Battery question!

[1911operator]

Im powering a small led using my cellphone battery for fun. and I have this question to ask.

Would using 4 AA batteries last atleast twice as long as my phone battery?

Phone battery: 3.7V 2100mah

4X AA: 5.5V (each 1900MAH) so to be safe 7500mah

Could I theoretically connect these 4 batteries to my cellphone and charge the phone twice? and also power the light twice as long?

 

[schizeckinosy]

Nope - if you connect the AA's in series, you have the same mah at a higher voltage, so in your case, 4.8v or 6v depending on chemistry, at 1900 mah. That is a little more energy than the cell phone (9.1 - 11.4wh versus 7.8wh) but not double.

 

[1911operator]

these are connected parallel btw. that should make a difrence right?

 

[jimboutilier]

Im powering a small led using my cellphone battery for fun. and I have this question to ask.

Would using 4 AA batteries last atleast twice as long as my phone battery?

Phone battery: 3.7V 2100mah

4X AA: 5.5V (each 1900MAH) so to be safe 7500mah

Could I theoretically connect these 4 batteries to my cellphone and charge the phone twice? and also power the light twice as long?

Volts x Amps = Watts 1.5x1900x4 = 11.4wh vs 3.7x2100=7.8wh There are boxes that allow you to use two or more AA cells to power/charge a USB device. In theory you could charge your phone about 1.4x via 4 AAs of that spec (adjust if you are talking Eneloops as they are only 1.2v each not 1.5, and there will be some loss converting to 5v USB current). Same for powering a light - its watt hours that give the best rough estimate of capacity.

 

[schizeckinosy]

In parallel you have 1.2v at 7600mah, or still 9.1wh of energy. TANSTAAFL

EDIT - Jim beat me to it.

 

[Jash]

If they're connected in parallel you won't have 5.5v, but rather 1.5v with four times the capacity.

 

[1911operator]

ah yea u guys are right, they are in series. sorry im a noob with this. :/ so what could I do to charge the cellphone that would allow me to get the most power and effiency?

 

[1911operator]

what if I connected 2 batteries in series, and then connected them to this: http://www.ebay.com/itm/Small-DC-2-...744?pt=LH_DefaultDomain_0&hash=item1e83b94400

so the output would be 5v 1a

 

[schizeckinosy]

what if I connected 2 batteries in series, and then connected them to this: http://www.ebay.com/itm/Small-DC-2-...744?pt=LH_DefaultDomain_0&hash=item1e83b94400

so the output would be 5v 1a

Yeah that's basically the type of booster that you need, but there are a ton of cell phone chargers already out there that do this for you, unless you are looking for a project!

 

[1911operator]

yea im looking for a project. I just tried that and the booster got really hot, i could put my finger on it for about 2 seconds and it burns. looks like its not liking that. is there another booster that would be better?

 

[schizeckinosy]

I'm not really up on these booster circuits, but I'd think you would want a heat sink for it - it is putting out 5 watts! Oh, and try running it on 3 cells so it does not have to boost so much.