Just wondering how this tester works?

[bigal_scorpio]

Hi to all and happy holidays,

I was just browsing on ebay and came across a tester that checks the state of car blade fuses.

That in itself is pretty simple, just a battery an LED and a resistor to check the fuse when its out and just an LED and a resistor will test them in circuit.

But this tester states that it will test the fuse either in the fuse box OR out! Now I can't figure out how it does that. Any ideas?

Below is the link to the item. It looks pretty simple but I guess there could be a whole mess of stuff in it. It just puzzles me how it can do what it says especially considering that in the fuse box the feed and load connections are not labelled.

Al
**broken link removed**

 

[JimB]

But this tester states that it will test the fuse either in the fuse box OR out! Now I can't figure out how it does that. Any ideas?

A lot of ifs and buts in there.

Out of fuse box.
A battery a LED and a resistor, touch the probes on to the blades of the fuse closes the circuit, the LED illuminates, job done.

In the fuse box.
Some auto blade fuses have the ends accessible by a small diameter probe when they are inserted in the fuse box. Then again some models dont.
So, it looks like some you can test and some to can't.
However, this does not take into account any external circuitry connected to the fuse. It could easily be that there is a circuit path to light the LED when the fuse is open circuit.

I think that the advertising people are writing cheques with their mouths that they cannot cash with their technology.

JimB

 

[Mr RB]

...
But this tester states that it will test the fuse either in the fuse box OR out! Now I can't figure out how it does that. Any ideas?
...

This is just a guess, but I have a low-ohms tester that I use for testing traces on PCBs, even when the PCB
has parts soldered in.

Maybe they do the same thing with the fuse tester? If there is a <1ohm and <0.1v present it knows the fuse is good, regardless of what else may be connected?