Battery technology can be very complicated, so we will explain the process here in vey basic terms. There are some very good resources available the public domain for those who wish to take their understanding to the next level.
It may seem obvious, but it’s important to remember to we need to put back into the battery any energy we use.
As we have seen in the general battery section, lead-acid batteries can be discharged to different states of discharge depending upon their type.
Whether that be the starter bank, the leisure system or an auxiliary bank, such as the bow thruster, in order for us to have the power we require on hand that charge should be put back in as soon as possible.
Our fully charged lead acid battery cell sits at around 2.1 volts. Remember the batteries we are used to are multiple cells, usually six to a case. So for familiarity we will refer to a fully charged battery voltage being 12.6 volts
Easy, you’d think all we need to do is to put our amps back in at 12.6 volts and everything will be OK. Not so, as battery voltage rises, so does the resistance. Therefore we effectively have to charge at a higher rate to force the battery back to a full state of charge.
So why not just use a constant higher voltage, such as 14 volts for example to recharge the battery. Well thats what older battery chargers and basic dynamos on vehicles used to do. Many years ago, however there wasn’t the technology available to the general market for living off batteries like we now do. As our demands have increased, so has technology. We now require maximum potential at minimum cost and this is reflected in battery charging technology.
By just putting an unregulated, constant voltage into the battery we would not get the value from the unit we require. So, why is that?
Well, this is where it can get complicated so you will have to trust us when we say that the correct charge voltage is critical. Too little and the battery life will be shortened. Too much and guess what!
Charge voltages range from 13.8 to 14.4.
The balance is one between maximum service life, maintenance and ease of use.
Charging at a constant 13.8 volts would give maximum service life and the battery would remain cool. The flip side is that charge ties are slow (we need that power now)!, battery capacity will gradually decline and sulphation may occur.
Charging at 14.4 volts would charge the bank faster, the capacity would be more consistent and there will be less sulphation. However, at this voltage there will be the production of volatile gas, the battery would need constantly topping up and over time there would be a severe overcharge.
So now we can see why it can be complicated getting the balance right. Fortunately technology has given us the intelligent multi-stage battery charger. If you haven’t got one on your battery banks yet hopefully the above has convinced you that it would be an investment worth making.
Three Stage Charging
Three stage charging is best described as bulk, equalisation and float. There are chargers that promise more stages but we will keep it simple.
01 Bulk Stage
The bulk charge basically fast charges the battery close to full capacity. It regulates the voltage in order to rapidly replace lost amps whilst minimising heat build-up and gassing. It applies constant current at increasing voltage as the resistance to charging increases.
02 Equalisation - Absorbsion Stage
After a regulated period of time depending upon state of discharge, original battery capacity and the rating of the charger unit itself, the charger will switch to the equalisation phase. Once the voltage peaks, the charger decreases the current. It holds the peak voltage and forces the battery to accept the last few amps of it’s capacity by dropping the current.
If you can imagine eating a box of chocolates. By stuffing them all in at once you will feel fuller quicker but may be ill, forcing you to stop. A little later you may have extra capacity. By eating them slowly, one at a time you could manage a lot more before you felt ill and full!
03 Float Stage
The final stage of charging is known as the float stage. This stage lowers both current and voltage to maintain the optimum capacity of the battery and to compensate for any natural self-discharge.
There are a number of different methods available to us to put charge back into the battery banks.