DIY USB Battery Power Pack

Should I include diode for reverse polarity protection?
Oh yes... deffinitely, if it can go wrong, it will go wrong.

Would I need voltage regulation?
Prob' not

Anyone got any experience/ circuit diagrams?
Not me, sorry

Del

Hi. Try this link. This talented young engineer has produced several interesting projects. This is something like you suggested. You can also ref this from MAKE...

http://www.ladyada.net/make/mintyboost/

-k-

You matched out the voltages all right, but what about the current requirements?

You matched out the voltages all right, but what about the current requirements?

I thought it would just pull the current it required until the batteries went flat, am I wrong?

texteditor

Re-chargeables will have plenty of current capability.
Like you say it's just batter life you need to worry about, and the volts dropping as the batteries discharge (again rechargeables are better than alkalines).

Check the battery manufaturers website (or any battery website) they give good info.
Del

please note that store bought aa/aaa batteries have 1.5v each, NiMH and NiCd batteries genereally have 1.2v of potential (http://en.wikipedia.org/wiki/List_of_battery_sizes)

for charging devices, you may need more current than your baterry-only voltage-matched pack can provide. You could use more batteries to increase the current, but you'll need a way to step down the voltage to 5v (standard usb). A zener diode should do the trick here - if the input voltage is at least 2 volts higher than the desired voltage, it can stablize voltage while not decreasing current.

with a 7.5v (five double a's) input, you can use a 5.1v zener diode (rated for at least 5610mW) and a 2 ohms resistor (rated for at least 2640mW) to make a voltage regulator capable of providing at 1000mA of current (generally twice as much as your computer's usb port can provide, and enough for even the most demanding devices) at ~5v.

wire your batteries up in serial to get 7-9 volts. (5x1.5v = 7.5v, or 6x1.2v = 8.2v, or whatever, you'll need between 7 and 9 volts).

wire the positive wire of your battery pack to the resistor.
wire the other side of the resistor to the diode's cathode and the usb's + wire
wire the negative wire of your battery pack to the diode's annode and the usb's - wire

check http://www.reuk.co.uk/Zener-Diode-Voltage-Regulator.htm for more info