Measuring fuse voltage to determine circuit current

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Measuring fuse voltage to determine circuit current

Postby GeoffSmith » Thu 29.03.2018, 20:40

Very useful diagnostic tool on this website:

https://www.powerprobe.com/fuse-voltage-drop-charts/
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Re: Measuring fuse voltage to determine circuit current

Postby lotusflasherman » Thu 29.03.2018, 22:22

You've got me on that one Geoff ... :smt017

not sure how you get on the fuse blades to read in millivolts and if a 30 amp maxi fuse is 0.00195 Ω, according to the chart, contact resistance of the probes is likely to be significant..

I just pull the fuse out and use the milliamp scale on my multimeter.... seems easier .. :-D
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Re: Measuring fuse voltage to determine circuit current

Postby GeoffSmith » Thu 29.03.2018, 23:12

No need to get to the blades Phil. Just plug your voltmeter into the convenient connections on the back of the plug.

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Re: Measuring fuse voltage to determine circuit current

Postby Simon_P » Fri 30.03.2018, 00:24

Useful - does it work in practice Geoff?

Phil, I presume it is simple V=I.R so using voltage drop across the fuse of known resistance to give Amps.

Probably most useful for measuring loads on the larger fuses where putting an ammeter in the circuit is less practical.
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Re: Measuring fuse voltage to determine circuit current

Postby Rambo » Fri 30.03.2018, 09:51

GeoffSmith wrote:No need to get to the blades Phil. Just plug your voltmeter into the convenient connections on the back of the plug.

Image


Well, i never knew that. You learn something new every day ;-)
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Re: Measuring fuse voltage to determine circuit current

Postby lotusflasherman » Fri 30.03.2018, 14:46

Song from Porgy and Bess -" It ain't necessarily so" ... sums it up.

30a.jpg


I know what I'd find fitted when if I went to use that method.. :lol:

Top one has visual 'fuse blown' , lower one needs electrical test on contacts - or withdraw for visual.
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Re: Measuring fuse voltage to determine circuit current

Postby lotusflasherman » Fri 30.03.2018, 15:25

Simon_P wrote:Useful - does it work in practice Geoff?

Phil, I presume it is simple V=I.R so using voltage drop across the fuse of known resistance to give Amps.

Probably most useful for measuring loads on the larger fuses where putting an ammeter in the circuit is less practical.


Yes, it's Herr Ohm's clever idea... fuse element has a certain resistance and the heating effect is square of the current x R so 10 amps give 100R watts, 11 amps gives 121R watts.
Not too tricky to make a fuse that carries 10 amps but melts at 11 amps by changing it's ability to get the heat away.

Even the cheap multi-meter that lives in my little toolbag in the boot reads up to 10A on a dedicated terminal, most of them do...
Anything more and I use a cheap clampmeter that goes round the wire, that will read to 600A.

clampmeter.jpg
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Re: Measuring fuse voltage to determine circuit current

Postby johanvanboven » Fri 30.03.2018, 15:34

If you're not so good in calculating, buy this: https://store.snapon.com/Specialty-Circ ... 69765.aspx

Choose the type of fuse and the tool does the rest. Very easy to quickly detect leakage current.
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Re: Measuring fuse voltage to determine circuit current

Postby peteoddcar » Thu 26.04.2018, 20:41

I have been using one of these for a while it works ok, to determine the level of current, before connection of Fluke multimeter. The current measurement seems to correlate with the Fluke.
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