In this chapter, we deal with AC power, how it comes in, gets measured, and switched to power other components like the LED lights, ventilation, or DC power supply. We also look into building a DIY Uninterrupted Power Supply from a car battery and an old UPS to keep the DC power supply on during a power outage.
To avoid electrocution, never work on the Arduino while the AC power is connected or the UPS is turned on.
Before we get started let's do a quick rundown of all components that need powering and their approximate power consumption. It's important to have an estimate of the maximum expected power usage for sizing cable diameters and fuses.
AC power:
LED lights - 500W
Internal fan - 40W
Exhaust fan - 60W
Reservoir air pump - 5W
DC power supply - 180W (over-sized for the worst-case scenario, for two Hempy buckets and one Aeroponics tote running at the same time)
Based on the above estimates the total energy consumption of the grow tent is around 800W. When selecting a fuse you should oversize it by at least 35%, on a 120V outlet a 10A, and on a 240V outlet, a 5A fuse should work fine. It is also a good idea to add a double pole - double throw switch to be able to cut power to the grow tent completely.
PS: North American 240V outlets have split phase wiring where ACL and ACN from the above drawing are both hot (120V-120V that are 180° out of phase) and should have a fuse on both wires (2 x 5A/125V).
A switching power supply powers the Arduino modules and the DC components connected to them (pumps, solenoids, sensors...). Size the power supply to the worst-case scenario when all DC devices are on, plus 20-30%.
DC power:
Hempy bucket water pump - 25W / bucket, 50W total
Aeroponics high-pressure pump - 40W
Aeroponics spray solenoid - 40W
Aeroponics bypass solenoid - 40W (Cannot be turned on at the same time as the spray solenoid)
Arduino modules: >5W total (Main, Reservoir, Hempy, Aero with all sensors)
Taking into account the solenoid restrictions the total power usage is 130W (12V - 11A) when all components are on. I have selected a 180W (12V - 15A) switching power supply. You can find an in-depth overview of the 10A version of this power supply in this DiodeGoneWild video.
12V - 15A DC power supply with 220V/110V AC input toggle
AC input and dual DC outlet terminals, voltage adjuster potentiometer
Before wiring the power supply I recommend taking it apart and re-applying the thermal paste on all three transistors. Many times these power supplies fail due to inappropriate heat-sink contact, causing them to overheat. Mine was no exception, the thermal paste only covered a portion of the main and secondary transistors, and there was no thermal paste between the casing and the internal small heat-sink at all.
Main switching transistor - Almost no thermal paste
Ditching the thermal pad and using a generous amount of thermal paste instead
Main switching transistor - Doused in thermal paste
Secondary transistors - Insufficient thermal paste
Applying thermal paste between the casing and the heat-sink
Secondary transistors - Thermal paste all over them
After reassembling the power supply we need to hook it up to AC power and adjust the output voltage to 12V using the DC voltage adjuster screw. Use a multimeter to measure the voltage between V- and V+ ports while adjusting the voltage potentiometer.
AC power connected
Output DC voltage adjusted to 12V using the potentiometer
DC power cables connected
Mounted with the ventilation holes facing upwards
Having an uninterruptible power supply is critical with an aeroponics setup where roots could dry out within an hour during a power outage. Due to cost reasons, I decided to power only the DC devices like the Arduino automation modules, pumps, and solenoids during an outage. My goal was to keep the aeroponics system operating for up to 24 hours without power. Without frequent misting, the plants would be dead within a few hours, while losing the lights and the ventilation is not crucial. Technically you could run the entire grow tent off a large UPS that can provide 800W/h for hours, but the price of the batteries would be huge. Another option would be to detect the AC power outage and automatically dim the lights and slow down the internal and exhaust fans.
The idea of using an old UPS with a car battery came from:
https://www.instructables.com/Make-your-computer-UPS-last-for-hours-instead-of-m/
https://www.instructables.com/UPS-Battery-Upgrade-15-Hours-Backup-Time/
First, we need to know the power consumption of the devices that should be kept on during a power outage. For two Hempy buckets + one aeroponics tote, this is 130W/h. Since the DC power supply is only around 80% efficient the actual power consumption is around 160W/h (worst case). In a general rule of thumb, you should look for a UPS that is rated for twice the actual power consumption. I have selected a 400VA (Volt-amps) rated UPS that can provide around 320W/h (Assuming a pretty low 0.8 power factor). Make sure the UPS uses a single 12V battery (or two 6V batteries connected in series) if you plan to use a single car battery. Some UPS-es use 24V batteries where you would need to connect two car batteries in series.
400 VA UPS with dead batteries
One AC input (C13), two AC outputs (C14 connector)
UPS circuit + dead batteries (12V total voltage)
Once you have a UPS make sure it is powered off and completely drained before opening it. After removing the case disconnect the internal batteries and remove them since we are going to use an external car battery instead. When selecting the cable to connect the battery keep the length to the shortest possible to avoid voltage drop. Make sure to use a 2 core cable with at least AWG 14 / 2 mm² thick wires that are rated to carry 40A up to 2 feet / 60 cm in length. (You can find a wire size calculator here).
Drill a 0.796inch / 20mm hole into the UPS's back and install a PG13.5 wire gland in it, then route the cable through and secure it by tightening the wire gland. Install matching connectors (male 6.3mm spade connectors in my case) to connect to the DC- and DC+ cables of the UPS circuit board. Make sure the connectors are well insulated and the is no chance of the wires shorting out.
Hole for the wire gland drilled in the UPS back
AWG 14 cable routed through
Only 2 cores used: DC- (blue) / DC+ (brown)
Spade connectors to UPS DC- and DC+ cables
(Old battery connection points)
The last step is to connect the battery. For this, we will need two car battery terminals, two wire lugs, one butt connector, and an inline heavy duty fuse holder with a 30A glass fuse. Connect the DC- cable to the negative terminal using a single wire lug, and connect the DC+ cable to the inline fuse holder using the butt connector, then install the other side of the fuse holder to the positive terminal using the second wire lug. Attach the wire lugs to the battery, then install the 30A fuse into the fuse holder.
Battery terminals with an inline 30A fuse on the positive terminal
UPS installed on top of the battery with an air gap for cooling
