Thoughts on Open Rack, and High Voltage DC vs AC power distribution in the data center
I just got back from the OpenCompute hardware technical session in Boston last week.
There was a proposal for 380V DC that was actually +/- 190V DC. The presenter was stating that it is possible to control and manage 190V DC where 380V DC presents challenges. Either Panduit or Anderson was there saying the same as you that they had a connector that could keep the arcing contained during a hot plug/unplug event and was approved by someone.
Also present were established power supply vendors. They expressed the sentiment that there didn’t seem to be a need for high voltage DC distribution in the data center. They can get similar power supply efficiency using high voltage AC inputs where the safety is much better understood. Copper wire sizes would be similar for high voltage DC as AC for similar voltage and power levels.
High voltage DC is currently used internal to power supplies where the active power factor correction circuitry drives a set of high voltage bulk capacitance and the DC outputs draw from that high voltage source. That design is ripe with opportunities to provide additional value to users of IT equipment without resorting to DC distribution to the rack.
It’s a bit of chicken and egg. No equipment can accept 380V DC so no one installs 380V DC infrastructure, so no one makes equipment to use it.
Additionally, the argument that high voltage DC could eliminate UPS output stages assumes that UPS only use batteries for energy storage. Such an assumption eliminates the use of flywheels and other UPS techniques which are equally effective, but don’t feature high voltage DC.
Personally, I don’t see the point. I think it’s a better idea to eliminate 120V and get to 277/480V AC or 240/415V AC inside a data center so we could eliminate significant copper and transformer costs without needing an _entirely new_ infrastructure. Just use the existing power cord standards we already have in place.
That together with low-voltage (12V) distribution inside a rack as standardized by Open Rack seem to make the most sense to me. It offers the benefits without needing massive changes in the ecosystem.
It’s important to remember that the initial Open Rack proposal of three power zones with 277/480V and 48V feeds was just a Facebook example configuration designed to work with their existing V1.0 data centers. Power supply and rectifier vendors have a number of different products that could be much more interesting to customers with existing 120/208V power distribution with A/B feeds. Penguin Computing intends to work closely with these vendors to bring these products to our Enterprise, Cloud and HPC customers.