Looking at the switching route it might be better to step up and have a few big cells, maybe 2 C or D, rather than multiple AA. I understand the power density should be better. However I do accept that it is hard to get the circuit to start, I have seen a magazine 'design idea' putting two boost converters in parallel, one to start the equipment and the other one would only work when the output voltage was high enough, but handled higher current. Also if space permits it's worth looking at DIY switcher designs, if the current is low enough discontinuous PFM can be used with close to zero quiescent current. Oliver. ----- Original Message ----- From: Vasile Surducan To: Sent: Wednesday, September 06, 2000 9:47 AM Subject: Re: [EE]: powering from NiCads > On 5 Sep 00, at 22:16, w. v. ooijen / f. hanneman wrote: > > > I must power a datalogger (16F84, 24LC256, LM75, IR LEDs, TSOP17 IR > > detector) from NiCad or other rechargeable batteries. Current use ~ 3 mA, > > must run for 14 days, so 2AH is plenty. But how should I get the right Vcc? > > My experience with standard A3 style (500mAh or more) NiCd > accumulators show this batteries like a great discharge current ( > about 100mA or more) for a long life and good level maintenance. > Even if batteries are complete new after two weeks of standing > without any load the potential will be under 1.1 V ( in a best case ) > In your place I will use a greater than 6V solution ( maybe 7.5 or > better 9 V) and a good stepdown regulator. > The cheapest one may be done with a CMOS flip-flop and a small > ferite transformer . Up to 90% efficiency may be achieved. > Max or LTC regulators for a good cause also... > Vasile > ********************************************* > Surducan Vasile > mail: vasile@l30.itim-cj.ro > URL: http://www.geocities.com/vsurducan > ********************************************* > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.