I am starting a new project! (Always starting new projects before the last one is finalized ) This project is a desire to solve a problem in my warehouse. We have approximately 13 lighting circuits that run on 277V. Currently, my warehouse guys go to the breaker panel and flip on all 13 circuits individually. I do not like this process for several reasons including: breakers are not designed to be switches and they are degrading (and have been for 20 or more years), employees have to enter a dark warehouse to get to the breakers, the lighting breakers are on 2 separate panels which is confusing (and may be of differing voltages). In researching the solution, there is such a thing as a ārelay panelā for lighting control. A relay panel is installed in between the breaker panel and the load. It takes the place of physical wall switches and allows some automation based on I/O from other systems. In my search, I really like the offering from Lyntec because of the built in web server and various bus interfaces (DMX, BacNet, Etc.) However, the one supplier I found online was selling a 16-relay panel for approx. $5,000 USD. For that price, I might as well indulge my proclivity for EE projects.
I donāt like re-creating the wheel if it already exists for a reasonable price. But in this instance I canāt find exactly what Iām looking for. I like the offerings from ncd.io that @rickkas7 mentions from time to time. The boards look very clean and well engineered. I have a few issues that are preventing me from using those off-the-shelf solutions. I started to formulate some design criteria based on a comparison to the ncd.io heavy-duty relay panel:
- Must handle 277V @ 20A single-phase (and lower single-phase voltages. i.e. US Standard 120V).
- 277V is common in industrial and warehouse settings specifically for lighting. It allows longer run with less voltage drop (or perhaps a greater allowable voltage drop based on a standard 5% allowable loss.)
- All of my lighting has been converted to LED fixtures which I believe act as inductive loads.
- I am selecting components based on 300V @ 30A for a safety margin.
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I want more than just the ability to turn things off and on. I would like to add current and voltage monitoring and a record of power usage in the last x days/weeks/months/etc. I think this is a great application for the Photon (of which I have several). I also like how the ncd.io boards are multi-board compatible and use adapter boards to accommodate other platforms. (I hope that isnāt patented.)
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Must have basic automation available in other commercial panels such as relay groups, schedule-based events, I/O-based events, internet/phone/app control, etc. Again, a great application for the Photon.
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Should be modular and forward-thinking in terms of expansions. To that thought, the end-user should be able to select the number of relays they want to install. Also, there should be a separation of the controller and the relay board.
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I would like to have visual indication of which circuits are āOnā from the exterior of the electrical panel. I would also like the ability to toggle those circuits from an exterior switch or button.
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System should have capability of adding remote switches and visual indicators in order to actuate the circuits (think a button panel next to the security alarm panel 100ft away from the relay panel.).
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(ā¦might be a duplication of #3, but very specifically, I would like to turn all the lights on when our security system is deactivated. And conversely, turn all the lights off when the security alarm is activated. So some sort of contact closure input from that panel is the ultimate goal.)
That covers the general project criteria. I have started to put together a Bill of Materials and research the components to build the relay board. At the same time, Iām keeping my eye on what hardware is needed for the controller interface. My criteria for the relay board includes:
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Must choose a relay for 277V @ 20A. Being that the LED drivers act as inductive loads, I know there may be issues with contact arcing on the relays. So the relay should have protection from contact arcing and power surges. In general, I will over-specify the voltage ratings when selecting components.
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Must provide an electrician-friendly way of hooking up circuits. The ncd.io heavy-duty relay board only provides quick-connects. It is costly, labor-wise, for an electrician to crimp or solder a quick connect onto every high-voltage wire connection in the panel (it may be against code for all I know.) All those wires will be solid conductors (12 or 14ga) usually MC (not romex in commercial applications) which may not be the best for quick-connects as well.
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Low voltage must be isolated from high-voltage via transformers or other galvanic isolation. Most relay panels also have a physical separation barrier so the board must be laid out so that such a barrier will be effective (cannot mix low voltage components on the high-side of the board and vice versa).
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Cost is of concernā¦ try to balance cost vs desired feature set. I donāt have a maximum cost specified but if I can do 32 circuits under $1000, I think that would be great!
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Must include a relay override/disable switch for electrician troubleshooting. Relay should be able to be forced into an permanent on state as well as a permanent off state. And then also a position to give control back to the I/O of the controller.
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Would prefer to include both current and voltage sensing circuitry.
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Should have LED indicators for āRelay Actuatedā, āCurrent Flowingā and āVoltage Presentā. Current and Voltage indicators are dependent on implementing those respective sensing circuits.
I did a lot of research on how to do the current and voltage sensing portion of this circuit. I ended up using SMD current sense transformers and a quad op amp to do the AC to DC conversion as well as light the current/voltage sense indicators. I am using the Precision full-wave AC/DC Converter circuit in that link (modified to only use +12v and GND, and the input will be 0-5v AC and output should be 0-5V DC). I would appreciate any input from all you experts out there if there are any issues using that circuit.
Here is the Relay Board v0.1 circuit (this is only for one relayā¦ once prototyped and perfected, Iāll create a 4-relay and 8-relay version):
Here is the bill of materials so far (currently, the cost is at approx $16/relay. for a 32-relay panel, that is $512. This is just for the relay board and does not yet include the controller.):
After this is finalized, Iāll move on to the controller but I already have some of the components selected. Iāll save that for a subsequent post.
I appreciate any community feedback.