Battery discharged.

The method of discharging the battery has a decisive influence on the durability of the battery, mainly the value of the current drawn and the discharge time.

The discharge of the battery is accompanied by the following (presented in a simplified way) reaction between the plates (active masses) and electrolyte:

analyzing this reaction, can be explained, why the density of the electrolyte decreases during discharge. Sulphuric acid (dissociated) reacts with the active masses of the plates, resulting in an acidic residue (SO₄) is bound to lead dioxide (PbO₂) on the positive plate (more precisely, lead), and on the negative plate with lead (Pb) spongy, forming lead sulphate in both cases (PbSO₄). At the same time, the amount of water in the electrolyte increases, which reduces its density. The more discharged the cell is, the lower the density of the electrolyte and the more lead sulfate there is on the plates. Continuous undercharging of the cell (battery), e.g. when driving in the city with frequent engine starts and lights on, causes excessive deposition of lead sulphate in the plates. Lead sulfate clumps and clogs the pores of the discs, making it difficult or impossible for the electrolyte to penetrate into them and reducing the capacity of the cell (battery). This leads to sulphation - irreversible changes in the structure of the plates. Normal charging of a sulphated battery does not produce good results, therefore a special type of charging is used - desulphation charging.

The basic condition for the correct operation of the battery is periodic control of the degree of its discharge and appropriate counteraction, to prevent sulphation of the plates, often profound and irreversible.

The battery is most heavily loaded when the engine is started. Under normal conditions, the highest current is drawn from it (so-called. starting current). At this time, chemical reactions in the active masses and the electrolyte take place very rapidly (this is very bad for battery life).

The current drawn by the starter is not always the same value. It depends on the value of mechanical resistance (friction), that affect the starter rotor. The smallest current the starter draws then, when idling (in bulk), i.e. when it rotates without driving any device (a case unheard of in a vehicle). The biggest, when its shaft is fully locked. The starter then flows through the so-called. short-circuit current (in the event of a vehicle breakdown, e.g. engine seizure). Between these current values ​​lies the current of normal operation of the starter. Worth knowing, that the starter reaches its maximum power at exactly half the short-circuit current. Means, that with proper energy use of the starter, the starting current should reach this value.

Remarks. Frequent use of the starter motor when the battery is constantly undercharged leads to rapid sulphation of the battery cell plates.

Starting the car engine with a starter motor should be as short as possible. It should be in the interest of every driver, that all assemblies and systems cooperating with the engine are efficient.

Due to the value of the current charging the battery when starting the engine, it is worth remembering about:

• pressing the clutch pedal (especially in winter), so as not to additionally burden the starter with the frictional resistance of the oil in the gearbox,

• limiting the current drawn from the battery during start-up by receivers other than the starter motor, especially headlights.

Characteristic values ​​of currents drawn by starters of selected domestic cars.

the car brand	Starter rated power [W]	Characteristic currents [A]
		idling	start-up	short circuit
Polish FIAT 126P	500	25	140	235±10
FIAT 127P, 128P	800	30	170	315
Flag 1100P	800	30-40	170	290 ±10
FSO 125P 1300/1500	1500	50	300	575
Polish	1500	65	270	540 ±20

 

Types of battery charging.

1. Top up:

• it is charging, the purpose of which is to replenish the electric charge in the battery,

• all three charging methods can be used here:

■ at a constant voltage value of from 2,35 do 2,45 V/cell,

■ at constant current:

— single-stage — charging current I_order = 0,1 Q₂₀,

— two-stage — charging current in the first phase I_order = 0,1 Q₂₀ and in the second with value I_order = 0,05 Q₂₀,

■ at constant current and voltage:

— in the first phase — with the charging current I_order = 0,1 Q₂₀,

— in the second phase — at the charging voltage U_order = 2,4 do 2,45 V/cell.

2. Boost:

• this is an accelerated battery recharge used only in emergency cases, to continue driving; Supercharging allows you to bring a large amount of charge to the battery in a very short time, e.g. for approx 0,5 h can be supplied this way around 50% electrical charge needed to fully charge the battery:

• recharge is usually performed:

■ two-stage with constant charging current:

— in the first phase (until the gassing voltage occurs) current with a maximum value of I_order = 0,8 Q₂₀ (e.g. for a battery with a capacity of Q₂₀ = 34 A h this current will be I_order = 27,2 A),

— in the second phase (until fully charged) with a current of I_order = 0,1 Q₂₀,

■ one-stage with constant charging voltage U_order = 2,4 do 2,45 V/cell; in the initial charging period for a battery charged in 35 do 40% the charging current at this voltage can reach even 0,9 Q₂₀, then it will begin to decrease and reach approximately the following average values:

— 30 A for batteries charged in 50%,

— 15 A for batteries charged in 75%,

— 2 And for batteries almost fully charged.

3. Equalizing charge:

• is only used to equalize the state of charge of all battery cells; in this type of charging, a charge is applied to the battery after it has already shown signs of being fully charged - this is known as. overload;

• they are usually carried out in one stage at a constant value of the charging current I_order = 0,05 Q₂₀, delivering an electric charge to the battery 2 do 3 Q₂₀[A· h];

• overcharging is harmful to the battery, but in cases of necessity, they are used for up to three days, but with a current not greater than I_order = 0,05 Q₂₀.

4. Desulphation charging:

• carried out after finding the sulphation of the battery plates (the causes and symptoms of sulfation have been described previously);

• in the case of deep sulphation, desulphation charging may not give any effect or only give short-term effects; all right, but sometimes only short-term effects are achieved by recharging the battery several times (3 do 4 cycles) with each time the electrolyte is replaced after charging with distilled water; the last charging cycle is carried out, filling the battery with a density electrolyte 1,26 g/cm³ and loading by any method (however, desulphation charging current is most commonly used);

• usually carried out in one step at a constant value of the current I_order = 0,02 do 0,05 Q₂₀ (until fully charged); is recommended after approx 12 h charging done 2 h break; after charging is completed, its effects should be checked, assessing the state of charge of the battery; if it is at least 70%, the above-mentioned top-up is carried out, if not, the desulphation charge should be repeated and the electrolyte replaced several times.

Summary of typical values ​​of charging currents for selected batteries of domestic production

Battery type	Capacity electric Q20 [A ·h]	charging currents [A]
		0,02Q20	0,05Q20	0,01Q20	0,08Q20
6SC34, 6SC34F	34	0,68	1,7	3,4	27,2
6SC45, 6SC45F, 12M2	45	0,9	2,25	4,5	36,0
6SE60, 6SE60MN	60	1,2	3,0	6,0	48,0

 

Ways to charge the battery.

Charging methods:

1. At a constant voltage value:

• constant voltage is maintained at the battery terminals during the entire charging period, the charging current automatically decreases;

• the charging voltage is set in the range from 2,35 do 2,45 V/cell, i.e.. from 7,05 do 7,35 V for batteries with rated voltage 6 V and from 14,1 do 14,7 V for batteries with rated voltage 12 V;

• the method of constant voltage is charging the car battery: due to the possibility of constant overcharging of the battery, the value of the regulated voltage of the generator is fixed at 2,4 V/cell, i.e.. 7,2 V in the installation 6-volt and 14,4 V in a 12-volt system.

2. At a constant current value:

• single-stage - the value of the current flowing through the battery is maintained at the same level during the entire charging process, i.e.. I_order = 0,1 Q₂₀ (e.g. for a battery with an electric capacity Q₂₀ = 34 A h the charging current is 3,4 A);

• two-stage - a constant value of the charging current is maintained for each of the two charging phases separately:

■ in the first phase (until the gassing voltage is reached) I_order = 0,1 Q₂₀,

■ in the second phase (until fully charged) I_order = 0,05 Q₂₀;

• when charging with the constant current method, the charging voltages are different, and their value is fixed at that level, to get the desired current flow.

3. At constant current and voltage:

• the method is two-stage:

■ in the first charging phase, i.e.. until the gassing voltage is reached, the battery is charged with constant current, e.g. I_order = 0,1 Q₂₀,

■ in the second charging phase, i.e.. until it shows signs of being fully charged, the battery is charged with a constant voltage value in the range from 2,4 do 2,45 V/cell.

The listed charging methods apply depending on the type of charging, i.e. from function, which loading is to be performed.