H Bridge protection when motor is acting as generator

MrAl

Joined Jun 17, 2014
8,231
That looks like it should work as a shunt regulator, but we were also talking about current limit or at least a way to turn off the bridge when the motor slides back.

What else we dont know though is what he wants to do control wise. Does he want to try to prevent slide backs from happening.
 

Thread Starter

enggricha

Joined May 17, 2014
87
Try this circuit:

View attachment 198053
EDIT:

So, TS's problem is completely solved, H bridge, Gate drive and also the rest of the circuitry will not be fried.
Instead resistor BRAKE_LOAD may be connected solenoid coil, for solving some mechanical problem, in this situation.
That does look like a solution. I'll try this out. I was kind of loosing hope and was considering switching to a different gear box, that will mechanically prevent the robot from rolling / sliding back.
 

Thread Starter

enggricha

Joined May 17, 2014
87
That looks like it should work as a shunt regulator, but we were also talking about current limit or at least a way to turn off the bridge when the motor slides back.

What else we dont know though is what he wants to do control wise. Does he want to try to prevent slide backs from happening.
Ideally yes, try and prevent slide backs, but at this time protecting the electronics is the primary requirement.
 

Thread Starter

enggricha

Joined May 17, 2014
87
Try this circuit:

View attachment 198053
EDIT:

So, TS's problem is completely solved, H bridge, Gate drive and also the rest of the circuitry will not be fried.
Instead resistor BRAKE_LOAD may be connected solenoid coil, for solving some mechanical problem, in this situation.
This will work even if the 24V rail is powered off right? Looks like it will. Just confirming.
 

Danko

Joined Nov 22, 2017
1,077
This will work even if the 24V rail is powered off right? Looks like it will. Just confirming.
Yes, it will.
Braking will even more effective, when 24V power is off.
For this case circuit should have path for base current.
For example, it may be indicator "POWER ON":
1580738938315.png
EDIT:
@enggricha
---------------
M1 - IPP045N10N3GXKSA1 - £2.21, mount on big heatsink or on robot chassi (if aluminium).
D - Schottky, 15...25A.
Resistor BRAKE_LOAD - 1...3Ω.
======================
Problem: some times when the robot is climbing up an incline and for any reason slides back if the incline is too steep, the motors are acting as a generator and they fry the H bridge, Gate drive and also the rest of the circuitry.
Why robot slides back (guess):
Because of small gear ratio, when robot is climbing, motors work in regime, close to inrush.
Resistor R55 sees too big current and driver U9 send FAULT to MC.
MC waits some time, then put driver U9 to SLEEP.
So, no PWM on H-bridge, motors are free and robot accelerates back.
High voltage. Electronics burns down. That's it.
How to check it:
Easy. Only treadmill for robot needs to be made.
After it, with firmly fastened robot, you can measure any signals at different velocities and in both directions.
 
Last edited:

Thread Starter

enggricha

Joined May 17, 2014
87
Yes, it will.
Braking will even more effective, when 24V power is off.
For this case circuit should have path for base current.
For example, it may be indicator "POWER ON":
View attachment 198205
EDIT:
@enggricha
---------------
M1 - IPP045N10N3GXKSA1 - £2.21, mount on big heatsink or on robot chassi (if aluminium).
D - Schottky, 15...25A.
Resistor BRAKE_LOAD - 1...3Ω.
======================

Why robot slides back (guess):
Because of small gear ratio, when robot is climbing, motors work in regime, close to inrush.
Resistor R55 sees too big current and driver U9 send FAULT to MC.
MC waits some time, then put driver U9 to SLEEP.
So, no PWM on H-bridge, motors are free and robot accelerates back.
High voltage. Electronics burns down. That's it.
How to check it:
Easy. Only treadmill for robot needs to be made.
After it, with firmly fastened robot, you can measure any signals at different velocities and in both directions.
Thanks Danko for taking time and explaining it in this detail. Very grateful to you. I will try it and get back to you.
 

Thread Starter

enggricha

Joined May 17, 2014
87
@Danko I made a PCB and tried the circuit with a bench power supply and it is doing what it is expected to do. However, the LED on the 24V side is glowing, even when the 24V rail is powered off and there is voltage on the Bridge side. Is this expected? This would imply current flowing through the base of transistor to the LED? Is that safe?
 

Danko

Joined Nov 22, 2017
1,077
@Danko I made a PCB and tried the circuit with a bench power supply and it is doing what it is expected to do. However, the LED on the 24V side is glowing, even when the 24V rail is powered off and there is voltage on the Bridge side. Is this expected? This would imply current flowing through the base of transistor to the LED? Is that safe?
After power is off, LED may glowing from voltage of charged electrolytic capacitors in robot circuit and from rotating by inertia motors.
Current MUST be flowing through base, when voltage on the bridge side is higher than voltage on power supply side, to prevent emergency (high voltage) situation.
It is expected and absolutely safe.
 
Last edited:

Thread Starter

enggricha

Joined May 17, 2014
87
After power is off, LED may glowing from voltage of charged electrolytic capacitors in robot circuit and from rotating by inertia motors.
Current MUST be flowing through base, when voltage on the bridge side is higher than voltage on power supply side, to prevent emergency (high voltage) situation.
It is expected and absolutely safe.
Thanks again for clarifying.
 
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