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I am trying to control a motor remotely by using a relay. The relay is rated for 5-60 V DC, 100 A. The motor is a brushless DC motor, rated for 48 V, 10 A continuous. The relay switches on once the control signal is given from the microcontroller and the motor starts running. However, after some time, the motor suddenly stops while the relay is still on. When I checked the current waveform on a DSO, there was a sudden peak when the motor stops. When I disconnect the relay and connect the motor directly to the supply, the motor runs fine. Another point is the motor works fine when I run it at a slightly lesser speed.

Do I need to add a flyback diode or any other noise surpression circuit?

Power Supply: 54 V, 10 A battery SSR: FOTEK SSR-100DD

Block Diagram:

enter image description here

Oscilloscope Image: The resolution is at 1 A/ division. The motor had run for a few minutes prior to this.

enter image description here

Please point me in the possible direction of error. Thanks.

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    \$\begingroup\$ What is the power supply that you are using, and what specific model of relay? Please add that information to your question \$\endgroup\$
    – Bryan
    Commented Aug 18, 2023 at 4:58
  • \$\begingroup\$ Welcome! Sounds like some internal trip, either on the inverter inside your motor, the SSR or your power supply. Please post oscillograms and a schematic or block diagram. \$\endgroup\$
    – winny
    Commented Aug 18, 2023 at 7:11
  • \$\begingroup\$ @Bryan, edited my post to add the same, thanks! \$\endgroup\$
    – tris06
    Commented Aug 18, 2023 at 7:52
  • \$\begingroup\$ @winny I've added a block diagram and the oscilloscope image now, thank you. \$\endgroup\$
    – tris06
    Commented Aug 18, 2023 at 7:52
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    \$\begingroup\$ Zero hits on "SSR-100DD" on their webpage. The SSR-75DD is 32 V DC rated only. Fake product? \$\endgroup\$
    – winny
    Commented Aug 18, 2023 at 8:04

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SSR-100DD does not exist in FOTEK catalogue, which would lead me to believe they are fake. enter image description here

An EEVblog post confirms that this is a popular fake SSR from several vendors on ebay: https://www.eevblog.com/forum/reviews/warning-dont-buy-fotek-solid-state-relays/

enter image description here Image borrowed from said page of one cracked open with a 20 A rated BJT inside it.

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