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Old 23-09-2011, 07:58   #1
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Absorption Voltage?

My Victron charger/inverter -- newly installed this summer -- has an option to set the absorption voltage at 29.4 or 30.0 volts instead of the default 28.8 volts (equivalent, obviously, to 14.7 or 15 volts instead of 14.4 volts for a 12 volt system).

The manual says: "

Absorption time
The absortion time depends on the bulk time (adaptive charge curve), so that the battery is optimally charged. If the ‘fixed’ charging characteristic is selected, the absorption time is fixed. For most batteries, a maximum absorption time of eight hours is suitable. If an extra high absorption voltage is selected for rapid charging (only possible for open, flooded batteries!), four hours is preferable. With DIP switches, a time of eight or four hours can be set. For the adaptive charge curve, this determines the maximum absorption time."

I am struggling to get the specific gravity of my batteries up to normal after letting them go flat in May. I am wondering if a higher absorption voltage would improve the efficiency of the charging process.

I am using Varta Leisure Hobby semi-traction batteries. I have temperature and voltage sensors on the batteries.

Oh, and one other question: Anyone know how to hook up a computer to the late-model VE-Bus Victron charger/inverters? The manual is infuriatingly vague.

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Old 23-09-2011, 09:11   #2
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Re: Absorption Voltage?

According to the VARTA Instruction Manual

“... Recommendation:
a.) Standard charging method:
IU charging characteristics with I = 10 % of nominal capacity.
The maximum charging voltage should be 14.1 – 14.4 V.
b.) Permanent charge:
Limit charging voltage to 13.38 V (2.23 V/cell).
If charging voltage is below 13.2 V (2.20 V/cell) an additional charge with
higher voltage is necessary in regular intervals to ensure the battery is
completely charged.
In alternative use charger with IUoU charging characteristics with I = 10 %
of nominal capacity.

c.) Charging to avoid acid stratification
Use IU charging characteristics with a higher charging voltage (up to 16 V).
This „overcharge“ should only be used for short time period to avoid
water loss.

- The OCV (open-circuit voltage) after charge should be 12.7 – 12.8 V.
- For every 0.1 V difference to 12.7/12.8 V the battery should be charged for
1 hour.
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"

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