Data Center - Power
MSB – Main Switch Board directs and monitors electricity coming into the data center from the power grid. If the MSB detects a loss in voltage pressure, it will automatically kick the load over to battery backup, and eventually to generators, to avoid interruption in power.
UPS – Uninterruptible Power Supply provides backup for the entire data center in case of power outages. Protection by these battery- or flywheel-powered systems is near-instantaneous, and they fill in until a secondary power source, such as a generator, come online.
ASTS – Automatic Static Transfer Switches transfer power between multiple sources – typically from an unstable source to a stable one .
PDU – Power Distributions Units distribute power to gear in cabinets and cages in a data center. They could be compared to functionaries in government agencies; you have to go through them to get to the power.
BCM – Branch Circuit Monitoring measures and monitors how much power each customer uses. These devices ensure that the power feeding into customers’ systems is operational and also tracks how much power is consumed.
Amps, volts, ohms, and watts
- Amps: The actual electrical current, or moving electrons, coming through the power lines. Many devices are rated based on the amps they use or can support (such as outlets). A wall outlet might be rated for 15 amps and a Computer plugged into it may consume 2.5 amps, leaving a comfortable margin.
- Volts: Often referred to as the "pressure" pushing amps through a designated path. A server may have an electric plug rated for 110 or 120 volts (but can run at differing levels of voltage). A higher number is better since this achieves better electrical efficiency. Many of the household devices we use every day run at 120 volts. One AA battery may run at 1.5 volts.
- Ohms: The resistance that slows electrical current, causing impediment (perhaps due to the size of path). Defined as "the amount of resistance that allows one ampere of current to flow when one volt of potential is applied to it."
- Watts: The actual electrical power at hand that is used by a device such as a server or network switch. A heavily loaded server might use 450-500 watts or more.
Amps = watts / volts
In case of a Computer, it uses 300 watts on a 120 volt outlet, so therefore draws 2.5 amps.
Volts = amps x ohms
.25 amps being resisted by 12 ohms would result in 3 volts
Watts = volts x amps
A server hooked into a 120 volt outlet running at 3.2 amps would consume 384 watts
a server rack is installed with power strips that offer a 20 amp capacity, and it's up to you to figure out how many servers you can safely plug into that strip. If these systems use 208 volts and you estimate that at maximum load they consume 400 watts of electricity, you can calculate the amps involved by dividing 400 by 208. The servers use 1.92 amps each (this can vary based on load), whereas if they were at 120 volts, they'd use 3.33 amps. This means they'll draw less current. Since the power strip can accommodate the use of 20 amps, hypothetically you could hook 10 of these servers into it.
AC and DC power: Alternating current (AC) and direct current (DC) are two types of current (or voltage) used by electricity.
- AC current generally operates at 120 or 240 volts and is considered "traditional" power, which is used by grids around the world. It can be transformed into different voltages quite easily. AC current "changes direction" frequently, up to 60 times per second (also known as Hertz or Hz).
- DC current is a bit harder to quantify. Unlike AC, it remains constant and doesn't change direction. It's commonly associated with batteries or stored power such as that in a UPS. A car battery might run at 12 volts for instance. A laptop will work off DC power if on battery.
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