Competent grow room electrical advice needed

graying.geek said:

Looking for some best-practices electrical advice. I've been doodling with Mycodo on a Raspberry Pi for data collection and monitoring, but would like to transition to using the Pi to control some of the high power devices in the grow room; e.g. lights, heater, chiller, etc. My grow room is 6' x 4' x 8' with an 80 liter hydro reservoir, 1200W heater, 400W of LED, 39W UV light, dehumidifier and chiller. Everything is 120V.

I expect my electrical skill level is slightly above average; I install breakers, new circuits, outlets and switches without problems. I had a 100A subpanel installed in my grow room, so adding/changing single-phase breakers, circuits, etc, is a piece of cake. My weakness, which become obvious pretty quickly, is in the theory, so don't expect me to explain "inductive load" or how a SS relay works, because I don't know. I realize not understanding the "whys" can get me into trouble pretty quickly, hence I'm looking for some seasoned advice.

Everything is surface mount from the breaker box. My intent is to run 12-2 Romex through conduit from the breaker box to a "project box" containing the pi and relays (I expect to need a fan), then 12-2 through conduit to the respective outlets. I'll combine if it makes sense, but the default will be for each controlled outlet or outlet cluster to have it's own relay and its own 12-2 wire pull backed by a 15-A or 20-A fuse in the breaker box. I have plenty of slots in the box so I plan to use 1 circuit to back each relay, and run multiple circuits through the same conduit both to and from the project box.

Here's the questions that bubble up:

1) Do you see any safety issues?

2) Should I use GFCI outlets?

3) I understand that the SSR-40DA relays work well (?) for these applications, but may not trigger at the 3.3V signal from the Pi. Is it advisable to use one of the small 8-relay boards to use as a 5V trigger for the SSR-40DA?

4) I realize some of this is over done, but it's what I have on hand. Will it cause any issues now or ever?

5) What am I missing?

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shimbob said:

I would suggest looking into Tasmota-enabled devices. I use Mycodo for our grow as well, and once attempted to interface a 4-relay board to the RPI to control things. One AC shock later and I reevaluated my desire to mess with AC.
Now I have 3 Tasmota-enabled devices for a total of 10 remotes controlled outlets and they work great.

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JOO©E said:

You can use a LL MOSFET to hold back 12VDC from a power brick until 3.3V is applied to the gate. If MC pin Vmax is 3.3V & pin Imax is 16mA, or a total of 52mW, then a requirement of 12V @ 7.5mA, or 90mW, is not possible to achieve with a boost converter. You can boost the V but at a loss of I. You can't boost finite power, only voltage.

You'd have to implement some sort of switching circuit to regulate (turn on and off) a seperate power supply capable of triggering the SSR. I'd use a cheapo AC/DC wall adapter (only need 1) with a few MOSFET's (as many as you had relays). Wire the SSR's in parallel with the 12VDC output of the AC/DC adapter, and then insert small n-channel FETs between the relays and ground. Google MOSFETs if you're not familiar. Your Pi would trigger the GPIO high, which turns on the FET, which turns on the SSR, which allows mains to device. If the SSR is controlling an inductive load then you'd want to use a varistor (MOV) and RC snubber to protect against switch off arcs and transients. You can put fly back diodes across your SSR input to protect the FET's from any sort of inductive spike as well. Motors can draw 5-10× more current at startup than normal operation (transformers 10-20× more than normal operation), so make sure the SSR you're using can handle the peak currents your devices will draw at startup.

I'd also run a ground to all the outlets too. Test the SSR (on off ect) with the intended devices to ensure functionality before installing. Certain circuitry can cause phase shifts between voltage and current and/or irregular waveforms which effect the ability of the SSR to operate as intended, so test first to ensure and save on headache later. There is recommended spacing for conductors given their proximity, total number, gauge, and current carried. I'd check your device currents and how many conductors compared to the size of conduit to verify you're working safe. You're probably fine, but just something I mention because I'm not sure how many circuits you plan in running.

*This is all assuming your SSR is DC input and not AC input.

How to Safely and Efficiently Switch Current or Voltage Using SSRs

The solid state relay (SSR) is a safe, versatile, rugged on/off switch between a low level control signal and an AC/DC load, but needs to be applied carefully.

www.digikey.com

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graying.geek said:

You know, I've looked at these briefly as an alternative, but despite being a retired IT guy, I'm not familiar enough with these critters to understand how they work. Are they just wifi devices that connect to my wifi router via one of the 802.11 protocols and use SNMP or something similar, or do they require a hub or cloud service?

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