I am trying to figure out the working of this circuit to control a shovel motor but can't. Any help/suggestions appreciated, thanks.

 

This circuit has multiple problems.
The connection from Q1 emitter to motor pin 1 shorts out Q2/Z4 and Q3/Z3.
When RE1 and RE2 are low then Q1 is reverse biased.

Have a look at the H-bridge circuit. There is a lot of information on WWW for this including both discrete vrsions and IC versions of this circuit.
For instance http://www.bristolwatch.com/ele/h_bridge.htm

 

Thanks, I can see that if RE1, 2 are low, motor would move forward, but for counter-clockwise, could not fathom RE1=1 and RE2=2 ???
Also never heard of Zener NMOS, PMOS mentioned in the Note below:
-MCU controls the direction of the motor, for clock-wise operation RE1 and RE2 are low, for counter-clockwise, RE1=1 and RE2=2 -When RE1=1 the Zener NMOS is turned ON and Zener PMOS is turned off for flyback diode to coincide with direction fo motor rotation. Otherwise RE1=0 and NMOS is OFF and PMOS is ON -The Relays also have a flyback diode(below)

 

I think RE2 = 2 is a misprint. Read it as RE2 = 1.

 

Thanks. This circuit does not seem right; what do you think?

 

Thanks. This circuit does not seem right; what do you think?

I would agree. Where did you get that from?

 

I had someone design it. What I see wrong is that S, D are tied together. Do you agree, see anything else I missed?

 

I had someone design it. What I see wrong is that S, D are tied together. Do you agree, see anything else I missed?

Then fire the person you hired and get someone who knows electronics.

 

Do you agree, see anything else I missed?

The battery and the motor voltage linked. That may be intended or not. There is no sign of an input to the MOSFET gate.

 

There is a connection to the MOSFET from R17 to the MOSFET gate.
Can I ask another one - cannot see how this diagram will work

 

I can show you how to control a motor using an L298N board.

 

Yes. Would like to control it from the ST32G474 MCU

 

You can order the L298 motor controller for under $5 and wait for it to arrive.
Or you can go and pick one up today at your local electronics store for $15.