Operator's Interface: USB Chicklet + Battery

[Al Skierkiewicz]

Mike,
I respect Mr. Buchmann and read through the Battery University article you linked to above. It still goes against the training I have received so I am researching a little deeper. I have Mr. Buchmann's book at home so I will go through that. What I find interesting is the difference in belief between older engineers and those much younger as if there has been a disconnect (no pun intended). The fact that so many hold true to connecting batteries in parallel as a bad idea and the fact that so many products exist to make this happen (diode arrays, high power Shottky diodes, etc.) makes this a worthy subject of detailed analysis. It may have more to do with battery chemistry than a blanket statement about all batteries. I have observed self discharge in parallel gelcell batteries and wet lead acid batteries when people in the field (field TV production) tried to extend production time. Sometimes this discharge took place over night but certainly over a few days. All production vehicles with a battery supply use either a high current contactor to switch batteries or a diode array to put batteries in parallel. Of course, batteries are charged separetely.

[Dave Flowerday]

Mike & Al,
Sorry for continuing to drag this thread off-topic, but I have a comment: it seems like I see batteries in parallel all the time too. Two examples that come to mind are the large banks of batteries used in electric forklifts and extremely large UPSes. In both cases I've seen banks of batteries that are clearly wired in parallel with large metal bars connecting the battery terminals together (and obviously no diodes involved). I think in these situations it is common to see sub-groups of batteries in series, with the sub-groups then tied together in parallel. I'll have to doublecheck but I think there is an example of this setup sitting not more than 20 feet outside our playing field area in the Motorola warehouse from an old UPS.

Does this sound familiar to either of you? If I remember this correctly then it certainly seems that there are situations where batteries can be wired in parallel without diodes efficiently.
Dave

[Mike Copioli]

The theories taught do suggest that it is a bad practice. However, it in fact is a common practice that works. I have had to contend with the perils of parallel placement of lead acid batteries in my truck and also in the ambulances at my workplace. The perils being when one battery dies(end of life cycle) it takes the other ones with it. That is why it is recommended that all batteries in a parallel bank be replaced at the same time. I do appreciate both theory and practical application. I also believe that whatever works..works. Which suggests to me that sometimes theory is just that...theory. To answer you query David, I have had the same encounters with UPSs and also with Hi-los. Boats do the same thing. There is a selector switch for 1,2 or both. Good luck at all of your regionals. I am looking forward to continuing this discussion at nationals. After we win of course.

Ha ha.