Well, problem one is hydrogen. A car battery will emit some hydrogen. If the area is not well ventilated, it will ignite. Hydrogen is amazingly easy to ignite - if it gets out you can generally expect it will catch fire. The amounts released tend to be small, and under the hood, it's tough to get the concentration up to the lower explosive limit, but it does happen. Inside, of course, the opportunities are greater. Although hydrogen is not terribly energetic, it can nevertheless make quite an impressive detonation. Also, car bateries are intended to be discharged at a fairly serious clip. Your car's starter draws hundreds of amps. However, they are not real good at getting discharged slowly, and if you discharge them slowly AND deeply, they will be damaged. Deep cycle marine batteries are generally a little better for long stints at relatively low discharge rates (tens of amps instead of hundreds!) SLA's aren't all THAT expensive, but if you can contain the acid, and if you can provide good ventalation, and if you are willing to deal with the discharge issue (in a backup situation maybe you just replace the batteries after an event) they can be a nice, inexpensive source of power. 72/73 de WB8RCR http://www.qsl.net/wb8rcr didileydadidah QRP-L #1446 Code Warriors #35 ----- Original Message ----- From: "Ed Browne" To: Sent: Wednesday, March 31, 2004 1:28 PM Subject: [EE:] battery backup > Can anyone think of a reason not to attach a car battery in place of the > sealed battery in a battery backup system? I've got a few of these > carcasses laying about because it's always been cheaper to buy a new one, > but a cheap car battery could breathe new life into them. Clearly, I don't > want to turn it over and spill acid, but think of the backup time available! > > Thanks, > Ed > > -- > http://www.piclist.com hint: To leave the PICList > mailto:piclist-unsubscribe-request@mitvma.mit.edu > -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu