Conference vmszoo::rc

>    TO 4.8 WHERE IT STAYS FOR ABOUT 1 HOUR. AT WHAT POINT SHOULD YOU
>    RUN THE BATTERY DOWN TO? IS THIS METHOD ACCURATE OR SHOULD I INVEST
>    IN A DIGIPACE TYPE OF CHARGER/DISCHARGER.

    The Sanyo technical literature I have specifies the discharge
    point of a NiCad cell to be when the voltage on the cell drops to
    less than 1.1 volts.  Your RX pack is a 4 cell battery, with fully
    charged cells producing 1.2 Volts, you see a higher voltage for a
    while because of a characteristic of NiCads that lets them charge
    to a voltage higher than their cell voltage, however this higher
    volatge is lost very quickly under load.  When the pack drops to
    around 4.4 volts, consider it discharged.

Bob, that is about right for a good pack.  The ESV puts a standard 
      250 milliampere load on the battery to measure its voltage.   When
      the battery is fully charged, it will read about 5.35 volts, or
      about 1.3 volts/cell.  

      After its been under the load for about 10 minutes, it
      drops to its rated voltage of 4.8, or 1.2 volts/cell.  It should
      maintain this rated voltage for between 1 and 2 hours, depending
      on the quality of the batteries, the age of the pack, and the
      pack's "memory".  Normally a pack is considered discharged at 4.4
      volts or 1.1 volts/cell.  After it reaches this point, further
      discharge will rapidly drop the cell's voltage to nearly zero,
      and possibly damage the cell.
      
      Memory comes from the pack being repeatedly recharged without
      being allowed to drop to its 1.1 volt/cell level.  This is why
      it is recommended that batteries be "cycled", or purposely
      discharged to 1.1 volt/cell about once in six weeks during the
      flying season.  In modern batteries this effect is much diminished
      and this is mostly done as a precaution nowadays. 

    On a slightly different topic about batteries....
    
    Let's talk about rebuilding a transmitter battery pack...
    
    I cut open a futaba pack last night.  It has 8 cells, plus 1 
    spacer cell.  As I build the new pack, what do I do about...
    
    - end to end battery connections.  The original seems to have
    these little cups.  Should I try to salvage these cups??  If I do,
    do I solder them to the new batteries??  Or should I just solder
    the batteries end to end best I can??  Or should I just rely on
    mechanical connections??
    
    - mechanical connections...  Is that just plain old heat shrink
    wrapping that they use??  If I don't use the little cups, I do 
    I insure a good connection between batteries??
    
    Thanks,
    jeff
    

What I did on my Futaba 5LK was to get the solder tab batteries and
simply string them together.  The installation was so tight I
couldn't get even a layer of black tape around them, so I just stuck
them in with a little foam padding between the pack and the back cover. 
I removed the button connector pieces in the Tx, and connected the
batteries directly to the wires -- I had to disassemble the charging
connector to do it.  BTW, I measured a current of 150 mA, steady
state transmitter drain. 

Beware a bad connection.  I had one on my pack, luckily it chose to
open while I was giving the controls one last shake before going
out.  That was one fast mission abort!

If you do not have solder tab batteries, and I've noticed that
they've dissappeared lately, I've had good luck using solder wick,
available at Radio Schlock for the connections.  The stuff is used
to soak up solder for PC board repairs, and is full of resin and
good stuff to get the solder flowing.  Beware of overheating the
cell; use a small iron and get the job done quickly.

    THANK YOU FOR THE INFO. WHEN A BATTERY IS FULLY CHARGED, SAY 5.1
    VOLTS, THEN IS LEFT IN THE GARAGE FOR 1 WEEK, IS IT NORMAL FOR THE
    BATTERY TO READ SAY 4.8. HOW MUCH WILL DISSAPATE FROM LACK OF USE?
    
    

    Be careful of packs that have sat for more than a day or two after
    charging.  Sometimes internal cell leakage can discharge a pack
    in a week's time.  A pack at 4.8 volts is not safe to fly with.
    	Also, don't solder to standard nicads if you can help it.  You
    can easily ruin the seals that prevent them from drying out.  Solder
    tab batteries are available or what I have been doing is buying
    receiver flight battery packs from TOwer and cutting them apart.
    Then you can solder to the tabs and not ruin the batteries.  Often,
    Tower's price for replacement 600MaHr receiver packs is less than
    the cost of four AA cells, so cutting them apart for individual
    cells makes good economic sense as well.  They don't come with
    connectors.
    
    Charlie
    

My receiver pack, a Royal 4.8V pack about 3 months old, does not
discharge to 4.8V in a week.  I'd be suspiscious (sp?) of one that
does, but I'd just be more careful of it.

The reason that you should't fly with a pack that reads 4.8V is that
nicads will drop quickly to that value, as we discussed previously,
then they will stay there for a good while, then drop relatively
fast to 4.4V, then really drop off to 0. You don't know where on its
discharge curve a pack that reads 4.8V is -- I like to see it a
little higher, simply so I know that it is not on the 4.8V "flat
spot" yet. 

Good point on the receiver packs, Charlie; is that the standard
Tower receiver pack?  I think it was you who said that they tie two
of those together for the transmitter.  Wish I'd done that when I
replaced my TX batteries earlier this year.  

    The tower pack that I bought was made by Sanyo and the latest ones
    are rated 600 MaHr.  I have found using my cycler that different
    packs discharge differently. (voltage vs time)  I took my plane
    home after it was reading about 4.8 volts on Dave's meter and put
    it on my cycler without charging it.  I got 30 minutes at 250 mA,
    so I could have put in a couple more flights.  I then fully charged
    it and I only got a little over an hour.  This indicates that this
    pack should be replaced anyway since it is only putting out about
    1/2 of its rated capacity.  I'll cycle it a couple of times and
    if it doesn't respond, I'll replace it.  Eight bucks for a new pack
    is cheap insurance.
    
    Charlie
    

    I did kind of ask this question at the end of one of my other notes,
    but I'll ask again.
    
    With my 12v starter battery, I have a simple trickle charger.
    
    I have no guage or meter to tell me of battery condition, so how
    much should I charge it - seeing as I don't know how low it has got,
    nor when it has reached 'peak' capacity ?
    
    Is it safe to simply plug in for a long period, or will I cause any
    damage through over-charging this battery ?
    
    Basically, I don't want to be stuck on the flying field with a weak
    battery (for starting my heli), nor do I wish to fry the unit.
    
    
    Note that with my rx/tx ni-cads, I usually run them right down
    and then give them an overnight charge (also with a simple charger).
    I guess this should help to avoid the supposed 'memory problem'.
    
    Is this a reasonable practise ?
    
    J.R.

    J. R.
    	I assume your starter battery is lead-acid (gel cell).  Two things
    you don't want to do is let it run down or over charge it.  I don't
    know of any good way to measure how much to charge a gel cell.  I
    usually put mine on the regular charger for a couple of hour after two
    or three flying sessions.  If you heavily use the starter, you might
    have to charge it more often.  Unlike Nicads, these batteries don't like
    to be deep discharged.  You should not leave the battery on your
    regular charger for long periods of time.  This will boil the water out
    of it.  If you put your ear near the battery you can hear the bubbling
    while it is charging.
    	With your Nicads, it is not necessary to run them down before
    charging if  you use an overnight charger.  It's good to cycle them
    periodically to check their condition though.  I use trickle charging
    at 10-15 ma to keep my Nicads fully charged and ready to use.  I then
    put them on overnight charge after use.  I try to estimate the charge
    time based on how many flights I took.  If I just took a couple, I
    might charge for 3 or four hours and then switch to trickle.  I have a
    dual rate charger in my car that I use regularly in the summer.  I fly
    at lunchtime and I charge at 50Ma after I fly and switch to trickle
    when I get home after work.
    
    Charlie
    

>>                            -< I'll Try to Answer >-
    Thanks, the information seems quite helpful and relevant.
    
>>    know of any good way to measure how much to charge a gel cell.
    
    OK then, anyone know how I could check the charge in this battery ?
    
    In the mean time I will follow usual practice of *some* charging
    after each period of use.  If the battery does give up on me when
    trying to start the model on the flying field, I can at least borrow
    someone elses battery, although inconvenient.  Depending on the flying
    site, I may also use jump leads from the car battery (boot-mounted)...
    
    
    Next, what's the best way to check the ni-cad charge level ?
    
    Should I buy some form of battery tester, or fit some led's to the
    model to indicate the state of the rx battery ?  [U.K.] Recommendations ?
    
    J.R.

    Use an Expanded Scale Voltmeter that includes a load resistor.  You
    should have about a 200mA load on the batteries when testing them.  You
    can get an ESV for about $12 from Tower and it has inputs for both a TX
    and RX.  You supply your own leads.  I wouldn't be without one.
    
    Charlie
    

>>    can get an ESV for about $12 from Tower and it has inputs for both a TX
    
    Thanks, I now know what to look for - although I'm in the U.K.
    
    J.R.