| A Beginner's Guide |
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During construction and testing it is usually more convenient to use a battery box with different tappings or a mains- powered power supply unit. The miniature nature of SMT calls for very small batteries. Most SMD projects have been designed to have very low power requirements, either by working at low voltage, or with small currents, or both. The use of CMOS is one way of achieving this. Circuits which operate intermittently have been designed to take very little power when in their quiescent state. In many cases, the finished project can be powered by small button or similar cells. An appropriate cell can be selected, from the many types now available, to suit the circuit requirement. |
| Some of the types are explained here. | |||
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TYPE |
V |
mAh |
NOTES |
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Mercuric oxide button cell, HG3, 8mm diameter |
1.35 |
40 |
For low -voltage, low-current circuits, that run intermittently |
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Mercuric oxide button cell, HD625, 16mm diameter |
1.35 |
360 |
Low-voltage, medium current run for prolonged periods |
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Zinc-air button cell small, e.g. A13, 8mm diameter |
1.4 |
70 |
Double the life of mercuric oxide cells of the same size |
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Zinc-air button cell medium, e.g. A675 12mm diameter |
1.4 |
400 |
Low-voltage, medium-current, or continuous operation |
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NiCd rechargeable ,AAA, 10.5mm dia., 44mm long |
1.2 |
180 |
Cheap to run but store relatively little power. |
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Zinc-carbon cell, AAA |
1.5 |
500 |
Last longer than NiCd cell . |
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Zinc-chloride cell |
1.5 |
500 |
High current |
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Alkaline cell, AAA |
1.5 |
1000 |
High current, high capacity |
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Lithium coin cell, CR2016 20mm diameter, 1.6mm thick |
3.0 |
60 |
Good for long periods of very low quiescent current with short periods of high current |
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Lithium coin cell, large, CR2430, 24.5mm diameter, 3mm thick |
3.0 |
200 |
Good for long periods of very low quiescent current with short periods of high current |
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Alkaline lighter battery size 27A 8mm diameter, 28mm long |
12 |
13 |
High voltage but small capacity |
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Alkaline lighter battery size 23A 10mm diameter, 28mm long |
12 |
24 |
High voltage but small capacity |
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Alkaline PP3 battery 49mm long, 2.65mm wide, 16mm deep |
9 |
500 |
Voltage is about 8V under load |
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Nickel cadmium PP3 battery |
- |
100 |
Most give only 7.2V but expensive types give 8.4V |
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