Testing fuses with bench power supply - CV vs CC

[badrequest400]

In the video linked below, Louis Rossmann tests some fuses by setting bench power supplies to the rated voltage of the fuse and limits the current using high power resistors. My question is why not use the bench power supply in constant current mode and connect the power supply directly across the fuse? The voltage across the fuse at any given current will be the same and it would be quicker and easier to set/start/increase the current than messing about with the resistors?

[Kim Christensen]

I can see using resistors if you had a crappy power supply that couldn't handle higher currents at a low output voltage. (Max voltage across pass transistor at max current)
But with any decent power supply, using it in CC mode is the way to go.

I didn't watch the video, but it could be that he's testing to see the max voltage and current it can safely break without a plasma arc forming inside the fuse and thus current continuing to flow. Fuses have both a max voltage and current rating.

[Doctorandus_P]

I did see a part of the video and it's quite silly. I quite agree with Louis's rants about the fruit brand, but this does not make much sense. Using the built in current limit and dialing up the current would be a better method of testing to get more accurate results. Ramping up the current with a predictable rate (or example 2s for an Amp) would make the measurement more accurate and repeatable / predictable.

Louis is a pretty smart guy overall. My best guess is that he is dumbing it down on purpose so people who are not familiar with lab power supplies and their current limiting can also understand the test.

The voltage rating of fuses does have an effect. When a fuse blows and turns from a (nearly) short circuit to an open circuit, a high voltage may suddenly develop and there is a potential for a continuous arc though a plasma. But this is not really an issue for these very low voltages (but it is more of an concern for DC than for AC).

Also, the resistors he is using are supposed to be mounted on a heat sink. They are quite delicate and easily damaged by overheating. The ceramic type of resistors are much more robust, but because of their higher temperatures, they are also less accurate (which is not important here).

[edpalmer42]

I haven't watched Louis' video, but I have used Kerry Wong's technique for fuse testing.  My results followed the same pattern as Kerry's.

[Jwillis]

I'm not surprised by the results that Louis Rossmann found in his experiment. And I have absolutely no intention of attempting to discredit such findings. nor the knowledge of Louis Rossmann.
Private tests were done on Bussmann ATC (made in the U.S.A)and bulk Dynaline fuses (imported from China) specifically sold in this region.
Test rig was a 0-40V 0-20A DC power supply, electronic load, and Bussmann ATC fuse panel. 2 DMMs and a precision DC current clamp to confirm readings. 5 test samples from each manufacturer confirm the findings of  Louis Rossmann.

But there is some thing that gets neglected and misunderstood in many tests done to various products privately imported from other countries.
Products produced here(North America), must comply to the regulations specified by the particular legislative bodies that oversee the manufacturing, testing and sale of such products.
All fuses manufactured in North America are subject to tests and standards set by UL, IEC, NEC, CSA, and other regulator bodies that may be applicable to the product. Automotive Fuses manufactured in North America are no different but are also subject to scrutiny from the  Automotive Standards Council.
So these Automotive fuses manufactured here would have a fusing current of 125% of rated. As an example, a 5A standard blade fuse under the UL standard should break at around 6.25A.
Tests that I did on 5A standard ATC blade fuses confirm that standard.Eaton Bussmann fuses used in the test are subject to UL standards and the Automotive Standards Council and are listed as such.
Also keep in mind that even imported fuses used at the time of automotive manufacturing must also comply to these standards and imported vehicles must have Fuses that comply to the standards set by North American safety standards, Department of Transportation and other such regulatory institutions.

But these standards do not apply to fuses sold as general purpose. The fuses that are sold at various outlets such as  Amazon, Ebay, Aliexpress, and other sources are in fact compliant to IEC standards and do not need comply to UL or ASC standards. Manufactures outside of North America, European Union, UK and Oceania (Australia New Zealand) only need to comply to the IEC standards.

Finding the IEC standards can be difficult, since the literature must be purchased from the IEC. What information that is available freely can be vague and scattered. This inability can often lead to radical conclusions about many products.
The IEC does not cover specific automotive standards other than the coupling of EV's to grid power. The standards used for low voltage, low amperage is covered under the IEC 60269-1 to 4 and IEC 60947-4-1, apply to fuses used and/or sold Outside regions regulated by the UL and  Automotive Standards Council, including similar regulations adopted/legislated  in other regions around the world. 

After some digging, these test standards can be viewed here EEP under Conventional Non-Fusing and Fusing Currents. As the table states, the fusing current can be a much as 2.1 times the nominal current rating for fuses rate below 4Amps

I will neither condemn nor defend Amazon, Aliexpress and other such vendors for selling these fuses in North America since there are no applicable regulations that govern their use for general purpose. Even bulk fuses sold here may not follow UL compliance. UL compliant standard Blade fuses can be purchased at these vendors and may even be listed as such. But this compliance costs more. If you buy cheap, you get cheap.
The purchaser must be aware that the safety regulations here do not necessarily apply to other countries and that some products that are imported and sold here need not comply to the national safety standards if the product is for private use or general purpose.

People must do their own investigations concerning the safety of the products that they buy. Trust but VERIFY. Or purchase such products from reputable vendors and/or manufacturers that must comply to the regulations applicable to the product.


As a note. The fuses that I tested did indeed follow either UL or IEC compliance. The fuses that Louis Rossmann fell way outside any compliance and that people need to be aware that such products exist.