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A CSA View of Electric Power

A CSA View of Electric Power. CPIS 210 9/7/2010 John Beckett. Where Does Power Go?. Everything we use in IT goes into heat If our business is transmitting radio waves, that subtracts from what we are using – but in IT this is an insignificant fraction. How Much Power?.

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A CSA View of Electric Power

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  1. A CSA View of Electric Power CPIS 210 9/7/2010 John Beckett

  2. Where Does Power Go? Everything we use in IT goes into heat If our business is transmitting radio waves, that subtracts from what we are using – but in IT this is an insignificant fraction

  3. How Much Power? • Power = Voltage * Current • 120 volts at 30 amperes = • 3600 watts • 5 volts at 30 amperes = • 150 watts • It isn’t the voltage or the current, but the combination!

  4. Ohm’s Law Current is limited by resistance The current (I in amperes) in a circuit is the voltage (E in volts) divided by the resistance (R in ohms) I=E/R Which means: R=E/I E=IR

  5. Power & Resistance Chart

  6. What if your source isn’t perfect? • Every power source has an effective internal resistance • So when we apply a load, the output “sags.” • This reduces voltage available at the load, and may cause logic instability • It also causes heat to be generated in the power supply

  7. Causes of Source Resistance Design/Quality issues Low-capacity power transformer Cheap semiconductors, inductors Thin wires “Cold” solder joints CSA Issues Long wires Poor or worn-out connections

  8. Combatting Source Resistance • PC Power Supply: • Only one device per “snake” • Fans go at the end of the chain • They use less current and draw is steady • Use high-quality power supplies • Capacity is a clue • Weight is a clue • Experience is evidence • Destroy and discard worn connections • Don’t use extenders or adapters

  9. Power Supplies Are Inefficient At 350 watts of output, 78% efficiency means the total power use is 350 / .78 = 448 watts. So the power supply is dissipating 98 watts of heat when the load is drawing 350 watts. Less-efficient power supplies put out more heat at a given load. When the load draws 550 watts, the power supply is putting out over 200 watts of heat!

  10. Consequences of Heat Increased energy consumption Increased load on HVAC Reduced product life Inconsistent performance Lockups Thermal breakdown – permanent failure Fire

  11. Reducing Heat Buildup • Don’t create the heat • Reduce processor speeds • Inactivity “sleep” and “hibernate”modes • Lower-voltage processors • Get rid of the heat • Proper thermal conductive joint • AMD: Paste dries out, use a pad • JB: After x years, re-do the joint • Plenum • Planned airflow driven by fans • Pay attention to what’s inside that PC box

  12. Power Reliability • UPS – Enough power to run until you shut down properly, or to ride out a glitch • Generator – Plan to run things you need to run • Be aware that fumes are dangerous, even fatal • If you have redundant supplies in a device, they should be powered from separate electrical circuits

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