fuse testing

[John Frum]

I was idly thinking it might be useful to make a test bed for fuses/breakers
    Just in case anyone is interested
    Here is an implete list of the pieces

    stimulus
        power source
        big cables
        big bus bars with posts
        a fuse to protect the test bed
        a disconnnect switch
        various fuse holders
    instrumentation
        thermal camera
        a regular video camera
        stop watch and/or countdown clock

    all the other circuit components have to tougher than the fuse under test(fut)
    
    q: how to connect the fuse?
    q: how to measure the current?
    
    *video camera is not absolutely necessary, could just use a data logger.
    *really should not let these tests run unattended.
    
    q: is fire protection required?
    q: is this all something that can be automated on one of the tiny embedded platforms?

    *fuse testing does not scale so well
    q: whats the biggest fuse that we need to test?
    
    Feel free to spec components and answer questions.
    Also would be cool if you asked questions.

 

[BiduleOhm]

q: how to connect the fuse?

With wires? ? more seriously I'm not sure I understand the question.

q: how to measure the current?

Shunt (a very big one, the 1 kA one from Victron or Deltec would be nice) + digital storage oscilloscope

q: is fire protection required?

It definitely is, a fuse can explode (a properly designed one shouldn't unless you go over its specs, but you never know...) sending molten metal and case shrapnels so fire + blast protection is required.

q: is this all something that can be automated on one of the tiny embedded platforms?

I guess it can but I don't think it's worth it since a lot of the process can't be automated anyway. And you're not a fuse test facility so you'll not test hundred of fuses all day long.

q: whats the biggest fuse that we need to test?

One of those? ?

All the usual fuses (see pages 33-34 of this PDF) from 50 A to 500 A would be nice.

Also would be cool if you asked questions.

How do you limit the test current? because sending 20 kA in a fuse rated to break 1 kA max will definitely result in the fuse exploding.

 

[John Frum]

With wires? ? more seriously I'm not sure I understand the question.

I was thinking some kind of heavy duty duty clamp like highly conductive wise grips

Shunt (a very big one, the 1 kA one from Victron or Deltec would be nice) + digital storage oscilloscope

Sounds pricey

It definitely is, a fuse can explode (a properly designed one shouldn't unless you go over its specs, but you never know...) sending molten metal and case shrapnels so fire + blast protection is required.

Is a welding booth with a plexiglas observation port too much?

One of those? ?

How do you limit the test current? because sending 20 kA in a fuse rated to break 1 kA max will definitely result in the fuse exploding.

That is a good question.
I don't know the answer but I hope it hums like this

 

[BiduleOhm]

I was thinking some kind of heavy duty duty clamp like highly conductive wise grips

I don't think it's a good idea because you'll have a high contact resistance. I think just two cables with terminal lugs on the end would be simpler, cheaper and better.

Sounds pricey

It can be for the DSO, but you can always use a cheap (but decent) USB oscilloscope, it should be enough.

Maybe the 500 A shunt is resilient enough, I'm not sure, the best would be to ask the manufacturer.

Also, it all depends on what you want to characterize and with what accuracy. If you just want to know if the fuse blows then no need for all of this ?

Is a welding booth with a plexiglas observation port too much?

If it were me (and it'll be in a few months as I'll need to do at least one short circuit test...) I would not stay in the same room as the fuse and just use a camera or a mirror to observe. It simpler and safer. Also there's some danger with the UVs from the arc, using the camera has the advantage to be totally safe for this, but not the mirror.

I don't know the answer but I hope it hums like this

Unfortunately it's DC so no hum... but +1 for the BTTF reference

 

[MattiFin]

Here is your shunt:

30 kA rated current so should handle 1 million amps briefly.
Next we need few large batteries...

 

[Hedges]

Here is your shunt:


30 kA rated current so should handle 1 million amps briefly.
Next we need few large batteries...

Looks good to me!

My breaker tester is for AC only, uses a 100A current transformer.
For higher currents, that goes on the primary side of a 1:3 9000VA current transformer, and I have 3 of those.
I regulated AC current with heating elements (presently a bunch of oil-filled radiators.)
Reasonable capabilities are 100A x 3:1 multiple x 3 in parallel for 900A @ 40Vrms (zero volts while breaker under test is closed).
That will draw 300A at 120V from my 125A circuit, good for a couple minutes.

I had tried my 230A "buzz box" arc welder first, but it has so much leakage inductance (by design) that it drooped the voltage seen by the heaters and wouldn't deliver the current desired. Therefore the low-leakage toroid transformers I now use.

 

[Roswell Bob]

Why would you want to test a fuse? Just look at the fuse curves. Crappy off-shore breakers I can see testing.

 

[Hedges]

Why would you want to test a fuse? Just look at the fuse curves. Crappy off-shore breakers I can see testing.

Because a number of fuses sold in the US were faulty?

I did, for that reason:

Testing automotive fuses

After watching a video (sorry can’t find it now) showing resistance testing of cheap fuses and name-brand ones, I decided I’d better test the ones I’ve put in our cars. In the video, it was said that previously Harbor Freight sold fuses, but later recalled them and didn’t carry anymore. Fuses...

diysolarforum.com

The various sets I tested were good. But they did have the same element in two different value fuses (close enough for consumer work.)

The breaker tester I've also set up is for Square-D QO breakers. Only up to 100A so far, which lets me test fast-trip of 20A breakers an slow trip of 70A. I plan to extend its capabilities to 1000A when I get around to it.

"Trust. But Verify"

I've been seeing questionable results with some of these breakers in use. Like a 100A that tripped repeatedly below 70A and eventually wouldn't reset for a long time. Some 70A that had high and variable resistance (imbalanced current through parallel inverter relays about 3:1)

 

[Roswell Bob]

Ok, thanks for the response. Good intel. I'm aware of the crappy breakers. Wasn't aware of the crappy fuses. I would stay with the brand names that I've trusted over the years for fuses. Gould/Shawmut, Carbone/Ferraz were my favorites.