My fuse keeps blowing, what could be the reason?
There are three most common reasons: the fuse rating being chosen too low (it should be 125-150% of the continuous current), a fast-blow characteristic fuse being caught by the normal starting pulse, and the motor drawing more current than expected because mechanical resistance has increased. Cable damage and loose connections also cause fuses to blow.
Carry out the following checks in order:
- Verify the rating. Measure the continuous current under load. The fuse should be 125-150% of that value. In an application drawing 12 A, a 15 A fuse is marginal.
- Check the characteristic. Fast-blow fuses (most ATO/blade types) do not tolerate the starting pulse. If it blows at start-up, that is almost certainly the reason; switch to a slow-blow (T/TT) type.
- Check the mechanics. Binding, lack of lubrication, dirt on the rail or a deformed part raises the current. Disconnect the motor from the load and run it unloaded; if it does not blow unloaded, the problem is mechanical.
- Inspect the cable. Crushing, moisture ingress and worn insulation touching the chassis cause short circuits. Look especially at cable passing through moving points.
- Tighten the connections. A loose terminal creates resistance, heats up and distorts the current profile.
- Reduce the starting frequency. Repeated starts heat the fuse cumulatively.
Reducing the pulse at its source is the most lasting solution: the soft start and stop function of the KS250, or the ramp set with the RMP pot on the PT500, lowers the pulse to typically 2-4 times the rated value. Consider increasing the fuse rating as a last resort, and make sure the cable cross-section carries the new value.
The full topic: DC Motor Driver Selection Guide