Fuses

[CookieOldParticipant @cookieold]

Hi All , i am wiring 2 brushless motors with 2 ESC,s i have a fuses between the battery and each ESC . Is it nessesary to have fuses between the ESC,s and the motors

Dave

[CookieOldParticipant @cookieold]

[Dodgy Geezer 1Participant @dodgygeezer1]

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…

[Dave MilbournParticipant @davemilbourn48782]

I don't put any fuses between a brushless ESC and the motor. In fact I'm running my small Turnigy motors without fuses anywhere (I shall probably regret it!).

DM

Edited By Dave Milbourn on 11/01/2016 10:24:19

[Colin BishopModerator @colinbishop34627]

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

Colin

[Dave MilbournParticipant @davemilbourn48782]

Posted by Colin Bishop, Website Editor on 11/01/2016 16:29:11:

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

Colin

I doubt it, Colin. Remember the old schoolroom saying: "Do as I say but not as I do"? I'm comfortable enough with the electronics that I use in my own models to know when a fuse is necessary or could be left out.

My late friend and mentor Craig Talbot never fitted fuses to any of his models…but I do fit them where I think it's necessary. If the absence of a fuse in one of my boats ever results in a burn-out then I will publicly eat the remains of the model and allow someone to video it and put it on You Tube!

One thing I have now decided on is to fit some type of low-voltage alarm. I am going to try one of Dawnmist's LiPo monitors because it makes sense to me to do so. **LINK**

Dave M

[Paul TParticipant @pault84577]

Dave

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

Paul

ps I have a video camera

[Colin BishopModerator @colinbishop34627]

Yes, people who know what they are doing can probably get away unfused. But the model boating forums are littered with posts from people who have fried their speed controllers when a fuse of the correct rating would have saved them.

My Dad was in the electricity supply industry and he taught me good practice so I do fit fuses and once or twice they have saved me some grief.

Probably if you need to ask then you ought to fit them!

Colin

Edited By Colin Bishop, Website Editor on 11/01/2016 19:10:54

[Malcolm FraryParticipant @malcolmfrary95515]

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.

[Dave MilbournParticipant @davemilbourn48782]

Paul
Yes, that's a promise.

Colin
Quite..

Malc
Thanks!

DM

[Dodgy Geezer 1Participant @dodgygeezer1]

Posted by Malcolm Frary on 11/01/2016 22:39:37:

 

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. …

 

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

[CookieOldParticipant @cookieold]

Thanks Lads ,

Best Regards Dave

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