Batteries and Alternator (How many batteries have a boat)

Classification of battery

Basically, there are 3 types of batteries, lead-acid, absorbed gel and electrolyte.

The lead-acid batteries are the most common batteries. Batteries are used cars and boats generally.

Its value is best. It is characterized as a non-tight (must be kept vertical), which needs maintenance (need to replenish distilled water) and can be dangerous, as we discuss battery.

The plate is constructed of porous lead plates, using a dilute sulfuric acid solution as an electrolyte with distilled water (30% sulfuric acid, 70% water). It is characterized by high temperatures hold up well, not low temperatures, where the electrolyte can be reached to freeze. A more heat, higher voltage at its output presents.

Gel batteries have the electrolyte in gel form and therefore less likely to have liquid spills. They are theoretically maintenance batteries, although in practice must periodically fill them with distilled water.

Absorbed electrolyte batteries, called AGM (Absorbed Glass Mad). They are batteries of about 3 times more expensive than lead-acid but have the advantage that they are really no maintenance, do not use liquid electrolyte (no spill), can be put in any position, they can be used with normal chargers , and hardly produce gas when recharging, since hydrogen is recombined with oxygen to produce water.

All batteries need recharging later to deliver the energy they receive (download). The number of charge / discharge is limited to a maximum 1500 cycles. Then the battery internal resistance increases and you have to proceed with the replacement.

If a battery is not used, it is unloaded slowly. The lead-acid batteries, if not charged, they lose monthly about 15% of capacity, while the gel and AGM make between 1 and 3%.

Total self-discharge of the battery may irreparably damage it.

Load voltages and maintenance depend on the battery type:

  • Batteries 12 V lead-acid and AGM
  • Or load voltage = 14.8 Volts
  • Or maintenance voltage = 13.8 volts
  • Or voltage battery charged to 100% = 12.8 volts
  • Or voltage battery charged to 50% = 12.2 volts
  • Or voltage battery charged at 0% = 11.6 volts

If a newly charged or is less than the 12.2-volt battery is damaged, it must be replaced.

Many starters or could not start with a voltage of the 12-volt battery.

Or charging current ≈ 25% nominal AH

Batteries 12 V gel:

  • Or load voltage = 14.4 Volts (voltage slightly lower than lead-acid)
  • Or maintenance voltage = 13.5 Volts
  • Or current nominal load ≈ 10% AH

The Ampere-Hour battery capacity measures it. It is a measure of the amount of current the battery can deliver in a time period. For this capacity, batteries start measured over a period of 5 hours (C5 type), while for the service batteries is measured at 20 hours (C20 type). For example, if a battery can deliver 3 amps for 20 hours, will battery 3 x 20 = 60 AH (AH = ampere-hour).

Another important value of a starter battery amps peak can deliver, ie, the instantaneous current that can be supplied.

starter batteries, a characteristic parameter is the CCA (Cold Cranking Amps). CCA is the current that can supply the battery for 30 seconds at -18 ° centigrade, keeping the output voltage to an operating value. CA (Cold Crack), also called MCA (Marine Cold Crack), which is the same but at 0 ° C is also used.

In the service batteries deep cycle, the most interesting parameter is the RC (Reserve Capacity) “reserve capacity”, which is a number of minutes a battery can supply a current of 25 amps while maintaining the output voltage to an operational value.

Batteries and Alternator

Batteries and Alternator How many batteries have a boat

How many batteries have a boat? What are they for?

The starter battery provides plenty of power to the starter motor for a short time. It does not support extended well discharge cycles. The maximum number of cycles of loading / unloading is approximately 400.

In addition to supplying power to the starter motor, it is also often used for this battery:

  • Anchor windlass
  • Bow propeller engine
  • Electric winches

Starter battery MCA = 800 A, 650 A CCA =

Weight: 17.5 Kg

The battery service or provides less current but for a long time. They are called deep cycle batteries, as they can be downloaded for longer without spoiling reach. The maximum number of charge / discharge is about 2000. Basically provides power to the following:

  • Internal and external lighting
  • Navigation lights
  • Refrigerator
  • Pressurizing water pumps
  • Bilge pumps
  • Navigation equipment, radio, GPS, radar
  • Autopilot
  • Service battery (deep cycle), 90 AH
  • RC = Reserve capacity = 175 minutes (providing 25 A)
  • Weight: 20kg

There are dual-use batteries, ie, starting, and service. A service battery deep cycle battery can serve as a starter, but not the other way around.

  • Battery dual-use (starting and service) MCA = 650 A, 65 AH
  • Reserve capacity = 120 minutes (providing 25 A)
  • Weight: 17.7 Kg

Starting batteries are lead-acid plates thinner than lead batteries such service. The separation between the plates is very small starter batteries. Thus lead poses the electrolyte (diluted sulfuric acid) much more surface so that the instantaneous current is greater. This makes the starter batteries are smaller than those of service.

The battery discharge service is much slower than in starter batteries, and therefore in charge will be the same, the service batteries (deep cycle discharge) need more time to load.

  • There are boats that instead of a battery of service have two, one for key safety elements such as bilge pumps, navigation equipment and radio, and another for the rest of the aforementioned elements.
  • Some ships carry only one battery with double start function and service. In this case, the battery is the type of service, but with a larger (20% more capacity than a standard deep cycle), thus achieving instantaneous current required for the starter.

How the service battery is selected?

The power consumption of a boat of 12 meters, with all instrumentation, including radar, VHF and SSB radios, lights, refrigerator, microwave, TV, etc., and accounting for average usage time, is estimated at 10AH (ampere every hour of the day). If we admit for the service battery autonomy 6 hours prior to recharge, we would get 60 AH. If the depth of discharge admit battery for deep cycle service is 40% of capacity, we would need a battery of 150 AH, which would take two 90 AH batteries as shown in the figure below.

The burden of lead-acid battery should not be performed more than 1/8 of its rated capacity in ampere-hours, so to recharge two batteries 60 AH 90 AH parallel, the charger will supply 90 / 8 = 11.25 amps per battery. We need for loading at least one time

60 AH / 11.25 hours = about 5.3 hours. As are two batteries in parallel, the total load current would be 22.5 amps.

Such power is not a problem for a 100-amp alternator.

How do you check if a battery is good?

There are two measurement systems, one using a voltmeter, and another using a hydrometer. We assume that we use the voltmeter own ship.

The battery voltage is measured. You can use the control panel voltmeter boat itself or a multimeter measuring volts DC and placing two points on the battery terminals.

If the measured volts to 12.7 volts are above, it is that the battery is charging.

We are interested in temporarily stop charging the battery to see the real voltage. There are three possible scenarios:

  • Or the boat is docked in the port, the boat engine is stopped, and the battery is charging by the internal charger plugged into 220 volts AC of the pontoon boat. We interrupt the battery charge, either by disconnecting the 220V AC plug the dock or from the boat AC panel own control, putting off the decision corresponding to said switch.
  • Or Engine running. The engine alternator is rotating and producing tension and the necessary current, ranging regulator (usually a small box with wires is attached to the alternator itself), and then goes to the battery via spacers emitting diode load. We interrupt the battery charge simply by turning off the engine of the boat.
  • Or the ship did not have the engine running and not plugged into 220 volts AC of the pontoon. In this case, there is nothing else to do and proceed as illustrated below.

Once performed the above operation we measure the battery voltage. If this is less than 12.7 volts the battery is properly charged to 100% capacity.

If the measured voltage is less than 12.7 volts two interpretations:

  1. The battery was not fully charged. In this case you have to put it back in charge and to wait a reasonable time it is fully charged.
  1. If the battery and charging had long and 12.7 volts is not reached, it is likely that the battery is in poor condition and has to be replaced


Precautions with lead-acid batteries

The lead-acid batteries have internally diluted sulfuric acid. Continuous sways and nods of a boat can make such an acid spill, which is dangerous, first by burns and corrosion may cause, and secondly, if mixed with seawater, to have this salt (sodium chloride), hydrochloric acid and deadly poisonous gasses for people occur.

Charging a battery inevitably produces hydrogen and other gasses, which are discharged to the outside through holes having the battery filler caps themselves. Hydrogen gas is highly explosive until a ratio of one part by air 50. If a spark occurs for any reason, the battery may explode, spraying sulfuric acid all around. Hands, skin, eyes, etc. people can suffer severe burns.

Care must be taken when putting two batteries in parallel by the typical cables sold everywhere. If when connecting a spark occurs, the battery may explode. The first thing to do is ventilate the area of battery plugs, even fanning the area with a paper towel, etc. Negative batteries are always connected to each other to the mass of boat engine and the chassis. we only connect the red cable from the positive battery, which will do it with gloves, goggles, and completely covered with clothes, to minimize the effects of a possible explosion and subsequent spill of sulfuric acid.

Or hydrogen gas continuously produced by a battery that is charging is also explosive, highly corrosive. Placing a battery should be away from the most sensitive parts of the engine, hoses, belts, etc.

Where a boat batteries are placed?

Should not place them in the same engine compartment, as it degrades heat batteries much.

Should be placed in a ventilated, which on a boat is very difficult, because if we put up, plus the boat lost stability, the batteries may fall, resulting in danger.

The problem of placing them in the bilges of the boat, as there is a flood, water will soon reach the batteries, causing the resulting short and inutilizándolas. From there it stops working bilge pump, instrumentation, lighting, etc., seriously affecting the safety of the ship.

Is it a car battery for a boat?

The car batteries are designed to always being charged by the car alternator, ie load when the engine is running, which is almost always, that is, the time when a car is with the engine stopped and the lights are minimal. Car batteries are not designed to suffer downloads more than 5% of its capacity.

Battery service of vessels, on the other hand, are deep cycle, admitting discharge cycles up to 50% of its capacity (in some special batteries up to 80%). This is the case of a Houseboat under sail and lights, autopilot, refrigerator, etc. connected.

If we placed a car battery and service battery of a boat would get first that within a few hours had been discharged, and secondly we had spoiled said battery, because as we said before is not designed for deep discharge.

The marine alternator

The alternator is coupled to the motor boat with straps device, and whose purpose is the production of electric current to recharge the batteries.

The alternator generates electricity by means of a rotor which produces a rotating electromagnetic field within a set of fixed stator coils calls. The AC (Alter Current or AC) power collection in the stator is subsequently rectified by means of diodes and converted to DC (Direct Current or DC). The rotating element is the inductor, needs to produce its magnetic field a small current, so a small part of the current collected in the armature (stator) is recycled back to the rotor. This is achieved by means of slip rings in the own axis of rotation, and a continuous carbon brushes in contact with them. For that reason, they are called self-excited alternators.

Clearly, the alternator own brushes in your brush with slip rings can produce a spark, which can be lethal to a boat that uses gasoline fuel. So special alternators or use brushes with no sparking or use brushless alternators are used in these cases. The latter are less effective, but at least they are safer.

The size of the alternator is in line with the size of the batteries, ie against larger the power requirement of the boat, the greater must be the alternator.

The alternator is coupled to the engine of the ship through transmission belts to join both the pulleys. When the alternator is small enough with a single strap, but if the alternator is larger two or more pulleys are made.

Normally the size of the alternator pulley is smaller in diameter than the motor, so that rotation of the alternator is faster than the engine. This will facilitate the charging of the batteries when we are sailing at low engine rpm.

How an alternator is selected?

Normally the maximum charging current of the lead acid battery is 25% of its nominal value, ie, a battery of 100 AH (ampere-hour), can be recharged with a maximum current of 25 amps. Gel batteries and AGM support loads between 25% and 40% of its capacity in ampere-hours.

Therefore we need an alternator capable of supplying this current even at low engine speeds.

There are basically two types of alternators, the small armor, and large armor. The first provide maximum current between 75 to 150 amperes and the second between 150 and 200 amperes.


The alternator regulator

The DC output voltage of the alternator diodes connected to the batteries, recharge them occurring. Clearly there to regulate this voltage, and a battery of 12 Volts need a voltage for charging (about 14.4 volts), which also depends on its state of charge. The element that regulates this voltage regulator is called.


What the regulator is to analyze the output voltage of the diodes, and depending on the state of charge of the battery will vary the voltage injected into the inductor (rotor) through the brushes. This works in a closed loop, if the output voltage of the battery is excessive, making the regulator is to inject less current in the inductor and vice versa.

The controller is physically electronics box usually attached to the alternator itself. Normally the alternator is supplied with its own regulator.


105a coupled alternator regulator (Volvo-Penta engine)

The controller type depends primarily on the type of batteries that have, lead-acid, gel or AGM, as different types of batteries are charged with different voltages, which makes more difficult the choice of the regulator.

There are basically two types of regulators, simple and sophisticated.


Simple regulators simply provide a fixed voltage at its output. This voltage of approximately 14.4 volts will batteries for recharging. The problem with these regulators is that they fail to charge the battery to 100%. When the battery is discharged, the voltage difference supplied by the regulator and the battery makes a much current pass. This current decreases as the battery are recharged, since the voltage difference decreases, reaching the current to 0 amps when the difference is 0 volts.

Sophisticated regulators charge the batteries in 3 stages. In the first stage, called “high load” apply a similar simple voltage regulators, but as the voltage difference between regulator and battery decreases, increase the charging voltage, the voltage regulator up about 15.5 volts. In a second stage, called “absorption”, the regulator voltage decreases as the battery approaches 100%, and in a third stage, called “float”, the controller only supplies a voltage maintenance battery (about 13.1 volts) to keep 100% charged.

Apart from the three phases that characterize the sophisticated regulator may also have sensors battery temperature as the charging current dependent on said temperature?

Another sophistication of these regulators is that compensate the voltage drop produced by the diodes in the charge removal step. They do this by remote sensing with cable battery voltage.


Is it an alternator for a boat or car?

No, the car alternator does not supply large currents quickly as the alternator / regulator itself of a car does not let the batteries are discharged too.


In a Houseboat in which we sailed sailing for a long time, the batteries are discharged fairly (consumption of auto-pilot, navigation lights, refrigerator, etc.). When launching the boat engine it takes to recharge the batteries quickly

Apart from the above reason, the marine alternator must be much more robust and reliable than a car, among other things by the saline environment to which it is subjected.

Way to isolate the pontoon boat

In order to prevent galvanic corrosion and electrolytic boat, two mounting are made:

Isolation transformer. The primary of said transformer feeds the 220V AC shore side and the secondary AC 220 V AC isolated feeds the ship, according to the following scheme.

Marine isolation transformer must have a privacy screen between the primary and the secondary. This screen is connected to the land of the pontoon.


One of the outputs of the secondary is connected to ground and neutral ship.

Galvanic Isolator. A diode bridge is used according to the following scheme:

When the potential difference between the ground and the ground pontoon boat is not more than about 1.6 volts, the galvanic isolator works well, preventing leakage currents to ground the boat dock land. Furthermore, the galvanic isolator if not prevent bypass of a ship ashore apparatus, reach the differential triggered.

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