Although they are both forms of regulated switching circuits, dynamic braking and choppers each have their own specific advantages and disadvantages. A dynamic brake is a self-contained module containing a transistor, a controller and a resistor and it works by using the controller to monitor DC bus voltage levels. The controller then registers these levels and switches on and off with the switching circuit (or transistor) as and when is needed. Another regulated switching device (generally used for more heavy duty systems) is a 'chopper', and we will go into the differences between dynamic braking and choppers later in more detail.
As an example of how dynamic braking works we will use a 460-volt drive with an optimized working voltage of 650 that will fail once it reaches 810. The dynamic braking module is used in this instance to regulate the voltage to 750 volts. When the bus is pushed up to this voltage the transistor switch turns on and this lets the current flow into the transistor. The energy turns to heat and the voltage starts to drop, when it hits 735 it turns off again.
Electrically, dynamic brakes and choppers achieve exactly the same thing and serve exactly the same purpose; the main difference is in their construction. A chopper is a less self-contained module than a dynamic brake as the module itself only houses a regulator circuit and a transistor, which means the resistor, can be mounted apart from the module itself (up to 100 feet away). This is handy in more intensive systems as it means that if the resistor gets very hot it won't overheat the rest of the chopper. It should also be noted that they are both rated different with choppers rated in 'amps' and dynamic braking rated in 'horsepower'.
There are still applications however, in which it would be preferable to use dynamic braking. Loads with a duty cycle greater than 20% are better suited to a chopper (if a dynamic brake exceeds a 20% duty cycle load it WILL fail), but a low regenerative duty cycle can be handled more efficiently with dynamic braking.
No matter what regulating circuit you use, precautions need to be taken. Both devices will need to be connected at the capacitor bank nodes of the DC bus. Some drives will have a DC bus connection at the input bridge rectifier nodes but these connections points should definitely not be used. If the connection is made here then the current in either the chopper or dynamic braking system will pass through the DC link choke that will produce a voltage spike when the power switch is turned off, this will cause an instant system failure.
As an example of how dynamic braking works we will use a 460-volt drive with an optimized working voltage of 650 that will fail once it reaches 810. The dynamic braking module is used in this instance to regulate the voltage to 750 volts. When the bus is pushed up to this voltage the transistor switch turns on and this lets the current flow into the transistor. The energy turns to heat and the voltage starts to drop, when it hits 735 it turns off again.
Electrically, dynamic brakes and choppers achieve exactly the same thing and serve exactly the same purpose; the main difference is in their construction. A chopper is a less self-contained module than a dynamic brake as the module itself only houses a regulator circuit and a transistor, which means the resistor, can be mounted apart from the module itself (up to 100 feet away). This is handy in more intensive systems as it means that if the resistor gets very hot it won't overheat the rest of the chopper. It should also be noted that they are both rated different with choppers rated in 'amps' and dynamic braking rated in 'horsepower'.
There are still applications however, in which it would be preferable to use dynamic braking. Loads with a duty cycle greater than 20% are better suited to a chopper (if a dynamic brake exceeds a 20% duty cycle load it WILL fail), but a low regenerative duty cycle can be handled more efficiently with dynamic braking.
No matter what regulating circuit you use, precautions need to be taken. Both devices will need to be connected at the capacitor bank nodes of the DC bus. Some drives will have a DC bus connection at the input bridge rectifier nodes but these connections points should definitely not be used. If the connection is made here then the current in either the chopper or dynamic braking system will pass through the DC link choke that will produce a voltage spike when the power switch is turned off, this will cause an instant system failure.
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