2
\$\begingroup\$

Is using a relay and some switches a standard way to reverse a motor or is the preferred method to use a H-Bridge? The circuit for reversing a motor with a relay looks like this: Circuit

Note that this circuit is just to show the relay and motor connections. The main control would be the coming from a PIC not an op-amp.

Me and my teacher are having disagreements about the best way/standard/preferred way to reverse motors, so what would engineers do?

\$\endgroup\$

4 Answers 4

6
\$\begingroup\$

Whenever I have done motor control it has been with an H-Bridge. But the ideal solution depends on several factors:

What is the voltage/current required? For <24 volts and <5 amps, an H-Bridge is normally the preferred solution. The reason for this is the MOSFET's that can handle those voltages/currents are easy to get, easy to design with, and fairly inexpensive.

Is speed control, dynamic breaking, or regenerative breaking required? If so, an H-Bridge is again usually the best.

But in the case where there is no speed control, and the frequency of "direction reversals" is low, and/or the voltage/current is very high then a relay could be a good choice.

The main selling point of the relay is its simplicity and ease of use. An H-Bridge will always perform better but it is harder to design, sometimes can be more expensive, and adds complexity that is not always required.

\$\endgroup\$
1
\$\begingroup\$

How about the best of both, use a relay to switch the motor direction and a power device to control the speed of the motor (It's how early speed controllers worked - it was a lot cheaper to just have a single power stage, and a relay could switch easily - you just need to make sure the motor is going slowly when switching to avoid arcing in the relay)

So 1 pin would control the motor and 1 PWM output run a power stage to control the speed.

(A power stage could be a simple as a resistor, a transistor and a reverse protection diode)

\$\endgroup\$
1
1
\$\begingroup\$

If you are switching a lot of current, a relay is cheaper (especially in the old days when high power transistors cost a lot more!), a H-bridge has the advantage of PWM speed control, and instant reversal.

For small currents, (<2A) a single chip H-bridge is economical and more compact. For heavy duty high current motors, the reverse is true, a relay will be cheaper and smaller than a high-power H-bridge.

If you don't need electronic speed control, and aren't changing direction zillions of times an hour, a relay is a fine solution, and a heckload easier to debug.

\$\endgroup\$
0
\$\begingroup\$

You can also get speed control with an H-bridge. They are popular because of that.

\$\endgroup\$
1
  • \$\begingroup\$ I hadn't thought of that. Yes I say H-bridge and that relays are a non standard way. He's all for the relays. \$\endgroup\$
    – Dean
    Apr 4, 2011 at 21:39

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.