I bought 4 nos FOTEK SSR-40 DA Relay.

I need to use this relay to start 4 number single phase exhaust fan, please refer below specification of exhaust fan.

Single Phase AC Induction Motor

230V 50Hz 1Ph AC

Input 90W Max Current 2A

Insulation Class E

Capacitor: 4MFD/440V AC PF-0.9

Please refer below basic schematics of connection

When SSD relay triggered from Arduino Microcontroller board the relay LED illuminates but FANs are not ON, they sounds and the fan blades rotates vary slow (approximate one rotation in 20-30 Seconds).

I don’t know why this is not switching correctly, while connecting without SSD directly all FAN working ok.

The current rating of relay is 40 A and all 4 FAN current rating is not more than 12 A.

Can anyone help me in diagnosing and identifying the problem here.



These relays are rated for 3-32VDC input, but I had problems with these relays too, it needs more than 3V to fully turn on.

As a test, try switch the relay on with a 12V supply instead of an arduino

Remember to disconnect the Arduino pin before touching the 12V !!

If that SSD is Chinese don't be surprised if the main triac inside is rated for a lot less then 40 amps.
Also check the temperature of the SSD. It might need a heat sink.

Thanks @guix , I used transistor 2N2222A to trigger SSD relay for 12V and it worked properly. Many thanks...

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The SSD relay is working when I used transistor with Arduino at 12V. I left the all 4 exhaust fans for 2 hours and then checked SSD relay temperature, it was not heating. But yes if I will increase load then will definitely use heatsink. Thanks for the suggestion.