The Battery Care in Renewable Energy: The Use of Multi-stage Battery Charging System

The batteries that are used in renewable energy do not come cheap. An average renewable energy deep cycle batteries costs between $200 to $600. They are expensive and the leading cause of failure is usually attributed to the way it is used and the type of battery charger in use.

My friend rcently upgraded his batteries after his a bad charger destroyed his batteries. He had to upgrade by getting 40 numbers of 12V 150AH.

^{The New 12V 150AH Gel Deep Cycled Batteries all in battery rack}

He had to remove the bad batteries and sell it as scrap. That was a big loss to him



^{The ones damaged by the bad charger}


Most often than not, you must have heard of multi-stage smart battery chargers that comes at a premium cost. You may wonder why that should be so.

What is a multi-stage smart charger?

These are microprocessor chargers that are designed to automatically select the best charging schedule, charge voltage, and charge current for each specific battery in a non-linear manner.

The standard charger is usually referred to as dumb or linear charger. It has a constant voltage and current. What the linear (dumb) charger does is to apply a constant charging voltage to the battery, the voltage rises as the current put on the battery continue to drop until the amps almost zero. The battery is deemed to be charged when in reality it is not.

The multi-stage charging system

Stage 1 (Bulk or Boost Charge)

Every battery charger function is to get batteries charged. This first stage the charger puts in the maximum rated current and voltage into the battery as long as it could safely do so, i.e without leading to overheating of the battery. This level of charge applied is known as the battery's natural absorption rate. This absorption varies for different battery makes. For a 12V AGM battery, this voltage ranges from between 14.4V to 14.7V. The gel type battery is slightly lower than the AGM battery type at not more than 14.2V to 14.3 volts. This means a 12V 20A battery charger will constantly deliver 20A to the battery until the battery voltage reaches 14.4V to 14.7V, this is usually at between 75-85% of battery charge level.

This is the fast charging stage at this stage quickly replenishes a drained battery. The risk of overcharging is not applicable due to the battery not near full charge.

Stage 2 (Normal mode charge or Absorption Charge )

This absorption mode varies for different chargers, but it is usually around the time that the battery is 80% fully charged. The battery charger automatically switches the battery charging mode to absorption mode at this stage.

This part of charging is slower compared to the bulk/boost mode. The voltage is held constant, say at 14.4V for AGM. This prevents the voltage from climbing higher, a condition common on linear chargers. The battery is then forced to "absorb" the last of the charging current needed for it to be fully charged. In other words, the battery charging continues as the battery charging current slowly reduces until the battery is charged fully.

Stage 3 ( The float charge or maintenance charge)

At this stage of the charging, the battery is almost full. The float mode of different chargers vary, but universally, the range for float charging is between 85% to 95% of battery charge level. Here, the terminal voltage reading of the battery tapers down to between 13.2V to 13.8V (maximum voltage of a 12V fully charged battery). The charging current decreases till it enters trickle charging. This is very low amperage charging designed to keep a battery fully charged or maintain its standby voltage when in use.

A battery on trickle charge can stay months at this stage 3 mode of charging.

Most smart chargers are 3-stage chargers, but there are some that have more stage. This comprises of one more stage known as Equalisation Charge mode. This equalization are sometimes considered another stage.

Stage 4 (Equalization charge stage/mode)

This is controlled overcharging of battery in order to restore all cells to equal capacity cell voltage. Thus the equalization charge. It is something that could be scheduled in some chargers and others choose after some weeks to automatically equalise their batteries.

This is usually done on higher capacity wet cell batteries. This is to prevent sulfation. Sulfation occurs in lead-acid batteries when batteries are left idle for long, charged insufficiently or left for long without charge. That is the stratification of electrolyte over a long period. For a 12v battery, the equalising voltage go as high as between 15V to 16V, making the batteries gas (boil and release gas) thereby knocking off any lose sulfation that may be on the battery plate. This is just for a short period ( maximum time is usually 15 minutes).

Conclusion

What if we decide that the cost of buying a smart multistage charger is too high and decide to go with the cheaper alternative; the linear aka "dumb" charger?

Well, the result is not usually what you may like. Bloated batteries like the one you see below are the usual result.

^{Source: Battery destroyed by wrong charging}


Even when they do not bulge and blew up, you run the risk of killing the battery by the consistent overcharging thereby reducing the expected battery backup hours.

Always go for the smart charger for fuller charging, with its resultant longer battery life.

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Ref: 1, 2.