Well, spring is just around the corner and some of us will be looking
forward to warm
and a more relaxed way of life. The batteries many of us stored away for
on a temperature controlled constant potential battery charger
to be re-installed in our boats and vehicles.
there will be a few batteries here and there that have been on charge
winter but cannot deliver any current. They are victims of a phenomenon
largely caused by in appropriate charging potential or deep discharge
often deadly condition, this is the subject of our first article.
Ok so your
batteries died. Could it have been avoided, possibly but it is difficult to
unless the history of the cells is well known. The best thing to do is
replace the cells,
after them for as long as possible, charging them correctly, and apply appropriate
protection. Have a look at our second article and learn how to avoid
problems next time
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Editor: Alan Fidler.
Alan is the owner and manager of CBC Design, a leading battery management
in the UK. He has worked in the industry for over eighteen years and
has designed charging equipment and battery monitors for some of the world
ARTICLE: Sulphation in Lead Acid Cells. Author: Alan Fidler.
of us who work with batteries on a daily basis have undoubtedly come across
at one time or another. The symptoms are always the same. The
reaches the float voltage on a charge cycle very quickly drawing hardly any
to do so. On discharge, the battery has no capacity and the voltage drops
quickly in seconds or minutes rather than hours.
course the problem may not manifest itself until a load is applied for the
the battery was put into storage or discharged the last time. The
maintained the float voltage but the battery still won't work because the
left in a fairly inactive state and sulphation has begun.
is sulphation and how can it be prevented?
electrolyte inside a lead acid battery is usually in the form of a liquid
batteries are left in a discharged condition or are simply not used, the
absorbed by the lead plates and a substance called lead sulphate is
The sulphate forms an insulating layer on the plates which increases the
resistance of the battery and prevents it from drawing or delivering
not kill the battery completely though if it is discovered early enough.
typical example of a sulphated battery is a vehicle type which struggles to
over in winter but recharges quickly once the engine starts. The battery
for the rest of the day only to repeat the performance the following
sulphation is the biggest cause of premature cell failure in most
and automotive applications. There is a school of thought that suggests
periodic exposure to a higher potential of 2.45 volts per cell can help to
sulphation or break it down where it has arisen. however we already
that a high charge rate can cause internal heating of the battery which
plates and if this happens, the battery is permanently damaged.
higher charging voltage certainly helps in some cases, but it should only
cells are displaying the symptoms already. We would NEVER recommend
higher than normal charging voltage to a healthy battery. If you recharge
correct way for the application in which it is used, sulphation will not be
visited websites during our research into this subject which state that
batteries benefit from a charge rate of 14.5 volts instead of 14.1. We
since the application is cyclic in nature but there are other
stand-by, where this potential would damage the cells permanently. As
advice is to check the battery manufacturers data and follow their advice
reality, the actual charge voltage depends upon the application in which
used. Traction and automotive batteries require a different charging
batteries used in standby applications. Often, an installation for standby
higher charging voltage or boost level at all but sulphation never
occurs because the batteries are discharged every month or so, religiously,
then immediately recharged.
sort of regime prevents sulphation even though the charging voltage never
volts per cell at 20oC.
thing is certain. There is a point when a battery become so severely
cannot be recovered, ever. Batteries have a finite life and will eventually
dispite your best efforts. We managed to squeeze 4.5 years out of a battery
with a three year life in a vehicle in the UK which is about as good as it
battery manufacturers recommend constant potential charging methods with
equalising charging voltage on cycled cells to get the best performance
Furthermore, they are very keen that users should use temperature
compensated chargers in applications where the ambient temperature
varies. This is by far the best way to prevent sulphation in the first
place. Charging the batteries correctly at all times as well as making them
do some work occasionally will do more to prevent failure than anything
interesting point is that cells which are partially sulphated are actually
testing of a typical constant potential battery charger. The float voltage
the minimum of charging current whilst a suitable load allows the current
to be set. Healthy batteries take time to charge up from a partial self
this can be somewhat frustrating so, sulphation can be beneficial
to some anyway!
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ARTICLE: Protecting Sealed Lead-Acid Batteries. Author: Alan
Nicad batteries which, as far as abuse is concerned are more forgiving,
lead acid batteries demand particular conditions to work at their best.
There is a distinct voltage band within which a lead acid cell will
operate. Push the cells above or below it for any length of time
and they will be permanently damaged.
acid batteries need to be protected then, particularly from deep discharge.
If a typical
is allowed to fall much below 1.55 volts per cell and is left in this state
it will never recover, no matter how long it is left on charge. It has been
and must be taken out of service. A dreadful waste I am sure you'll agree.
first problem, Overcharge, stems from a charger failure or incorrect
float voltage setting.
charging a battery does two things, it causes the battery to gas and pushes
temperature of the cells above recommended levels. This usually results in
buckled plates, lost electrolyte and in the case of most lead acid
batteries, a damaged pack.
the battery must be protected if you want total peace of mind. If the
which the battery is employed isn't a critical one, it may just be
inconvenient when the
fails but in some applications, failure could lead to loss of life.
is though a third condition which we covered in our first article,
that of sulphation
also cause problems and it must be prevented for as long as possible or
early stage if reliability of the cells and the installation as a whole is
summarise, we have three conditions that must be avoided if we want the
batteries, high voltage, low voltage and cell sulphation. Ignoring any one
of these three
voltage alarm is by far the best way to protect the cells from over
charge. It can be configured to energise a siren or led and disconnect
the charging supply to prevent battery
We also recommend fitting a fuse in series with the charger output positive
protect the battery in the event of a charger rectifier diode short. Sadly,
diodes have a
to go short circuit when failing rather than blowing open circuit and this
unrestricted current flow and a high charging voltage.
discharge is prevented by using a Low Volts Disconnect device. A typical
volts monitor and a heavy duty relay or contactor which disconnects the
load when the
reaches a pre-determined minimum. A siren or led can be energised by the
the user that the battery is approaching its minimum limit.
can be avoided by charging the battery correctly and discharging the cells
basis to keep them active. Wet lead acid cells must be topped up with
water. Maintenance free cells require nothing other than the above to keep
really all there is to it. Protect the batteries from these three
conditions and you will
many years of service from them. Neglect any one of the above and you will
having to purchase new cells prematurely.
Look after your batteries and your batteries will look after you!
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Questions from Roger Burrows!
happens if a Sealed Lead Acid Battery is overcharged?
lead-acid batteries are usually fitted with special vents
release some of the pressure that build up in the battery
heat. The battery is permanently damaged of course.
a battery be protected from overcharge?.
fitting a fuse in series with the charger output in case of
and by using a High Volts Monitor or Alarm to detect the
charge condition so action can be taken before the battery
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