Thermal Camera vs Milliohm Meter for short finding?

[Rooster Cogburn]

I'd rather only invest in one of them for now, which one would you recommend for short finding in repair jobs? Voltage injection + thermal camera or finding the short with a milliohm meter? Can you also recommend the cheapest device that you'd consider worthwhile for the task? On AliExpress it seems you can get an Ok looking thermal imager for ~150EUR and a milliohm meter for ~100EUR.

[RoGeorge]

A thermal camera is more useful, because a defect is not always a solid short to be detected, can be a component not that shorted but only heating more than usual.

Then, a "shorty" detector is easy to improvise, there are various examples online if you search the terms.  They can be easily built in a weekend at most, while a thermal camera is not something one can DIY.

[MadTux]

A couple of Amps from PSU and about any 6 1/2 digit DVM does the job, as m/µohm-meter.

Inject voltage limited current on short and measure voltage drop, same as 4wire Ohm measurement, but with much more current, i.e. more voltage drop and more precision.

Thermal cam gives you the area with most resistance, that might or might not be the shorted part.

[kripton2035]

for finding shorts, nothing is better than the "shorty-with-display" ...
and it's cheap to make yourself too.
http://kripton2035.free.fr/Projects/shorty-display.html

[Rooster Cogburn]

What exactly is this 'shorty' device? Is it just a milliohm meter?

I don't have a 6 1/2 digit DMM and I think buying one would be more expensive than the other two devices.

Can you recommend a cheap thermal imager that is still useful for repair tasks?

[RoGeorge]

What exactly is this 'shorty' device? Is it just a milliohm meter?

Kind of, but with an audio indicator, faster and easier to use than looking at a display and reading numbers.
https://hackaday.io/project/3635-shorty-short-circuit-finder

[Gyro]

Yes, a shorty is effectively just a milliohm meter.

Build yourself a simple milliohmmeter If accuracy isn't important then just make a current source with an LM317 and a couple of clip leads, or use the bench PSU curent limit. The most basic 3 1/2 digit DMMs have at least a 200mV range. With a current source set at 1A, the 200mV range will read up to 200mOhms with a sensitivity (after the decimal point) of 100uOhms. If you want higher sensitivity then build a simple x10 or x100 Opamp stage. The input impedance is going to low, so use a bipolar opamp rather than CMOS. Pick one with offset null pins so that you can trim it for a 0 reading.

The important thing is Kelvin sensing (not sharing the Current and Voltage points). Clip the current leads across the the board supply (or wherever you have the short) and then probe around the points on those nets until you get the lowest mV reading.

You can build something like that for <$5 and save your money for a Thermal Camera - which might actually be a less sensitive method unless you crank the current up.


P.S. You don't need a 6 1/2 digit meter, a 3 1/2 or 4 1/2 meter with a 20mV range would be just as good for this.... The Aneg 8009 comes to mind, it's cheap, has a 10mV range and is supposed to have a 1uV (1uOhm @1A) resolution, although I think it has a dead zone below 5uV.

[Rooster Cogburn]

Hm, seems like people here are also divided between thermal imaging and resistance based methods :/

I have a Fluke 17B+, which is a 3 1/2 digit meter and kinda useless for anything <1Ohm. I have a Peak ESR meter that goes down to 0.01Ohm but is also limited by being 2-wire.

The shorty seems like a really neat device, but I'm not really up for a project like this. It involves an Arduino and I'd have to get a case for it etc., I'd rather just buy some kind of meter.


These Vici VC480C+ meters seem neat:


Specs: https://ae01.alicdn.com/kf/S591a11dab36649c0a22daf906bf89603w.jpg


There's also the YR2050:




The probes are kinda useless with both of them, not sure how cheap/available 4-wire sharp-tipped probes are. Here's a review of both devices from Learn Electronics Repair:



(Haven't watched it yet!) Edit: Just watched it. The Vici seems like a decent choice, too bad it's so bulky and the probes are also bulky :/


As far as thermal imagers the UNI-T ones seem good, but are somewhat expensive. There's the knock-off looking Noyafa NF-521 for ~150EUR:



The cheaper sub-100EUR options all look a bit useless.

[kripton2035]

what about this one : https://www.aliexpress.com/item/1005005441679117.html
or this one : https://www.aliexpress.com/item/1005003219839921.html

[kripton2035]

I would still make my own set of probes, reusing a multimeter set of probes and adding 4-wire connection.
the provided kelvin probes are not ideal for short-circuit searching.

[kripton2035]

I bought these some times ago to make my own 4wires probes
https://www.ebay.com/itm/224967965835

[Rooster Cogburn]

Those cheaper meters seem to be missing a zero/calibration function? Guess they would still be usable for short finding, we're only interested in the relative values...

Seems like making my own probes wouldn't be too hard, but I don't really know much about that, like how much error would be introduced by having the current source/voltage sensing wires joined earlier etc. Can't you just buy these probes? A quick search on AliExpress didn't give any results :/

[kripton2035]

it was quite easy to make them: just solder the wire at the end of the metal part of the probe.
I used a shielded cable, and connected the shield to the ground of the meter.

[mzzj]

I'd rather only invest in one of them for now, which one would you recommend for short finding in repair jobs? Voltage injection + thermal camera or finding the short with a milliohm meter? Can you also recommend the cheapest device that you'd consider worthwhile for the task? On AliExpress it seems you can get an Ok looking thermal imager for ~150EUR and a milliohm meter for ~100EUR.

Thermal camera is way more usefull for repair jobs than milliohm meter. Like 100 times better in most cases.
If I would have to spend 20 eur for milliohm meter or 2000 euros for thermal camera for repair purposes I'd pick the thermal camera.

Ideally I'd like to have adjustable focus and manual temperature scale for pcb repair camera but with 200EUR budget you have to probably skip on both.
(Focus issue can be fixed with ZnSe lens from aliexpress.)

[Rooster Cogburn]

it was quite easy to make them: just solder the wire at the end of the metal part of the probe.
I used a shielded cable, and connected the shield to the ground of the meter.

Hm, I can't for the life of me find sharp-tipped four wire probes or those 'DIY' ones on AliExpress. Searching for Four-wire / Kelvin probes yields nothing but those useless clamps and I don't know what the ones you linked on eBay would be called except 'DIY' and that also yields no results :/

Thermal camera is way more usefull for repair jobs than milliohm meter. Like 100 times better in most cases.
If I would have to spend 20 eur for milliohm meter or 2000 euros for thermal camera for repair purposes I'd pick the thermal camera.

Could you explain why? If you have a shorted component on a PCB, why is a thermal camera 100x better than a milliohm meter?

[delvo]

You inject voltage and usually find the problem in seconds. Also in cases where I dont think it will be easy to find it with a miliohm meter.

For example I had a WD15 dock with a shorted cap. One of the ones circled in the picture (not my picture, didnt take one at the time) is shorted. Can a miliohm meter find which one it is? They are all in parallel. Maybe yes but they are so close together I dont think its going to be very clear which one is shorted. I injected a little voltage and the right one just lights up.

[kripton2035]

One of the ones circled in the picture (not my picture, didnt take one at the time) is shorted. Can a miliohm meter find which one it is? They are all in parallel. Maybe yes but they are so close together I dont think its going to be very clear which one is shorted.

yes, you need to have a stable milliohm value and you can detect which one it is
see example here :

[Rooster Cogburn]

One of the ones circled in the picture (not my picture, didnt take one at the time) is shorted. Can a miliohm meter find which one it is? They are all in parallel. Maybe yes but they are so close together I dont think its going to be very clear which one is shorted.

yes, you need to have a stable milliohm value and you can detect which one it is
see example here :

Considering that those milliohm meters use a ~100mA current, would it be only safe to use it like in the video, directly across components that are either shorted or parallel to a short? I'm just thinking simply placing one probe on ground and then poking around the circuit would have quite some destructive potential with that kind of current.

Any idea what I need to search for on AliExpress to get probes like those that allow me to connect two wires to the tip?

[mzzj]

Could you explain why? If you have a shorted component on a PCB, why is a thermal camera 100x better than a milliohm meter?

With milliohm meter you have to trace and check lots of components on the pcb. On multilayer board you can't even trace suspicious components but you might have to blindly measure bit of everywhere. 
Plus typical component shorts are not super-low ohmic in value: Looking for 0.5 ohm short on PCB means that you are trying to find difference between 0.501 ohms and 0.500 ohms.
Having 10 parallel MLCC's next to each other and  you might have real difficulty trying to fiqure out the shorted one with milliohm meter.
With thermal camera all it takes is one look and 99% of the cases the shorted component shines like a beacon even if there is 500 components on the board.

Milliohm meter has other uses (namely measuring very small resistances) but for electronic repair it's not high on priority list.
Current limited power supply + cheap DMM does the same as milliohm meter for repair use.

[Rooster Cogburn]

Ok, gotcha.

Just trying to find the most economic solution that would help me in these situations. I could get that VICI meter for ~70EUR shipped but would need to figure out the probe situation, who knows if I can get some decent probes or make them myself. An actually thermal camera would be considerably more expensive, at least 150EUR, probably more. And I'd need to upgrade my bench PSU, too. Got a really crappy once. Has current limit but the thing is really janky in terms of adjustment etc.

[kripton2035]

Considering that those milliohm meters use a ~100mA current, would it be only safe to use it like in the video, directly across components that are either shorted or parallel to a short? I'm just thinking simply placing one probe on ground and then poking around the circuit would have quite some destructive potential with that kind of current.

the shorty-with-display illustrated here sends around 35mA of current on the probes, but at a few millivolts only.
I use it often and never destroyed a device under test with it.

[Rooster Cogburn]

Considering that those milliohm meters use a ~100mA current, would it be only safe to use it like in the video, directly across components that are either shorted or parallel to a short? I'm just thinking simply placing one probe on ground and then poking around the circuit would have quite some destructive potential with that kind of current.

the shorty-with-display illustrated here sends around 35mA of current on the probes, but at a few millivolts only.
I use it often and never destroyed a device under test with it.

Seems like the VICI is a bit more aggressive then:



That seems enough to blow up an LED? ;-)

How does the milivolts thing work? I would've expected these are constant current sources and hence the voltage is a function of the resistance encountered?

Also could you tell me what those 'DIY' multimeter probes are called so I can order them from AliExpress and make my own Kelvin ones?

[Rooster Cogburn]

I searched for like an hour, you can't buy actual 4W/Kelvin probes or any of those 'DIY' probes anywhere on AliExpress. Makes those meters kinda useless to me as I'll not be able to procure a suitable test lead.

[aeg]

Hm, I can't for the life of me find sharp-tipped four wire probes or those 'DIY' ones on AliExpress. Searching for Four-wire / Kelvin probes yields nothing but those useless clamps and I don't know what the ones you linked on eBay would be called except 'DIY' and that also yields no results :/

Here you go: https://www.aliexpress.com/i/2251832085353684.html

But I think you'd be better off getting them from the known good eBay seller.

[kripton2035]

strange that aliexpress is quite 2x the price of ebay !