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Equipment for a Modern Gaffer

Batteries and Charging

Picture - Electrics

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Why a section on batteries?

Well partly because I spent 15 years of my life working for a battery manufacturer and so a decent battery  installation was a MUST when specifying the boat.  There are many advantages to Nickel Cadmium batteries on a boat: long life, greater operating temperature range, little voltage drop-off with increasing discharge, and the ability to use a greater proportion of their rated capacity.  They are however VERY expensive, even when you work for the manufacturer. 
Technically we have two quite different electrical requirements on our boats: a very high current for a very short period is needed for engine starting, whilst a modest discharge current  is required for as long as possible to power our  domestic services.  Ideally we would use different types for the two functions.  But, what happens when one fails?  A true deep-discharge type will not be able to provide the cranking amps needed to start your engine, whilst a small engine starter won't provide the discahrge capacity to  keep the lights (and the instruments, and the fridge) going for too long.  Having decided on the type of batteries to use, how about keeping them properly charged, and how do you know just what state of charge they are in? 

This section explains the solution we finally decided upon, with some of the justification for our choices. 

1. The Batteries
Sowester "Super Marine" ( 80Ah + 130Ah)

These lead calcium batteries are a hybrid between a deep discharge and engine starting battery.  They were chosen as the best compromise between price, technology, and the desire for an all-purpose power source.
We have a 130Ah model for domestic services and an 80Ah version for engine starting.
The two batteries are totally isolated from one another under all normal circumstances.  A third battery switch allows one battery to supply both functions in an emergency. [Email me for a basic circuit diagram.]
These batteries are manufactured by MBD, whose Technical Department can be contacted on freephone 0800 393674 (in the UK).
Chione  T London O/N 901053 R.T. 6 54/100
2. Battery Charger (Mains)
Poweramp 'Merlin' 12/15-2
 Morven Electronics
Picture - Merlin Charger No battery will regain its maximum capacity unless you use a proper charging regime.   Essentially, we would like to charge them quickly, charge them to their fullest potential, and then float them at "full" for long life.

This is a 'switch mode' charger (making it small and efficient).
Uses a three phase charging regime: bulk phase, acceptance phase  (also known as the absorption or soak phase), followed by a float charge.
Two isolated outputs with a 15A maximum charging current.
Can be left permanently connected whilst in the marina.

Note on sizing the charger: This charger drops down to float voltage at 25% of the maximun charging current (i.e. at 3.75A).  Ideally, this should occur when then charging current drops down to 2-3% of battery capacity.

There are several useful papers on marine electrical system design in the West Marine Advisor.

Chione  T London O/N 901053 R.T. 6 54/100
3. Voltage Regulator
Sterling Advanced Alternator Regulator
Sterling Marine Power
Picture - Sterling Advanced Regulator The voltage regulator on your engine's alternator is designed to recharge an engine starting battery.  Normally, engine start batteries only become marginally discharged and a crude charging regime will make very little difference. [If you have a blocking diode to split the alternator's charge between two batteries you'll also have the problem that the regulator is sensing the voltage at the engine not at the batteries.  The blocking diode is likely to drop the voltage by around 1 volt.]

For these reasons an external regulator is desirable.  The Sterling version has:
A three stage charging regime (see last entry).
Choice of absorption phase voltage - 14.4v or 14.8v.  (Check your battery spec., we use 14.4v for most of the year but 14.8v in Winter.)

Chione  T London O/N 901053 R.T. 6 54/100
4. Battery Monitor
Link 10
Cruising Equipment
Picture - Link 10 Battery Monitor Shining Star Award The final piece in the jigsaw. 
  No matter how well you arrange the charging regime, how do you know:
if the batteries are fully charged?
how much capacity you have left? (My batteries can be taken down to an 80% discharge level providing they are to be immediately recharged.)
how much longer will they last at present consumption rates?

This compact meter provides answers to these, and more, questions on its digital readout.  A simple set of LEDs also provides a continuous visual indication of remaining capacity.

Chione  T London O/N 901053 R.T. 6 54/100

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