Will this relay driving circuit work or can it be improved?

Question

I am building an IoT connected ECU for electric 2 wheelers.

3.3v is from an ESP32.

• Relay
• Optocoupler
• Diode

I am working on a budget and I am also new to designing that's why I want to know if this even work or if I am doing/missing something obvious.

PS: EV controllers have an ignition wire which when connected to the battery supply positive will start the vehicle. Sigpad is where this ignition wire will be attached. BATT_IN in +ve of my 48V pack. Ignition pin is connected to ESP32's GPIO35.

Answer 1

No, it won't work. The relay coil is 64 ohms, which means it requires more than 50mA, and the absolute maximum for optocoupler is 50mA, so the ratings are exceeded. The optocoupler is not meant to drive so high currents.

Besides since the optocoupler is not even connected in a way to isolate anything, it will be much cheaper to replace the optocoupler with a general purpose transistor which can handle the relay current.

Answer 2

The optocoupler seems unnecessary, the relay already acts as an isolator. Unless the 3.3V is only available on an isolated area? Also if Ignition is directly connected to an ESP32 pin, you need a current limiting resistor for the LED optocoupler.

I think a simple MOSFET would be efficient and cheaper.

^{simulate this circuit – Schematic created using CircuitLab}