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Electrical Fundementals > DC Sources Of Electricity > Flashcards

DC Sources Of Electricity Flashcards

1
Q

What is the charging voltage of a 20 cell battery with each cell having an internal resistance of 0.1 ohms, charged with a current of 5 amps?

A

10.5 volts

Total battery internal resistance = 0.1 * 20 = 2 ohms, Total circuit resistance, including leads = 2 + 0.1 = 2.1 ohms, V = I * R = 5A * 2.1 ohms = 10.5V.

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2
Q

How long could two 10V, 20 Ah batteries connected in parallel supply normal current across a 10 ohm load?

A

40 hours

Use Ohms law to work out the current (1A). Two batteries in parallel then rating is doubled (40 Ah).

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3
Q

A battery rated at 40 Ah will supply 200 mA for how long?

A

200 hours

200 mA = 0.2 A. 40 Ah / 0.2 A = 200 hours.

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4
Q

What does the life of a zinc-carbon battery depend upon?

A

the amount of zinc

The zinc is slowly eaten away in a zinc carbon battery (primary cell).

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5
Q

When checking the SG of the electrolyte in a lead acid battery, what should you do?

A

check all cells because they may be different.

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6
Q

The PD at the terminals of an open circuit battery with a small internal resistance will be?

A

the same as the EMF

EMF is the battery voltage (i.e. that which is written on the side of it) and the PD is the actual terminal voltage. If it is open circuit, no current flows to drop a voltage across the internal resistance so they are the same.

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7
Q

An accumulation of hydrogen on the plates of a battery is known as?

A

polarization.

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8
Q

What part of a battery is covered in hydrogen during polarization?

A

Anode.

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9
Q

Which of the following is most likely to cause thermal runaway in a nickel-cadmium battery?

A

High current charging of the battery to more than 100 percent of its capacity

Thermal runaway usually occurs on charging.

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10
Q

The method of ascertaining the voltage of a standard aircraft lead-acid battery is by checking?

A

the voltage off load

If just checking the voltage (as opposed to a charge test) then the battery must be off load to prevent the internal resistance dropping the terminal voltage.

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11
Q

What is the total capacity of two batteries 12V and 40 Ah each in series?

A

24V 40 Ah

Batteries in series - voltage increases but capacity remains the same (vice versa if they were in parallel).

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12
Q

If a battery has low internal resistance, then the?

A

no load voltage will be greater than on load voltage

The internal resistance will always drop the voltage and reduce the terminal voltage. It is the same whether it is high or low internal resistance - just a matter of ‘how much’.

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13
Q

Conventional current flow inside a battery is from?

A

anode to cathode.

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14
Q

In a voltaic cell, what is the build-up on the cathode called?

A

Sulphation.

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15
Q

Two 12V 40 amp hour batteries connected in parallel will produce?

A

12V 80 ah.

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16
Q

What is the voltage drop across each resistor in a parallel circuit with a 24-volt source supplying 48 watts?

A

24 volts

Resistors in parallel, voltage across each one is the same and equal to the source voltage (if nothing else is in series with them).

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17
Q

What is the ampere-hour rating of a storage battery that is designed to deliver 45 amperes for 2.5 hours?

A

112.5 ampere-hour

Ampere.hours means amps * hours.

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18
Q

If a nicad battery is not to be used immediately it should be stored?

A

fully dissipated

Ni-cad batteries must be stored fully discharged. Often with a metal bar across their terminals to ensure they are fully dissipated.

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19
Q

In a mercury cell, the steel casing is?

A

the positive terminal

The ‘outer can’ is in contact with the zinc anode, which is positive.

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20
Q

To improve the life of a dry cell it would be manufactured with?

A

more zinc.

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21
Q

In a simple voltaic cell, the collection of ions on the cathode causes?

A

sulphation

The formation of lead sulphate on both plates of a lead acid battery is called SULPHATION.

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22
Q

The electrolyte in a nicad battery would rise if the battery was?

A

charging.

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23
Q

Two 2 volt 10AH cells are connected in series, the output voltage and the capacity would be?

A

4 volt 10 AH

Batteries in series - voltage doubles, but the rating stays the same.

24
Q

The electrolyte in a nicad battery is?

A

potassium hydroxide.

25
Q

In a Leclanche cell, the plates are made of?

A

zinc and carbon.

26
Q

In a simple voltaic cell, polarization reduces output voltage because of the?

A

build up of hydrogen on the anode.

27
Q

When the temperature of the electrolyte in a battery increases, the SG?

A

goes down

Volume rises with temperature, but mass does not. SG is a measure of the electrolyte density (which is mass / volume).

28
Q

The Daniel Cell electrodes are?

A

copper and zinc.

29
Q

In a thermocouple, where is voltage measured?

A

At the cold junction.

30
Q

Mercury cells are covered with a metal cover?

A

as a positive terminal.

31
Q

The capacity of a battery is measured in?

A

ampere-hours.

32
Q

A battery’s internal resistance is determined by?

A

IR = (OCV – CCV)/ i.

33
Q

What is the formula for determining a battery’s internal resistance?

A

IR = (OCV – CCV) / i

34
Q

Why are there more negative than positive plates in a lead acid battery?

A

The positive plates are prone to warping if the chemical action is taking place only on one side.

35
Q

What is the approximate internal resistance of a Leclanche cell?

A

0.02 ohms - 4 ohms

36
Q

What happens to an aircraft battery on charge from the aircraft generators?

A

Battery voltage to decrease to zero until it is fully charged.

37
Q

What effect does hydrogen have in a battery cell?

A

Polarization.

38
Q

What is needed to generate electricity with a fuel cell?

A

Oxygen & Hydrogen.

39
Q

What should a ni-cad battery found to be below normal capacity do?

A

Be re-charged with a freshening charge.

40
Q

To prevent the electrolyte from freezing in cold weather, a battery must be kept:

A

Fully charged.

41
Q

How does the internal resistance of a battery off load compare to on load?

A

The same.

42
Q

What is the result of connecting two 12V, 40Ah cells in series?

A

24V 40Ah.

43
Q

How long will a 24V 40AH battery discharge at 200mA last?

A

200 hours.

44
Q

What happens to the electrolyte level of a ni-cad battery during discharge?

A

Falls during discharge.

45
Q

What component is energized by light?

A

Photodiode.

46
Q

What does the formation of white crystals of potassium carbonate on a properly serviced Ni-cd battery indicate?

A

Over charged.

47
Q

What does thermal runaway cause?

A

Violent gassing, boiling of electrolyte and melting of plates and casing.

48
Q

What is a primary cell?

A

Can not be recharged.

49
Q

What does a low insulation resistance in a lead/acid battery indicate?

A

Case leakage.

50
Q

Which terminal should you connect first when connecting a battery to the aircraft?

A

Positive.

51
Q

What is the purpose of an ammeter in a battery charging system?

A

Rate of current used to charge the battery.

52
Q

For how many hours will a 140AH battery deliver 15A?

A

9.33 hours.

53
Q

What part of a nickel-cadmium cell helps to prevent thermal runaway?

A

The separator.

54
Q

When does a nickel-cadmium battery emit gas during charging?

A

Toward the end of the charging cycle.

55
Q

What is the internal resistance of a battery?

A

The resistance present inside the battery while connected to a load.

Electrical Fundementals (19 decks)

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