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BATTERIES  / CELLS


   Once you have chosen your motor,  you'll need a source of electricity. You  could  use a very long extension lead from you car's cigarette lighter but  most of us use re-chargeable batteries.

    A  battery  or  cell's positive end or pole (+ve) should  be  consistently  wired RED and the negative pole (-ve) BLACK. Stick to this colour code and  you'll  have  less problems.  Use heavy grade stranded wire,  as least  as  thick as the wire on the cell packs to prevent power losses and burn-outs.  If  two  batteries packs are connected in series,  then  the  output voltage is doubled.  If they are connected in parallel,  then the current is doubled.  In the first case the motor spins faster for  a  short  while,  in the second the motor spins slower but  longer.  Never  connect  different voltage cells in parallel i.e.,  the two pack MUST be of  equal voltage and ALWAYS the same type i.e. NiCads only or Gel-cells only.

Series                                                           Parallel

For a proper explanation, have a look over at ...
Fast Electricals

Batteries in series:
Batteries in parallel:

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    NICADS  are  the most common re-chargeable  batteries used in radio models.  The name Nicads comes from Nickel Cadmium of which the batteries are made.  These  are very powerful and robust  batteries that can explode if abused.  To  give you an idea of the power of nicads just 20 cells wired  correctly  will  probably  start  your car!  The main power cells are just  a  little  smaller  than standard  batteries and called sub-C's and the ones used  in  radios  are  the same size as AA or pencells.  All NiCad individual  cells  produce  1.2 volts without exception.  The power cells are usually made up  in to packs of 6 or 7  giving 7.2 and 8.4 volts respectively. The capacity  of  the  cells  is  measured in Amp-hours (AH) which tells  you  how  much  current they can supply and for how long. (1200 mAH = 1.2 AH). In theory a  1.2 AH cell will supply 1.2 Amps for an hour, or 72 Amps for 1 minute, but  cells  are not 100% efficient and you can't ever actually get this and  in  the  latter  case  you  will  certainly  destroy  the  cell. 

 

MATCHED  PACKS

  Battery packs made up of cells that all have exactly  the  same  electrical  characteristics.  That is,  no single cell is weaker  or  stronger  than  another.  The whole pack will therefore discharges at  the  same rate and time.  This means you get all the useful available power out  of  all  the cells as opposed to an unmatched cell pack where a weak  cell  will  hinder  the  rest.  Matched  cells were mainly used  by  the  racing  fraternity  but now,  even though still quite expensive they are a  better  long  term investment as a matched cell packs are less likely to fail  due  to a cell failure.  
 

TRANSMITTER & RECEIVER CELLS

 

 

   The  usual  plastic  receiver  battery   holders   supplied   with   radio    outfits   tend to rust and split after  a while.  Nowadays I always solder  the  four AA size NiCad's together with a charging socket and on/off switch   then  cover the cells with heat shrink plastic.  Get yourself  a  Transmitter  and  receiver battery  charger   and  change   the   receiver  charge plug  to suit the  type  of  socket   you've  fitted to your cells.   I use DC coax plugs and sockets, the type used on portable radios and tape  recorders. From time to time check the physical condition of the cells and  Tx  battery  box  because  when they start to get old they  grow  a  white  "fungus"  around  the  positive  end  which needs to be  cleaned  off  and  polishing.

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LEAD-ACID Batteries

 
LEAD-ACID  Batteries are similar in construction to car batteries and  are  used  to  power scale boats and sometimes to a power IC  engine  starters.  There  are three type of lead-acid batteries,  Gel,  Wet and Cyclon cells.  Wet  cells,  (similar to a small car battery) aren't used  much these days  as  they  have  to  used upright and give off  hydrogen   gas   which   is  explosive.  The  liquids now take the form of a gel and are held in sealed  cases  to prevent any gas leakage,  these are termed Gel-cells and are the  most common form of modellers lead-acid battery. Cyclon cells are a sort of  'dry' gel-cell. Gel-cells have much greater capacity than  nicads  but are  much heavier. This makes them  ideal  for  scale  models that you want run  for   long periods and may need a lot of ballast anyway.  Gel-cells should not  be  used  in  fast boats with high a current drain as  even  these  sealed  gel-cells  will vent hydrogen if strained too much which will also  reduce  their life. For this same reason gel-cells must never be charged in an air  tight  container  such  as watertight radio boxes and  submarine  pressure  hulls.

  
Unfortunately  you  can't use your NiCad charger on  gel-cells,  you  need   another  charger.  Gel-cells  are  robust  but can be  easily  damaged  by  overcharging or discharging too quickly.  At first I bought one of those chargers built into a large black mains plug,  I was  told  "connect  up the battery and leave it for 16 hours and your  battery  will  be  fully charged".  BE CAREFUL,  THIS IS NOT  ENTIRELY  CORRECT.  I  followed this advise only to find that I had overcharged two new gel-cells  which totally destroyed them. A destroyed gel-cells makes a sizzling noise  which  means  get  you  wallet out.  I then did  a  little  research  into  gel-cells  to find out what went wrong.  It amazed me to find that not one  in several model  shops could give me any useful information on charging gel-cells.  I  decided to get the information from other sources.

( I  believe that the latest type of these charges are now automatic - but 'once bitten, twice shy'. Ask the shop keeper if the charge has automatic shut-off before parting with any money.)


    Information  was  forthcoming from two main sources,   RS  components  and  Maplin,  who  both  supply  automatic gel-cell chargers.  RS   supplies  a  detailed  data sheet on all sorts of batteries (Sheet no 10574) and Maplin  whom now sell a few different types, some in kit form,  provide  a  explanation  of  how  gel-cells  should  be charged it and how their charger does  it.  I  won't  bother  you with all the  details  (as I don't fully understand all of them  myself),   but  the  data  sheet is very specific that gel-cells  must  be  charged  with  a  carefully controlled constant voltage. Also they MUST be  charged to their Amp-Hour (AH) capacity and no more,  overcharging results  in  overheating  which  produces  the afore  mentioned  hydrogen  gas  and  hissing.  A  gel-cell  initially charges at a high current  then  steadily  drops off as it charges up. The battery is deemed to be fully charged when   the  current falls to a determined level.  The Maplin charger cuts off  at  180mA  and  45mA on the RS,  anywhere between the two should therefore  be  safe indicator.

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

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SAFETY,  PROTECTION &   FUSES

    If  you want to a safety  device can be fitted somewhere in the main power  circuit to prevent a burn up or melt down during a overload. Theses can be  normal  fuses,   an electronic  fuse and circuit limiters. Most people use  car  type  an  in-line  fuse  holder but   circuit  breaker  can  also  be  installed. Both will mean rescuing a dead boat off the water but they will  save  most  of the electrics.  Circuit breakers just have to be reset  and  away  you  go,  a  fuse will have to be replaced.  An  electronic  current  limiter  will limit the maximum  current  in a circuit or shut the circuit   down then  reset automatically.  You'll have to investigate these circuits  for yourself,   but many  of the home electronic constructor magazines and  books  have circuits that  can  be  adapted if you are of that persuasion.  I  have built quite a number electric boats and none of them now have  any  type  of  electronic  protection because,  a) I don't push the  motor  and  batteries  to their limit i.e.  a maximum of 14 cells to  any motor and  I  don't  overload  the motor with a propeller that will give me less than  5  minutes  run time.  & b) it's pretty silly to hold throttle open when  you  can see that the boat is struggling or the motor is jammed. If you want to  go  competition  racing then you will have to push these limits  but  this  series of articles are aimed at the fun and club racer.

   Another form of protection is by using proper connections between battery,  controller and motor.  Use straight runs of heavy grade stranded wire,  (I  use 25 Amp stranded wire as a minimum),  between each component.  Soldered  the  wire where possible and cover with heat shrink tubing.  For  pluggable  connections eg. batteries the normal
Tamiya connectors are good enough for  sports  boats but for higher power boats,  gold professional plated  plugs  and  sockets  are  available from the model car  world.  Check  the  metal  inserts  in the plugs from time to time for corrosion and tightness,  they  may  need cleaning,  re-soldering or squeezing back to shape with a needle  nose  pliers.  Only use 'chocolate block'  strip connectors (below) if you  are  experimenting  at  the lake side.  When your happy with  the  set-up,  remove  the  chocolate block connectors and solder it properly  and  cover  with shrink wrap insulation.


And Finally - don't work with the boat on your lap.
If the motor fires up....

BUZZzzz! @#!!*^%$%&*!!  & off you go to hospital!!!
 

 

For more information ( and probably much more accurate ),  click over too...

 

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

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