Aah, thats what I was looking for! mAh's, I couldnt see anything like that on any batteries. So to get 20 hours, I could put 2 pairs off AAA batteries in series, in parallel, so that the voltage is doubled, so it the mAh! Thanks for clearing that up... ----- Original Message ----- Wrom: WZIDREXCAXZOWCONEUQZAAFXISHJEXXIM To: Sent: Tuesday, July 09, 2002 2:55 PM Subject: Re: [EE] Suitable power supply workings-out > > It takes a 3V power supply, the operating current is 40 to 70mA, > > and the output power is 3mW. However, I don't know how to work > > out (for example) what battery(/batteries) to use > > You start with the milliamp-hour (mAh) or amp-hour (Ah) rating > of the battery. AAA batteries are a few 100 mAh, depending on > the type (red, black, alkaline, heavy duty etc), AA could be up to > 1000mAh / 1Ah, C and D cells are into the Ah > > So, if you have 2 x AAA batteries rated at say 400mAh each, then > you would be able to power your laser at 40mA for (400/40) hours, > oir 10 hours. I believe the rating is from fully charged (~1.65V) to > 1.0V so you may see the laser output dropping off before the 10 > hours. That's for batteries in series - add the voltage, the current > reserve is the mAh rating. For batteries in parallel the voltage is > the same as for one battery and the current reserve doubles. Two > AAAs in series - 3.3V at 400mAh, two in parallel - 1.65V at 800mAh > > Note that different battery types have different terminal voltages > because of the different chemistries used. Alkalines (and most 'dry' > or carbon-zinc) are 1.65V, NiCd are 1.2V, then you have silver, > thionyl chloride, sealed lead, lithium, metal hydride - on and on > > Grab a catalogue and/or look through some www battery sites > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > > > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body