adam@misoft.UUCP (08/18/87)
In article <8708040222.AA14785@ucbvax.Berkeley.EDU> TROTH@TAMCBA.BITNET (Richard M. Troth) writes: >[] I forget where I read that "every precious drop" >of magic fluid that leaks out (usu due to heat) shortens a NiCds life. Is there any truth in the rumour that using Nicads infrequently shortens their life, but using them frequently extends it? -Adam. /* If at first it don't compile, kludge, kludge again.*/
ray@cs.rochester.edu (Ray Frank) (08/24/87)
Some questions about nicads to you nicad wizards and some observations of my own. First, I would like to begin by admitting to what some might consider a cardinal sin: fast charging(3C) of slow charge nicads. The nicads used in my radio control plane are the 'charge for 14 hour' types at 45ma. They have a 500ma capacity. I charge them at about 1.5 amps. You have to be very careful not to let them get hot. They stay cool just until they are at full charge and then they'll heat up rapidly and would probably explode shortly after that. I usually don't charge them to full capacity. How do I know when the batteries are fully charged? With an amp meter in series with the charging source I watch the current gradually go down in increments of a few hundred mills/minute until at some point at which the current will not continue to go down and in fact will actually reverse slightly and it is at this point that the nicads are fully charged. I've asked several people what the difference is between slow charge nicads and fast charge nicades. Mostly the answer they give is that the fast charge nicads are vented to release the heat. Does any one know if this is true and if there are other major differences? I've been fast charging my nicads all summer long and flying with out a battery failure. I realize that the nicads will not last as long by fast charging them but if this is the only thing I can expect from doing this to them I'll be satisfied. Finally, does any one know of a reliable way to determine how much charge is left in a nicad? For example, I can safely fly for about 120 minutes on one charge before bringing it in and recharging it. As the battery life decreases this 120 minute figure will decrease also. I have measured my fully charged nicad pack at 5.2 volts (4 AA) and after about 2 hours they are down to around 4.8 volts. But they will still read over 5 volts even after 90 minutes of flying so they begin dying all at once and this can be dangerous when 500 feet in the air. I bring the plane in every 45 minutes or so to check the voltage. By the way, I fly slope gliders and if my neck and batteries held out I could keep one up quite easily the entire day so you can see it is important to monitor the nicads and it is also nice to be able to charge the nicads from your car battery rather than leaving the hill for the day and waiting 14 hours for them to charge. Any suggestions and help would be appreciated as I LOVE my glider and wouldn't want it to crash because of a nicad failure. ray
philip@axis.fr (Philip Peake) (08/25/87)
In article <1619@sol.ARPA>, ray@cs.rochester.edu (Ray Frank) writes: > > Finally, does any one know of a reliable way to determine how much charge is > left in a nicad? For example, I can safely fly for about 120 minutes on one > charge before bringing it in and recharging it. As the battery life decreases > this 120 minute figure will decrease also. I have measured my fully charged > nicad pack at 5.2 volts (4 AA) and after about 2 hours they are down to around > 4.8 volts. But they will still read over 5 volts even after 90 minutes of > flying so they begin dying all at once and this can be dangerous when 500 feet > in the air. I bring the plane in every 45 minutes or so to check the voltage. > By the way, I fly slope gliders and if my neck and batteries held out I could > keep one up quite easily the entire day so you can see it is important to > monitor the nicads and it is also nice to be able to charge the nicads from > your car battery rather than leaving the hill for the day and waiting 14 hours > for them to charge. I am new to the RC aircraft game, but I must admit that the same thoughts have occured to me - I also would be most upset to see my aircraft either nose dive into the ground, or to fly away into the distance until its fuel was exhausted (it would probably go a long way ...). One Idea I did consider, having found no way to tell how much charge is left, would be as follows: Put a second set of NICADS, (actually two sets, one for the servos, and one for the radio), together with a small voltage measuring circuit which would be responsible for switching in the second set when the first failed. It would also have to give some indication, since I would use much smaller capacity cells for the backup. As a warning, I thought of placing a xenon tube (small camera type) somewhere on the underside of the aircraft, and this would start to flash - it should be visible even in daylight. I suppose that this is only possible if you have extra carrying capacity in the aircraft - for a glider ? Any better ideas would be welcome. Philip
phd@speech1.cs.cmu.edu (Paul Dietz) (08/26/87)
In article <284@axis.fr> philip@axis.fr (Philip Peake) writes: > Put a second set of NICADS, (actually two sets, one for the > servos, and one for the radio), together with a small voltage > measuring circuit which would be responsible for switching in > the second set when the first failed. It would also have to > give some indication, since I would use much smaller capacity > cells for the backup. If weight is a consideration, why not just use non-rechargeable batteries? They have higher energy density, and since these are for "emergency" use only, I don't see any need for these to be rechargeable. Plus, isn't it easier to verify the health of throw away batteries? (i.e. would using a second set of nicads just move the problem back a stage?) -- Paul H. Dietz ____ ____ Dept. of Electrical and Computer Engineering / oo \ <_<\\\ Carnegie Mellon University /| \/ |\ \\ \\ -------------------------------------------- | | ( ) | | | ||\\ "If God had meant for penguins to fly, -->--<-- / / |\\\ / he would have given them wings." _________^__^_________/ / / \\\\-
mages@trane.UUCP (Mikey Mages) (08/27/87)
In article <1619@sol.ARPA>, ray@cs.rochester.edu (Ray Frank) writes: > > By the way, I fly slope gliders and if my batteries held out I could > keep one up quite easily the entire day so you can see it is important to > monitor the nicads Just a thought....you might try putting a current or voltage comparator on board the glider that senses your nicads. Combined with a transmitter and a receiver on you radio control unit you could trigger an LED or audio indicator when its time to bring the plane in for recharge. -- ptsfa!trane!mages
rees@apollo.uucp (Jim Rees) (08/28/87)
Is there any truth in the rumour that using Nicads infrequently shortens their
life, but using them frequently extends it?
Using them infrequently damages them, but not permanently. You can recover
the full capacity by putting them through a couple of discharge-charge
cycles.
The worst thing you can do to nicads is reverse-charge them, as happens at
the very end of the discharge cycle when one cell has completely discharged
but the rest of them keep forcing current through the dead one. For this
reason, you should stop using nicads at the first sign of a drop in voltage.
A cell that has been damaged in this way will appear to have a dead short
internally. Often you can "fix" these by putting a very large (~10C)
charge current through them briefly (~1 second) to burn off the internal
short. This fix often only lasts until the next discharge cycle.
The second worst thing is to overcharge them at greater than a 1C rate
(for example, >1 amp for a 1 amp-hour cell). Up to 1C, the extra power
is harmlessly dissipated as heat, but over this rate, and the cell starts
to dry out. Old HP calculators came with chargers that way overcharged.
I suspect this was a way of making money on replacement batteries, which
cost $20 for $4 worth of cells (a different kind of overcharge), but
maybe I'm just paranoid.
The best way to treat nicads is to fully discharge them once a month,
stop the discharge immediately when the weakest cell drops below a
volt, then charge them completely at a 1C rate for 16 hours.
This is all based on personal experience and manufacturer's literature.ray@cs.rochester.edu (Ray Frank) (08/29/87)
In article <36f19f36.b8ab@apollo.uucp> rees@apollo.uucp (Jim Rees) writes: >The best way to treat nicads is to fully discharge them once a month, >stop the discharge immediately when the weakest cell drops below a >volt, then charge them completely at a 1C rate for 16 hours. > >This is all based on personal experience and manufacturer's literature. Won't a great deal of heat result in a 1C charge for 16 hours? Won't this heat result in a possible exploding battery or at the very least a damaged battery especially if the battery is not vented? You mentioned that a charge over 1C should never be used but in nicads used in RC cars, a 3C charge rate is common and in fact a quick charger bought at the local hobby stores charges the batteries at 3C. If you have a battery pack that has four cells and one of them has accidently been reversed charged, or internally shorted as you say, when these cells are fully charged what will the shorted cell read on a volt meter? ray
rees@apollo.uucp (Jim Rees) (09/01/87)
Won't a great deal of heat result in a 1C charge for 16 hours? Won't this
heat result in a possible exploding battery or at the very least a damaged
battery especially if the battery is not vented?
Sorry, slip of the keys/mind.
.1C (one-tenth C) is the max safe charge rate without overcharge detection.
The standard charge is .1C for 16 hours, which allows for a full charge
even at a very low efficiency.
I've seen quick chargers go as high as 10C, but you'd better have some
pretty sophisticated full-charge detection circuitry at this rate.
If you have a battery pack that has four cells and one of them has accidently
been reversed charged, or internally shorted as you say, when these cells are
fully charged what will the shorted cell read on a volt meter?
If you burn off the short first, it will be 1.2 - 1.25, just like a normal
cell. If you don't burn off the short, it won't take a charge at all,
and even after 16 hours of .1C it will still read < .1v.
Now, can someone post similar guidelines for gel-cells? I have one that
self-discharges in about two weeks, and won't take a charging current
over 100 ma (it's a 5 ah battery) without exceeding 2.25 volts/cell.
Is it NFG?brice@pnet01.CTS.COM (Brice Fleckenstein) (09/03/87)
I think he ment to say "use a .1C charge for 16 hours", not a 1C charge. 10% of capasity for 14-20 hours is the normal Nicad charging reccomendation by 95%+ of the manufacturers.
jans@tekchips.TEK.COM (Jan Steinman) (09/03/87)
<<<Now, can someone post similar guidelines for gel-cells? I have one that self-discharges in about two weeks, and won't take a charging current over 100 ma (it's a 5 ah battery) without exceeding 2.25 volts/cell. Is it NFG?>>> I inherited quite a number of these from the trash bin at a previous job, so I've had some experience reviving them. Gel-cells, being of your basic lead-acid chemistry, are charged at a constant voltage, as opposed to the constant current used to change NiCd cells. Maximum "trickle charge" voltage is 2.3 volts per cell -- gel-cells can safely dissipate an indefinite charge at this potential. In addition, there is a "maximum bulk charge rate", which is typically .2C. Extremely dead cells may go above this rate if fed from a 2.3V/cell charger. Going above this rate will cause excessive outgassing, which will eventuall dry out the electrolyte. When the electrolyte dries up, the cell develops a high impedance, refusing to accept much current at the 2.3V/cell potential. To fix this situation, you need a drill press, a 1/4" to 3/8" bit, and a syringe. Clamp the cell in the drill press vise, and set the stop in order to drill about 1/8" through the cover. Be careful! If you do not clamp the cell tightly, or do not set the stop properly, the bit will dig right into the cell, destroying the vent seal and possibly the whole cell! Once you have a neat little hole in *just* the plastic cover, use a small nail or tack to poke a small hole in the rubber vent seal. Fill the syringe with distilled water, insert the syringe into the vent seal hole, and add as much water to the cell as it will take. ****IMPORTANT**** ****WEAR EYE PROTECTION!**** If you have over filled the cell, fluid will squirt out when removing the syringe! Tilt the syringe toward you, and have some acid-resitant (like polyethelyne) backdrop to avoid damaging your work area! Using a constant-current source, charge the cells at a .1C rate. THis may require as much as 20V/cell if the cell is extremely dry. Check the fluid often, replenishing a s necessary. When the cell voltage falls to about 2.5V/cell, switch to a constant voltage, 2.3V/cell charge for about a week to absorb any free fluid left. At the end of this period, remove any unabsorbed fluid with the syringe. BE CAREFULE! THIS IS BATTERY ACID! DISPOSE OF PROPERLY! If you damaged the vent seal during the drilling operation, you can touch up with silicone caulk. Do not use too much, or the cell might develop excessive pressure during the outgassing that accompanies charging. I've had great luck with this process, although I've destroyed a few cells in developing it. :::::: Software Productivity Technologies --- Smalltalk Project :::::: :::::: Jan Steinman N7JDB Box 500, MS 50-470 (w)503/627-5881 :::::: :::::: jans@tekcrl.TEK.COM Beaverton, OR 97077 (h)503/657-7703 ::::::
SPGDCM@CMSA.BERKELEY.EDU (05/13/88)
MSG:FROM: SPGDCM --UCBCMSA TO: NETWORK --NETWORK 05/12/88 14:40:39
To: NETWORK --NETWORK Network Address
From: Doug Mosher
Subject: nicads
To: misc-consumers@ucbvax sci-electronics@ucbvax
I have an electric drill and an electric screwdriver which have nicads.
In the past I kept nicad devices (e.g. an electric shaver) on trickle
charge, and eventually they got wek and died. So i tried just
charging these new tools when I wanted to use them.
But they seem to be getting "shallow" quickly. Some of what I have read
on usenet indicates that maybe I should be leaving them on trickle
charge rather than disconnected.
SO: for rarely used nicad-powered appliances, is it best to
charge when needed, or leave on trickle, or some other combination?
( )
( Doug Mosher <SPGDCM@CMSA.Berkeley.edu> )
( 257 Evans, Univ. of California, Berkeley, CA, 415/642-5823 )
nicadsbobc@killer.DALLAS.TX.US (Bob Calbridge) (09/17/88)
I have a need to re-enstate some nicads that have developed dead shorts. I have read discussions concerning zapping the cells with a relatively high voltage (including 12 volt car batteries) for brief times until the shorting condition disappears. This is my question. Once the resistance of the cell has been restored, is there a given amount of resistance that is necessary? That is, should I quit once I've gotten any resistance reading, or is the job not done until the resistance reaches a minimum level? Appreciation in advance. Bob