Solid State Relay for a mains Motor

Thread Starter

128ITSH

Joined Jul 20, 2017
101
Hello everyone!
I'm designing a remote control for an electrical roller shutter in my house.
I don't know much about it's motor, but by driving it with a fuse in series I know it draws less than 1.25A (at 230VAC.
Right now the Motor is controlled by two switches on the wall, as shown here:
switches.png
I would like to replace these switches with 2 SPST SSR's, with both connected to live in on one side, and to motor live up/down on the other side.
The Switching of the Neutral wire will be bypassed, so it will always be connected to the motor.
The thing is I don't know which SSR to choose. Random turn on? Zero Crossing?
This document states in page 2: "Random turn-on solid state relays are commonly used with inductive loads, where the phase shift between voltage and current can cause problems with zero-crossing relays". (what problems?)
In the same document it is said that a zero-crossing SSR minimizes surge currents (which come from the motor).

I am looking at this SSR (which is zero-crossing), and the Datasheet says: "The snubber circuit is integrated to prevent malfunction caused by the rapid rise of voltage on the output side, such as inductive load and current".
Zero-crossing SSR's are much easier to find than and cheaper Random ones, But I don't know which to buy since I want them to work reliably for years, and both seem to have pros and cons.

So my question is: What type of Solid State Relay should I choose, and what ratings should I take into account when choosing.
Thank's in advance!
 

MaxHeadRoom

Joined Jul 18, 2013
28,510
Those I/O SSR's are zero crossing which is what you need.
2amp Min.
Also look for the Opto22 kind, they can usually be had cheap on ebay and the later types have fuse in them.
You do know that most SSR's are low voltage DC control?
Max.
 

Thread Starter

128ITSH

Joined Jul 20, 2017
101
Thank's for your help!
I know these are DC controlled. I will feed a PSU from the wall to get 5V, and have an MCU and IR receiver to control the SSR's.
Looked at Opto22. They don't distribute through Digikey/Farnell/mouser, but through local, small distributors. There is one here at israel, but the website doesn't work, so I will stay with the model in the first post.
However, I would like to know why does zero crossing is the right type of SSR for switching motors.
 

MaxHeadRoom

Joined Jul 18, 2013
28,510
The basic difference is that zero crossing is where you don't need phase control, IOW the whole cycle of power can be applied.
Random switching types is where phase angle control is required in order to variably control a load. Or in the case pf the crydom type, they switch on immediately regardless of the phase angle point at the application of power.
Max.
 

AlbertHall

Joined Jun 4, 2014
12,328
I think it would be wise to incorporate some system to completely preclude both 'up' and 'down' being active at the same time - including the situation where one of the SSRs fails short circuit or the software goes rogue.
 

btebo

Joined Jul 7, 2017
100
Those I/O SSR's are zero crossing which is what you need.
2amp Min.
Also look for the Opto22 kind, they can usually be had cheap on ebay and the later types have fuse in them.
You do know that most SSR's are low voltage DC control?
Max.
Max - I thought zero crossing SSRs were mainly for resistive loads and one used random crossing SSRs on inductive loads....Was I taught incorrectly?
 

MaxHeadRoom

Joined Jul 18, 2013
28,510
Max - I thought zero crossing SSRs were mainly for resistive loads and one used random crossing SSRs on inductive loads....Was I taught incorrectly?
If you read down the bottom of the pdf they state 'However most Crydom zero crossing SSR's work well with motor loads, just that historically we have recommended random turn on.'
Small motors such as the OP's I don't see a problem.
Max.
 

btebo

Joined Jul 7, 2017
100
If you read down the bottom of the pdf they state 'However most Crydom zero crossing SSR's work well with motor loads, just that historically we have recommended random turn on.'
Small motors such as the OP's I don't see a problem.
Max.
Thanks - I failed to read the data sheet and was just making sure I hadn't totally lost it on general applications.
 
Top