Measuring fuse voltage to determine circuit current

[GeoffSmith]

Very useful diagnostic tool on this website:

https://www.powerprobe.com/fuse-voltage-drop-charts/

[lotusflasherman]

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

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 ..

[GeoffSmith]

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

[Simon_P]

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.

[Rambo]

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

Well, i never knew that. You learn something new every day

[lotusflasherman]

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..

Top one has visual 'fuse blown' , lower one needs electrical test on contacts - or withdraw for visual.

[lotusflasherman]

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

[johanvanboven]

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.

[peteoddcar]

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.
https://rover.ebay.com/rover/0/0/0?mpre ... 0439841044

[Tuga2112]

i came across this a few years ago when hunting a parasitic drain (cant remember which car)

as far as im aware this technique has limited uses in the elan. (with exception for cars with alarm/imobiliser systems and faults in related circuitry)
it seems to be mroe common in modern cars

https://www.youtube.com/watch?v=T6rDTtxaeJ4
[youtube]https://www.youtube.com/watch?v=T6rDTtxaeJ4[/youtube]

[sideways]

I'll stick with my Avometer 8sx for this sort of thing, easy to use and you will never lose or misplace it.

[david924s]

I'll stick with my Avometer 8sx for this sort of thing, easy to use and you will never lose or misplace it.

Also handy if you need a step up to reach stuff, brilliant piece of kit if a little dated but at least you have to understand what you are trying to do and how to do it when using it not like the newer meters.