do you mean charger for mobile phone?usually,the charger are constant voltage to charge the mobile (4.2V)then when the battey's voltage have reach to 4.2V then change to constant current to charge the mobile

Tom, you are brave and you said it right, I hope you don't get too much Flak from the "others".....

I gave you a GA for bravery.....

Andy, I get flak from most, and have the scars to prove it. Not worried about it. I can argue my points, and I couldn't care less about the "approval" of my peers. You are all my peers, regardless of viewpoint. I can only try to get people to think (or shoot them, but that has a whole 'nuther set of consequences).

Me and Flak are old friends...but that's for your comment.

O, it is excellent to have a giant's strength; but it is tyrannous to use it like a giant.

- William Shakespeare

Couldn't you just say 'I dont know',or even better don't say anything.That was a pointless long winded insulting diatribe.

Try to read between the lines to extract the kernel of a question and have a little patience with those who don't have a perfect grasp of English.

The question is legitimate as the charging of batteries is becoming more complex with constant voltage,constant current,temperature limitation and individual cell management involved.We can all probably learn from the input of some battery specialists.

You imply that all we need is a tranny, reccy,and a pair of leads with big croc clips,those days are gone,listen and be educated

Let me see if I can pose a similar question (at the risk of life and limb) that may elicit an answer that will help our poor frayed and disparaging original poster, Sanmani. Be not afraid sir. We all risk the same fate. Here tis>>> I have acquired (OK I bought it "as is" on Ebay) a Radio Shack small palm sized digital camera. Sorry I do not have the model number or paint specs, but it does not power up even when on a charger and the battery installed. I has a lithium-ion battery that has 4 terminals no combination of which shows any residual charge or voltage when tested using a Fluke digital multi-meter. There are no markings on the battery that would indicate the positive or negative terminals. I have read on other threads on CR4 of the dangers of diddiling with this type of battery due to the possibility of releasing the smoke in a violent event. The question>>> can this battery be safely charged/tested knowing only the facts presented, is the battery likely to be dead beyond recovery, what needs to be done to test the camera without the battery if anything? I have girded myself in armor so fling away if you must.

TAKE BATT OUT OHM FOR GND

I hesitate to suggest the following while the health and safety brigade are watching,but what the hell,I'm sure that if you just wear goggles and gloves you will survive relatively unharmed,after all it isn't a hand grenade.

Cut open carefully the plastic case,use either a soldering iron with an old bit sharpened to a knife edge or a miniature saw blade in a high speed tool,(gloves mandatory).There is usually an obvious line where the case was glued together so follow that if possible.

Prise open the case with minimum damge so you can glue or hot weld it back together.

You should then see what the external contacts are doing,probably one pair is to a temperature sensor or switch and the others to the actual battery.

The other possibility is that the individual cells have connections for charge balancing,i.e. to charge each cell individually,but if you charge the cells in series at a very low rate there is little risk.The balancing and other precautions are mainly to enable rapid charging.

Identifying pos and neg is usually easy as the manufacturers use coloured wire from battery to contacts or it's obvious which is the 'case' of the bat. which is neg.

You can try charging using a car battery charger and a small 12v say 2 watt bulb as a limiter .Dont try charging without a limiter.Few batteries can be destroyed or be hazardous if you limit the charging current to a few hundred milliamps.

I've manage to ressurect almost every dead battery I've come across so far,albeit often with only a fraction of the original performance but enough to use the camera,etc.

Best of luck,but be careful out there.

OK health and safety nuts,you can have a field day.

Here is the short end:

Vac - - |Transformer| -- |Rectifier - - Regulator - - Pulse Circuit| - - Battery

I hope you don't care to wind your own inductors for the transformer. Buy this for sure. Voltage down and current up!

Most chargers are made for AC voltage sources, save your car. So guess what... you need a rectifier.

Rectifiers are simple circuits. A Google search should do you good (try the Wheatstone Bridge - I'm looking at one right now on Wikipedia).

So now you got voltage swinging from Vpeak to 0 Volts only. Still, it swings.

So your regulator (a capacitor next to it somewhere too) should change this.

Bang, you got a factor (proportional to the number of turns on your inductors) of your Vpeak from your original AC feed regulated almost at the same voltage (less your Vdrop from the Core losses, stray fields, and resistance on your transformer, regulator, resistor network on your bridge, etc.).

Awesome, you have your DC source, but guess what Daniel Son, This crap charges nothing.

This only provides a DC source at the voltage you need (if you bought the right transformer).

To charge you need a specialized circuit for the battery specified. All rechargeable battery types use different circuits. Here is a simple sample for a Li-ion circuit: http://www.shdesigns.org/pdf/lionchg.pdf.

I am sure Metal Halide Batteries need different circuits.

I remember in school (years ago) we were asked to provide a similar project, and the batteries we chose used a complicated pulse driven charge for the battery bank (these were the most efficient, and quickest charging at the time).

So, Green One, good luck. Read before you ask your next question (try Google, Wikipedia, etc. first then enter the Den of Knowledge). Play with caution also, Reckless Inquirer (batteries will explode if you do not design safety mechanisms (voltage controlled switches can work well with some logic flip-flops).

If you can buy the technology, don't waste your time re-inventing the wheel (my family already has long standing patents for these great shapes, perhaps one day you can invent a pill to make men manlier), just ride with the one you can.

Oh, and next time, try to be more precise in this forum. Your question gave no specs. (The name of this place is GlobalSpec - BTW) and so we can't give you specifics on what you ask about. This frustrates those that are Guru's in the field because you still have to learn to ask the right questions.

But don't lose hope. The Guru's still gather around the Oracle and wait for you and me to learn how to ask the questions that will bring light to our projects. I think this pill you will make, should smell bad to women (so that they do not ingest the Manlier pill, it could mean the end of femininity as we know it).

For now, you read until your eyes burn about Transformers, the Wheatstone bridge, and rechargeable batteries and their uses young grasshopper. Soon, answers to questions not available on general literature will be ready and adequate for your elder masters.

With honor (no honor in asking without you looking for the light yourself), respect (you can not come back here and post silly remarks to counter others' foolishness), and persistence (you can not give up until you finish your quest with success) you will be charging telephones around the world soon!

=)

BTW - take nothing personal but take it like a man (you might need a pill for that).

It seems you can find what you interested at CR4 forum threads.

Meanwhile, charging the NiCd or Lithium battery is very complex process. It's impossible to do that safely and effective without applying microprocessor which should control a lot of parameters mentioned at Oldeng post. I would suggest you to visit for instance Microchip site or any forum dedicated PIC controller programming (one quite suitable for this purpose) to find there more detail descriptions.