AC Transformer 230vac

[hobby41]

hi all, my problem is that whille charging a 12v 1500mah battery, the charger just got hot started to smell and shut down. I have opend it up and tested the pcb which had no problems, but i didnot get any readout on the secondary side of the transformer, my mate has since taken the outer heat tape off and found a small square black device on the secondary, so he bypassed this with a peace of wire and it all works, my question is what do i replace it with for safty, as it has no markings on. thanks....

[vtech]

You can either use a regular fuse or a micro thermal cut-off rated at about 130 degrees celsius.