12v battery help

[andy_con]

im trying to find a decent 12v battery with charger to run some leds, these leds -


http://www.ebay.co.uk/itm/3018083492...MEBIDX%3AITive


been making some bits like this using them






and have been using a mains adaptor, but that's rubbish I need a small 12v battery.I know you can get these but I'm not sure they would last very long at all and they aren't rechargeable.


http://www.ebay.co.uk/itm/Genuine-2-...WKtUxAhvanyone


got any suggestions?

[buffo]

According to the E-bay listing you posted the LEDs you are using draw 400 ma. How long do you need to run them on a single charge?

I would suggest a 3S LiPo battery. Something like a 2200 mAhr pack would last nearly 5 hours on a single charge and cost around $15 if not less.

Here's an E-bay link for a $12 battery that would work. And here's a link to a $16 charger for it.

Adam

[andy_con]

Well no set time but a few hours.

Thanks for the link but look at the size of it, I might as well use 8x aaa batteries which make 12v perfect.

I was after mobile phone battery size

[lasersbee]

Since you don't require a high output current battery... you could also use
tubular 3 Li-Ion batteries of your choosing. They make them in a lot of
different sizes and capacities and are rechargeable.

Jerry

[buffo]

Well no set time but a few hours.

If you only need a few hours, you could cut the battery size in half and go with a 1000 mAhr pack.

That being said, the pack I linked to is roughly the size of a stick of butter, which really isn't that big. It can also be found in a shorter, wider pack that is very close to the size of a deck of playing cards with the same capacity. (And again, you can cut that in half if you can live with a 2-3 hr battery life.)

Thanks for the link but look at the size of it, I might as well use 8x aaa batteries which make 12v perfect.

8 AAA batteries in series won't last nearly as long as the battery I linked to, and if you buy rechargeable AAA batteries it will end up costing more. (Not to mention the fact that 8 AAA batteries would make for a larger pack as well.)

I was after mobile phone battery size

A mobile phone battery is 3.7 volts. You'd need 3 of them in series to get 12 volts. At which point you are at the same size as the battery I linked to.

Sorry dude, but Lithium-ion and Lithium-polymer are the two best choices for power density. Non-rechargeable alkaline batteries don't even come close. If that isn't enough, then you're stuck with an AC power adapter.

One thing that might help is to actually measure the current draw of the LEDs. If they don't draw the full 400 mA that is spec'd in the E-bay listing, you can get away with a lower-capacity battery (and thus a smaller package) and still have decent run-time.

Adam

[catalanjo]

@ Sorry dude, but Lithium-ion and Lithium-polymer are the two best choices for power density. Non-rechargeable alkaline batteries don't even come close. If that isn't enough, then you're stuck with an AC power adapter.

Have to disagree here a bit here ...... NiCads will also hold big charges and have the advantage that they can be stored "discharged".
I have the feeling that these will get used in fits & starts with maybe months in between.
(They also don't tend to explode when they get upset or neglected)

Cheers

[lasersbee]

Have to disagree here a bit here ...... NiCads will also hold big charges and have the advantage that they can be stored "discharged".
I have the feeling that these will get used in fits & starts with maybe months in between.
(They also don't tend to explode when they get upset or neglected)

Cheers

Using a proper charger with Li-Po and Li-Ion batteries and some common storage
procedures will keep them safe.
The Ni-Cad batteries are well know to have a "Memory" effect. They will not hold
a full charge if re-charged before depleted.
Ni-Cad batteries also grow wiskers in the dielectric when not use for periods of
time causing internal shorts discharging the battery and making it near impossible
to re-charge them fully. There is of course DIY procedures to reduce the wiskers
after they have formed.
Been there done that. Only Li-Po and Li-Ion batteries for me.

Ultimately the choice is yours....
BTW.... there are no Ni-Cads in laptops.

Jerry

[catalanjo]

@ Using a proper charger with Li-Po and Li-Ion batteries and some common storage
procedures will keep them safe.

Agreed but "proper charger and common storage" might well not be Andy's cup of tea.

@ " They will not hold a full charge if re-charged before depleted."
....good odds on him leaving lights switched on until batteries are fully depleted!

@ " Ni-Cad batteries also grow wiskers in the dielectric when not use for periods of time "
...even when fully discharged

If so,...... I bow to superior knowledge/experience ! .....Andy, sorry for bum steer.

@ "There is of course DIY procedures to reduce the wiskers after they have formed." = NiCad shaving ? ...care to elaborate ?

Cheers

[buffo]

Lithium Polymer and Lithium Ion batteries have greater voltage and charge density when compared to Ni-Cd and NiMH batteries of the same size and weight. In the case of the NiCD, the capacity difference is better than 40%.

Also, as stated above, you don't have memory issues with any Lithium batteries. NiCd batteries have been on their way out for a long time now, and for good reason. (They suck compared to modern battery technology.) NiMH is better, but it is still nowhere near as good as today's Lithium-based batteries.

As for the long-term storage issue, that is only a major factor for Lithium Polymer technologies. You can store a Lithium Ion battery at full charge or at zero charge if you want. This is one of the reasons why laptops and phones use Lithium Ion and not Lithium Polymer batteries.

Truthfully, Li-ion is the better choice in nearly all categories except price. They are nowhere near as cheap as Li-pos are. But they can be charged very rapidly (Li-pos generally can't), they can be discharged even faster than Li-pos, and they are more resistant to mechanical shock damage than Li-pos.

Regarding charger safety, this goes for all batteries: use the appropriate charger or bad things can happen! You can damage a NiCd by improperly charging it as well. The difference is that Lithium batteries (and especially Lithium-Polymer batteries) can get hot enough to catch fire due to the extremely high charge density *and* the reactive nature of Lithium...

Adam

[Bbe]

Something like this+this+this+maybe this=12V and AA size