I was looking at an old battery powered electric lawnmower I picked up as the previous owner didn't want to buy a new board to replace a ruined old board. Tried to study how it was designed - it appears it has a huge 80A contactor...or rather, a 80A relay. It appears to be SPDT to control the motor. A 30A relay protects the circuitry.
The weird thing I don't quite get is how this thing is connected. The common contact is connected to the motor. The NO contact is connected to the battery, which is expected, so when the relay is activated, the common is connected to the NO contact and runs the motor.
The weird thing is that the NC contact of that relay also has a connection - it's connected to (apparently) a diode's anode! The cathode of the diode appears to be connected to ground. This is a BIG diode... a stud diode.
While this appears to also provide faster slowing of the blade when the motor is shut off, couldn't a resistor or simply connecting the NC contact to ground do, instead of an "expensive" diode? Would the diode really protect the relay contacts that much better than just using a resistor?
The weird thing I don't quite get is how this thing is connected. The common contact is connected to the motor. The NO contact is connected to the battery, which is expected, so when the relay is activated, the common is connected to the NO contact and runs the motor.
The weird thing is that the NC contact of that relay also has a connection - it's connected to (apparently) a diode's anode! The cathode of the diode appears to be connected to ground. This is a BIG diode... a stud diode.
While this appears to also provide faster slowing of the blade when the motor is shut off, couldn't a resistor or simply connecting the NC contact to ground do, instead of an "expensive" diode? Would the diode really protect the relay contacts that much better than just using a resistor?
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