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Battery Tips
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21.Mercury:
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Good batteries have been made using Mercury. These are not now in general use, because
of potential pollution. Silver-Oxide or Zinc-Air cells make good or superior alternatives.
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22.NiCd:
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Nickel-Cadmium batteries. Rechargeable. The archetype power tool battery. Due to
the Cadmium content this battery must be disposed of safely. NiCd batteries have
gained a bad reputation for their Memory Effect (wrongly or over-emphasized in my
opinion), which can reduce their voltage with age. NiCd batteries prefer to be charged
when they show a drop in power (to over-discharge a battery pack risks ‘voltage
reversal’, of the weakest cell). Store as they are, and recharge before use. NiCd
batteries self-discharge. They lose about 40% of their charge in 4 weeks. NiCd batteries
have a low internal resistance:
- They can deliver a high current
- They don’t overheat easily in use
- They can be charged quickly.
Used sensibly they have a life span twice that of NiMh or Li-ion batteries. 1.2
volts per cell, reasonably constant over the discharge cycle.
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23.NiMh:
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Nickel Metal Hydride. In some ways a successor to NiCd batteries, in some ways still
inferior.
- No special disposal necessary
- Increased capacity
- Less 'memory effect'
Slower charging - a Fast NiCd charger, one of less than 8 hours is generally unsuitable.
Don’t recharge until the power begins to fall. Store discharged.
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24.Parallel:
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If a number of similar cells are connected together positive to positive, negative
to negative, the voltage will be the same as a single cell and the capacity to deliver
current will be the sum of the total - in theory. In practice, it is much better
to use a bigger capacity single cell. NiCd, NiMh and Lithium cells should not be
connected in parallel. See Series
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25.Primary Battery:
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Not rechargeable e.g. Traditional torch battery. Connecting to a charger may be
hazardous.
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26.Replacing Batteries:
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Always replace all the batteries in a circuit if you replace any. Never connect
different types of battery together. The stronger batteries can reverse the polarity
of the weaker. There is a small risk of rupturing a cell. Check the terminals are
clean and making good contact. Put the batteries in the right way round. Raised
Pip to the + or red terminal. Nose to tail, the pip of one battery to the base of
the next. Often a coil spring pushes on the base of the battery and a flat contact
connects to the pip.
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27. Sealed Lead Acid Batteries:
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2 .0 volts per cell The Sealed Lead Acid battery is the traditional wet cell car
battery, re-designed as a dry battery. The electrolyte is gelled and absorbed onto
a glass fiber mat, and the areas of the anode and cathode greatly increased. Although
the cost of manufacture is higher, sealed lead acid batteries or “gel cells” have
a longer life, higher capacity and are safer than wet cells. These batteries must
be stored in a charged condition, they self-discharge at a moderate rate. Therefore
they should be re-charged at least once a year to remain in good condition, even
if only stored. If the temperature is raised - garden shed in summer - recharge
more frequently. SLA batteries can be used anyway up, but charge upright. See Vent
You can replace a wet Lead Acid battery with a Sealed Lead Acid battery, of similar
capacity without altering the circuit or charging circuit. Use with advantage in
all small vehicles including sports vehicles. Freeze/ thaw stable, withstands lower
temperatures better fully charged. Car Batteries and to a lesser extent SLA batteries
can evolve Hydrogen and Oxygen whilst being charged. These gases form an explosive
mixture. Allow ventilation to batteries whilst charging.
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28.Secondary Battery:
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Rechargeable. e.g. NiMh Mobile Phone battery. (Nickel/Metal Hydride). The action
of the battery is reversible; connected to a light bulb it makes light and discharges;
connected to a charger it recharges-- the charger forces the chemical reaction to
go the other way.
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29.Self Discharge:
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Batteries, stored, unused, lose their charge (age), slowly with time. The rate of
self-discharge depends on the type of battery. Alkaline batteries and most primary
batteries have a good shelf life - they self-discharge very slowly. The rate of
self-discharge rises rapidly with temperature, the ideal storage temperature is
between 4 and 15 Deg. centigrade. These are guide figures, for the loss of charge
in 1 month at 20 Deg. C.
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Alkaline
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Primary
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>1%
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Sealed Lead-Acid wet cell
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Secondary
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11%
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Sealed Lead Acid dry cell
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Secondary
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9%
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Li-ion
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Secondary
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35%
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Lithium Manganese Dioxide
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Primary
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0.1%
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Magnesium-Sea Water
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Primary
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>0.5%
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NiCd
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Secondary
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40%
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NiMh
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Secondary
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50%
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Silver-Oxide
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Primary
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0.5%
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Zinc-Air
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Primary
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>1%
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Zinc-Air, tab removed
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Primary
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35%
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30.Series:
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Cells are often connected in series to increase the voltage. Negative electrode
is connected to positive electrode to make a daisy chain of cells, a battery of
cells (hence the name battery); we would now say battery pack. The cells should
always be similar cells. Never replace one cell in a series, always the lot. The
battery pack is only as good as the weakest cell. See Parallel
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31.Tag:
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When rechargeable cells are assembled into a battery pack, they are connected in
series by tags welded to the battery. In large-scale production the connections
may all be welded without any soldered joints. This gives joints with the lowest
resistance. On a small scale, or when the currents are lower or in repair work soldering
to tags is much easier than soldering on to a battery.
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32.Temperature:
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Common batteries like the same temperatures as humans. They won’t work well in low
temperatures. High temperatures shorten their life. This factor needs careful consideration
if batteries are going to be relied upon in an emergency. Store at max. 25C, preferably
less. A camera battery in a black case in the sun or a lead-acid battery in a greenhouse
will have a shorter life. Special batteries are made for other temperature ranges.
Lithium batteries perform best of the common batteries. The risk of a power tool
battery pack, used on a building site, having a shorter life increases as the battery
becomes bigger. As the tool is worked hard, the battery temperature rises. Working
at elevated temperatures is bad for the battery. The cells are packed close together
with no room for the heat to escape. NiMh cells with their higher internal resistance
are more at risk than NiCd cells.
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33.UPS:
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Uninterruptible Power Supply Units: keep a computer and its data safe and running
what ever happens to the power supply - lightning, voltage drop or droop, surge,
fuse blown or supply cut can be programmed to save current work and close down after
a set number of minutes protect the phone and computer from surges induced by lightning
in the phone line correct the power from a local generator- including 110 volts
AC. Also capable of protecting Fax machines or any other essential equipment.
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34.Vent:
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If a current passes through a cell, gases can be evolved. The internal pressure
could rupture the cell if it is sealed. Most dry cells are fitted with a vent to
relieve this pressure. The vent automatically reseals. This is why Sealed Lead acid
batteries should be charged upright.
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35.Voltage:
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The voltage of batteries is quoted as ‘nominal’ because it varies during the life
of the battery and the amount of current being taken from the battery. If the voltage
of a new battery is measured (across a large resistance) it may be a little higher.
This will soon drop to the nominal voltage and later in life the voltage will drop
further - the torch becomes less bright as the battery gets used up. The voltage
of Alkaline batteries droops in a curve during its life. Lead-Acid, Zinc-Air, Silver-Oxide
and NiCd batteries have a much more constant voltage - a ‘flat’ discharge/time curve.
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36.Watch Batteries:
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Although various chemistries have been used, most batteries are Silver-Oxide with
Alkaline as a cheap alternative. If you don’t have the original battery code you
can safely go on the size of battery.
Provided you can open the watch with a suitable tiny screwdriver or knife (the choice
of tool depends on the watch not the user) changing the battery is easy.
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37.Zinc-Air:
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1. A battery with Zinc as one electrode and Air as the other, which saves carrying
one electrode around as air can be collected, as it’s needed. These cells have a
high capacity for their volume and have replaced silver and mercury cells for use
in hearing aids. They have been described as “super long life” hearing aid cells.
As supplied, with an adhesive tab, they have a long shelf life. As soon as the tab
is removed air is allowed into the cell and the cell begins to self-discharge. Its
life will then be about four months whether it is used to not; putting the tab back
is not very effective. Zinc-Air cells offer very good value for money because of
the quantities used in hearing aids. Voltage 1.4 volts. There is a possibility of
these cells not working in very dry atmospheres; I have not heard this reported
in Europe.
2. Development work has been done on Zinc-Air fuel cells to power electric vehicles.
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