by Gavin Sorrell

240 Volt Charging

  A battery lifetime approaching ten years is possible if properly maintained at 100% charge for all of its life when not in use. Remember, starting batteries should not be allowed to discharge below 80% and deep cycle batteries below 50% of capacity. If your battery has lasted only one or two years, don’t blame it, charge it.
  The key is to maintain a disciplined charging cycle. It is not good enough to expect the motor with an average alternator to recharge the battery after a trip if you have enjoyed the stereo or turned lights on at night. Also, you must compensate for self discharge which is approximately 1% per day for flooded lead acid batteries. If the boat is moored, a solar panel is essential to keep the battery maintained. If the boat is stored at home or at a marina, 240V charging is the answer.
  In the past, battery chargers consisted of a lump of iron, some copper wire and a rectifier. They dumped a random charge into the battery, commonly causing battery gassing and overcharging. Undercharging was also typical as there is usually no way of telling if the battery is fully charged.
  The current generation of chargers are constructed like switch-mode computer power supplies. These multi-stage chargers are compact, lightweight and efficient. They usually have a much higher output than the old ferro-resonant charger. Most importantly, they are intelligent.
  The multi-stage charger can sense the battery status and react accordingly.
  The first stage is the bulk charging stage where the charger will charge at the full rated current until the battery voltage reaches the set absorption voltage.
  The following stage is the absorption stage where the absorption voltage is constantly maintained while the battery absorbs the full charge. Charging current progressively falls during this stage, which can last several hours.  Once the battery is fully charged, the charger switches to the float mode, where the voltage is maintained at a lower level. Most chargers will sense when loads are placed on the battery and then act as a power supply, so that power is not drawn from the battery.
  This is sometimes referred to as the fourth stage.
  Most smart chargers have selectable settings to cope with the different charging requirements of flooded lead acid, AGM or Gel batteries. The beauty of these chargers is that they are designed to never overcharge the battery and to maintain it at 100% level.
  After your boating trip, you can head home, connect the charger and leave it on 24/7 without fear of damaging the battery. The great advantage is that every time you take the boat out, you are assured that the battery is 100% charged. I consider smart chargers to be an investment in battery longevity rather than an initial cost.
  It is important to size the charger correctly. Current capacity (Ampere rating) should be at least 10% but no more than 25% of the battery Ah rating.
  Some AGM batteries can tolerate higher charging current, so consult the battery manufacturer’s specifications.  Many multistage chargers have a temperature compensation facility.
  This means that the charge rate can be automatically adjusted to compensate for changes in battery temperature.
  This can be significant in larger installations. The temperature sensor is often incorporated in the charger, but a better system is to have it located on the battery case and wired back to the charger.
  Desirable features in a charger are: thermal overload protection, reverse polarity protection against accidental reversal of the output leads, short circuit protection, output overload protection, interference suppression and charging status display.
  Many battery chargers have two or three outputs, enabling connection to multiple battery banks without using splitters or voltage sensitive relays.
  There may be variations in the charging voltage and current from the different outputs to cater for different sizes of battery banks, e.g. deep cycle and starting banks.
  When using a charger, make sure it is switched off before connecting or disconnecting from the battery and always connect the battery cables before connecting to 240V. If you are contemplating a permanent installation, be aware that the 240V wiring must be installed by a licensed electrician.  
  Next month: Solar Charging.

*Gavin Sorrell works in collaboration with Aquavolt Electric Boat Parts. Tel: 02 9417 8455 www.aquavolt.com.au