Path: utzoo!attcan!uunet!seismo!sundc!pitstop!sun!amdahl!greg From: greg@uts.amdahl.com (Greg Bullough) Newsgroups: comp.sys.ibm.pc Subject: Re: Exploding clock cards Message-ID: Date: 16 Dec 88 18:33:07 GMT References: <16800395@clio> <119@mother.dde.uucp> Reply-To: greg@amdahl.uts.amdahl.com (Greg Bullough) Organization: Amdahl Corporation, Sunnyvale CA Lines: 37 In article <119@mother.dde.uucp> mbe@dde.uucp (Martin Berg) writes: >In article , greg@amdahl.uts.amdahl.com (Greg Bullough) writes: >> .. >> Well, there's more to the story, now. The card was replaced by a >> very concerned dealer. I plugged in the new card, pulled the battery, >> put a VOM across the clip, and turned on the computer. VOILA! >> +5 VOLTS! Great design, huh? I cannot find a blocking diode, so I >> assume it was left out of the design. >> >> Can anybody correct me if I'm wrong. It IS a no-no to put a positive >> over-voltage across a lithium battery, isn't it?? > >What input impedance does your VOM have ? > I used an 100,000-ohm/volt FET VOM for this debacle. >Could it be that it is so big that even a large resistor (say > 100 Kohm) >from the +5 V to the battery could give this result ? There was a resistor from the battery to the supply. 100 puny ohms. That reminds me... I should check the total resistance from the B+ line on the pin-out of the card to the battery positive. I don't THINK there are other resistors in the circuit, but I may be mistaken. In any case, a little diode has provided the proper kind of resistance and settled the issue entirely. The potential on the battery never rises above it's rating, now. Nothing like a bit of dining-room-table engineering. >If this is the case, the current flowing from to supply to the battery >wouldn't hurt the battery. Ah, yes, but the key was that the current (or something else) hurt one battery VERY badly. And it takes a lot more heat than is ambient in that section of my PC to cause a spontaneous explosion of a lithium battery. Greg