Path: utzoo!attcan!uunet!mcvax!enea!dkuug!dde!mbe From: mbe@dde.uucp (Martin Berg) Newsgroups: comp.sys.ibm.pc Subject: Re: Exploding clock cards Summary: Input impedance of VOM ? Message-ID: <119@mother.dde.uucp> Date: 14 Dec 88 16:27:18 GMT References: <16800395@clio> Organization: Dansk Data Elektronik A/S, Herlev, Denmark Lines: 24 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 ? 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 ? If this is the case, the current flowing from to supply to the battery wouldn't hurt the battery. By big input impedance I mean something like 5-10 Mohm. -- mbe@dde.dk | "The answer is 42" or | A. Douglas ..mcvax!enea!dkuug!dde!mbe |