How to select dynamic braking resistor?

How should I select the Ohm value and power rating for a dynamic braking resistor? This DBR will be used in a DC Converter that supplies 680 VDC to four AC Drives for (2)30 Hp and (2)60 Hp, 460 VAC motors. The braking duty cycle is about 10-20%.

But, what you haven't told us is how intense the braking action is. Is is possible to have all four motors in full hp braking at the same time. That would be 180hp or 240 kw.

Or, it could be as little as 5hp if only one motor is braking at a time and only slightly at that.

You need to analyse your application in this regard and advise back to us. Then we can help you.

mmm, in the worst case two 60 hp motors will be breaking to completely stop at the same time ... but the 4 motors share the DC bus , so I think the duty cycle is increased.

Like DickDV says, we need to know:

a) What the load is. And,
b) How soon do you want it stopped? And,
c) How often that you plan on stopping it (duty cycle).

There are safety concerns as well.

But looking at the size of the motors that you want to control, I would think that regenerative drives would really be the better way to go. But that depends on how often you stop your motors, and how fast that you need to stop them.

Application design info: http://www.filnor.com/html/products/dbr.html

BTW, I hope that you are using an external fan to cool your motors.


Congrats on Mexico beating Belize.

The load is a steel slab extractor from furnace, it has vertical and horizontal linear movements. First the 30 hp motors move up the slab, it takes 5 seconds. Then the 60 hp motors get it out from the furnace and put on the roller conveyor, it takes another 5s. Then it wait for 8-10 minutes for other slab, and return to the initial position, it takes the same time but now without load, to get the new slab. One or two motors could be running in each movement, it depends on the slab size.

So I think the duty cycle is about 3%.

Thank you,

Ha, ha, Mexico, Mexico, RA, RA, RA!!!

Well, did you look at the Filnor site?


1. Calculate the motor/drive wattage:
Motor Wattage (MW) = Motor or Drive horse power (HP) x 746

Motor Wattage (MW) = 120hp * 746 = 89520W


2. Calculate the peak wattage:
Peak Wattage (PW) = MW x BT

Peak Wattage (PW) = 89520 * 1.5 = 134280 (assuming 150% Braking Torque)


BT = Brake Torque
• Use 1.0 for 100%
• Use 1.5 for 150%


3. Calculate the required resistance:
Resistance = (DC bus voltage)^2 / PW

Resistance = 680^2/134280 or ~ 3.44 ohms


4. Calculate the Duty Cycle (DC)
DC = Braking Time / Cycle Time

Duty Cycle (DC) = Negligible (5 or so seconds out of 8 - 10 minutes?) OK, 3%


5. Calculate the DB resistor wattage:
Regeneration Type: Normal Braking - - - DBrw = (PW x DC )/2
Maximum “On Time” is 60 seconds for normal braking type.
Regeneration Type: Overhauling Load - - - DBrw = PW x DC
No maximum “On Time” for overhauling load type.

You'll have to pick whether it's a "normal" braking or "Overhauling load" braking type of application. But it doesn't look like "Maximum On Time" is going to be an issue for you.


6. Calculate the DB resistor current:
Bi= PW/RESISTANCE

(Wouldn't that be the square root of PW/RESISTANCE?)

In this case, I get 197 amps. It sure beats 39,034 amps.


7. Calculate the Braking Current:

DBi = DBrw/RESISTANCE

Again, you will have to pick the type of braking that you need. And you'll need to take the square root of Filnor's formula.


Or better yet, hit the "Get a quote" button and let their guys figure it out for you.

http://www.filnor.com/html/products/quote_dbr.html


I'm depressed, the Netherlands lost today. Go Germany!