The maximum current rate (in Amps) that the cells  can  charged or discharged at.  Exceed this value ie,  shorted  out,  fast  charged  too fast or too long and  the cells life is reduced or they could  blow  up.  An indication of over charging is when you see the same battery  pack  you've just bought half the price in another model shop!  Sorry back  to the point, overcharging causes the cells to overheat and vent off gases  through  the top indicated by a fizzing noise.  If this  happens,  switch  everything off,  disconnect the batteries and run!!  You will have  certainly  shortened  the life and reduced the AH capacity if you  haven't  destroyed them entirely.    

   Some modellers want their batteries charged as quickly as possible and  forcing as many Amps into the cells as possible,  this is known as fast  charging.  There  are lots of cheap fast chargers around with  a  clockwork  timer  that stops charging after the set  time  expires.  These  chargers  have  the tendency to either under or overcharge your  cells  as  they  don't  employ any method of checking the charge level of the  cells.  A  better way of fast charging is to use an automatic charger.  The best  types are 'peak detection' chargers.
   These chargers  accurately  monitors  the  cell  pack  voltage  and  then  automatically  stops  charging when the cells reach the set voltage  which  corresponds to maximum charge.  The temperature of cells rises in relation  to the amount of current flow in to of the cells, so a THERMAL CHARGER  has  a  temperature  sensor, called a thermistor, that  measures  the  cells  temperature   and  automatically  shuts  off  when  the  cells  reach  the  temperature  corresponding to full charge.  The thermistor MUST remain  in  contact  with  cells  because if it falls off the charger may  just  keep  charging.  The  instructions with the thermal charger will state what  the  full  charge temp should be,  on some it's adjustable.  A separate digital  monitor  with probe can also be used to check the temperature of the cells  whilst  using  a clockwork charger but obviously you'll need  to  manually  switch  off the charger when the full charge temp is reached. 

There are a  lot  of  good automatic chargers around,  some  relativity  cheap,  others  featuring  digital meters,  cycling circuits and computers,  others  sing,  dance  and  make the tea.  Make sure you don't pay for gimmicks  that  you  don't need.


  These charge the batteries at a very slow rate, taking up to 12  hours but they are cheap, effective and reliable. Trickle chargers are too  weak to overcharge the cells so are safe if left on charge too long.  I've  sometimes  forgotten cells  on trickle charge for 2 or 3 days and no  harm  has  been  done.  The  main advantage is that packs will  last  longer  as  trickle charging puts much less stress on the cells than fast charging.  I  slow  charge my cells during the week and then peak charge them the day  I  take the boats out.  

Did  you  know that you can't fully re-charge your nicads?  When you  have  used  your nicads,  they are not completely discharged,  some charge still  remains.  As nothing is 100% efficient,  lets say your cells are only 98%,  efficient,  that means that the cells will only accept 98% charging of the  discharged space,  you'll lose 2%.  With every succeeding partial charge /  discharge cycle,  your cells could loose another 2%. It's then easy to see  that after 10 cycles your cells could be down as much as 20% of their full  capacity.  This is why you see some modellers completely discharging their  battery  packs with a car headlamp bulb connected to the cells,  (a 15 ohm  10  watt resister with a 12v car side light bulb across the cells would be  less  stressful).  This  ensures that all the cells are discharged  evenly  down to nothing so allowing them to be fully fast charged to,  in our case  98%,  you  only loose the same 2% every re-charge.  Most people agree it's  best  to  leave the cells discharged for storage and only charge  them  as  required.   

The new NicalMetal Hydrides Cells don't suffer from this problem.

 Transmitter  (Tx) and receiver (Rx) nicads aren't worked very hard and are  always  trickle charged so should only need to be fully discharged once  a  year  at  most  by  leaving  the transmitter and  receiver  on   at  home.  Re-charge  them  and make sure they are all OK on a meter.  Cells  can  be  checked on an meter set to volts then Amps,  dodgy cells will have a lower  voltage and current reading than the rest.  Take the current readings on a  setting  of 20-30 Amps range and as quick as possible as you are  actually  shorting the cells. This test can be done on the main sub-C cells BUT ONLY  ONE AT A TIME AND VERY QUICKLY.    If in doubt - Don't!


 Well  all  of this is just my opinion,  but what the hell do I know!

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