Case Study 3 : AC-DC Power

Hope this helps someone who has a physics exam, paper, or problem to do. These ca

Good afternoon supervisor, I understand that one of the power racks has experienced a power failure, and you want me to assess the damage that has been done to determine what the cause of the power failure is, and what need to be done to restore the server rack. Before getting started with my diagnostics It would be beneficial if these electric diagnostics test would be done during the evening, when there aren’t many other factions or devices that can affect the equipment. It is important that I ask if any changes have been made to the server rack since its installment, such as: has it been moved, are all servers within the rack properly working, has this power failure happened before, have there been any other issues associated with this rack or any others? It’s important that we address these questions before the actual examination. In addition, has there been any work done on the data center itself, which is important to know to help in our diagnostics.

Looking at the power schematic diagram gives us an understanding of how power is flowing from our power source to power our sever racks, taking a look below is a brief description of this flow of power;

Power is flowing from our main power source or our generator/Utility company AC Power is converted to DC Power by way of a converter. AC power which is alternating current, meaning electrons don’t flow just in one direction like in Direct current or dc power, but they alternate back to and fro. Dc power is what is used to power devices, and batteries use dc power as well. That dc power is then directed to the battery, although batteries already provides dc power, the dc power  or the battery does not provide enough voltage to power our high tech devices, in our case our data center, and our server racks.  In order for the dc power or voltage to be increased in the battery to power our devices, it must go through an inverter, which we see in the diagram, the inverter is what increases the voltage of the battery. The dc power of the battery is then converted to alternating power gain which then is sent to power our devices. Another part that is important to this diagram that is not showing is the circuit and the type of circuit itself. Since only one of our server racks lost power, it’s apparent that they type of circuit we are using is a parallel circuit. So the dc power that is converted in the battery using the inverter that dc power that is inverted to ac power then travels through our parallel circuit to power our server rack. We understand that there was a power failure and there could be a few different reasons why this power failure occurred. A few reasons could be a semiconductor stopped working, the wattage of the inverter could have exceeded the wattage of the device we are powering, in our case the server rack, the battery within ups over loaded or overheated, a transformer was over voltage, meaning that a voltage is greater than that at which a device or circuit is designed to operate. Also it’s possible there could be an issue with the cooling system within the transformer.

However, since power only went out in one of our server racks its possible this narrows down our possible causes to either our parallel circuit overloading or the battery within ups over loaded or overheated. With this being said there are a few ways we can test our circuit and transformer for overloading, move from there to resolving the issues and getting power restored. Its important to check and make sure the UPS is properly plugged up and power button is turned to see if that had been the cause of the power failure before proceeding.


For testing if a circuit is overloaded.

  1. Turn circuit off
  2. It’s important to make sure the UPS is turned off and unplugged from the wall
  3. Using a clamping ammeter which is used to check overloads and shorts that are in progress and determine whether the electric current is running through the circuit.
  4. It’s important that the ammeter is clamped to a single wire, and not a cable for accurate testing.

If the clamp ammeter test positive for circuit overload, then a safety fuse can be used, which can be connected in series along the main supply? This safety fuse allows for the entire line of current to pass through the fuse, so when you have multiple devices connected in a parallel circuit the voltage doesn’t super seed causing an over load or power failure. The current in that line won’t go over the amperes in that fuse.

Furthermore, in order to test if the battery within the UPS is overload or over heated and needs replacing.

  1. UPS systems comes with self-tests to test the battery life of your UPS, typically your battery life should last 3-5 years, however other factors could affect this time should as temperature, or the cooling systems of the server rack .
  2. If the UPS “on-line” lights up and stays on then battery replacement is needed.
  3. Be sure to recycle the batteries
  4. Replace batteries of UPS with same battery type and voltage
  5. Be sure to use assistants when replacing the batteries.
  6. Issue should be resolved

The power should be restored within the server rack after completing these tests and either or both works.


Relectric. (2003-2008). Circuit Breaker. In How to Test a Circuit Breaker. Retrieved Feb 14, 2013, from

Electrotinik. (2013). A Magazine On Electrical Engineering. In What are the reasons for transformer overheating?. Retrieved Feb 14, 2013, from

Ed Grabianowski. (2011). HowStuffWorks. In How DC/AC Power Inverters Work. Retrieved Feb 14, 2013, from


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