Earth4Energy

Home generated electricity is now a very popular topic. There are a great many manuals to choose from which vary a lot in the quality of information they deliver. There are also many so-called ‘review’ sites which claim to offer unbiased ‘honest’ reviews and yet seldom point out the shortcomings of these products.

A solar battery can be connected in a battery bank in either a series or parallel configuration. But if the batteries are of different capacities or types, how are they best connected?

First of all it is not a good idea to be connecting a solar battery in series with another one of different capacity (Amp-Hour or Ah). This is because the charge controller will attempt to manage the charging procedure based upon the combined voltage of the two batteries. Being connected in series, both of the batteries have the same charging current running through them, so the one with the lower capacity will become fully charged first and end up being overcharged while the larger one will never receive a full charge at all. On the other hand, under load the smaller battery will discharge excessively, dropping its voltage rapidly and causing the upstream inverter to cut out. Needless to say, the stresses on the batteries under such conditions can be excessive and even dangerous.

Connecting a solar battery in parallel is usually fine even if the capacities are different, as long as the batteries are of the same type. It’s not good to mix batteries of different chemistry because they will have different charging profiles and will once again confuse the charge controller which can only present one voltage profile to the pair for charging.

It is also best not to mix old batteries with new ones as the old ones may well leech from the new ones and ruin them, especially if the system is not kept fully charged.
Handling and working with batteries safely requires care and attention. Batteries can be hazardous in many different ways including the electrolytes, gassing, temperature and electrical hazards. It is vitally important to adhere to all the correct safety procedures and carefully follow instructions when you build your solar battery bank.

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