Victron energy VE.Net DC Datasheet download pdf (Page 72)

Gel and AGM batteries

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Disadvantages of the traditional 3-step charge curve:

• During the bulk phase the current is kept at a constant and often high level, even after the gassing voltage (14,34 V

for a 12 V battery) has been exceeded. This can lead to excessive gas pressure in the battery. Some gas will escape

trough the safety valves, reducing service life.

• Thereafter the absorption voltage is applied during a fixed period of time, irrespective of how deep the battery has

been discharged previously. A full absorption period after a shallow discharge will overcharge the battery, again

reducing service life. (a. o. due to accelerated corrosion of the positive plates)

• Research has shown that battery life can be increased by decreasing float voltage to an even lower level when the

battery is not in use.

11. Battery charging: longer battery life with Victron 4-step adaptive charging

Victron developed the adaptive charge curve. The 4-step adaptive chare curve is the result of years of research and testing.

The Victron four-step adaptive charge curve solves the 3 main problems of the 3 step curve:

• Battery Safe mode

In order to prevent excessive gassing, Victron has invented the ‘Battery Safe Mode’. The battery Safe Mode will limit

the rate of voltage increase once the gassing voltage has been reached. Research has shown that this will reduce

internal gassing to a safe level.

• Variable absorption time

Based on the duration of the bulk stage, the charger calculates how long the absorption time should be in order to

fully charge the battery. If the bulk time is short, this means the battery was already charged and the resulting

absorption time will also be short, whereas a longer bulk time will also result in a longer absorption time.

• Storage mode

After completion of the absorption period the battery should be fully charged, and the voltage is lowered to the

float or standby level. If no discharge occurs during the next 24 hours, the voltage is reduced even further and the

battery goes into storage mode. The lower storage voltage reduces corrosion of the positive plates.

Once every week the charge voltage is increased to the absorption level for a short period to compensate for self

discharge (Battery Refresh mode).

12. Battery charging in case of standby use: constant voltage float charging

When a battery is not frequently deeply discharged, a 2-step charge curve can be used. During the first phase the battery is

charged with a limited current (the bulk phase). Once a preset voltage has been reached the battery is kept at that voltage (the

float phase).

This charge method is used for starter batteries in vehicles, and in uninterruptible power supplies (UPS).

13. Optimum charge voltage of Victron VRLA batteries

The recommended charge voltage settings for a 12 V battery are shown in table 3.

14. Effect of temperature on charging voltage

The charge voltage should be reduced with increased temperature. Temperature compensation is required when the

temperature of the battery is expected to be less than 10°C / 50°F or more than 30°C / 85°F during long periods of time.

The recommended temperature compensation for Victron VRLA batteries is -4 mV / Cell (-24 mV /°C for a 12 V battery).

The centre point for temperature compensation is 20°C / 70°F.

15. Charge current

The charge current should preferably not exceed 0,2 C (20 A for a 100 Ah battery).The temperature of a battery will increase by

more than 10°C if the charge current exceeds 0,2 C. Therefore temperature compensation is required if the charge current

exceeds 0,2 C.

Fig. 4: Four-

step adaptive charge curve

12.5

13.5

14.5

egatlov egrahC

100

120

tnerruc egrahC

Battery Safe Float

Battery Refresh

Storage

Figure 3:

Four-step adaptive

charge curve

Calculated absorption time

Fig. 4: Four-step adaptive

charge curve

1 2 ... 67 68 69 70 71 72 73 74 75 76 77 ... 83 84

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Victron energy VE.Net DC Datasheet Page 72

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