You need to look at hold current not trip current. Hold current is the maximum expected normal running current. A 'polyfuse' with 750mA hold was used on old RP 1B but is not enough for a RPi 2 or 3.Ivovis wrote:I know I am resurrecting a very old post but the OP question is still as relevant today as it was four year ago.
No one has suggested adding a fuse to the line supplying the GPIO, I have just had a rummage about and found the fuse below;
PPTC Resettable Fuse, MC36 Series, 750 mA, 1.3 A, 16 VDC, Through Hole, -40 °C
Available in the UK from here;
http://uk.farnell.com/multicomp/mc36245 ... dp/1861145
Now this fuse has a trip current of 1.3A the T075 on board fuse has a 1.5A trip current, as far as I can tell, you would have to have very heavy load on the USB sockets to even come close to this, so I am not expecting this small difference to be a problem.
The reason I have opted for this instead of an actual T075 is for ease of use on a breadboard prototype, does anyone have any reason why this is solution is a bad idea?
So would using a similar polyfuse with a hold current of 2.6A, a trip current of 5.2A, and a max voltage of 24V be a good option - better than the 16V one on the RPi? The supplier I linked to doesn't have one with a max of 16V - at least not that I found. Is the max voltage the max voltage before the polyfuse itself is damaged? If say 20V were put on it - does that mean that up to 2.6A at 20V would make it to the RPi? That is why I was looking at the first one that was max of 6V - trying to keep a higher voltage from getting to the RPi.Burngate wrote: ↑Tue Apr 30, 2019 8:45 amTrip current and hold current appear right, but the maximum voltage is only 6v, whereas the one used on the 3B+ is 16v
In normal use, that shouldn't make any difference - there shouldn't be more than 5¼v - but then, normal use isn't what the fuse is there for!
And we hear tales of people putting 24v on their Pi - the 16v fuse wouldn't protect in that instance, either!
Well, maybe for safety sake - I'll go with the trip and hold current listed - but I'll go with the 12V max version. It sounds to me like that would cause the polyfuse to fail even before the one on the RPi. I'd rather have to remove the SMD polyfuse and replace it more often than replacing the RPi. There's no reason for more than a little over 5V to go to the RPi - so I can understand the 6V model I asked about before being a bit close for comfort in terms of damaging the polyfuse - but 12V - no reason to be near that and if the polyfuse fries - so be it.