Would a PTC fuse meant to protect an LED operating at 60V/350mA (max specs) need to actually be rated for 60V or would a lower voltage (like 30V) work just fine? Here it seems like current is the main issue, and not so much voltage. I understand high voltages can cause arc-overs, but in this case 60V really isn't that high. Also, fuses rated at >60V are larger compared to small PTC fuses with voltage ratings of only 30V.
Any ideas?
Thanks!
They need to be rated for the correct voltage. The reason is that the when the fuse breaks, their is a space created which stops the current flow. If the space is too small because the voltage is to high it is possible that electricity arcs over the fuse and continues to flow despite the over current condition. The higher voltage in combination with the current also means that more power (watts) are traveling through the fuse. That creates heat, which a lower rated fuse might not be able to deal with from a structural standpoint.
Thanks, I understand there could be arcs, but for only 60V (max) would that be an issue? Just curious.
androidfanboy:
Would a PTC fuse meant to protect an LED operating at 60V/350mA (max specs) need to actually be rated for 60V or would a lower voltage (like 30V) work just fine? snip
Maybe not.
A PTC fuse operates by warming up, the resistance increases to 'break the circuit'. When it cools down the resistance drops back to a low value and the fuse has 'reset'.
At some point in the middle of the fuse 'tripping' it is just like a resistor, the current depends on the voltage across it. The device is designed for a voltage range and tripping current so the right sort of temperature is reached to 'break the circuit'. Too high a voltage may damage the PTC during this transition.
Yours,
TonyWilk
OK thanks! I guess it's best to just use the right voltage rating and not try to cut corners.