why the charging rates should be so different depending on the type of battery?

Nick

No I haven't sorry Nick. Its an interesting observation though .I can only assume that AAA batteries don't need to supply such a high sustained output. AAA are usually only used in TV remotes, MP3 players/ipods ,and other low -load devices

Why is the output voltage only 2.8volts ? Presumably it only charges 2x batteries at a time or does the charger have two seperate charging circuits?

[njlarsen]

I looked at the charger I had at home yesterday, and if I remember correctly, it said 2000 mA. Now that is a lot above the 500 mA mentioned above, and again makes me wonder: why would it be better with faster charging? Don't you damage the membrane inside the battery (if I have even half way understood how a battery works)?

Any references on fast charging being good for the NiMH batteries?

thanks
Niels