Fair enough, Doug. You clearly know a lot more about fuses than I do, so I bow to your superior wisdom.

Cheers,

John

MBN FLEET BROADCAST
FROM: CIC OPERATIONS
TO: ALL COMMANDS
COPY: CAPT. TD MBN US NE DIVISION
SEC: PLAIN
SUBJ: OVERALL WORLD SITREP
MSG: SNAFU; SET DEFCON TWO; END
SIGNED: FLEET (AKA Doug😎)

"Which for our practical purposes is the cube root of not a lot"
Which is about how I feel about the current world situation...
Sorry, but it is Doug's fault. He gave me the lead in.😁😂😁

Hi John,
Re " (no idea how much voltage drops across a fuse, btw, but there will be some)."
No there won't!
At least nothing that you can measure on a typical hobbyist digital multimeter, which will probably have a max sensitivity range of 100 to 200 mV; milli volts i.e. 1/1000V.
You would probably need a high spec lab voltmeter with a sensitivity range of 100 nano volts or better (that's 100billionths of a volt😮, 10 to -9 or 1/1,000,000,000) to measure any voltage drop at all.
So your digital multimeter will register 0.00V. Try to measure the fuse resistance and the result will be the same 0.00 Ω.
This is due to the resistivity of the wire used, specified as mΩ per metre, which is a function of the material and thickness/cross sectional area.
E.g. typically a wire of cross section area of 1.5mm² has a resistivity of ~4mΩ per metre.
Thus for a typical fuse of 1cm length made of this wire will have a resistance of ~4/100mΩ.
Or 4x10 to the minus 5 Ω; 0.00004Ω.
The voltage drop across it is of course proportional to the current flowing, demanded by the load (i.e. motor) you are applying to the power source.
E.G. 10A in the example wire above would produce a drop of 10x0.00004V --> 0.0004V.
= ~ 40nanoV. Which for our practical purposes is the cube root of not a lot😁

Cheers, Doug😎

seems that this issue is a mine field so between the motor and the esc I will look into the circuit breakers

There are lot's of sources for auto reset breakers. Auto parts stores is an easy one. The other is electronic supply houses. I'll post some links if you need them

Great idea Toradog
What kind of circuit breaker do you use, where do you get it?

I agree with the Commodore. I would not use a fuse in my drive line circuit, unless I had nothing else. Instead, I use self re-setting circuit breakers. Easily obtained and inexpensive. Fuses are fine for auxiliary circuits, and sometimes need because of the low amp rating need for protection. All that said, I would definitely provide some form of protection in the drive circuit. ESC's and motors can become expensive.😊

I gave up using fuses years ago. They always caused a headache, no matter what size I used. It always seem to blow at the worst possible time. I realize I’m taking a chance not using a fuse but so often the least little bit of grass or leaves in the prop and the fuse blew and the boat ended up drifting around in the lake. If you don’t have a fuse, and your prop gets fouled, you can always go forward and a stern to clear it.

I am sorry for your loss.
I am a bit confused by your description though. You have given the supply voltage, 7.4 V, and that your ESC is rated at 40 amps, and your motor size, and that you had 25 amp fuse in line.
What I do not see is what the maximum current draw of the motor should be, ie, stall current. That should be the deciding factor of your fuse size. The current capacity of the ESC is not as important, because your motor should never draw more current than the ESC' capacity.
I looked thru so spec charts for 550 DC can motors and the highest current draw I found was 8 amps. That is a far cry from the 25 amp fuse you installed. I would be very surprised if a 10 amp fuse would not be much more likely to protect you in the future.
😔😔😔

Dammit!!!

I always put the fuse between the ESC and the motor so I've still got RC in the event of the fuse blowing, which is fine if the boat has an alternative means of power (sails or sculling with the rudder which works best in my experience if the rudder's not balanced.). Otherwise, I can't see that it makes any difference. I suppose that putting the fuse between the ESC and the motor might save the ESC if the fuse blows quickly enough and it's the motor that's causing the problem. You could, of course, put 2 fuses in; one between the battery and the ESC and one between the ESC and the motor. If you're willing to put up with the additional voltage drop (no idea how much voltage drops across a fuse, btw, but there will be some).

its most confusing over where a fuse goes between the battery and esc or esc and motor and what size the new escalator is a hobbywi ng 60 amp and motor brushed 550

Always a bummer when stuff like this happens. Hope you get it sorted soon.