1. Which of the following is not an example of a rechargeable battery?
   a. Sealed lead acid
   b. Ni-cad
   c. Lithium ion
   d. Zinc carbon
   
   
2. A transformer is used to:
   a. convert AC voltage to DC voltage.
   b. reduce AC ripple.
   c. regulate output voltage.
   d. step down or step up AC voltage.
   
   
3. A full wave bridge diode assembly is used to:
   a. convert AC voltage to DC voltage.
   b. reduce AC ripple.
   c. regulate output voltage.
   d. step down or step up AC voltage.
   
   
4. Filters are used in power supplies to:
   a. convert AC voltage to DC voltage.
   b. reduce AC ripple.
   c. regulate output voltage.
   d. step down or step up AC voltage.
   
   
5. Any type of rechargeable battery can be used with a power supply.
   a. True
   b. False
   
   
6. Which of the following 12-volt transformers can safely provide 3 amps of current?
   a. 3 VA
   b. 12 VA
   c. 40 VA
   d. Any of the above
   
   
7. The best way to check the condition of a standby battery is to measure its open circuit voltage.
   a. True
   b. False
   
   
8. What is a nominal float charge for a 12-volt 7 AH lead acid battery connected to a working charger?
   a. 12 VDC
   b. 12 VAC
   c. 13.8 VDC
   d. 13.8 VAC
   
   
9. AC voltage can be represented by a sine wave, while DC voltage is represented by a square wave.
   a. True
   b. False
   
   
10. You can increase the standby time of an alarm system simply by adding sufficient batteries to the control’s power supply.
    a. True
    b. False
    
    
11. When selecting a standby battery, what factor(s) should be considered?
    a. System voltage
    b. Standby time required
    c. Design of power supply
    d. All of the above
    
    
12. Switched mode and linear-type power supplies are identical in design and function.
    a. True
    b. False
    
    
13. The amp hour (AH) rating of a battery indicates how much surge current it can provide.
    a. True
    b. False
    
    
14. You can increase the standby time of a power supply by connecting batteries in series.
    a. True
    b. False
    
    
15. You can check the proper operation of a transformer by measuring its output voltage:
    a. under full load.
    b. under no load.
    c. without any battery connected.
    d. with AC power turned off.
    e. None of the above

What’s Wrong with This?

Wally `Larman installed a security system that required a 24 volt DC power supply with standby power. Wally selected a 24 VDC power supply that could provide sufficient current for the system and used two 12-VDC batteries to provide the standby power. He made sure that the battery type was compatible with the power supply and connected them in parallel as shown in this diagram, but the system did not function properly. Can you see what Wally did wrong and what he must do to correct the problem?

5-Minute Tech Quiz Answers

1. d

2. d — A typical power supply has four major parts: the transformer which reduces the input voltage; the rectifier, which converts the AC voltage to DC voltage; a filter, which reduces the amount of AC ripple; and a regulator, which keeps the output voltage constant under varying loads.

3. a

4. b

5. b — Power supplies are designed to charge specific types of batteries, typically sealed lead acid.

6. c — To determine the VA rating, multiply the voltage by the current. In this case, that would be 12 volts times 3 amps, which equals 36 VA, so only the 40 VA transformer has sufficient capacity.

7. b — You should measure the voltage while the battery is connected with the AC input disconnected and see if the voltage remains steady over a period of time.

8. c — Although the exact voltage may vary depending upon manufacturer, typically a 12-volt lead acid battery will have a nominal charging voltage of approximately 13.8 VDC.

9. b — Both sine and square waves are examples of AC voltage.

10. b

11. d

12. b

13. b — The amp hour (AH) rating is an approximation of how much current the battery can supply over a period of time.

14. b — To increase the standby time, connect the batteries in parallel within the restrictions of the control/power supply. Connecting batteries in series will increase the voltage.

15. a

Answer to: What's Wrong with This?

Wally’s problem is caused by the way he connected the two 12-volt batteries. By wiring them in parallel, he could increase the amount of standby time, but the voltage will remain at 12 VDC, which is not acceptable for a 24-volt system. He can wire the batteries in series as shown in this diagram, which would increase the voltage to 24 VDC, or use one 24-volt battery with sufficient AH rating to meet the needs of the system. It is very important that you match the batteries to the charging circuit and that the configuration you use is acceptable for the intended application.