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What is voltage sense?

No matter how thick, every cable has

some resistance, resulting in a certain

amount of voltage being lost between the

battery charger and the batteries. This

voltage loss depends on the thickness of

the cable and the battery charger current.

A battery charger measures as standard

the voltage at its output terminals. Due to

the cable losses the voltage is higher than

the battery voltage. The output voltage

of the battery charger minus the voltage

loss across the cables is the battery

voltage. When a lot of voltage is lost on

the cables, the battery charger might

switch to the absorption phase too early,

which means that the battery will not

become fully charged or charging time

will increase. To compensate for voltage

loss via the cables, sense wires have to be

connected between the battery charger

and the batteries. These (thin) cables

ensure that the battery charger measures

the voltage directly on the positive and

negative terminal of the battery instead

of on the output terminals of the battery

charger. The voltage lost during charging

is compensated and the batteries are

charged quickly and effectively. The

voltage drop over, for example, a diode

splitter (battery isolator)can also be

compensated in this way.

First step:

BULK phase

In the bulk phase, the battery charger

delivers its maximum current, e.g.

50 amps for a ChargeMaster 12/50

and battery voltage increases. The

duration of this phase depends on

the battery capacity, charger capacity

and any consumers connected to the

battery during charging. The bigger

the battery, the longer this step takes;

the larger the charger, the shorter

the stage. If consumers such as a

refrigerator is connected, they will

also need to be powered by the

charger, reducing the charge

current going into the batteries and

increasing the time necessary for

charging.

Second step:

ABSORPTION phase

The second step, the absorption

phase, begins once the battery has

reached its maximum voltage. At

this point the battery is around 80 %

full, and the charge current begins to

slowly decrease.

At 25 °C, the maximum voltage is

14.25 volts for a 12 V battery and 28.5

volts for a 24 V one. In this stage the

battery is charged to the full 100 %,

which takes approximately three to

four hours, depending on the battery

type, the battery charger and the

charge amount.

Third step:

FLOAT phase

Once the battery is fully charged at

the end of the absorption phase, the

float phase begins. The Mastervolt

battery charger switches over to a

maintenance voltage so that the

battery remains fully charged and

in optimum condition. Any existing

consumer loads are also powered.

The charger remains in the float phase

until the battery voltage falls due to

a major load, or the battery charger

is unplugged because the power

connection was removed.

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What is a temperature sensor for?

When charging the battery, the exact charge voltage is of the essence. The charge

voltage must be adjusted to the temperature of the battery. When the battery is

cold, the charge voltage must be slightly higher to charge the battery fully. In high

ambient temperatures the charge voltage must be reduced to ensure the battery

is not overcharged. Mastervolt battery chargers are set as standard to a battery

temperature of 25 °C.

When the temperature sensor is connected to the charger, the output voltage

will vary by 0.03 V per °C for a 12-volt system and 0.06 V per °C for a 24-volt

system. This is in accordance with the advice of most battery manufacturers. At

a temperature of 15 °C for instance, the maximum charge voltage for a 12-volt

system is 14.55 volt, and at 30 °C it is 14.1 volt. The corresponding values for a

24-volt system are 29.1 and 28.2 volt. At a temperature of 12 °C the voltage is not

further increased to protect the connected loads from excess voltage. At 50 °C the

charge voltage will be reduced to 12 or 24 V to protect the battery in these high

temperatures. The connection of a temperature sensor ensures that the battery is

quickly and safely charged with the right voltage.

TECHNICAL BACKGROUND

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What is 3-step+ charging technology?

Mastervolt’s 3-step+ charging technology is the fastest and safest way to charge

gel, AGM, Lithium Ion and open flooded type batteries. It consists of the following

phases:

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