On Fri, Jul 19, 2002 at 11:43:57AM -0500, Lawrence Lile wrote: I just wanted to agree with Lawrence on all counts. > A good sealed lead acid battery (Check www.mouser.com) should meet your > requirements well. Don't buy a car battery. Agreed and agreed. The only real problem I see below is that the draw is so light that it won't really cycle the battery at all. I'd advise float charging it overnight. The Amp-Hour rating is projected over a 20 hour draw. So most any battery would have no problem with the 100 to 200 milliamps you're projecting. > > You are not limited by weight IIC. > > Cost will be lower for sealed lead acid batteries Yup. There's a recent type called AGM that's extremely simple to use. > > Charging a lead-acid battery is really simple and they are hard to destroy Right on the destroy. However I've been learning more about charging. In deep cycle applications a three state charger does the best: Stage 1: BULK CHARGING. Feed the battery as must of the rated current (usually C/20) until it reaches the trigger voltage of 2.4V per cell (14.4V) Stage 2: ABSORPTION CHARGING: Charge at the 14.4V rate until the battery is drawing less than 1/10 of 1% of its rated charge. That's it. It's now full. Stage 3: FLOAT CHARGING: Charge at 2.3V/cell (13.8V) indefinitely. But as I said, the current draw is so light you can probably just float charge every night (or every other night) and be absolutely fine. > > Nicads are finicky, take special chargers, and can die unexpectely from not > charging correctly. They are also expensive. Agreed on all counts. > > OTOH, they are lightweight and store more enegry per Kg. But not worth the hassle here. As for the high current, simply fuse the battery. BAJ > > --Lawrence > > > ----- Original Message ----- > From: "sam woolf" > To: > Sent: Friday, July 19, 2002 11:31 AM > Subject: [OT] lead acid vs niCad batteries > > > > I need to get some rechargeable batteries for powering an art exhibit. The > > batteries are powering six constantly on sensor units which each draw 16 > mA, > > and which occasionally cause small relays to be triggered. The exhibit > needs > > to be able to operate without power problems for 8 to 10 hours, and can be > > recharged at night. Not sure whether nicad or lead acid batteries or > > some-other are the most suitable. Would appreciate an outside opinion.. Am > > slightly worried about high current possible with lead acid batteries > could > > somehow fry my electronics, but am also worried that nicad batteries won't > > last long enough, or that they will suffer from 'memory effect' and leave > > the exhibit conked out in the middle of the day. > > Any thoughts? > > > > > > _________________________________________________________________ > > Join the world s largest e-mail service with MSN Hotmail. > > http://www.hotmail.com > > > > -- > > 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 > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body