Hey Wombat, more info please!
For those old codgers who use braces ,but no belt, here's my definition of your "string"
A big shunt diode will protect an ESC , in conjunction with a fuse ,where the person is COLOURBLIND i.e. prone to connect the battery the wrong way round.
A reverse-polarity induced fault current is likely to destroy fully electronic (non-2-pole relay ESC's ) on 12 volts even when a fuse is present.
An alternative is a low resistance FET transistor to block reverse voltage altogether.
My semi fuse ref was only because Martin said he heard polymer PTCC's were faster than fuses (I think thats what he meant)
Like you, I know (i squared t) and have used up a few sheets of log graph paper too! :)
What more information, Barry, you sure like to get your thrupence worth.
Liked the installation - though the banana was perhaps gilding the lily (unlike my more normal practice which seems to be more akin to polishing a 'xxxxx')
I have a reluctance to put in series diodes to protect the user from connecting the unit up incorrectly as they suck up power. A parallel diode when used as a flywheel protection device is fine. I have had to do this on one case because the the built in flywheel diodes in the FETs weren't up to the job when used with some rather hot motors. The thinking on the three fuse system was this:
1/. Main line fuse - last ditch protection when all else fails to prevent the possibility of fire
2/. Fuses on each motor line to protect the ESC in the event of a motor jam - I would suggest this even if the ESC has protection itself after seeing a few protected ESCs let out the magic smoke given that encapsulated ESCs do not have a smoke reinstallation valve.
3/. Fuses on the input to each ESC - really only needed in a multiple motor application - if one of the ESCs goes PHUT, this fuse should fail leaving the rest of the system operational allowing you to limp back to the shore.
Polyfuses - I suspect the characteristics will be similar to Varistors - I use those for mopping up the energy from lightning strikes along with spark-gaps and transient diodes - on the higher current ones the thermal mass could make the characteristic a bit soggy on marginal overloads . My preference is still for something that gives you a clear indication of a problem. Polyfuses ISTM are for applications where overload is to be expected (for instance finger trap protection on car winders or surge protection on a telecomms line) rather than where it is a sign of an abnormality on the the system.
Wom
The Prat-in-the-hat's trivia
Banana error - one of the classic programming errors - when you fail to terminate a loop correctly. From the little girl who stated "I know how to spell banananana, I just don't know when to stop"