Conference vmszoo::rc

    Jacque,
    If the cells are reading 0 volts after an overnight charge, then
    they are definitely dead. However, double check that the charger
    was actually working. Possibly no charge was reaching the cells.
    
    Old nicads that have been laying around for awhile will read 0 volts
    but will come back up to ~ 1.2 volts per cell after a short charge
    time, IF they are not defective. 
    
    I'd be reluctant to use any old nicad cells in an airborne system.
    
    Terry
    

        I've successfully zapped dead cells back to life, but as Terry
        says, I wouldn't put them in a TX or RX. If you need batteries for
        your starter, glow plug, or walk-thing, use them there.
        
        Here is how I zap a nicad cell. Note that you can do this only to
        one cell at a time, not a whole battery pack. Please note that
        this could be hazardous: wear safety glasses and full protective
        clothing. Don't blame me for any injury or anything else - the
        IRS, the bank, and the wife already have claim on all my assets.
        
        I use my old 12v slot car transformer to charge up a large
        electrolytic cap (steal one from an old computer power supply).
        Match polarity on all three devices, transformer, cap, and cell
        (see crude schematic below). When fully charged, touch the wires to
        the nicad. You will see lots of sparks. After a couple cycles of
        this, check the nicad with a voltmeter. If still dead, repeat a
        couple more times. eventually, you will either give up and throw
        the cell away, or have a voltage on the cell. If the latter is the
        case, then charge it normally, and probably cycle it a few times.
        It may now work normally, or it may die again soon, indicating you
        really should have pitched it.
        
        				/
        	+---------------+------/  ------+
        	|		|		|
        	| +		| +		| +
        	Trans		Elect.		Nicad
        	Former		Cap.		Cell
        	| -		| -		| -
        	|		|		|
        	+---------------+---------------+

    re Kaplow's zapping technique

    1.	What he is doing is this:  The battery can grow nickel crystals
    inside that can short out the electrode.  These tiny whiskers can be
    destroyed by extremely high [but brief] currents.

    2.	I have used a car battery to do the same thing.  DO NOT CONNECT
    both terminals of the cell to the car battery; just make the ground
    connection and slap the other wire across the "hot" car battery
    terminal [as a way to get a SHORT duration current].  WEAR PROTECTIVE
    GOGGLES AND HEAVY GLOVES; the damn cell might explode.

    3.	Wait a few minutes for things to cool before a repeat.

    4.	If it doesn't work, you have an open, not a short.   Junk it.
    	If it does work, use it in a flashlight, etc., not for RC.

    Thanks for the info.
    When you say explode, how much of an explosion can it give ( ex. Enough
    to take your nail out, finger out, arm out, etc.)
    
    The intention is to try and use the cells for spark plug ignition.
    
    
    Thanks
    
    Jacques
    

    I had a sub C cell in my son's RC car pack suddenly short. It was in
    the car at the time and did some serious damage. It sounded like an
    M-80 firecracker (1/4 stick of dynomite) and did about as much damage
    to the car. I'd be very careful. The cells can also "vent" their
    contents out the little holes in the top. The do this when they get too
    hot so let them cool in between.

        re: .3
        
        I'd be VERY wary of using a cer battery or the like for this. They
        can vent explosive hydrogen gas, and the spark from slapping the
        wire could cause an explosion. Car battery explosions are MUCH
        more dangerous than nicad explosions. Use a power supply or other
        non-venting source.
        
        The only nicads I've ever seen explode were also as a result of a
        direct short in a pack )charge jack failure. It sprayed some
        caustic junk a couple feet and did a meltdown on the plastic case.
        It got QUITE hot! I don't know what the failure mode in zapping
        might be, and really don't wnat to find out.
        
        Bob

>>        I'd be VERY wary of using a car battery or the like for this.

    Bob is right.  The workaround is trivial, but we are putting "a varnish
    finish on a rock".   Unless you know what you are doing, it generally
    isn't worth it.  Junk the sucker.


    re   someone else's comment about venting   

    Any RC NiCd that has vented has a terminal disease, and I am not making
    a pun.  Once vented, soon to be trashed.  The vents are safety vents,
    not breathing holes; they are spring loaded to keep them shut until the
    alternative to opening is rupturing.

    Alton

    Thanks for all the advise. After consideration and reading your
    replies, I have decided that they cells where not worth the risk and
    I'm going to ditch them.
    
    Thanks all
    
    Jacques
    

    The circuit a few notes back is not correct.  You need diodes between
    the transformer and the capactior unless you also want exploding
    capacitors.  I have used the zap trick many times on shorted cells, but
    they usually don't last all that long afterwards.  I'd invest in new
    ones unless you like to tinker.
    
    Charlie
    

        Diodes? Where? The transformer in question outputs 12v DC already.

    
    
    I'm not sure where to put this so....
    
     When recycling my trans. batt. and rec. batt. I charged them for 12
    hours and took them off charge. The usual charge is 14 hours(?) I had
    to go to work and didn't want to charge it for 20 hours. My queastion
    is can I put it back on charge for the additional 2 hours or will in
    some way create the memory at the 12 hour charge.
    
    Batteries and charging are my weakness.
    
    Bruce
    

    It won't bother your batteries a bit to have their charge period
    interrupted and continued later.
    FWIW the "memory" question is largely a religious one, and it's
    worth noting that G.E. ni-cad documentation dismisses it as a 
    factor in any normal consumer use.
    
    Terry
    

    The latest (March 1992?) issue of QST, the ham radio mag from the
    American Radio Relay League (equiv of AMA), has an article on the care
    and feeding of NiCds. This guy did work on satellite power systems,
    that use NiCds - a super critical application.
    
    He mentions that memory of a NiCd is often mistaken for reduced
    capacity of a NiCd, i.e., a 600 mAH pack that is constantly drained
    to half capacity, and then recharged, then 'learns' to behave as just
    a 300 mAH pack.
    
    In reality, he asserts that such a NiCd pack would exhibit memory by
    its terminal voltage dropping (a tenth of a volt?), and not a 50%
    reduction in capacity.
    
    He cites satellites, that orbit the earth, and are in shadow (when
    they discharge) and sunlight for regular intervals, ARE CYCLED TO
    ELIMINATE THE MEMORY PROBLEM JUST ONCE A YEAR!!!!!!!!
    
    In short - he says that for NiCds used for ham applications (hand held
    radios), memory is a non-issue. I would suspect that his conclusion,
    assuming they are valid, can also be extended to cover our RC TX/RX
    packs, since these transmit CW with RF power outputs of 1 W or less
    (compared to handhelds that go up to 5 W).
    
    On another note, there is also an article on RC planes in the same
    magazine - which makes interesting reading and material for
    evangelising.
    
    ajai

    One of the other benefits of cycling is that then YOU know what the
    battery capacity is. If you have a weak cell, you can detect it earlier
    than waiting for a full failure in the air.

    re .13
    
    This pretty much agrees with what the G.E. engineers say in their
    ni-cad applications manual.
    
    From personal experience, I believe the memory dogma is a non-issue.
    
    Cycling batteries at intervals will catch declining performance,
    but this has nothing to do with the memory folklore.
    
    Terry

    
    I am lost for an answer to this problem I am having with my Rx pack.
    It's a 1200mA Futuba pack. I am running it in my Acro-Wot with 4 servos.
    All Servos are now the 3000 series. Running an on board ni-checker. I
    used to be able to fly all day with the pack but now I am lucky to  get
    6-9 flights out of it. Checker reads full scale after a charge but
    drops down after each flight. In the past I got a days flying (say 20+
    10 minute flights) in and the pack had still most of the charge
    remaining.
    
    On Saturday evening I decided to replace the throttle servo from A
    micro servo to the std 3000 series type. I had also put ball raced
    clevis's on the ailerons, and elevator which totally eliminated any
    slop but the servos did drag a little. Anyway I put a little slop into
    the aileron and replaced the throttle servo and all the servo noise was
    eliminated. The engine is rubber mounted and can pull on the throttle
    servo a little but this setup was OK in the past and did not cause much
    grief.
    
    Great now I can get back to a good long days flying.... not so the
    problem persisted and I got the usual 6-9 flights. With the last flight
    losing total Rx power and going into failsafe. Very lucky in the
    landing - I got it most of the way and then the battery went - it
    started to roll but the only damage was a twisted u/c and a broken
    propellor. I had a total of about 15 seconds from failsafe to total
    loss of power - not very acceptable. This has happened a few times now
    and I am not that happy with the situation. 
    
    I guess that I should scrap the pack, not too sure hold old it is but I
    would guess in the 2+ year range. I think that I will do some tests on
    the Battery to see if there is anything obvious. 
    
    You guys got any words of wisdom ? Could I have a bad cell ? 
    
    Regards,
    
    Eric.

Sounds to me that you've got either a cell going bad or a case of memory. The 
best thing to do would be to cycle the pack a couple of times and see if it 
persists in the low readings. The pack is only as good as the weakest cell.

    You need to cycle the pack and measure it's capacity.  You could also
    check the current draw of your Airborne system by putting an ammeter in
    series with the pack.  You could have a servo binding up and drawing
    excessive current.  If your capacity is ok, look for a bad servo.
    
    Charlie
    
    P. S.  PCM receivers are more voltage sensitive and will fail sooner
    than non PCM.  Some will quit if one cell goes flat.