Time Current Mesurements with Sweefuse DMM-44/100AR Multimeter Fuse - Page 1
Forum section: electronics / testgear

author: Bernd_2
author_rank: Contributor
timestamp: July 06, 2025, 11:51:31 am
content: Hello,Many an owner of a Fluke multimeter has perhaps had bad luck and forgotten to reconnect the test leads after a current measurement in the mA range before a subsequent measurement in the A range.And then the expensive Bussmann DMM-B-44/100 has tripped and here in Germany at least 11 euros are gone.You might have the idea of saving money and accepting one of the alternative offers on the well-known sales platforms. But is that really a good idea? For example, risking a Fluke 289 costing around 1000 euros to save 7-8 euros.As we will see below, clearly not. The current-trip time measurements I took with the Sweefuse suggest that the input circuit of the DMM will be damaged or even destroyed in the event of the above-mentioned incorrect operation.First a few pictures of the Sweefuse compared to the Bussmann fuse that was originally supplied with the Fluke 289 DMM.The cover of the Bussmann is made of approx. 1 mm thick fiber fabric, that of the Sweefuse of approx. 2 mm thick ceramic. Both are filled with sand, but while the sand in the Bussmann has a uniform grain size, the sand in the Sweefuse is unevenly finer-grained and sometimes powdery.In the Bussmann, the very thin fusible wire is held in place by a black plastic frame that is inserted in a clip in the caps; in the Sweefuse, it is simply embedded in the sand and contacted with the inner caps.Unfortunately, nothing is known about the alloy of the fusible wires, but the composition has a decisive influence on the triggering characteristics.I will present the measurement results in the next posts.Best regardsBernd

author: Bernd_2
author_rank: Contributor
timestamp: July 06, 2025, 08:47:42 pm
content: Hello,Here are the results of the current release time measurements for the Sweefuse and for comparison for an enameled copper wire with a diameter of 0.06 mm.The setup includes a Gwinstek ASR-2100R AC/DC power supply which is driven by a function generator via the external analog input with a positive pulse with different pulse durations and amplitudes.A rotary wire resistor with 26 Ω serves as a current limiter. Together with the inductance of 70 µH, this results in a time constant of τ = 0.003 ms for the measuring circuit. Voltage (C4) and current (C3) are displayed on the MXO5 oscilloscope using a differential probe and a current clamp. In addition, the melting integral I²t is calculated and displayed using the formula ∫ pow(C3) dt.The table shows all measured values and the calculated melting integral for both the sweefuse and the enameled copper wire.In the following diagram with the Time Current Characteristic Curves for the original Bussmann fuses, the measured values for the sweefuse and the enameled copper wire are added.https://www.eaton.com/content/dam/eaton/products/electrical-circuit-protection/fuses/data-sheets/bus-ele-ds-1047-dmm-b.pdfAs can be seen, the tripping times for the Sweefuse are far above the times for the Bussmann fuse. If you look at the curves for the Sweefuse and copper wire for the tripping times and the melting integral, you could assume that an even thinner copper wire is possibly also used in the Sweefuse.It is therefore probable that the sweefuse cannot protect the multimeter from damage in the event of incorrect operation and, even worse, cannot switch off the high short-circuit currents during measurements in the Cat III and even more so in the Cat IV range. This not only puts your valuable multimeter at risk, but possibly also your health and life.In the next post, I will show the oscillograms for the measured values in the table above.Best RegardsBernd

author: Bernd_2
author_rank: Contributor
timestamp: July 10, 2025, 01:19:11 pm
content: Hello,here are the first screenshots with the current tripping time measurements.First from the Sweefuse with a current of 2 amps, at which the fuse should trip after approx. 40 ms, but actually only trips after approx. 170 ms. The strong oscillations at the end of the arcing time are also remarkable.For comparison, the measurement with 0.06 mm diameter enameled copper wire, which takes almost 400 ms to burn out at 2 amps.It is interesting to note that the arcing time here is only about half as long as with the fuse and the oscillations occur at a greater time interval.Best RegardsBernd