fad@tropix.uucp (Frank A. DeWitt) (01/30/91)
If you want to do a little work you can buy the nicad cells that are in your battery pack for a LOT less money from a hobby shop that sells "R.C. cars". A set of 6 sub C cells (wired togeather in a pack) start at about $25 (for the 1.2 AH) Other sizes are available. These are very high quality batteries, they have to be thay are charged in 15 min. then "peaked" then compleately discharged in 4 to 5 min !!! By the way, if a race is short they discharce there batteries by connecting them to 4 to six tail light bulbs in parallel. When the light goes out the bat. is discharged and they begin charging. Frank DeWitt
cho@sol4.cs.psu.edu (Sehyeong Cho) (04/03/91)
I decided to follow the advice: "discharge the Nicad completely before recharge" I made a simple device that has two contact points and a light bulb for a car. Can a discharge be "too fast" or "too slow" so it can cause a problem? For instance, can I just short-circuit the +/- ? (Okay, assuming fire won't break out :-) I feel that the battery is warm after discharging with the lightbulb. One more question. There is a pop-up window with a "fuel gauge" in a Toshiba T1000SE. Amazingly, I can change the guage. So, I'm beginning to suspect that the reading is not a function of the remaining fuel - that is, it may be a function of initial setting , time and fuel use. (I mean, indirect calculation, not "measurement" of fuel.) If that were true, then it may not be very accurate. Would that also affect the function of the charger/low battery warning? (What will happen if I set the gauge incorrectly in the first place?) -- | Yesterday I was a student. Sehyeong Cho | Today I am a student. cho@cs.psu.edu | Tomorrow I'll probably still be a student. | Sigh.. There's so little hope for advancement.
cho@sol4.cs.psu.edu (Sehyeong Cho) (04/03/91)
In article <46Gdxpf1@cs.psu.edu> I wrote: >I decided to follow the advice: "discharge the Nicad completely before recharge" >I made a simple device that has two contact points and a light bulb for >a car. Can a discharge be "too fast" or "too slow" so it can cause a problem? >For instance, can I just short-circuit the +/- ? (Okay, assuming fire won't >break out :-) Someone replied: |The NiCad is made up of several cells in series, so you do NOT want to |completely discharge them, as you may reverse charge some of them, which is bad |news. Complete discharge only works for single cells (1.2V), and you should |add limiting resistor, as short circuiting NiCads is not good for its health. The advice I got from this news group was: If you charge a partially discharged Nicad battery, you may end up ruining the battery by what is called "memory" effect. Therefore you should completely discharge the battery before recharge it. Now I have two (apparently) contradicting theories. The only way to be consistent is perhaps "before you begin recharging the battery, make sure it doesn't have too much charge remained." But then how much is too much? Any idea? -- | Yesterday I was a student. Sehyeong Cho | Today I am a student. cho@cs.psu.edu | Tomorrow I'll probably still be a student. | Sigh.. There's so little hope for advancement.
dan@rna.UUCP (Dan Ts'o) (04/04/91)
In article <mn2G*3sf1@cs.psu.edu> cho@sol4.cs.psu.edu (Sehyeong Cho) writes: >Now I have two (apparently) contradicting theories. The only way to be >consistent is perhaps "before you begin recharging the battery, make sure >it doesn't have too much charge remained." >But then how much is too much? >Any idea? I would say to go down to 1 volt per cell. The standard NiCad cell provides 1.25volt per cell when charged. If you go too low, some cells will reverse (very bad). Cells that are dead tend to short themselves, forming little crystals that span the electrodes. You can save such a shorted cell by blowing the crystal with high current (either another NiCad or a big capacitor). But such cells are permanently crippled and tend to lose their charge faster and have less capacity then when new. Dan
jackw@nstar.rn.com (Jack Wiggins) (04/04/91)
Not to answer all of your questions but YES! If you discharge your battery too fast, you can risk fire, explosion and destroying your battery at the least! The fuel guage doesn't look at the battery itself because the NiCad battery doesn't change voltage much as it discharges until right at the end. The gauge keeps track of how long your machine has been operating and WHAT was operating on it. This way, you have some idea of how much power has been used. You can reset it because that reading is only aproximate and batteries have different capacities anyway. By the way, even a small NiCad battery pack is capable of putting several hundred amps into a short circuit. Don't get burnt! -- Jack Wiggins NSTAR conferencing site 219-289-0287 internet: jackw@nstar.rn.com 1300 newsgroups - 8 inbound lines uucp: ..!uunet!nstar.rn.com!jackw 99 file areas - 4300 megabytes --- backbone news & mail feeds available - contact larry@nstar.rn.com ---
jackw@nstar.rn.com (Jack Wiggins) (04/04/91)
Look at your circuit again. You can't "reverse charge" batteries in a pack unless the current is flowing backwards in ALL of them. Also, if you do get a reduced charge capacity because of the memory effect, a couple of full discharge-charge cycles will bring the battery back to snuff. -- Jack Wiggins NSTAR conferencing site 219-289-0287 internet: jackw@nstar.rn.com 1300 newsgroups - 8 inbound lines uucp: ..!uunet!nstar.rn.com!jackw 99 file areas - 4300 megabytes --- backbone news & mail feeds available - contact larry@nstar.rn.com ---
chao@oahu.cs.ucla.edu (Chia-Chi Chao) (04/05/91)
In article <9L9uZ4w161w@nstar.rn.com> jackw@nstar.rn.com (Jack Wiggins) writes: >Look at your circuit again. You can't "reverse charge" batteries in a pack >unless the current is flowing backwards in ALL of them. When NiCad is being discharged, positive current comes out of the positive terminal. When it is being charged, positive current goes INTO the positive terminal. When you put cells in series to form a battery pack, the weakest cell will reach 0V before the others do. It becomes a "load" in the circuit, and positive current goes INTO the negative terminal -- same as charging the cell backwards. I am not an expert at this, but this has been discussed in sci.electronics many times. >Also, if you do get >a reduced charge capacity because of the memory effect, a couple of full >discharge-charge cycles will bring the battery back to snuff. You can only reduce the memory effect, not totally eliminate it, especially in a battery pack. -- Chia-Chi Chao chao@cs.ucla.edu ..!ucbvax!cs.ucla.edu!chao
jackw@nstar.rn.com (Jack Wiggins) (04/05/91)
As long as current is flowing in the battery pack you cannot have a "reverse current" flowing into one of the batteries. Also, most battery packs "should" be made up of closely matched NiCads that would elimanate this effect anyway. "elimanate"? yeesh! eliminate... We aren't talking about theoretical absolutes here - just practical real world result, and yes, I shouldv'e said something about the memory effect being MOSTLY reversable since you'll always see some trace of it. It depends on how bad the original problem was, what brand of batteries, how old they are, and sometimes I believe what day of the week it is... The point is that if your manufacturer tells you how to treat the battery package, then you should really give him a listen, especially if you have a warranty to worry about. -- Jack Wiggins NSTAR conferencing site 219-289-0287 internet: jackw@nstar.rn.com 1300 newsgroups - 8 inbound lines uucp: ..!uunet!nstar.rn.com!jackw 99 file areas - 4300 megabytes --- backbone news & mail feeds available - contact larry@nstar.rn.com ---