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!