# First build help

Discussion in 'The Projects Forum' started by theU4life, Apr 10, 2013.

1. ### theU4life Thread Starter New Member

Apr 10, 2013
4
0
This is my first post so dont bash me too bad... I am trying to make one of those altoid can phone chargers and all the info i have found dont seem to be very safe nor efficient. My question is for the battery setup i.e. 2 9v with 5 volt reg. or 2 AA... The output on my charger is 5v 2A... Im not really sure if i want to use a voltage regulator because the voltage of the batteries can vary so much if voltage gets below the regulators min doesnt the regulators voltage become unknown? I also would like to mount a solar panel to charge the batteries and or supplement if batteries get low... The panel i have found the fit perfect on the can has an output of 6v max and 1.5W max... This is the first time ive tried to make or "design" something like this soo any input or advice would really be appreciated... Credit will always be given when due...Im not the type to just build a kit i really want to understand how to design circuits... BTW I am in school for electronic technology so i do have a basic understanding of most things.... Thanks in advance!!!

2. ### wayneh Expert

Sep 9, 2010
15,886
5,963
Look for MintyBoost. A well-travelled path. I'd go with the AA approach, since these hold much more energy.

Adding solar could be difficult. The way to approach this is to look at the energy balance. That is, start with the energy required to do what you want. Charging a cellphone battery requires a certain amount of mAh at a certain voltage, for example a battery might be spec'd at 2000mA•h at 5V. That means it can deliver 10,000mWhr or 10W•hr. But to actually drive that much energy into a battery, after all losses in circuitry and inefficiencies, sadly requires about twice that much energy. Now think about how much sunlight you have and time for charging in full sun. Maybe 4 hours at best? So you'd need a 5W panel for 4 hr to get the necessary 20W•hrs.

Sooo many of these solar power projects end abruptly once the reality sets in.

3. ### theU4life Thread Starter New Member

Apr 10, 2013
4
0
Thanks alot that info help alot... I might scratch this idea doesnt seems to be a very efficient charger after all that I have read...