How much power needed to charge a battery?

niallniall

Hello I am new here, Dont really know if I'm asking in the right place, but. Can anyone tell me how much power I would have to put into a 6v rechargeable battery to actually charge it. I am looking for the smallest ammount of power I can get away with to be able to Charge the 6v battery.

Thanks People.

DaleSpam

You should be able to charge it with an arbitrarily small amount of power if you are willing to spend an arbitrarily long amount of time. In fact, the smaller the power you use the more efficient the charging will be because you will have less heat.

-Dale

niallniall

Thanks Dale, How small is arbitrary? less than 1 v?

Pengwuino

Depends on what kind of battery you have (capacity wise). Volts is not a unit of power either. You will need to give it 6V i believe and how much power you need is completely dependant on what the capacity of the battery is.

I've never heard of a 6V rechargable battery (I've seen 4 1.5's in series....) so I wouldn't have a clue how much power you would need.

I believe a AA battery can supply roughly 3Watt-hours of electricity at normal draw which is about 1100 Joules of energy....

Danger

Since most 6V batteries are the spring terminal or screw terminal types, I have also never seen a rechargable version of them. The type that are available here will recharge AAA, AA, C, D or 9V. Anything else pretty much has to be bought new.

Pengwuino

ohhhhhhhhhh yah, those kinds of batteries. What are those things called with the spring terminals... lantern batteries?

Danger

Correctomundo, oh flippered one. Both types are. The spring terminal type fit inside a lantern housing. The screw terminal type actually becomes the main body of the lantern, because the lamp holder part screws onto the top of it.

berkeman

Welcome to PF, niallnaill. Do you know the relationship between power and energy? Are you familiar with the energy content of the batteries that you want to recharge? A volt is not a measure of either power or energy -- what exactly are you trying to optimize?

DaleSpam

Well, your battery is 6V so you will need at least 6V as indicated by others here. You can use an arbitrarily small current, meaning as small as you want, 1 mA or even less if you wanted. Power is voltage times current, so that could be as small as you want. (e.g. 6V * 1mA = 6 mW)

-Dale

rcgldr

The voltage just has to some amount over 6 volts, or since a typical 3 cell battery is really 6.6 volts, you'd need 6.6 volts to top off the battery. The initial voltage on a drained battery would be less, so you'd need less voltage, but as it approached full charge, you'd have to keep increasing voltage to just exceed that of the battery.

Most batteries include an capacity rating, but the actual capacity varies with the load (or charge rate). AA nicads for radio control models typically have about 1.1AmpHour capacity. AA nimh batteries hold about 1.7 AmpHours. LiPoly batteries are even better in terms of capacity versus weight, but usually come in flat packs, and are combined both in series and/or in parallel in a pack to increase current output (parallel) and voltage ouptut (series). Nicads, Nimh, LiPoly, and typical dry cell batteries work best when cold. Lead-acid batteries work best when fairly warm.

niallniall

Thanks for all the help guys and girls. I actually no nothing at all or very little about physics. Just what I learned in school basically, and the stuff I have read here.

So am I right in thinking that if I have the right battery, lets say 6v I can fully recharge it using a 6v supply?

Also how many watts is equal to 6v?

Thanks in advance for answers :)

Pengwuino

Volts and watts aren't the same unit so theres no way of saying what it's equal to. Since we're dealing with a battery, we say it's DC current.Watt is a unit of power. It is Joules/Second. Joules is energy, it's the water in the cup, it's the coal on the train, it is the main thing here. You can determine how many watts are being produced when you know the current being generated by multiplying the Volts * Amps (current). When you're looking at how many Joules can be stored in a battery... it's more meaningful to talk about WH (watt-hours). If your battery has 500Watt-hours in it, that means it can produce 500 watts for 1 hour or 250 watts for 2 hours etc etc. That means it can produce 500 Joules per second for 1 hour which tells you it has a capacity of 500wh's.

The problem is, in your situation, is that the battery is already empty. You will simply have to hook it up and let it charge because unless you know anything else about the battery, theres no way of telling it's capacity.

rcgldr

A typical 6 volt battery is really 7.2 volts, and charging voltage is a bit higher than this to top off the battery.