A very popular HIOKI instrument is the BT3554 battery tester. It’s a portable instrument designed primarily for maintenance purposes with voltage ranges up to 60V.
Of course the BT3554 won’t blow up when you accidentially apply 61V to it instead of the maximum 60V. In fact there are not many service cases for the BT3554 at all. However, about 9 out of 10 BT3554 that arrive in HIOKI’s service department in Frankfurt, Germany are identified to have suffered some sort of over-voltage. The majority of those cases could have been prevented simply by replacing the original fuse in the BT3554 with the exact same type of fuse once it blew – which typically happens after the BT3554 has been subjected to some sort of overvoltage.
So the easiest way to kill a BT3554 battery tester is by replacing a blown fuse with something else and then have another overvoltage situation occur. To be fair, replacing a fuse with a different type or value to the one specified would probably damage all kind of T&M instruments in an overvoltage situation and not only this specific battery tester.
The correct fuse for the BT3554 is a fast acting 630mA ceramic fuse (indicated by the “H” next to the capacity). Ceramic fuses have much higher breaking capacities than normal glass fuses. If a fuse needs replacing in the field to be able to continue with a job then it is typically more likely that there is a glass fuse flying around somewhere rather than a ceramic one (there is a spare fuse coming with every BT3554, by the way). However, replacing a ceramic fuse with a glass fuse (and even worse with any available value) makes it more likely that the instrument gets damaged when subjected to an overvoltage in the future. That might happen months later when it has been long forgotten that the glass fuse found in the van at the time was only to be used as a quick fix with the firm plan of ordering the right one once back at the base. But as you can see the required fuse in the BT3554 is nothing special but a standard ceramic fuse which is available from the same manufacturer (Littlefuse) at Farnell (SKU #1354537). Get some of them, put them in the BT3554 box and you can significantly reduce the risk of a repair case.
