3550 Battery HiTESTER Series
16
the current; this FET has an ON resistance of
over 30m Ω. These values are large
enough in comparison with the internal
resistance of the battery that they cannot be
ignored. The difference in resistance
between a good lithium ion battery and a
deteriorated lithium ion battery is also
sometimes quite small compared to other
batteries. Some nickel- metal hydride
batteries also include a PTC device.
Q7. What protection measures are
used for rechargeable nickel-
metal hydride batteries and
rechargeable lithium- ion
batteries?
A7. Nickel- metal hydride batteries have a low
hazard rating and are normally only fitted with
a safety valve to prevent explosion.
Lithium- ion batteries use organic electrolyte
and have a high energy density. Under
extreme conditions, such batteries may
explode or ignite. Therefore the following
protection measures are used: (1) Shutdown
separator (Separator holes close when
temperature rises above a certain level.)
(2)PTC elements (Resistance rises when
temperature rises.) (3)Safety valve
(Reduces internal pressure in battery.)
(4)Protection circuit (FET or similar is used
for temperature, current, or voltage control.)
Q8. What is sulfation occurring at
the electrodes of lead batteries?
A8. Lead sulfate (PbSO4, and insulating
substance) is deposited on the electrodes,
which reduces their effective area and
increases the impedance of the battery.
Q9. What is the dry- up
phenomenon?
A9. The reduction of electrolyte is called the dry-
up phenomenon. It occurs mainly when a
battery is overcharged.
Q10. What is dendrite? A10. Dendrite is a leaf- shaped crystalline metal
growth that can occur on the electrodes of a
battery. When it advances, the electrodes
may become short- circuited.
Q11. What is the memory effect? A11 When a battery is repeatedly discharged
partially and then charged again, the so-
called memory effect can develop which
causes a reduction in apparent capacity of
the battery. This occurs mainly with alkaline
type batteries (Ni-Cd, Ni-MH), not with lead
type and lithium-ion type batteries. The
memory effect can be countered by several
cycles of deep discharge and full charge.
Q12. What are rechargeable alkaline
batteries?
A12. The term rechargeable alkaline batteries
normally refers to nickel-cadmium (Ni- Cd)
batteries.
Q13. The resistance value of a
rechargeable lead battery differs
with every measurement.
What is the cause for this?
A13. The following causes are possible:
(1)The probe is applied to different points on
the battery terminals.
(2)The battery charge condition differs.
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