AVR-Chat

--- In AVR-Chat@yahoogroups.com, "C Sizer" <aussiecol39@y...> wrote:

> ... I want to use 4 x 2300mAh AA
> batteries in serial/parallel to
> provide me with 3V.

Sounds like alkaline cells at 1.5 volts each.

> The printer runs on 5V but consumes
> over 3.5A peak, so I require a DC-
> DC converter circuit... to provide
> 3V at 5A peak.

You mean to provide 5V/3.5A, which will suck six amps or more from 
your 3V battery. I don't think this will work. The internal 
resistance of alkaline cells will be too high and your 3 volts will 
sag something terrible.

Like everyone else, I suggest you switch batteries.  Use four NiMH AA 
cells to get 5V and regulate down to 3V. I don't think you'll need to 
buck down, just use a linear regulator, unless you're taking a lot of 
current at 3V. Although the capacity of the NiMH cells won't be 2300 
mA.h (I use 1800 mA.h cells but I think now you can do a bit better) 
I think they will actually last longer. This is because the alkaline 
cells will never give you full capacity at such a high discharge rate 
and you're avoiding power loss in the boost converter. High quality 
cells will be able to keep the voltage up because NiMH cells have a 
low internal resistance. For example, the 7.2 volt 6.5 A.h modules in 
my car have an internal resistance just a bit over 10 milliohms. I 
can get 60 amps or more from the 300 volt battery and the voltage 
stays up at 275 volts.

Graham.