I teach electrochemistry to students in chemistry. During each class, there is at least one student that manages to burn the 200mA fuse of our $15 multimeters.

It's quite annoying. I am thinking of replacing the wire fuses by electronic ones. The kind that resets itself automatically after a short time.

I know I won't find any electronic fuse that will fit the multimeter, but I am prepared to solder & add wires to fit everything in place.

However, I don't know how to select the fuse. The original piece is rated 500 V ; 200 mA.

Is there anything I need to consider prior to replacing 40+ multimeter fises with electronic ones ? Do you have any part number / manufacturer to recommend ?

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    \$\begingroup\$ That is a very low cost for a multimeter. Normally multimeters have mechanically large safety fuses in them. At least the ones I have seen. I assume they provide safety benefits far more extensive than could be provided by an electronic fuse. SO, I suggest you put your electronic fuse in series with the internal one. The electronic fuse should operate fast enough to prevent the internal fuse from blowing. But if there is some major fault the electronic fuse can't handle, the internal fuse will still provide protection. \$\endgroup\$ – mkeith Nov 29 '15 at 19:22
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    \$\begingroup\$ Buy them in bulk, 10c per class shouldn't worry anyone at all. You should be more worried about the safety hazard that is a $15 multimeter. \$\endgroup\$ – PlasmaHH Nov 29 '15 at 20:18
  • \$\begingroup\$ Thank you for your replies. We do measure currents up to 20 mA and DC voltages up to 3V (300 mV typically). Accidents occur when students shift from current measurement to voltage measurement without actually moving the cables from "A" to "V/Ω" and short-circuit the generator. My "issue" is not the price of the fuses, but the time I spend replacing all those fuses (I need to unscrew the long screws of the plastic box of the multimeter"). It's quite annoying actually. They are the very "common" sort of multimeters. And more like $25, I guess. My currency is €. Any fuse recommendation? \$\endgroup\$ – PeterG Nov 30 '15 at 0:06

If they are only working with voltages up to ~ 3 V, you could replace the fuse with a resistor. Say you want to limit current to 200 mA @ 3 V -- that gives about 15 ohm resistance. At the 20 mA, that will increase the DMM burden by about 0.3 V which may or may not be a problem.

3 V & 200 mA == 0.6 W -- use a 1 W resistor if you can find it.

Note that this won't protect if the meter is plugged into the mains (110 V or 220 VAC), and in fact would be dangerous.

Alternatively you could use a polyfuse polyfuse-- these are low R when cold and increase to higher values when hot -- however neither are these robust to protect against plugging into the mains.


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