Racer_Rob
Posts: 8
Joined: Mon Apr 03, 2017 8:07 am

Through hole F3 fuse equivalent

Mon Apr 03, 2017 3:17 pm

I have a Raspberry Pi 1 Model B which I'd like to power through the 5V pins using my own Pi HAT PCB and a regulated 5V supply.

I believe by not using the microUSB the only protection I'm bypassing is the F3 fuse (correct me if I'm wrong).

I want to put a through hole resettable fuse equivalent to the F3 on my PCB but I'm not clear if 1.1A is the trip current or the hold current?

Image

drgeoff
Posts: 10831
Joined: Wed Jan 25, 2012 6:39 pm

Re: Through hole F3 fuse equivalent

Mon Apr 03, 2017 4:42 pm

Hold.
Quis custodiet ipsos custodes?

Racer_Rob
Posts: 8
Joined: Mon Apr 03, 2017 8:07 am

Re: Through hole F3 fuse equivalent

Mon Apr 03, 2017 5:07 pm

drgeoff wrote:Hold.
Thanks for the reply. So something like this would be suitable:

RS 647-8522

Racer_Rob
Posts: 8
Joined: Mon Apr 03, 2017 8:07 am

Re: Through hole F3 fuse equivalent

Mon May 08, 2017 10:04 am

After some more reading (here and here), my understanding is the value printed on the fuse (0.75A) represents the hold current. It trips (i.e. is fully open) at 1.1A.

In which case a through hole equivalent would be more like 712-7480 on RS.

klricks
Posts: 7172
Joined: Sat Jan 12, 2013 3:01 am
Location: Grants Pass, OR, USA
Contact: Website

Re: Through hole F3 fuse equivalent

Mon May 08, 2017 12:10 pm

I believe the 1V1 (trip) printed on the schematic is not correct.
The part on the board is marked 750mA (hold).
Typically trip current is 2x hold so that would make 1.5A trip.
I can readily find fuses with those specs but can't find any datasheets with a part that has 750mA hold and 1V1 trip.
IIWM I would probably go with a ~1.0A hold device.....
Unless specified otherwise my response is based on the latest and fully updated RPiOS Buster w/ Desktop OS.

Racer_Rob
Posts: 8
Joined: Mon Apr 03, 2017 8:07 am

Re: Through hole F3 fuse equivalent

Mon May 08, 2017 12:50 pm

Thanks for the clarification, much appreciated :)

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