Back in July, we debuted the AC-powered OpenSprinkler v3.4, featuring a new, redesigned enclosure and several hardware improvements (read here). Building on that, today I’m thrilled to unveil the upcoming DC-powered OpenSprinkler v3.4 — the very first OpenSprinkler powered by USB-C! Check out some sneak-peek photos below:
This model shares the same sleek, low-profile enclosure as its AC counterpart. This means it features a single-layer circuit board, two extra sensor ports (SN3, SN4), and an external Ethernet connector for easy installation of the wired Ethernet module.
The key innovation, however, is the move to USB-C as the power source. This change offers several powerful advantages, rooted in our goal of modernizing the sprinkler control circuit.
Why Move Away from 24 VAC?
Traditionally, most sprinkler controllers rely on 24VAC to operate sprinkler valves. This is a dated standard with several notable drawbacks: 24VAC power adapters are heavy, bulky, expensive, and difficult to source outside North America. For international users, finding a compatible 24VAC adapter for their country is a major pain point. Furthermore, their output voltage is unregulated and they lack current limiting circuitry, posing a major risk in the event of a short circuit.
The Origin of DC-Powered OpenSprinkler
When I designed the first DC-powered OpenSprinkler, my goal was to eliminate the dependence on 24VAC and switch to DC power adapters, which are lightweight, compact, inexpensive, and globally available. DC power supplies also include built-in current limiting and protection circuitry — making them safer to use and resilient to faults.
However, to work with standard 24VAC sprinkler solenoids, a DC controller must simulate the behavior of a 24VAC solenoid using DC-only voltage. Specifically, under AC power, a solenoid coil naturally limits its current through inductive reactance:
1. Inrush Current: When the solenoid first activates, it draws a high inrush current (500–700mA) to energize the plunger.
2. Holding current: Once energized, the solenoid requires a lower, stable holding current (200–300mA) to remain open. Under AC power, this reduction happens automatically because the the plunger (now moved in) increases the coil’s inductance, which in turn raises it reactance and limits the current.
To replicate this effect under DC, OpenSprinkler uses a 7.5VDC adapter as its main power source. Since a typical sprinkler solenoid has a coil resistance of 30–40Ω, this voltage naturally produces the 200–300mA holding current required to keep the valve open. To generate the initial inrush current, however, it uses an internal voltage booster to momentarily raise the voltage to 21VDC. This dual-voltage method is essential, because the high inrush current is necessary to reliably open the valve, but if applied continuously, it can overheat the solenoid coil and significantly reduce its lifespan.
Why USB-C is a Game Changer
The DC-powered circuitry is a proven innovation that has allowed users to ditch the outdated 24VAC technology for years. The new v3.4 now takes this a step further by adopting USB-C as its main power source. This introduces three key benefits.
1. Universal Availability
USB-C is a global standard for everything from phones to laptops. This makes sourcing the power adapter incredibly easy, no matter where you are. These adapters are powerful yet lightweight, affordable, and feature built-in protection circuitry.
2. Adjustable Voltage (USB-C PD & PPS)
Modern USB-C adapters are essentially smart, adjustable power supplies. Those that support the PPS (Programmable Power Supply) standard can provide a continuous voltage range (e.g., any voltage between 5.0V and 15.0V). This is a game-changer for optimizing sprinkler valve performance.
Different solenoids have different coil resistances and ideal holding currents. By matching the holding current to the manufacturer’s spec, you prevent overheating (from too much current) and unreliable operation (from too little). With v3.4, you can now calculate and set the ideal input voltage for your specific valves, and the controller will negotiate with the USB-C adapter to provide it. This level of customization ensures best efficiency and reliability. For example:
- A 30Ω coil (older Orbit valves) with 250mA holding current works best at 7.5VDC
- A 60Ω coil (newer Orbit valves) with 200mA holding current works best at 12VDC
In previous DC models, you would have to swap the power adapter to match the voltage. With USB-C, the controller automatically negotiates the optimal voltage from a single USB-C power source.
3. Mistake-Proof Design
Previous DC models used a standard barrel jack. Despite our best effort to prevent mistakes, some users would accidentally plug in a 24VAC adapter (simply because the plug fits in), resulting in damage. USB-C completely eliminates that risk: an AC adapter plug physically cannot fit into a USB-C port.
FAQ
Q: When will it be available?
A: We are now accepting pre-orders for the DC-powered v3.4, with shipments expected by mid-November 2025.
Q: How does the controller customize the input voltage?
A: It has a built-in USB-C Power Delivery (PD) chip that negotiates the requested voltage directly with the USB-C adapter.
Q: How can I determine the ideal voltage to set for my valves?
A: Multiply your valve’s holding current by its coil resistance. Example: 250mA × 35Ω = 8.75VDC.
The holding current is typically specified in the valve’s datasheet. The coil resistance is also in the datasheet, or otherwise can be measured using a multimeter.
Q: Can I use any USB-C charger? What if mine doesn’t support PPS?
A: If the adapter supports PPS, the voltage can be set precisely. If your adapter only supports fixed voltages (5 V, 9 V, 15 V, etc.), it will select the nearest match.
Q: Does v3.4 still include an internal voltage booster?
A: Yes. The controller still needs to reliably generate an impulse voltage (21VDC) for the inrush current, which not all USB-C adapters can provide. The internal booster remains, ensuring consistent performance regardless of your charger’s capabilities.
Q: How much current can it support?
A: This is determined by your USB-C adapter’s power rating. A standard 18W adapter can provide roughly 2A at 9V, while more powerful (30W) adapters can supply even more current.
Q: Can I still use my 7.5VDC adapter with a barrel plug?
A: Yes, you can use a simple dc-female-to-USBC adapter like the one shown below. It’s a simple pass-through converter and does NOT do any voltage conversion. However, note that the input voltage will be fixed at your adapter’s rating (e.g., 7.5V) and will not be adjustable.
Q: How can I power v3.4 using a 12VDC solar setup?
A: If your solar power source has a standard barrel plug, you can use the same dc-female-to-USBC adapter shown above.
Q: Which expander is it compatible with?
A: Fully compatible with DC Expander v3, just like previous v3 models.
Q: Will DC v3.3 still be available?
A: Yes, we will continue selling the v3.3 model while supplies last. In the meantime, we will keep offering the v3.3 circuit board without an enclosure for repairs and DIY projects.
Q: Can I reuse my existing wired Ethernet module?
A: Yes — it uses the same W5500 Ethernet module as v3.3.
Q: I recently bought an OpenSprinkler DC v3.3. Can I exchange it?
A: Yes, if your purchase was made within the last 30 days, it qualifies for an exchange under our no-questions-asked return policy. Please see our terms and conditions for details.
