Danfoss VFD Broken Belt Detection

A customer wanted to show a “run” status from the VFD, but wanted to drop the run status if the current went below a certain threshold— this is sometimes known as “broken belt detection” where if the motor throws the belt and isn’t doing any work, we can get an alarm and drop the run status.

Some clients do this with an adjustable current sensing relay on the motor output wires, but these are sometimes finicky and require a manual screw adjustment.

If you want to do this on the VFD, here are the points that you should program:

22-60 “Broken Belt Function” set to [1] Warning

22-61 “Broken Belt Torque” set to 10%— this is the default, you may need to adjust this later

22-62 “Broken Belt Delay” default is 10s, I would set this to whatever the motor ramp up time is in 3-41 to give the motor time to ramp up to speed— maybe 30-60s depending on the motor. This will help avoid nuisance warnings while the motor is ramping up to speed.

5-40 Relay1 Function Relay set to [6] Running no Warning— this will give you the run status that you want, then drop if ANY warnings or alarms come in, including our broken belt warning W95. Set this to any of the outputs or relays that you want, I just use relay 1 as the example here.

0-21 Display line 1.2 set this (maybe temporarily) to [1622] Torque %. What this does is display on the top middle of the screen what the torque percent of the motor is at that moment. If you ramp the motor up and down you can watch this % change, then you want to set 22-61 a little BELOW the typical normal value of motor torque so that it will trip. Watch it under a few different load conditions and speeds and see what the normal values are.