RV FEATURE
INTO THE
VOLT
LITHIUM
IT IS IMPORTANT
BATTERIES
TO UNDERSTAND
PART 5
THE DIFFERENCE
IN VOLTAGE BEHAVIOUR WHEN
COMPARING LITHIUM BATTERIES TO
LEAD-ACID EQUIVALENTS.
We have discussed the higher capacity of
lithium batteries previously but the story
gets better. One of the characteristics of
a lithium battery is that the voltage does
not ‘drop-off’ (reduce) until much later,
compared to lead batteries. Power is all
about volts and amps (watts = volts x
amps). Electrical devices all require power
(watts) to operate and this is made up
mathematically from the voltage and amps.
The maths is simple. To operate a device, you
need constant power (watts) and if the amps
or volts decrease, the opposite must increase.
In a lead-acid battery, the voltage will drop
much soon than a lithium battery, which
means the amps must increase to compensate
and maintain power.
In fact, with lithium you need to be vigilant
because as the voltage stays higher for longer
it also will drop off quicker.
Lithium batteries contain sophisticated
electronics with inbuilt protection mechanisms
that include a disconnect (open circuit)
protection mode, which the battery will go
into if it is drained of power at 10V. This
should not be confused with a traditional low
voltage disconnect, which is a device used to
disconnect the loads connected to a battery
at a pre-set voltage of, say, between 11.5
to 12V. This ensures that the battery is not
damaged prior to being fully recharged.
More amps used means you have consumed
more of the available power from your battery
compared to a lithium, which will use less
amps as the voltage remains above 12V for
longer. In camping terms, this means longer
run time for fridges, radios and lights. If a lithium battery does go open circuit due
to extremely low voltage, the battery will
effectively drop to 0V. This is a problem as
most chargers need to see a minimum of 6
or 9V across the terminals to turn on. (All
BMPRO power management systems contain
an inbuilt system to protect batteries and the
ability to charge lithium batteries that enter
this mode).
Remember, though, that you can’t rely upon
monitoring the voltage of a battery. It can
only be used as a very rough guide as to the
amount of remaining capacity in a battery. I recommend that if a lithium battery goes into
low discharge mode that it is recharged within
a fortnight.
– BMPRO ambassador David Bayliss
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