OpenSprinkler autonomous – photovoltaics and LTE

I would like to introduce a project that I have been running for a year now: An OpenSprinkler DC installation with photovoltaics, batteries and LTE router.

The whole thing consists of the following components:

  1. 20W solar set with battery: https://www.amazon.de/gp/product/B01GNOFKEM
  2. OpenSprinkler DC+Ethernet housing kit + additional top hat rail holder for the charge controller
  3. DC-DC converter adjustable 5-36V https://www.ebay.de/itm/313260294331 + Velcro tape

First of all: The whole thing only works in summer and only when the sun is shining! I've had this running for a year now - with 5 solenoid valves that switch alternately.

The OpenSprinkler DC is designed for up to 12V. According to the manufacturer, you should not exceed this, otherwise overheating can occur. However, as I discovered, when the charge controller charges the battery, it generates a voltage of up to 14.5V - which is not good for the OpenSprinkler! I therefore strongly recommend a DC-DC converter that allows you to set the voltage to 7.5V.

The LTE router, on the other hand, requires 9 V to 36 V and therefore has no problem with the voltage. So DO NOT connect to the DC-DC converter!

1. Preparation

In order for the system to be accessible externally, i.e. via the LTE network, you need an IoT SIM card, optionally with a fixed IP. Why one? Quite simply, normal SIM cards do not allow access via the Internet, so OpenSprinkler could retrieve the weather report via the Internet, but the APP would not be able to access it. This is not the case with IoT SIM cards; they are specifically made for this case. Possible suppliers are:

  • Things Mobile: You can also book a fixed IP here
  • IoT Telecom
  • IoT Easy Connect from Vodafone
  • O2/ Telefonica IOT Connect

I booked a Things Mobile card with the fixed IP option.

Since it is much easier to configure the LTE router in the home network, you should do this. So put in the SIM card, power the router and access it via a web browser.

What is noticeable is that the OpenSprinkler boots much faster than the LTE router. Therefore the OpenSprinkler must be configured with a fixed IP!

 

UPDATE 08-2024

With a 30W / 12V solar cell: Yes, it worked as long as the sun was shining. That's why I added a 12V battery and equipped it with a charging controller. Important: OpenSprinkler can reach up to 12V, but the solar cells even provide 18V! I reduced this to 7.5V with a step-down module.
With the solar cell and battery it ran smoothly during the day, but as soon as the sun went down the battery was empty after 4-6 hours and the OpenSprinkler went out. However, it should be mentioned that I used the OpenSprinkler DC version and connected 8 standard solenoid valves that switch permanently (this is for testing, no water is connected), so they also constantly consume energy.
So that the OpenSprinkler doesn't constantly go out even in winter, I have now equipped the system with a 100W / 12V solar cell and so it now runs smoothly.
A controller charges the battery and automatically switches to battery when the sun goes down.

Photovoltaic solar 1 Photovoltaic solar 2