Ebay fuse testing

Addy

100 W
Joined
Aug 11, 2017
Messages
289
Location
BC, Canada
Hello. I purchased some cheap, compact glass fuses on ebay like these:
https://www.ebay.ca/itm/200Pcs-Glas...st-Blows-Fuse-3x10mm-250V-5A-BS1/263232945558

I thought they might be good for fusing individual cells when building battery packs. Before using them for that, I've done some tests on them to get an idea of how they perform.

The first thing I wanted to know was how much the internal resistance of these fuses is. To measure that, I apply a DC current through a fuse and measure the voltage drop across the fuse:
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Here I'm using a Turnigy Reaktor in foam-cutting mode as the current source. Using this I can apply up to 10A. The current is measured with one multimeter and another multimeter measures the voltage across the fuse.

When measuring with 1A of current through the fuses, The internal resistance was between 30-35 milliohms, which is similar to the internal resistance of some 18650 cells. Using a fuse like this for each cell would then be doubling the resistance in your battery pack.

At higher currents the internal resistance gets higher as the fuse heats up:
2A: 74 milliohm
3A: 120 milliohm
4A: 185 milliohm
5A: 340 milliohm

The fuses start to get really hot at this point!

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With the first fuse I was testing, it was getting extremely hot at 5A but it didn't open the circuit after 6 minutes. When I increased the current to 6A it was getting ridiculously hot and it even started melting the glass, so I stopped testing that fuse.

The second fuse I tested finally broke open after 4m30s at 6A. Other fuses required around 6-7A to break. I found that by adding more alligator clips to the fuse leads (as heatsinking) it would take around 8A to break the fuse.

These tests have changed my mind about using these fuses with lithium cells. The internal resistance is too high and I would not want to be putting so much heat into or near cells.
 

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ebay/aliexpress/alibaba "deals"

https://endless-sphere.com/forums/viewtopic.php?f=1&t=87975&hilit=fire
my cheap ass shipped illegally 18650 48v 20 ah battery from K battery (alibabba) caught fire in my garage, while charging.
 
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