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Idea need how to measure "high" DC current with dmm
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Chriss:
Hi!
I have a problem some time when I repair electronics around vehicle and I thinking to make a simple device to measure "high" current with my average dam.
Here is an example what is happening and why I need this:

Let's say I have problem in a circuit where a 25A fuse is fitted.
I found the fuse is blown but don't see any short but when I replace the fuse the circuit is fine some time ( hours maybe a day...) and then the fuse blows again.

I'm not sure is the fuse maybe the problem or something other in the circuit. Probably something in the circuit.
And now, I wish to measure the current on that 25A fuse with my ordinary dmm which can handle max 10A.

What would be the best solution for me but if it is possible a DIY project.

Thanks for any idea.
My best regards.
ejeffrey:
By far the best way to do this is with a clamp meter.  Some clamp meters are AC only, others can do DC as well.  You want the latter.

If you want a "DIY" project, the simplest way is an ammeter shunt that can handle >25 amps and won't unnecessarily burden your circuit.  Then you just measure with a DMM in millivolt mode.  For instance a resistance of 1 milliohm will give you a voltage of 25 mV and will dissipate about 0.5 watt.  You won't have tremendous resolution on most meters but it will be enough to see if you are close to the fuse rating.

For a really rough reading, measure across the fuse itself.  The resistance of the fuse is non-linear (rising with temperature), but the fuse datasheet should have hot and cold resistance or maximum voltage drop at rated current.  This should give you a good idea of whether you are close to the rating.
m3vuv:
what i do is use a 55watt headlamp bulb in place of the fuse,when the circuit is in the fault condition it just lights the bulb,when its lit you can then wiggle wireing looms to look for chafes etc and unplug things to see if the fault condition alters,its good as it saves blowing fuses and lets you see when the issue happens!,its a method ive used for 20+ years as a mechanic,its never failed me yet.
Chriss:
That stuff with the light bulb I also use when I do repairing on the bench.
What I need is exactly what ejeffrey wrote
--- Quote ---...to see if you are close to the fuse rating.
--- End quote ---

This is what for I'm searching for.
Sometime I have fuses like 30A or 45A etc. in cars and I really don't know how close the current consumption is compared to the fuse rating.

What do you think about this gadgets from Aliexpress:
https://www.aliexpress.com/item/1786770305.html?spm=a2g0o.detail.1000060.3.7c4d1a2erG1oc1&gps-id=pcDetailBottomMoreThisSeller&scm=1007.13339.146401.0&scm_id=1007.13339.146401.0&scm-url=1007.13339.146401.0&pvid=8161eced-495d-46c8-9d71-217515e2c754

Or this one:
https://www.aliexpress.com/item/4000058981609.html?spm=a2g0o.productlist.0.0.47812540F0Z7jN&algo_pvid=cbfb7e80-1f76-46ca-b28b-5df1cdc3cb39&algo_expid=cbfb7e80-1f76-46ca-b28b-5df1cdc3cb39-25&btsid=a5362224-ece3-47a7-b421-dbae43132a1c&ws_ab_test=searchweb0_0,searchweb201602_2,searchweb201603_55

Actually I could mV measure with my scope, I have one and that would be fine for me too...
m3vuv:
how about a shunt from one of the cheap led amp and voltmeters from ebay,the 50amp shunted ones should do the job,https://www.ebay.co.uk/itm/Digital-LED-100V-Voltmeter-10A-50A-100A-Ammeter-Panel-mount-volt-amp-meter/292661184098?hash=item4423f74662:m:m20lue267b7i5yJ3YWW36eA
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