Is it possible to use two rechargeable Li-Ion batteries of unequal sizes in series? I'm designing a device that will run at 4V, 25-30mA. The device is pager size so a 9-volt battery is too big. I thought I'd found the solution in RC car batteries. These are flat so they can lie on top of the circuitboard. They are polymer li-ion, 3.7V. They are available in two sizes: 750mA and170mA. Two 170mA batteries lasts only 7.5 hours. I need at least 15 hours. The case can fit one large battery and one small batteries, or two small batteries. Possibly I could fit one large and two small, or three small batteries. I set up one large battery and two small batteries in series. The voltmeter read 11.9V. I set up the device and came back ten hours later. The large battery was at 4.1V - fresh - and the small batteries were at -0.1 volts. They had puffed up. I charged them but they never went over 0.1 volts. How could the large battery be fresh and the two small batteries be destroyed? I can't figure out a way to measure current draining from each battery. Now I have two test devices running. Each has one large and one small battery, in series. The difference is that one device has the large battery connected to the positive terminal and the small battery to the negative terminal; the other device has the small battery connected to the positive terminal and the large battery connected to the negative terminal. Any other suggestions?
18 years ago
-- Electronic Anti-Stuttering Devices http://www.fluencydevices.com Thomas David Kehoe Casa Futura Technologies (303) 417-9752