Alkaline batteries will last longer. 1) They have a higher mAH capacity 2) They have a higher voltage, so the current will go down. (I assume=20 you are measuring current into the converter) 3) They don't self-discharge the way most rechargeables do. 5000 hours,=20 at 8 hours a day, 40 hours a week, is 2 1/2 years. Kerry Andre Abelian wrote: > Hi Bob, > > Thanks for your replay. According to my co worker boost converter was tak= ing 6=20 > ma > but after I checked it every things different now. According to my test b= oost=20 > converter takes only 0.24ma=20 > not 6ma and that 6 ma cames from Zbee module that I didn't know that defa= ult=20 > settings sleep pin was disabled. I removed the zbee and now total > current is 0.24ma. in this case assuming 80% of 2000 ma 1600/0.24=3D 6666= hours=20 > for safety I say 5000 hours. > The only thing I do not know can rechargeable battery last longer or none= =20 > rechargeable like duracell etc? > my circuit doesn't charge batterys.=20 > > thanks > > Andre > > > > ________________________________ > From: Bob Blick > To: Microcontroller discussion list - Public. > Sent: Sat, March 12, 2011 6:37:18 PM > Subject: Re: [EE]: Battery life calculation > > > > On Sat, 12 Mar 2011 18:10 -0800, "Andre Abelian" wrote: > > =20 >> What's the best way to calculate battery life if boost converter is >> evolved.=20 >> =20 > > wattage out / efficiency of conversion =3D wattage in > > =20 >> 1. I have boost converter that starts at 0.9v and batteries I used are >> 2xAA=20 >> at this moment I have 2 rechargeable batteries each one is 2000 mah >> total=20 >> voltage battery side >> is 2.4v and output of boost converter is 3.3v >> standby current boost converter takes 6ma assuming every thing else i= s=20 >> disabled or in sleep. >> I made a mistake in schematic by not enabling burst mode. it suppose >> to be=20 >> 38uA on stand by mode not 6ma. LTC3402 >> mod can be done but any time I do the mod the chip burns out.=20 >> 2. I use PIC24FJ256GB110 according to datasheet it takes 1ma run time >> assuming=20 >> 2v power but the clock is not mentioned so I do not know.=20 >> I am using 4mhz 3.3v and run time takes 5ma. I changed the crystal t= o >> 1mhz I=20 >> see very small difference in load. I used 4mhz >> only because of USB requirement. I am able to switch internal clock >> to=20 >> 4.000.000 when usb is not used and 48.000.000 >> when usb is plugged in. >> =20 > > The USB peripheral probably is to blame for the higher-than-predicted > current. But other peripherals you have enabled may also be having some > effect. > > > =20 >> my question is how should I calculate battery life based on 8ma load >> since there=20 >> is a boost converter that runs at 0.9v and=20 >> I know from passed that 80% of battery should be used. I know its rated >> as=20 >> current per hour lets say >> >> 80% of 2000ma =3D 1600ma/0.008ma=3D200.000 hours >> >> I am just adding extra 2 ma incase of enabling other IC chips. >> does this make sense? 200.000 hours >> =20 > > Small correction, I think you mean 8 mA not .008 mA > > I'd calculate the current required first by the wattage into the boost > converter. > > If you need 3.3V at .005A that is .0165 W. If your boost converter is > 80% then you need .020625 W in. At 2.4 V in that is .0086 A > > So your .008 A estimate is pretty close only if you need .005 A out. But > your battery voltage will not always be 2.4 so you can figure it better > if you know the average. > > But basically I would say 200 hours is not a bad estimate. But not if > you need another 2 mA for other chips. > > Friendly regards, > > Bob > > =20 --=20 Internal Virus Database is out-of-date. Checked by AVG Anti-Virus. Version: 7.0.289 / Virus Database: 267.11.13 - Release Date: 10/6/05 --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .