SSR minimum load current

[joth]

TIL that SSRs don't work if you put too light a load on them.

Specifically, wiring up all the Salus manifold actuators to be controlled from Loxone via 24V -> AC SSRs, they won't active. Putting another dummy load on the channel (e.g. a spare LED driver) and now they work.

Fortunately I had a couple mechanical relays so swapped most zones out for those and working okay. More relays on order. 

But funny, I'd always thought of mechanical relays being necessary for really heavy loads, had never considered they'd be necessary for very light loads. It does make sense though when I think about how a transistor works for example.

[Spreadsheetman]

Yes, triac-based SSRs have a min load current. They also can have a leakage current which means they may turn very light loads on by default.

You might be able to find photo-MOS based products that work down to zero load, but I don’t know what voltages are available in this type.

[Temp]

As I recall for an SCR it's called the "Holding Current", for Thyristors it's called the "Latching Current". Value will be on the data sheet.

 

Edit: I think this will also apply to solid state relays (SSR).

Edited March 5, 2023 by Temp

[joth]

Yah downside of ordering from AliExpress is imperfect datasheets.

Leakage current is presumably the amount let by when off, rather than minimum load needed to turn on.

 

https://m.aliexpress.com/item/32859607153.html