Shelly Pro 2 and DC voltage

[viliv]

Hello

can the Shelly Pro 2 switch DC voltage with the relays? It would be 24V DC.

The new ones don`t mention this.

[Olsche]

No DC switching is not supported with the Pro 2, a separate relay is required.

A alternative is Shelly Pro3: https://kb.shelly.cloud/knowledge-base/shelly-pro-3-v1

[thgoebel]

Unfortunately, the specification says something about switching alternating current only. If you have a look into the device and the built-in relay type, you‘ll find a HONGFA HF32FV-16. Its data sheet also only mentions contact details for AC load. So you have to read and use your common sense:

Switching DC voltage loads, especially inductive ones, such as motors and magnetic coils, significantly shortens the service life of relay contacts. The reason is that when direct current is switched off, there is no zero passage that extinguishes a possibly created arc. DC loads above 1A at 30V are generally considered critical by relay manufacturers. You can completely prevent switch-off light arcs by suitable switching measures (freewheel diodes) or dampen them with spark extinguishing elements.

Which load should be switched? What is the current consumption?

[MARC0]

Hello everyone,

I also plan to use a Shelly Pro 2 to switch DC voltage with very low currents and would appreciate some advice. My objective is to automate my blinds using a Shelly, and I currently have the following actuator installed: Warema Schaltaktor 4M/230.

My current setup has a three-position switch (up, neutral, down), which stays in whichever position it’s set to and switches the 24VDC respectively. When I move the switch to the "down" position, the blinds lower and continue moving even if I return the switch to the neutral position. The same applies to the "up" position — the blinds raise until the switch is moved in the opposite direction.

My questions are:

1. Is the Shelly Pro 2 suitable for controlling the blinds in this manner, considering there’s only minimal current to be switched?
2. Can I use Shelly's SW1/2 inputs to keep the existing switches working, or would you recommend having them in parallel (as the controller already handles invalid simultaneous up and down)? If so, I won't get the state of the HW switches.

If this works, I would need one Shelly Pro 2 per blind. I have four blinds. Are there better options for this?

Thank you very much in advance for your help and insights!

[thgoebel]

A very similar issue was posted here:

https://www.smarthome-forum.eu/thread/25746-connecting-shelly-plus-2pm-to-a-dc-awning-control-system/

(Most likely you may have to register in this forum to see the pictures and diagrams.)

IMHO, there is nothing to be said against using a Shelly pro 2. DC and very small current are no obstacle. But there are other alternatives: Shelly UNI plus or - if a cover/roller GUI should be present - a Shelly plus PM or pro 2PM or Dual Cover. But be aware: Despite the roller/cover mode, a calibration is not available due to the DC operation which allows no power measurements in the Shelly!

[MARC0]

Thank you for the link to the smarthome forum! Haven't found that posting before.

Yes, the issue of no calibration being possible is indeed a problem, or at least not very satisfying for me. 😕
It will cover the basic cases of opening and closing the blinds (keep for x seconds up / down), but the current state would also be interesting. The problem is that the Warema module is not really suitable for self-made automation - they offer their own "Smart Home" solutions.

Measuring the current in the motor circuit additionally might be a solution. I need to dig deeper into this, but I will try it with the Uni in the first step. Thank you!

[wooly]

measuring the current could be made in this way: measure the voltage on a small resistor in series to ground return of the actuators [use an UNI]