Download Topsl Battery Systems 3

TOPS’L BOAT 12V BATTERY SYSTEMS
INTRODUCTION
The battery systems of Innovator, Fourtop and Lacerta have few things in common apart from
the fact that they operate at 12v dc.
The basic minimum equipment consists of separate batteries for engine starting and
domestic/auxiliary supplies, battery switches, engine-driven alternator/regulator, shore-powered
charger, and domestic/auxiliary distribution board (DB). Innovator has splitting or isolating
diodes. Fourtop has a split charge relay, and Lacerta has an Adverc battery/charge
management unit.
All three boats have 1 battery (B1) dedicated to engine starting, and 2 batteries (B2/3)
connected in parallel for domestic supplies. Their makes and capacities are different, but they
are all generally of the Leisure dual purpose type (starting and deep cycling) with calcium/lead
alloy plates. However there are sealed/maintenance-free, semi-sealed/low maintenance, and
unsealed types scattered around the boats, requiring varying degrees of attention and
maintenance.
The boats also have different forms of charge regulation and, more significantly, different
battery switching arrangements which have in the past tended to influence the battery switching
routine for each boat, especially when motoring.
None of the following switching and regulation systems is ‘technically’ ideal.
The need to keep costs as low as possible means each system is no more than a compromise.
Two examples of compromise are (a) the fact that Fourtop and Innovator can’t separate the 2
banks during a long engine run, and (b) that they also appear to be machine sensed.
Battery technology and charge management devices have advanced during recent years.
A battery’s internal resistance increases with state of charge, which tends to protect against
unwanted charge current. Leisure type batteries with calcium alloy plates are now much more
resilient to the effects of over-charging (eg. a fully charged starter battery continuing to receive
charge because the domestic battery requires it), provided they are not subjected to excessive
over-voltage. With standard automotive regulators (tapering current type) over-voltage
shouldn’t be a problem, but some ‘booster’ regulators using higher charge voltages could do
some damage.
Although the old fashioned preference was to avoid over-charging a battery in order to prolong
its life, modern practice seems to find it less important. Perhaps the lower cost of batteries is a
factor.
The procedures below aim for a switching policy as nearly as possible common to all three
boats.
Obviously the switching and shore charger equipments are all different, but the commonality lies
(a) in the treatment of the starting battery during long alternator charge periods and
(b) in the approach to mains power disconnection prior to engine starting.
THE BOATS’ SYSTEMS
Innovator
The following information is based on Inno’s 12v circuit diagram, and some notes taken when
new.
Battery Switching (FIG.1)
Although it is normal for switching to be done on the positive side of the battery, Innovator’s
single main isolator is in the battery negative circuit. There are no positive main isolators. As
both battery bank negatives are coupled permanently, only one switch is required – on the
downstream side of the combined negatives. It is therefore impossible to separately isolate
either battery bank from its designated load except through the downstream starting contactor
and domestic DB CBs.
The battery banks are either both ON or both OFF depending on the main isolator state.
Splitting Diodes
The two banks are electrically isolated from each other by splitting diodes, and can’t be
paralleled.
Each battery bank is permanently assigned to its load (ie starting or domestic) and cannot be
changed without physically swapping the battery terminal connections.
The alternator output is connected to the single input of the splitting diodes so that both banks
receive alternator charge as long as the engine is running. The charging current in each (B1 or
B2/3) diode/battery circuit is proportioned according to the combined resistance of the diode
and the internal resistance of the battery. (Low when discharged – high when charged).
Warning:
With this arrangement the alternator can be isolated from the batteries when the engine is
running. If no domestic load is connected the open circuit risks damage to the alternator internal
diodes.
DB
A
M
SD
SPC
MBS
Domestic Distribution Board
Alternator
Starter Motor Contactor
Splitting Diodes
Shore Power Charger
Main Battery Switch
FIG. 1 INNOVATOR 12V SYSTEM
Alternator Regulation
Since Innovator’s splitting diodes can cause a voltage drop up to 0.7v in the charging circuit,
regulation should be battery sensed to compensate. However there is no evidence of a battery
sensing wire, so it is assumed that the alternator regulator is machine sensed – ie the regulator
senses the output voltage at the alternator terminals and doesn’t compensate for volt drop.
This means the battery terminal voltage will never be as high as the regulator thinks it is.
Unless engine hours are high, this arrangement is likely to result in a permanently undercharged
domestic battery bank, which will progressively reduce the available capacity until eventually it will
struggle to keep the tricolour lit during an overnight passage.
Shore power Charger
The shore power charger supplies only the domestic battery. This is not uncommon in modern
boats and relies on the fact that the starting battery needs little replenishment after a normal start.
There is a sensing wire from the battery to the charger.
Charger details are not to hand at time of writing , but characteristic is assumed to be IU0U type.
Fourtop
Battery Switching (FIG.2)
Each battery bank has its own Master isolating switch, and the two battery banks are permanently
connected to the alternator via a split charge voltage sensitive relay (scvsr) system.
DB
Domestic Distribution Board
FR
Fridge
W
Windlass
M
Starter Motor Contactor
A
Alternator
SCVSR Split Charge Voltage Sensitive Relay
SPC Shore Power Charger
S1/S2 Switch 1/Switch 2
B1/2/3 Battery 1/Battery 2/Battery 3
FIG. 2 FOURTOP 12V SYSTEM
Split Charge Voltage Sensitive Relay (Sometimes referred to as a Battery Combiner)
(The scvsr is functionally similar to the American Pathmaker relay. The latter allows vsr setting
adjustment and is more flexible all round, but because of its higher cost, is not used much by
European boat-builders).
Fourtop’s B1 battery is connected to the alternator output and to one of the scvsr main contacts.
The B2/3 bank is connected to its aux circuits and to the other scvsr main contact.
When not being alternator-charged, the two banks are normally isolated from each other.
When the engine is fired up the alternator replenishes the small amount of charge taken from B1.
B1 terminal voltage soon rises to a pre-set level at which the scvsr relay closes its main contacts
and parallels the two banks so that they both receive charge from the alternator.
When the alternator stops charging the relay opens and the banks are isolated from each other.
The scvsr can’t be overridden to allow manual paralleling or isolation of the 2 banks.
Alternator Regulation
Since there is negligible volt drop in the alternator charging and scvsr circuits (ie. no diodes),
battery sensing is less important, hence Fourtop’s regulation is machine sensed.
However, most sail boat regulators, being of the standard automotive type, work on a tapering
current characteristic. As the battery terminal voltage rises during charging, the difference in
voltage between this and the regulated output decreases, reducing the charge current
correspondingly. This tapering current means it will take a very long period of motoring to fully
charge the batteries. It is often quoted that batteries charged from automotive regulator controlled
alternators never achieve more than 75% charge state.
Shore Power Charger
As on Innovator the shore power charger is a single output type permanently connected to the
domestic bank. When shore power and charger CBs are switched ON, charging will commence.
(At time of writing technical manual not to hand for confirmation).
Lacerta
Battery Switching (FIG.3)
The arrangement here consists of a 4 position ‘make before break’ rotary switch designed for use
with 2 battery banks. The make-before-break feature ensures that open circuits to electronics
supplies and at alternator terminals are avoided when changing switch position.
The 4 positions are labelled OFF, B1, BOTH, B2.
Each bank is separately and permanently connected to one of the 2 inputs of the switch.
The switch output or common terminal is permanently connected to the starter, domestic DB, and
alternator output, which are permanently connected together and can’t be separated by switching.
There are no split charge relays or splitting diodes.
Switch position determines which battery bank supplies load and receives alternator charge.
This means either bank can be selected for engine starting or domestic load supply.
It also means both banks can be paralleled for supplying load and/or alternator charging.
DB
A
M
SPC
B1/2/3
BS
Domestic Distribution Board
Alternator
Starter Motor Contactor
Shore Power Charger
Battery 1/Battery 2/Battery 3
Battery Switch
FIG.3 LACERTA 12V SYSTEM
Adverc Battery Management Unit
Lacerta has an Adverc battery charge management system fitted, which works in tandem with the
standard regulator to provide a more efficient and quicker alternator charge pattern.
A sensor wire connected to Lacerta’s battery switch ‘common’ terminal monitors the terminal
voltage of whichever battery or batteries are selected by the switch.
The sensor wire tells the Adverc unit how to adjust the alternator voltage output to ensure correct
voltage at the battery, including compensation for charging circuit volt drops.
An optional battery temperature sensor has not been fitted to Lacerta’s batteries.
Shore Power Charger
The shore power charger is a Mobitron, 2 x 12v dc output, 25A max, with 3 phase IU0U
characteristic.
One 12v output is connected to B1 and the other to B2/B3 – both at the Battery Switch terminals.
Hence the charger is always connected to the batteries regardless of the switch selection.
It is normal for the outputs of a multi-output charger to be isolated from each other by internal
blocking diodes to prevent among other things, the batteries discharging into each other.
However they may not be independently regulated.
As it is not otherwise specified in Lacerta’s charger manual, it would be safer to assume that the
two outputs are isolated by internal diodes and that both are controlled by the same regulator.
SWITCHING PROCEDURES - Options and Limitations
Alternator Charging
There has in the past been a preference for switching off the starting battery (where possible) after
about 10 minutes of alternator charging. The aim was to avoid over-charging the starting battery
when the alternator was pumping current into a discharged domestic bank.
On Fourtop and Innovator, circuit design does not allow this option.
On Fourtop the starting battery (B1) is permanently connected to the alternator output.
The switches are simply a means of disconnecting the battery banks from their respective loads.
On Innovator, both batteries are permanently connected to the alternator via their isolating diodes.
All battery negatives are permanently connected together at the main (negative) switch input.
It is not possible therefore to manually or automatically isolate either battery bank from the
alternator except by opening the main switch.
IT IS ESSENTIAL TO AVOID THIS WHEN THE ENGINE IS RUNNING.
Manual disconnection of B1 from the alternator is only possible on Lacerta.
Shore Power Charging
Since Innovator’s and Fourtop’s chargers have single outputs to domestic banks only, and as there
is no information regarding isolation diodes in the charger outputs, the possibility exists that if the
charger is connected and switched ON, and the engine is fired up, the batteries will receive charge
from both sources.
Lacerta’s twin 12v output must be assumed to have diode isolation and could be safely left
energised from shore power while the engine is running. The charger diodes would prevent backfeeding of alternator voltage to the charger but wouldn’t prevent the charger feeding to the
alternator. The charger regulator would theoretically take over and ‘hunting’ would be avoided.
SWITCHING PROCEDURES - RECOMMENDED POLICY
Alternator Charging
Since Fourtop and Innovator are inflexible in their battery switching options, the nearest we can get
to a common switching policy is to bring Lacerta into line with these two - as follows:-
Start the engine on B1, then switch to BOTH once the engine has fired up, and leave on BOTH as
long as the engine is running*.
WHEN THE ENGINE IS SWITCHED OFF, SWITCH TO B2/3 OR OFF.
THIS IS ESSENTIAL TO AVOID ACCIDENTALLY DISCHARGING B1 IN A DEEP DISCHARGE CYCLE.
*It will be acceptable for those who prefer, to switch to B2/3 after 10 - 15 minutes on BOTH.
Shore Power Charging
Bearing in mind the charger connections and lack of diode isolation on Innovator and Fourtop, it
will be inherently safer to disconnect mains power ON ALL BOATS before starting the engine.
Either disconnect the power lead, switch OFF the 230v input CB, or switch OFF the charger CB.
MONITORING CHARGE STATE
Voltages in italics are approximate and are intended only for guidance.
In the absence of a meter integrating time with current to calculate Amp-Hours, the only practical
way to monitor charge state is to measure the open-circuit voltage of each battery bank.
The most reliable charge state indicator is the specific gravity (SG) of the acid electrolyte.
However since it’s impossible to measure SG of sealed batteries and since the open circuit voltage
of a lead-acid battery is proportional to the SG, this is the most accurate method remaining.
However it is essential to do this when the battery is rested. That is, it must not have supplied
current or received charge current for 15 – 30 minutes minimum. (Some experts suggest 1 hour).
Much has been written and discussed about the charged and discharged voltages of a lead-acid
battery. Amazingly, articles appear in the yachting press which sometimes give misleading
information on this subject. Many people believe that the charged-discharged voltage range of
12.7 – 11.7 applies to on-load conditions. Unless the load is in the order of a few milliamps, this is
not true.
In open-circuit conditions, a fully charged battery will typically indicate 12.6-12.8 volts, depending
on ambient temperature, battery temperature, how hard it has worked in a previous charge or
supply condition, and how much rest time it has had before measuring. The battery will indicate
11.6- 11.7 volts when discharged and in the same test conditions. The mid-point of 12.1 – 12.2 v
is the ideal time to start re-charging.
A battery just removed from charge will indicate around 13.5 volts, and may stay there for up to an
hour. A fully charged, healthy battery that has been supplying load for an hour or two could
recover and rise by up to 0.5 volts when disconnected.
Clearly it’s not practical to take the battery out of commission to rest it before measuring the O/C
voltage, unless a system similar to Lacerta’s allows domestic load to be transferred to B1 during
the measuring period. (Not advisable).
A rule-of-thumb and very approximate indicator is the on-load voltage, but this varies depending on
the amount of current being drawn. A battery starts fully charged with say 12.7 volts but drops
slightly when current is drawn, to say 12.2 volts. Heavy loads might even drop the voltage to 12.0.
A healthy battery voltage should stay constant for several hours before showing further drop
towards 11.7 or less. It’s a very rough-and-ready system but if the voltage drops to say 11.5 ON
LOAD, it should be charged asap. (This is a subjective opinion – some may disagree). The onload voltage at which a battery on deep-cycle duty is considered fully discharged is 10.5, and too
many full discharges will seriously shorten its life.
A battery on engine starting duty might briefly fall to less than 10.5 volts after up to 10 seconds of
cranking, but if it recovers to 11.5 - 12v (without charging) it should be OK. Fifteen minutes of
charge should get it back to normal.
Batteries don’t last forever. Even the so-called maintenance-free types need to be monitored,
even if only via a voltmeter. Check the built-in green light from time to time, and if you perceive a
slight deterioration in performance, check the electrolyte levels in those with removable plugs.
Don’t place too much reliance on the accuracy of the meter – remember we’re looking at a range
from 12.7 to 11.7 = 1.0 volt. Digital meters are generally more accurate at typically +/- 0.1%.
Moving coil or moving iron meters are usually +/- 5% or worse.
It’s best to use the meter as a trend indicator. You’ll get to know the charged/discharged
indications if you take the trouble to look at the meter fairly frequently.
Finally, try to be aware of how much current you’re drawing from the system. Avoid running all the
saloon and sleeping berth lights with the fridge blasting away, and be aware of the load the radar
and chart-plotter demand especially when the autopilot and tricolour are all ON during a long
sailing period.
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