So I have googled for more than an hour, trying to find the specific answer for this, and maybe Im searching all wrong, but here comes my question.

I have a USB-hub combined with one fast charging port, with ONLY power, and no data. The other day the fuse from the DC transformer (transfomer is at 5 volt, 3.5Amps) and the port failed after I connected an apperently faulty powerbank. The fuse is located right next to the USB port in the hub.

All the other, data-USB ports work just fine, even with only power from the DC transformer, but the 2.5 Amp charging port is dead.

The fuse on the board is marked with "J". But this gives me results of a 32 volt 1.25 Amp fuse... Is this the one I should go with?

I dont really get how the voltage and amperage of the SMD fuses coincides...

I would be so happy if I could get some help in findig a suitable small fuse for the job.

Best regards, Fredrik


I have a resettable PTC, 6 volts with a tripping current of 3.5A and a holding current of 2A (it seems on the documentation Ive found) on another board that I dont use, marked with K. Is this a good alternative?

  • \$\begingroup\$ How will you correct the cause of the fault? \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Dec 5 '17 at 20:15
  • \$\begingroup\$ any 1.25A fuse will work. the voltage rating determines the voltage at which the fuse will not "leak" current when it has blown. \$\endgroup\$ – jsotola Dec 5 '17 at 20:17
  • \$\begingroup\$ The faulty powerbank was a cheap one, that totally fried... The reason it became faulty was that I connected a iMax to it, wich it didnt like, then, when I tried to recharge it, it was already shorted out... Will not use this again... So the 1.25 fuse will give a total of 2.5 amps? \$\endgroup\$ – Fredrik Eliasson Dec 5 '17 at 22:57

I would suggest a thermal fuse. Powerbanks need to have a power source capable of handling its inrush starting current.

To avoid thermal problems with the supply you can choose a tiny SMT thermal fuse.

I might choose a 2A thermal resettable fuse. This means the MUST hold current = 2A MIN. and the MUST trip = 3.5A MAX. but it may trip at any current between 2A & 3.5A or lower if enclosed and higher if soldered to a heatsink. The polyfuse runs from 85'C to 120'C during protection mode.


They are cheap, (compared to shipping cost) so get a bunch in different ranges.

  • \$\begingroup\$ Thank you so much! This answered a lot. Will check into this. If I had the rep I would upvote!! \$\endgroup\$ – Fredrik Eliasson Dec 5 '17 at 23:01

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