Fuses save the things upstream of them.

I defer to Dave on electrical (and most other!) matters, but I believe that a full set of protection places fuses in a descending order along a length of wiring. So the max draw of the motors is 20A – put a 20A fuse in their leads. The ESCs can handle 50A (you should overspec the escs) – put a 50A fuse between them and the battery… and so on…

Oh dear Dave, your reputation will be in shreds… (and your boat in flames)

Colin

Dave

But are you brave enough to tell us if this ever happens.

Paul

ps I have a video camera

You can fit fuses between the battery and ESCs, and it is usually a GOOD IDEA. It saves the battery wiring and battery from internal faults inside the ESC. (and owners connecting the battery the wrong way round)

It is often desirable to fuse motor wiring in the case of BRUSHED, MULTIPLE motors on one ESC (but NOT singles). They are fed by 2 wires, breaking one breaks the circuit to that motor, leaving the other working.

There is no safe sensible way to fuse the wiring to a 3 phase (brushless) motor that will protect anything. A break in any one of the 3 wires will ensure that the other two suddenly carry unpredictable, but very high, currents, so all three would need fusing, all 3 would blow and there would be precious little way of telling where the problem started. Best to let the current limiting of the ESC do the protecting, all that it is looking after is a short length of wire and one winding of the motor. A fuse in this situation is just an extra fault liability.

I must admit that I hadn't thought in that much detail. But, If I do, I suspect that:

Brushless motors probably have two major failure modes:

1 – excess load causing overheating, leading to magnet failure and coil burnout.

2 – joint or wiring failure/short, resulting in motor stall and excess current through the energised circuit.

The first point is best dealt with by having a temperature detector – I'm surprised that built-in ones are not common. But if it persists and fails, the motor will end up with one wire broken…

For a brushless motor, I guess that you only need two fuses (for a star wind). That is enough to cover all three circuits, since they 'overlap'. You might be able to work out where the problem was by inspecting the motor afterwards, but one feature of these motors is that the magnets may be damaged if exposed to excess temperature – so it may be better to junk the motor and buy a new one anyway.

Given brushless motor amperages, I suspect that fusing the motor would be an attempt to protect against post-failure fire rather than saving the motor. In other words, you're protecting the boat. If Dave runs without such safeguards, that's good enough for me…but I guess that's the advantage of having confidence in the quality of his equipment….

Edited By Dodgy Geezer on 12/01/2016 15:22:45