Cheap DMM fuses?

[BillyO]

I bought these "Bassmann" 44/100 fuses shown below ($12 for 10) just to test them.  https://www.aliexpress.com/item/1005006609924328.html

I killed 4 of them - here's what I found out...

All 4 lasted over 5 minutes at 440mA

All 4 lasted over 1 minute at 1A

I tested two at 1.5A.  One lasted 9.8s, the other lasted 13.2s

I tested two at 2A.  They blew instantaneously.  Sorry, did not have scope on them, but they blew before I could start my stopwatch.

These results agree quite well with the genuine Bussmann specs.

The casing is very thick and strong ceramic.  I had to use a vise to break them.  There is no sand in them.  So, the 1000V rating for use in CAT IV or CAT III is not to be believed.

However, it seems they would do fine on the electronics bench, especially while you wait for your $15 Fluke fuse to arrive.

[Gyro]

Sadly very fake, but you knew that from the brand name.

Yes, they would be fine for low energy bench use*. The ceramic is surprisingly thick, a genuine one would be Melamine of course. Without the advertised arc quenching capability, the only issue is if it accidentally gets near a high energy circuit in future (fading memory, lack of 'round tuit', or selling the meter on).


Edit: *Without the thermal mass of the sand, they might even have a lower resistance / voltage burden than the real thing.

[BillyO]

For sure, temporary use only.  But they'd keep you going on the bench in the mean time.

The side of the box and the fuses states: "interrupting Rating: 10 kA 1000V" - I'm not buying that piece of fantasy.

[Gyro]

It would be interesting to compare their voltage burden at full current with a genuine one, as my edit above.

[BillyO]

I could try that.

[gamalot]

You can get cheaper Fluke fuses on LCSC.

https://www.lcsc.com/product-detail/C5128888.html

[Bernd_2]

Hello,
A while back, I took some measurements of 440 mA multimeter fuses called Sweefuse, which look very similar to the "Bassman" fuses shown here.

https://www.eevblog.com/forum/testgear/time-current-mesurements-with-sweefuse-dmm-44100ar-multimeter-fuse/msg5968777/#msg5968777

Unlike Bassman fuses, however, Sweefuse fuses are filled with sand; however, this sand is much more unevenly distributed and finer-grained than the sand used in original Bassman fuses.

In the meantime, I’ve purchased a number of “Bussman” fuses from a Chinese supplier, and as soon as I’m back on my feet, I’ll take the necessary measurements of the tripping characteristics using these fuses.

I’m curious to see whether the tripping time-current curve will resemble that of the original Bussman fuses or that of the Sweefuse.

Best Regards,
Bernd

[BillyO]

It would be interesting to compare their voltage burden at full current with a genuine one, as my edit above.

You're prediction was correct.  The genuine Bussmann fuse = 343.6mV, the fake Bassmann fuse = 147.1mV.

Quite a difference.

[Doctorandus_P]

However, it seems they would do fine on the electronics bench, especially while you wait for your $15 Fluke fuse to arrive.

I agree. It's not CAT IV, but plenty good for on your electronics workbench.

It is good to test such fuses. I've read stories of fake fuses that that did not even blow with a 10x overload.

[Gyro]

It would be interesting to compare their voltage burden at full current with a genuine one, as my edit above.

You're prediction was correct.  The genuine Bussmann fuse = 343.6mV, the fake Bassmann fuse = 147.1mV.

Quite a difference.

Thanks for doing the experiment Bill. It seemed logical but I've never been in a position to test it (no fakes). As you say, quite a difference.

[tooki]

However, it seems they would do fine on the electronics bench, especially while you wait for your $15 Fluke fuse to arrive.

I agree. It's not CAT IV, but plenty good for on your electronics workbench.

However, for the benefit of whoever else may end up with that multimeter (be it after your death, or if it’s stolen by burglars and sold at a pawn shop, etc), if anything other than the correct genuine fuses are used, the meter should be marked accordingly to indicate it does not meet its CAT ratings.

[BillyO]

... if anything other than the correct genuine fuses are used, the meter should be marked accordingly to indicate it does not meet its CAT ratings.

I think that is reasonable.   

[Fungus]

However, for the benefit of whoever else may end up with that multimeter (be it after your death, or if it’s stolen by burglars and sold at a pawn shop, etc),

Anybody who buys a meter from a pawn shop for use in high-energy environments deserves their award.

(Me? I'd expect no less than tin foil around the fuses in a pawn shop meter)

[tooki]

However, for the benefit of whoever else may end up with that multimeter (be it after your death, or if it’s stolen by burglars and sold at a pawn shop, etc),

Anybody who buys a meter from a pawn shop for use in high-energy environments deserves their award.

(Me? I'd expect no less than tin foil around the fuses in a pawn shop meter)

What does one gain by wishing harm on others??

[Salient666]

I bought a few of those fuses too but I'm eventually not going to use them.
See attached characteristic of a real 500mA SIBA fuse and one of these fake Bussmann (Bassmann) 440mA fuse.

[BillyO]

What were the test conditions?  (Current?  Did you use a current probe?)

Also, on the SIBA screen shot there is a big spike 50ms after the fuse blew.  Do you know what caused that?

[Salient666]

What were the test conditions?  (Current?  Did you use a current probe?)

Also, on the SIBA screen shot there is a big spike 50ms after the fuse blew.  Do you know what caused that?

I measured voltage over a 4 Ohm resistor. Had the test current set at approx. 1.5 3.5 Amp.
The thing is that instead of approx. 30ms this so called fast-acting Bassmann fuse took 150ms, thats 120ms extra your meter is given the chance to act as a fuse itself, not something you would want.
I have no idea what caused that weird spike btw.

[BillyO]

I measured voltage over a 4 Ohm resistor. Had the test current set at approx. 1.5 3.5 Amp.

Something is not adding up.  You say you used 4 ohms, but your scope shows nearly 4V.  According to ohms law that means just a tad over 1A was flowing.

At 3.5 Amps across 4 Ohms we should see about 14V.

[Salient666]

I guess I don't remember correctly the measurement variables then.
But the conclusion stays the same: I would never trust these Chinese knock-off fuses.

[J-R]

I posted before that I've been buying from this seller for a while and have not had any issues with receiving genuine items: https://www.ebay.com/itm/325240662386

For not too much money I now have a lifetime supply of fuses that I don't have to be concerned about.

[BillyO]

I guess I don't remember correctly the measurement variables then.
But the conclusion stays the same: I would never trust these Chinese knock-off fuses.

I have to disagree.  The "conclusion" is inconclusive.

Have you seen Dave's series on fuses?  (video 1377,  1677, ?).

Both your results would fit well within the range he found for a single fuse spec.

Even EATON do not provide an expected error specification for their time-current curves on their DMM-B fuses.  The reason for that is because it will be all over the map.

Fuses are not very predictable.

[BillyO]

I posted before that I've been buying from this seller for a while and have not had any issues with receiving genuine items: https://www.ebay.com/itm/325240662386

For not too much money I now have a lifetime supply of fuses that I don't have to be concerned about.

Good prices.  They have the COOPER logo on them.  Possibly some liquidated NOS.   Maybe time to stock up.

Anyway, I just got these to play around with.  Cheap fun.

[Doctorandus_P]

The thing is that instead of approx. 30ms this so called fast-acting Bassmann fuse took 150ms, thats 120ms extra your meter is given the chance to act as a fuse itself, not something you would want.

It really does not matter whether the fuse lows in 20 ms or 150 ms.

[Zoli]

The thing is that instead of approx. 30ms this so called fast-acting Bassmann fuse took 150ms, thats 120ms extra your meter is given the chance to act as a fuse itself, not something you would want.

It really does not matter whether the fuse lows in 20 ms or 150 ms.

Are you sure(IXTH60N20L2)?

[Doctorandus_P]

It really does not matter whether the fuse lows in 20 ms or 150 ms.
Are you sure(IXTH60N20L2)?

Why do you think a graph of a mosfet is relevant for a fuse in a DMM?