serge-de-smedt avatar image

What is the purpose for equalization please ?

Hi ,

I have a Victron SmartSolar MPPT 75/10 hooked on my VW California Camper equipped with a 140 W solar panel.What is the purpose of equalization please and what are the recommended settings ( frequency of equalization )?

Kind regards,


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Equalization requirements will depend on battery type/chemistry, and manufacturer recomendation.

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Justin Cook - Bay Marine Supply USA avatar image
Justin Cook - Bay Marine Supply USA answered ·

@Serge De Smedt, the purpose of an equalization cycle is to apply a high voltage charge (usually approximately 10% higher than recommended charge voltage) to an FLA battery for the purpose of removing the sulfate crystals that build up on the lead plates over extended periods of time; this becomes particularly necessary when your FLA battery has experienced multiple deep-discharges and/or an extended period of time left in a discharged state. If sulfation is allowed to build up excessively, this can lead to reduced battery capacity and -in some extreme cases- battery failure altogether. An equalization cycle is also useful for reversing a condition called "acid stratification" in which the acid concentration at the bottom of the battery is higher than the top.

In short, an equalization cycle is a deliberate overcharge that burns the sulfation off the lead plates in an FLA battery and agitates the acid to reverse any stratification that may be occurring.

That's the concept. The practice, however, varies greatly. Whether or not you should perform equalization cycles, what voltage you should use, how often, and what the specific procedure should be are all specific-battery-dependent variables that you must establish before attempting any settings adjustments in your MPPT.

Bottom line: don't mess with it yet. Study your batteries, find their manufacturer-recommended specs, establish whether or not your specific battery(s) would even benefit from an equalization cycle and if so, how often, what voltage you should use, and how much off-gassing you should expect during the process and what precautions you should thereby take. After you have firmly established all that information, then you can use that information to change the necessary settings in your MPPT.

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Great answer @Justin Cook,

Another benefit/feature of an EQ charge cycle is it pushes all battery cells in a series to a nearly certain full charge. This can be an issue when some cells in a bank are low voltage, and others are high.

eg battery presents as 14.4V for absorption voltage

All cells should be 2.4V, and probably are when new and fresh, but what usually happens over time is that eventually one might be 2.7V, others 2.4V and one is 2.1V.

2.4 + 2.4 + 2.4 + 2.4 + 2.1 + 2.7 = 14.4.

This is an issue with all Pb batteries, (including sealed AGM and gel that don’t normally get an EQ) - Flooded cells can cope better with over voltage, through gassing and consumption of the water in the electrolyte. Then you can be certain that all functional cells will be 'fully charged', though also considered overcharged.

So an example EQ voltage might 16V

This would push all the cells to gassing voltage range (>2.4V)

2.6 + 2.7 + 2.6 + 2.7 + 2.5 + 2.9 = 16

Another downside of overcharging batteries or excessive equalisation is shedding of the active material. The lead oxide paste that makes up the active part of the battery can be damaged/shed from the plate grids if there is too much gassing and agitation in the batteries. This will reduce the total usable capacity of the battery over time, and in the worst case could cause an internal short

Lastly the gas that is generated during Equalisation is explosive, so you have to make sure that it is appropriately and safely vented away.

Re-iterating Justin, You should never equalise a battery (above the relatively safe absorption voltages of 14.4V) without the clear written instructions from the battery manufacturer.