[SOLVED] How Relay based DC motor control works

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You can check that data in manufacturer datasheet, change of state can be in millions state changings.
 

The most common form of relay based DC motor control is to use the relay to switch the motor contacts to control the direction the motor runs. Relays can also be used to control speed by switching contact between voltages to apply to the DC motor.

Hope this helps.
Tahmid.
 

A H-Bridge should last forever and can switch thousands of times faster than a relay but in some applications a relay is more suited to the job. For example, I've worked with DC motors around metal smelting furnaces where the motor has to work in temperatures > 200C. These motors work on up to 1KV DC take thousands of Amps to start up, a H-Bridge would not stand up to the environment or the elecrical demands. The motors only stop and start maybe two or three times an hour. If the motor was much smaller, say in a toy, a H-Bridge would be more suitable because it can reach faster, can proportionaly control and draws less power.

Nobody mentioned you can also brake (as in slow down and stop) a DC motor with a relay or H-Bridge.

Brian.
 

Relays have many disavantages, but 2 unique advantages, Output and control are alwayss isolated due to the mechanical construcion, relay accept mistakes or short time high currents or even quick short circuits, any semiconductor will be damaged very easy with any kind off short circuit. In other words relays are robust slow and simple, While semiconductors are fast , reliable and fragile, Relays still used but is losing ground every day for semiconductors power devices
 

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