Maintenance and usage of submarine batteries
by Robert Derencin
There is one scene in the movie "Das Boot". The submarine was damaged during its attempt to pass the Gibraltar strait. The submarine went to the bottom of the Strait. Some equipment was damaged. The submarine batteries were partly damaged too. The submarine Chief engineer tried to salvage the equipment as good as possible. When he tried to salvage the batteries, he asked for a wire. Attempt of this article is to explain what happened in that scene and how batteries are important for a submarine. Some information in this article will be shown precisely (chapters two and three) and some information will be shown theoretically (chapter four). Numbers in the chapter four (electrical voltage and current) will be shown theoretically because of more easily understanding.
2. Historical development in WW1 and WW2
From the first days of modern submarines (those with motor propulsion) there was some kind of batteries in the submarines. From 1907 a diesel engine were used for a surface navigation and a DC (direct current) electric machine powered from a batteries were used for an underwater navigation. When a submarine was under surface all its equipment were powered from the batteries, electric machine, lights, internal communication etc. It means that from the first days the submarine batteries were vital for any submarine. In WW1 a submarine battery consisted of 55 to 120 cells. There were 2 to 3 batteries on a submarine. Each battery weighed from 370 to 600 kg. All together the batteries took from 8 to 16 percent of a submarine displacement. In WW1 a submarine was able to navigate underwater 50 hours with speed of 2 knots and 1 hour with speed of 7 to 10 knots.
In WW2 there were some improvements of the batteries. Some submarine was able to navigate underwater 80 hours with speed of 4 knots and 1 hour with speed of 16 to 17 knots. The Royal Navy type "T" submarine (1944/45) was fitted with 2 or 5 electric machines, the each one was from 1450 or 2900 horsepower. Underwater navigation speed by the electric machines powered from the batteries was up to 15 to 18 knots.
The US Navy "Balao" type submarine (1944/45) was fitted with 4 four Elliot Main (Electric Motors) two on each shaft, with a total horsepower of 2,740. While submerged, these motors were powered by two massive (each cell weighing 1650#) 126-cell batteries (in series) capable of delivering 5,320 Amp/Hrs each. The maximum surface speed with 4 diesel engines on line was 17 to 20 knots, with a range of 11,000 miles at 10 knots. The maximum submerged speed was 9 knots. Submerged endurance was 48 hrs. at 2 knots. Fuel capacity: 116,000 gallons. Patrol endurance: 75 days. (Or when torpedoes or food ran out.)"
3. Technical description
Batteries are unique sources of electric energy in underwater navigation on classic (diesel-electric) submarines. The submarine batteries are consisted of lead (Pb) cells. The submarine batteries have to be capable to store large quantity of energy. Usually there are 62 to 144 or even more cells. Wholly weight of batteries is 12 to 25 percent of a submarine displacement. There are usually two battery rooms on a submarine. Forward battery room is placed beneath the officer’s quarters and aft battery room is beneath control room. There are 2 to 4 batteries on a submarine. The cells in a battery are connected each other in serial connection and the batteries are connected each other in serial or parallel connection.
Technical description of cells:
- full charged voltage 2.1 V (Volts)
- density of electrolyte 1.28 kg/cubic meters (at 30 degrees of Celsius)
- charging voltage without gas up to 2.4 V
- charging voltage with gas up to 2.8 V
- minimum discharging voltage 1.8 V
Basic parts and construction of a lead (Pb) cell: Basic parts of a cell are a positive and a negative electrode and an electrolyte. The electrolyte is a conducting medium in which the flow of current is accompanied by the movement of matter in the form of ions. In the lead (Pb) cell the electrolyte is a solution of sulphuric acid (H2SO4) in distilled water (H2O).
The positive and the negative electrodes are made of specially manufactured lead plates. The positive plate is brown and the negative plate is grey. The plates are separated each other and plunged into the electrolyte. In order to make the battery capacity greater, the plates' surface must be as big as possible. Because of that there are the few lead plates in one cell container. The plates are placed mutually, the positive and the negative ones. The plates of same polarity (each "plus" and "minus") are connected by parallel connection, and because of that the battery has greater capacity.
Electric capacity of submarine batteries:
The electric capacity of the batteries is marked in "Ampere hours" (Ah). The capacity in the Ah shows how much and how long time is possible to get electric power from the batteries. Here is one theoretical example. If the capacity is 40 Ah, it is possible to get electric current of 0.5 A in 80 hours or electric current of 1 A during 40 hours.
It is known that is possible to get more electric power if we take less electric power during longer time than when we take more electric power during shorter time. Here is another example: If the capacity is 40 Ah we can take electric current of 0.5 A during 80 hours, but we can take electric current of 3 A in just 10 hours. In that case just 30 Ah of the same battery is useful. Rest of the capacity (10 Ah) we cannot use because voltage of a cell may not be less than 1.8 V. By the weaker electric current electrochemical process is able to get deeper layers of the battery plates (electrodes) and the capacity is greater.
Capacity also depends on environmental temperature. Capacity increases with increased temperature and vice versa. From temperature from 0 to 30 degrees of Celsius, if the power of the electric current is average, the capacity increases by 1 percent with each degree of Celsius rise in temperature.
Working principle of submarine batteries:
When we connect source of DC (direct current) and the battery terminals the electric energy is transforming into chemical energy. Parts of separated sulphuric acid (H2SO4) being chemically put together with solids of the lead (Pb) plates (electrodes). The battery is charged. When we connect the battery and an energy user (an electric machine, for example), the electric energy flows through the energy user and the battery being discharging. Flowing of the electric energy during charging and discharging of the battery is inversely. When the battery has been discharged the battery plates (electrodes) being changed to the primary state of solids.
Standards of submarine batteries:
- strength and capacity as great as possible
- high resistance to mechanic shocks (blows and vibrations)
- long time duration (long life)
- ability for fast charging
- in state of out of work, during the charging and discharging must develop hydrogen and other harmful gases as less as possible
- during inclination of a submarine (up to 45 degrees) the electrolyte must not flow out from a cell
Additional equipment for submarine batteries:
- mechanism for the electrolyte mixing (homogenize density of the electrolyte inside cells)
- telemetry instrument for measuring of temperature, level and density of the electrolyte
- telemetry instrument for voltage measuring
- cooling system for the batteries
- control indicator for rate of hydrogen in the battery room
- the battery room ventilation system
Charging of submarine batteries:
The submarine batteries must be charged from a source of DC (direct current). Voltage of the DC source must be higher than voltage of the batteries. Terminals of the source and the battery must be connected on the following way: "plus" with "plus" and "minus" with "minus". The charging of the submarine batteries must be as fast as possible. It depends about the cell technology and about the method of charging. The most efficacious method is "UI-method". The method begins with high electric currents, until to cell voltage of 2.4 V, i.e. up to beginning of gas. After that the charging continues with constant voltage and reduction of the electric current. A battery is full charged when the battery voltage and the electrolyte density are constant for a longer period.
The DC source is (the most often) a DC electric machine. The same DC electric machine works as a DC generator and as a DC electric machine for submarine propulsion. The DC electric machines/generators and additional apparatus for the battery charging are located outside of the battery room. When the submarine is surfaced the electric machine is powered by a diesel engine and works as a DC generator and produces DC current for the batteries charging.
Picture 1 shows situation when a submarine is surfaced. DC generators/electric machines (EM/G) are powered by diesel engines (DE). One part of produced electric power from the DC generators/electric machines is used for propulsion of the submarine propellers (P) and the rest of produced DC electric power is used for battery (B) charging. In this situation the diesel engines are full loaded. When the submarine's speed is faster the time of the battery charging is longer, because fast speed needs more electric power. Opposite, when the submarine's speed is slower the time for the battery charging is shorter. In that case, slower speed needs a smaller part of the electric power and the bigger part of the electric power remains for the battery charging.
When the submarine is under surface the diesel engine cannot operate (except in some cases). Then the DC electric machine (powered from the batteries) works as the submarine propulsion engine.
Picture 2 shows situation when a submarine is under surface. The submarine's diesel engines (DE) are out of work. DC electric machines (EM) are powered from the submarine's battery (B). In this case the DC machine/generator works just as DC electric machine, because there is no any production of the DC electric power.
Today submarines can be fitted with an AC (alternating current) generator. The submarines AC generators are fitted with AC/DC converter, because DC electric current is needed for the battery charging. The AC generators are more simple and easily for everyday maintenance.
Hydrogen and other harmful gases:
The hydrogen and other harmful gases are developed when a battery is charging or discharging. The gases are also developed during self-discharging of the battery (when the battery is out of work). Because of the self-discharging 1 Ah (Ampere-hour) develops 1 cubic cm of the hydrogen. The hydrogen is scattering from the battery room to other submarine spaces by means of ventilation. Mixture of air and the hydrogen higher of 4.5 percent is inflammable and the mixture higher of 9 percent is explosively. Because of all mentioned above, the battery room must be fitted with safety measures against the inflammable and explosively gases and the room must be fitted with good ventilation. Table 1 shows maximum concentration tolerance (MCT) of the battery gases and other substances in a submarine's air.
|Name of substance||Chem. formula||MCT /time of diving||Level of smell|
|Up to 1 h||Up to 24 h||Up to 90 days|
|Hydrogen in battery room||H2||2-3 %||2-3 %||2-3 %||0|
|Hydrogen in crew's space||H2||0.1 %||0.1 %||0.1 %||0|
|Aerosols of Sulphuric acid||H2SO4||0|
MCT is shown in cubic cm/cubic metre or in percentage. Level of smell is graded subjectively.
0 - no smell
1 - weak smell
2 - medium-intensity smell
3 - intensively smell
4 - very intensively smell
Everyday maintenance of submarine batteries:
When the batteries are full charged density of the electrolyte is raised. The density is controlled by means of specially instrument (areometer) designed to determine the density of the electrolyte. Picture 3 shows the instrument. Inside the instrument is a float. The float is marked with marks of various level of the electrolyte density.
- The battery voltage must be controlled constantly. But, simple measurement by means of a Voltmeter is not enough. The Voltmeter can shows high level of the battery voltage and the battery could be loaded insufficiently. For the reliably charging control the battery must be ridden by some energy user (radio, lights etc.). If the battery is enough charged the voltage decreasing (during the ridden) is small.
- The battery charging level can be determine by means of the cell plates colour. If the battery is enough charged (loaded) colour of the positive plates is dark brown. When the battery is discharged colour of the positive plates is bleached.
- The battery (cell) plates must be fully plunged into the electrolyte. The electrolyte evaporates by the time. Because of that the electrolyte must be supplemented with distilled water. If the electrolyte is spilled, the electrolyte must be supplemented with diluted sulphuric acid (in particular proportion).
- The battery cell voltage decrease by the battery discharging. When the voltage decrease below 1.8 V the discharging must be stopped and the battery must be charged again.
- The batteries temperature should be up to 40 degrees of Celsius. The temperature over 40 degrees of Celsius damages the battery. The temperature increases specially during the battery charging. Because of that the batteries are fitted with cooling system.
- The battery room ventilation is very important because of the hydrogen gases. Also, the battery room must be as clean as possible and the room must be free of any inflammable and explosively staffs.
- The batteries must be clean. The battery terminals must be clean and smeared with vaseline. Connection between the terminals and wires must be as good as possible.
4. Types of connections between the cells and the batteries
As mentioned in chapter 3, the cells are connected each other by serial connection, and the batteries are connected each other by serial or parallel connection.
In this chapter will be explained both types of connections. Values of strength of DC (direct current) and voltage are theoretically, because of easily understanding. From now the cells and the batteries are named "sources".
Serial connection of DC sources:
Picture 4 shows an example of serial connection. Three DC sources are connected serially. Positive pole of one source is connected with negative pole of another source etc. By the serial connection we get higher totally voltage. Totally voltage is a sum of the voltages of all serial connected sources.
From the three DC sources now we have one DC source. Total voltage of the DC source (U) is a sum of all three voltages (U1, U2, and U3).
U = U1 + U2 + U3
Example: U1 = 2 V
U2 = 3 V
U3 = 4 V
Total voltage is: U = U1+U2+U3 = 2 + 3 +4 = 9V
Energy user (marked with "R") is connected on the DC voltage of 9 Volts. Electric current is marked with "I". It is clearly that the same strength of the current (I) flows through all three sources and through the energy user.
I = I1 = I2 = I3
DC sources (cells and batteries) are connected serially when a higher voltage is needed. With the serial connection it is not possible to get higher strength of electric current.
Parallel connection of DC sources:
With the parallel connection is possible to get higher strength of electric current. Total electric current is a sum of currents of the all-parallel connected sources. It is possible to connect parallel just the sources of the same voltage. Picture 5 shows an example of the parallel connection.
Two sources are parallel connected. The negative poles of the sources are connected together and the positive poles are connected together. Voltages of the both sources are same. Because of that total voltage (U) of the both connected sources is same as a voltage of a particular source.
U = U1 = U2
Through the each particular source flows its particular electric current. The currents may be same but in practice the currents are different (depending of internal resistance of each particular source). Total electric current (I) is a sum of all currents, which flow through the sources. In this case:
I = I1 + I2
By parallel connection it is possible to get higher capacity of the sources (cells and batteries). If the capacity of one particular source (a battery) is not enough to produce required electric current the sources (batteries) must be parallel connected.
Let go back to the example shown by picture 5. Two sources are parallel connected. These are values of the sources' voltages and electric currents:
U = U1 = U2 = 2 V I = I1 + I2 = 3 + 4 = 7 V
U1 = 2 V I1 = 3 A U2 = 2 V I2 = 4 A
An energy user (R) is connected on the parallel-connected sources. The user is connected on the voltage of 2 V and through the user flows electric current of 7 A.
Once again: voltages of all parallel-connected sources must be the same. Even a little difference between the voltages is able to produce high electric current, which would be flows through the sources. It would be destroy the sources, because of the sources' weak internal resistance.
Combination of serial and parallel connection of DC sources: Picture 6 shows one combination of the serial and parallel connection. Three serial connections (of three sources each one) are parallel connected.
Values of particular voltages and electric currents:
First serial connection:
U1 = 2 V
U2 = 3 V
U3 = 4 V
I1 = 2 A
U = U1 + U2 + U3 = 2 + 3 + 4 = 9 V
Second serial connection:
U4 = 4 V
U5 = 3 V
U6 = 2 V
I2 = 3 A
U = U4 + U5 + U6= 4 + 3 + 2 = 9 V
Third serial connection:
U7 = 2 V
U8 = 4 V
U9 = 3 V
I3 = 5 A
U = U7 + U8 + U9 = 2 + 4 + 3 = 9 V
Total voltage of the combined connection shown above is 9 V. Total electric current is a sum of all three currents:
I = I1 + I2 + I3 = 2 + 3 + 5 = 10 A
The energy user (R) is connected on the voltage of 9 V and through the user flows the electric current of 10 A. By the combination of serial and parallel connection of DC sources is possible to get higher values of voltage and electric current.
The procedure in case of partly damaged DC sources (cells and batteries):
Sometimes some DC sources are out of work. It could be because of many reasons, mechanic shocks, electric short circuit, bad condition of the electrolyte etc. In order to at least some energy users continue to operate it is necessary to bridge over the damaged sources (cells and batteries). The bridge over is sometimes possible to get by means of manoeuvring switches.
The manoeuvring switches are intended for switching batteries and electric machines armatures (for submarine propulsion) in mutual serial or parallel connection because of graded voltage regulation. By the graded voltage regulation is possible to regulate rotation speed of the electric machine and its starting. If this is not possible, the damaged cells or batteries must be bridged over by means of totally new connections (new combination of serial and parallel connections of DC sources). But, in any case, "new" battery is never as good as the "old" one. Even if the voltage of the "new" battery is same as the voltage of the "old" (i.e. original) battery, electric current must be weaker because some sources are out of work. Because of that, in the case of partly damaged DC sources just necessary energy users could be operational (switched on). Unnecessary energy users must to be out of work (switched off).
In the first chapter (of this article) is mentioned the scene from the movie "Das Boot". The Das Boot Chief engineer tried to ensure at least some electric energy from the batteries and he asked for some wire. He needed the wire because of the new battery connections. The scene shows in an excellent manner a possible situation that could happen on any submarine.
Submarine batteries are vital for normal operation of the any submarine. Today there are conventional (diesel-electric) and nuclear submarines. On the both types of submarines there are the batteries.
Can any non-submariner imagine situation in which a submariner has to get action in a second? A submariner has to know his job perfectly. If the submariner is chief engineer or electrician (for example) he has to know state of the submarine batteries in any moment. And he has to ensure non-interrupted electric power supply from the batteries, anytime and in any possible (sometimes dangerous) situation.
In this article is mentioned just little part of knowledge about batteries. Some technical terms are mentioned without explanation (internal resistance, for example) and some technical terms didn't mentioned (internal voltage etc.). Once again, in the chapter four the values of voltages and electric currents are theoretical, because of more easily understanding.
This article was published on 19 Jun 2003.