In my large, complex system, just turning on the power has become a complex issue itself, as I now have seven power amplifiers (18 channels total) plus a dozen source and other boxes to power up in sequence.
Since this is all high-performance gear, I want to ensure it is fed the cleanest, most stable AC power, so the custom HT equipment room has a dedicated 240v 30Amp circuit feeding a 5Kva EquiTech balanced power toroidal isolation transformer. The ‘balanced power’ part means the outputs are +60Vac and -60Vac plus ground. No hot/neutral stuff, just balanced (also known as ‘Technical power’) 120Vac, so all downstream switching needs to open/close both legs of the circuit together.
Previously, I had divided the problem in three, one 30A input relay to switch the EquiTech transformer itself on or off. Then two 20A output relays, one for the sources and another for the amps. But the inrush from the amps is overloading the 20amp relay to that power strip. So, to address the challenge of power sequencing the many amps, I figured I’d solve it with some additional DPST (double-pole, single throw) relays. And since our loads are big power-hungry amplifiers, we need high amperage relays and wiring as well as a beefy enclosure to house the added relays and outlets. And finally, need to figure out how to sequence all of this so we have six or seven discrete steps.
After looking around for any existing commercial products that might fit the bill, it became clear that the requirements for high power AND DPST relays is not a thing, so we are going to have to DIY the solution. But not entirely, as some aspects, like the computerized control of sequencing can be addressed with an existing commercial product.
Using the SurgeX Access Elite ( https://espsurgex.com/product/axess-elite/
) 8 port sequencer, we can supply 120v control power and flip four 20A electromechanical relays to power sequence the amps. The SurgeX will also power one of the amps using its inrush protection circuits, as well as sequence the power to the MartinLogan Electrostats.
Now we need to solve two things: How to get power to the SurgeX and a box to house the relays and outlets that will be controlled by the sequencer.
Fortunately, there are these things called Power Distribution Units (PDU) that are a combination of outlets and breakers usually connected to a high-capacity cable or feed and housed in nice robust and safe NEMA-rated metal boxes. Seems like a good starting point, and sure enough, I found a NOS of a PowerVar PDU5800-25 at a decent price ($70) on fleabay, so I got it. Here's an image of it stock:
The PDU has a 30Amp rated feed cord and a couple of 25A rated breakers feeding two-phase outlets, and four low-rated SPST breakers feeding 15A outlets. We’ll be dispensing with the two blue-capped two-phase plugs and replacing one of them with an always on 20A outlet that we’ll be using to feed the SurgeX. The hole from the other plug will be used to route the relay control wires into the box for the four relays.
The existing low-amperage breakers will be discarded and in their physical locations is where the 20A 120v control electromechanical relays will go. Each bank of two relay/outlets will be connected to one of the 25A DPST circuit breakers.
Being a completist, I also added LED indicator lights to each relay, so I can see when a outlet bank is energized. I did have to buy 120v panel-mount indicators, and then saw out the inner LED assembly, as I was not into drilling four new 9mm wholes for the indicators, and I already have a 36mm x 19mm hole (from the breaker toggle) that I can use for my indicator light. Just need to find a translucent piece of plastic to put over it now.
There is also a single LED indicator next to the 20A always-on outlet to let me know when the box as a whole is getting power from the balanced transformer.
The hardest part turned out to be figuring how to secure the incoming relay control wires, but after tons of searching on the Grainger web site, found a plastic ‘plug’ for the standard 1.75” panel hole in which I could drill a ½” hole for a std. ½” cord connector that would securely hold the wires.
The box for this PDU is nice and roomy, and everything fits just fine. Lots and lots of crimping and wire cutting/stripping was involved in the total re-do of the guts, but it’s all done now and ready to go.
The unit is hardwired into the balanced power transformer for minimal current loss.
Now that it’s all complete from a physical standpoint, the next steps are to integrate the sequencing automation of the SurgeX with the rest of my home automation system (based on HomeSeer). Likely the Homeseer event will just send a telnet command line to the SurgeX to turn it on or off. For now, I just use the SurgeX web-UI to trigger the sequence. It takes about 2 minutes to fully power up the amps.
So there you have it, a complex system gets a complex power sequencer with some DIY bits.
And a pic of the final relay controlled PDU
The next few posts have pics and discussion of the build process.