Shellist Posted August 19 Share Posted August 19 Shelly offers so many different modules – it will take weeks to understand all of them. So I would like to address my question to you experts. I am planning to build a solar battery (DIY). Please find attached an outline of my brains effusion ... What I am looking for is a three-way switch that connects both cables (+ and -) on the DC side either to the charger (A) or to the inverter (B) - or to NUL (0) if none of them is used. Ideally the device also offers a temperature sensor. All my dreams would come true if they already offer such a thing for batteries including a function that shows the state of charge of the battery (which is not an easy thing ...). Quote Link to comment Share on other sites More sharing options...
Members thgoebel Posted August 20 Members Share Posted August 20 (edited) As food for thought a sketch: First step is to arrange a common ground for charger, battery and inverter. This simplifies the diagram and the switching components. Obviously, a Shelly pro 2 is suitable. This Shelly may be supplied by battery voltage, providing that the battery voltage is between 24V and 340V DC. Addendum: Shelly pro 2 has a HF32FV-16 relay which is not rated for DC, but for AC only (16A). This is caused by the contact material. Depending on the amperage and voltage of the battery, an intermediate contactor should be used with appropriate contact rating. Edited August 20 by thgoebel Quote Link to comment Share on other sites More sharing options...
Shellist Posted August 20 Author Share Posted August 20 Thanks for this. I thought about this solution before, but wouldn't it be better for safety reasons to switch both cables? The NUL-position on the other hand is absolutely neccessary: most of the time, both devices are decoupled from the battery! It is only charged (position A) when there is a surplus of solar power that is not being used. On the other hand, the battery power is only fed into the net (position B) when there is no solar power - at night, for example. In the time between none should be connected (position 0). Just imagine the shelly is connected to the charger and there is no surplus of solar power -> the battery will be charged by power from the power supplier (costs money - bad idea). On the other hand: just imagine the inverter is connected to the batterie and there is just or nearly enough power from sun for the house -> in this case I spend the power to the power supplier (for free - bad idea). Quote Link to comment Share on other sites More sharing options...
Members thgoebel Posted August 20 Members Share Posted August 20 (edited) Cannot follow the security doubts. And with both relay contacts open, current cannot flow in either direction. BTW: Please read the addendum concerning relay selection! Edited August 20 by thgoebel 1 Quote Link to comment Share on other sites More sharing options...
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