mike@amdcad.UUCP (Mike Parker) (01/29/85)
> > This newsgroup has been quiet lately. Does this mean that > 1) We all believe in capacitors >1 farad ? > 2) Batteries are not capacitors ? > 3) We have designed all the power supplies the world needs ? > 4) We are all quiet and shy people ? > O.K. maybe we can resurrect the nicad battery discussions, Remember all that talk about "memory" and nicads not fully charging if not fully discharged. I just got a cordless drill, and the instructions seem contrary to my beliefs about nicads. They say that I should recharge the moment that I notice a reduction of torque from the drill, i.e. without completely discharging the batteries. Can you damage a DC motor by running it on a lower voltage than it is designed for? If not then why should I recharge so soon? Mike @ AMDCAD
crs@lanl.ARPA (01/29/85)
ischarge *rate* (amps) rather than depth. I believe the confusion arises from the recommendation that a few *deep* discharge/charge cycles be to "erase" the cell's memory. In other words, if a nicad that is capable of supplying X amps is operated for a significant period at a load of Y amps where Y is significantly less than X, the nicad will, subsequently, be unable to supply X amps even though it is "fully charged". While it is often recommended that such a nicad be subjected to several deep discharge/charge cycles to restore it to its original discharge *rate* specification, care must be exercised in the case of batteries for the reason mentioned in my first paragraph (ie possible reverse charge of one or more of the cells). Charlie Sorsby ...!lanl!crs crs@lanl.arpa
crs@lanl.ARPA (01/29/85)
This is a reposting; the "f" key seems to have resulted in a mangled posting. Sorry about that. References: <215@abnji.UUCP> <597@amdcad.UUCP> > > O.K. maybe we can resurrect the nicad battery discussions, Remember > all that talk about "memory" and nicads not fully charging if not > fully discharged. > > I just got a cordless drill, and the instructions seem contrary to > my beliefs about nicads. They say that I should recharge the moment > that I notice a reduction of torque from the drill, i.e. without > completely discharging the batteries. Can you damage a DC motor > by running it on a lower voltage than it is designed for? If not > then why should I recharge so soon? > > Mike @ AMDCAD In reverse order: Yes, you can damage a nicad *battery* by excessive discharge. If the cells are not exactly matched, one may discharge before the others so that continued discharge tries to *charge* the discharged cell in the *reverse* direction, resulting, I believe, in a shorted cell. As I understand it, nicad memory has to do with discharge *rate* (amps) rather than depth. I believe the confusion arises from the recommendation that a few *deep* discharge/charge cycles be to "erase" the cell's memory. In other words, if a nicad that is capable of supplying X amps is operated for a significant period at a load of Y amps where Y is significantly less than X, the nicad will, subsequently, be unable to supply X amps even though it is "fully charged". While it is often recommended that such a nicad be subjected to several deep discharge/charge cycles to restore it to its original discharge *rate* specification, care must be exercised in the case of batteries for the reason mentioned in my first paragraph (ie possible reverse charge of one or more of the cells). Charlie Sorsby ...!lanl!crs crs@lanl.arpa
jans@mako.UUCP (Jan Steinman) (01/30/85)
In article <597@amdcad.UUCP> mike@amdcad.UUCP (Mike Parker) writes: >I just got a cordless drill, and the instructions seem contrary to >my beliefs about nicads. They say that I should recharge the moment >that I notice a reduction of torque from the drill, i.e. without >completely discharging the batteries...why should I recharge so soon? Because the batteries will go a few days after the warranty expires, you (and thousands of others) will buy a new drill, the drill maker's stock will go up, the GNP will increase, more investment will take place, and more people will have jobs so they can buy cordless electric drills. It's the American way, you commie! :*) -- :::::: Jan Steinman Box 1000, MS 61-161 (w)503/685-2843 :::::: :::::: tektronix!tekecs!jans Wilsonville, OR 97070 (h)503/657-7703 ::::::
tomk@orca.UUCP (Tom Kloos) (01/31/85)
Far worse than not discharging a nicad battery completely is reverse
charging it. This can easily happen in multi-cell packs where one cell
discharges to zero before the rest of the cells do. As the other cells
continue to supply power, the dead cell is 'charged' backwards. This
unfortunately seems to contribute to partial or total shorts, thus
leading to much shorter (no pun intended!) cell life.
If your drill has only a couple of cells, it's likely that the motor
won't provide useful torque before the weaker cell can be damaged.
In pieces of equipment with many cells in series (like my 2 meter
ham handheld), the equipment will still function reasonably well as the
battery pack becomes weak, thus easily allowing significant operation
with a cell under reverse bias.
Since nicads develop 'memory' only after many identical
charge/discharge cycles, it's probably safer as a general rule to start
charging before any one cell has a chance to discharge completely. If
memory becomes a problem, cycling the cells to zero INDIVIDUALLY a
couple of times is the best way to fix them. That way, the reverse
bias problem can be avoided.
-Tom Kloos, WA7NJK, Tektronix, Wilsonville, Oregon
Ignore paths in header. Use this:
uucp: ..{ucbvax,decvax,uw-beaver,hplabs,ihnp4,allegra}!tektronix!orca!tomkron@brl-tgr.ARPA (Ron Natalie <ron>) (02/01/85)
> > O.K. maybe we can resurrect the nicad battery discussions, Remember > all that talk about "memory" and nicads not fully charging if not > fully discharged. > > I just got a cordless drill, and the instructions seem contrary to > my beliefs about nicads. They say that I should recharge the moment > that I notice a reduction of torque from the drill, i.e. without > completely discharging the batteries. Can you damage a DC motor > by running it on a lower voltage than it is designed for? If not > then why should I recharge so soon? > You don't get the memory effect because the batteries are not fully discharged. You get the memory effect when the batteries are constantly charged and discharged over exactly the same range. This occurs when you have very precise chargers that kick in at the same voltage each time. The problem was noticable on space flights when a battery charger was overengineered. -Ron
piety@hplabs.UUCP (Bob Piety ) (02/01/85)
>I just got a cordless drill, and the instructions seem contrary to >my beliefs about nicads. They say that I should recharge the moment >that I notice a reduction of torque from the drill, i.e. without >completely discharging the batteries...why should I recharge so soon? Since the discharge curve of a nicad is rather flat, the moment you "notice a reduction in torque" is when the cells are ALMOST discharged. I believe they recommended that point since most users would still use the drill to finish that last hole. Waiting until the drill quits altogether is discharging the cells TOO deeply. Bob