AVR-Chat

4 NiMH batteries is a good starting point, but remember that you'll
only get 4.4 - 4.6V (series total) over most of the discharge curve.


At 06:17 PM 7/30/2004 -0000, you wrote:
>--- 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.
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