Power Distribution Unit with Relay controlled outlets – Build thread - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 15 Old 11-25-2018, 03:54 AM - Thread Starter
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Lightbulb Power Distribution Unit with Relay controlled outlets – Build thread

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.
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post #2 of 15 Old 11-25-2018, 03:57 AM - Thread Starter
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This is what the stock internals of the PowerVar look like, note the nice heavy gauge wiring. I'll get to re-use much of that in my re-do.

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post #3 of 15 Old 11-25-2018, 04:01 AM - Thread Starter
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After removing some of the stock parts so I have some room, I checked to see that the new relays will fit and can be secured. They do.
Also shown, a stock panel light, but as mentioned, we cut off the tops and extract just the LED assembly (which has a diode and a resistor in line to make it work on 120Vac). I then wrap the resistor with electrical tape to insulate it from the other leg, and then put shrink-wrap tubing over both.

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post #4 of 15 Old 11-25-2018, 04:03 AM - Thread Starter
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Here we are partially through the process of installing the relays and wiring them up to the breakers

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post #5 of 15 Old 11-25-2018, 04:09 AM - Thread Starter
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And here is the final view of the components inside the PDU. The Relay control wire is a cut-off 2-prong extension cord, with crimped on connectors that also have the thin LED wires going in, all are held securely with heat shrink covers.

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post #6 of 15 Old 11-25-2018, 04:12 AM - Thread Starter
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And here is the complete PDU with the 30Amp feed wire and the relay control snake



And a close up of the top. Still missing are the translucent covers for the relay indicator LEDs.

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post #7 of 15 Old 11-25-2018, 04:29 AM - Thread Starter
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This is the diagram of one of the elements in the PDU, showing we feed balanced power to a breaker, then route both legs through a Double Pole Single Throw relay that is controlled by the 120vac control signal, which also has an LED indicator to show when the relay is activated.

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post #8 of 15 Old 11-25-2018, 04:37 AM - Thread Starter
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All the sequencing is done by this guy, the SurgeX Axess Elite. Here pictured before installation into the rack.

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Last edited by JonFo; 11-26-2018 at 04:04 AM. Reason: spl
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post #9 of 15 Old 11-25-2018, 08:38 AM - Thread Starter
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Fully Deployed into the snake-pit:

The yellow outlets are the SurgeX sequencer, four outlets control the PDU relays, one other has an Amp and the last one on the right, powers the Electrostatic speakers AC feed.



No comments about cables, you try and have 18 channels of amplification in 7 amps, a dozen other devices and not have a LOT of cables. I'm into results, not bling, so don't really care about looks. Plus this is all in a dedicated equipment room only I ever see.
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post #10 of 15 Old 11-25-2018, 09:02 AM - Thread Starter
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@DonH50 You had previously inquired about power sequencing and control, so figure you'd get a kick out of this one.
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post #11 of 15 Old 11-25-2018, 06:07 PM
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Pretty impressive, thanks!

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
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post #12 of 15 Old 11-26-2018, 08:01 AM
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It seems to be part of a balanced AC circuit, so a few questions:
1] Where is the required GFCI?
2] Where is the label indicating that it's a balanced circuit?

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post #13 of 15 Old 01-13-2019, 07:32 AM - Thread Starter
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Quote:
Originally Posted by Speedskater View Post
It seems to be part of a balanced AC circuit, so a few questions:
1] Where is the required GFCI?
2] Where is the label indicating that it's a balanced circuit?
Good points, the GFCI is in the EquiTech unit, and I recently added the labels as specified by code to the PDU and to another outlet strip that is also linked to the balanced Power unit. Only I ever touch this gear, but it's now to spec in case someone else ever touches it, but it will the last thing they do in their lives

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post #14 of 15 Old 01-13-2019, 07:55 AM - Thread Starter
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Added one more element to this system to now fully automate the power sequencing based on the status of the main zone on the AV8802 pre-amp that drives the system.
This came about because the wife complained it was too complex to crank up the system, she wanted just to use remotes, not an app.

The Marantz AV8802 has two 12v output triggers and can be independently assigned to go positive based on selected input or enabled zone.
I set the 8802 trigger setting to be Main Zone triggers ON, all others were set to 'ignore'. That way the trigger goes on whenever the preamp is on, regardless of input, and goes off whenever the preamp is put into standby.

Now, there is a challenge: the SurgeX sequencer external trigger sensor is a dry-contact-closure circuit. Meaning it's designed to have a passive switch used to indicate whether it is 'on' (switch closed) or 'off' (switch open).

So we need to take a 12vdc signal and turn that into a dry-contact-closure path. No problem, ELK has a nice little board just for that that will take 12v (or24v if one snips a resistor) input to toggle the contacts in a relay. It has a protective diode and even an led to indicate status. Nice screw terminal strips for connections make it easy to wire up. About $12.
https://www.elkproducts.com/product-...arge-terminals




Put it into a small enclosure, drill some holes for wires and voila!

While I used it for a dry-contact circuit, the 912b relay could be used to switch other voltages necessary to drive larger relays or other trigger inputs that demand a higher current than the Marantz can generate.

Now the amp stack sequences up whenever the preamp is turned on, and will sequence down whenever the preamp is turned off.

I use the main home automation to provide some sleepy-head protections, such as enforcing the off state for the preamp if on after 1am. It does the same thing for the projector.

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post #15 of 15 Old 04-19-2020, 08:20 PM
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Very nice set-up! Thank-you for sharing.

I'm curious if you ever managed to set-up the SurgeX with automation software. I picked up a three SurgeX SX-AX20 units not realizing the only way to trigger them automatically for "activities" is via Telnet. It's probably easy for someone with basic programming skills, none of which I have. I have the Harmony Elite remote/hub, but Telnet seems to be above its capabilities, so I'm looking at EventGhost and/or Home Assistant. A lot of work just to turn on amp and processors.
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