I will get down to power configurations more when the budget grows but I have chosen high voltage 240V AC with an L6-20R to L6-20P 20A 208V commonly available. The power poles are 20 port c13 - c14 and 4 port c19 - c20. This higher current leads to lower amperage meaning more servers can run in your rack. Be careful to know you BTU and wattage calculations as well to prepare your power for your devices and and appropriate cooling. Cooling info is sometimes as btu by the vendor but if you do not know your btu, you can find it with a simple calculation:
amps x volts = watts
watts x 3.41 = BTU/hour
max output for an R610 = 2,968.6 BTU/hour
max output for an R610 = 2,968.6 BTU/hour
I am using in this configuration Dell R610 series servers as I was able to get a bunch of them cheaply with a good amount of memory inside. I'll explain the hardware in another post.
Taken from http://teamsilverback.com/knowledge-base/data-center-power-selecting-the-right-voltage/ and a much better reference to explain why to choose high voltage and how to calculate cooling as well.
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What Voltage Should I Use? 120V, 208V, 240V, AC or DC?
Choosing the right voltage standard for data center design will have a significant impact on power utilization efficiency, cost of implementation, TCO, cooling efficiency, and space utilization. Specifically in North America, 120V Single Phase AC power is often used by tradition over sensibility and is dramatically less efficient and more costly than higher voltage options.
Most modern information technology equipment is designed to operate at 100V to 250V to accommodate North American 120/208V, Japanese 100/200V, and 230V used in the rest of the world to allow for worldwide power compatibility. Without going into confusing power calculations and details (readily available on the web if interested) using the highest voltage available is widely regarded as the most efficient choice striving to reach the 85-90% efficiency range. The emerging standards recommendation for data centers in North America to move to 240V power significantly improves efficiency over 120V distribution, requires less wiring, uses smaller step down transformers, and is less costly to implement.
North American UPS standard output power of 277/480V can be stepped down to 240V with a single-winding autotransformer. For 120/208V power distribution, an isolation transformer is required with two windings, primary and secondary. The single-winding autotransformer for 240V power is typically 90% smaller and less costly than the PDU isolation transformers required for step down to 120/208V.
While some advocate using DC over AC power citing power efficiency benefits, the availability of DC power delivery systems outside of telecom equipment racks is not widely supported and the proposed efficiency gains are similar to the gains achieved by operating at 240V AC over 120/208V AC. Thus, standardizing on 240V AC power can achieve similar benefits at a much lower cost, with less complexity, and provide greater overall compatibility.
Top 10 Reasons to Use 240V Power over 120V/208V
1. 277/480V to 240/415V step down autotransformer is 90% smaller and less expensive than 120/208V PDU isolation transformer
2. Elimination of large PDU transformers reduces cooling costs and requires less space
3. 240V distribution yields the same power capacity with nearly half the current as 120V
4. Fewer circuit breakers required – Reduces points of failure
5. Fewer branch circuits to racks – Reduces wiring cost, weight, and bulk
6. Less wiring bulk increases airflow and cooling efficiency, decreases cable weight
7. Branch circuit conductor wires for 120V distribution are 2-3 times larger than 240V yielding the same power capacity
8. Using higher voltage at lower amps for the same power yield allows for use of smaller conductor wires thus reducing capital costs and reducing line lost due to resistance
9. Nearly every other country outside of North America is already operating at similar 230V distribution – worldwide consistency has many practical benefits
2. Elimination of large PDU transformers reduces cooling costs and requires less space
3. 240V distribution yields the same power capacity with nearly half the current as 120V
4. Fewer circuit breakers required – Reduces points of failure
5. Fewer branch circuits to racks – Reduces wiring cost, weight, and bulk
6. Less wiring bulk increases airflow and cooling efficiency, decreases cable weight
7. Branch circuit conductor wires for 120V distribution are 2-3 times larger than 240V yielding the same power capacity
8. Using higher voltage at lower amps for the same power yield allows for use of smaller conductor wires thus reducing capital costs and reducing line lost due to resistance
9. Nearly every other country outside of North America is already operating at similar 230V distribution – worldwide consistency has many practical benefits
10. Moving from 120V to 240V increases efficiency by 2-3.5% per server – accumulated over 100’s of servers this adds up to significant energy savings and greater capacity "
The reasoning behind power poles with c20 is simple. ANY ups with anything to c19 is fairly easy to find to connect the entire power pole to UPS power and maintain a single rack configuration.
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