svoboda@motcid.UUCP (David Svoboda) (07/10/90)
Why can't nicads be used in parallel in order to increase the current
capacity? By experience I know that one simply uses larger cells to
obtain higher capacities, and only links two or more cells together to
increase battery voltage. What gives?
Dave Svoboda, Motorola CID, RTSG, Arlington Heights, IL
uucp => {uunet|mcdchg|gatech|att}!motcid!svoboda
internet => motcid!svoboda@chg.mcd.mot.com
All change is not growth, as all movement is not forward.phil@ux1.cso.uiuc.edu (07/10/90)
You should be able to get more current from parallel batteries, but there are some problems with connecting them in parallel. When charging them in parallel, the characteristic of the cells during the charging cycle can cause some problems, and might potentially lead to a run-away current condition. This is not likely to happen unless the cells are in different conditions. If one cell is weaker than another, the stronger one could be trying to charge the weaker one, and can potentially overcharge it if the weaker one is too weak. Off the production line, capacities of cells can vary by plus or minus as much as 5%. Between different batches this might be more. So it is not easy to avoid the problem. Within a cell, all the chemical surfaces can be thought of as many cells in parallel. However they are likely to be fairly uniform. I have used Nicads in parallel before, but this was under conditions of full and equal charge. I've never charged them in parallel. --Phil Howard, KA9WGN-- | Individual CHOICE is fundamental to a free society <phil@ux1.cso.uiuc.edu> | no matter what the particular issue is all about.
henry@zoo.toronto.edu (Henry Spencer) (07/10/90)
In article <3902@ash31.UUCP> svoboda@motcid.UUCP (David Svoboda) writes: >Why can't nicads be used in parallel in order to increase the current >capacity? ... There is a general problem with paralleling voltage sources: they aren't all guaranteed to have precisely the same output voltage, and various troublesome things can happen as a result. A muscular nicad might try to charge a feeble one, for example. -- NFS is a wonderful advance: a Unix | Henry Spencer at U of Toronto Zoology filesystem with MSDOS semantics. :-( | henry@zoo.toronto.edu utzoo!henry
brianr@phred.UUCP (Brian Reese) (07/13/90)
In article <1990Jul10.150245.9902@zoo.toronto.edu> henry@zoo.toronto.edu (Henry Spencer) writes: }>In article <3902@ash31.UUCP> svoboda@motcid.UUCP (David Svoboda) writes: }>Why can't nicads be used in parallel in order to increase the current }>capacity? ... } }There is a general problem with paralleling voltage sources: they aren't }all guaranteed to have precisely the same output voltage, and various }troublesome things can happen as a result. A muscular nicad might try }to charge a feeble one, for example. What's the harm in tying them all together using forward biased diodes? Sure, it'll result in a diode drop, but if the load can accomodate it, that shouldn't be a problem. Brian -- Brian Reese uw-beaver!pilchuck!seahcx!phred!brianr Physio Control Corp., Redmond, Wa. brianr@phred.UUCP "Sticks and stones may break my bones, but whips and chains excite me!" All opinions are manf. suggested and are subject to change without notice.