I hate multimeters now
suicidal.banana wrote 12/06/2017 at 19:26 • 3 pointsJust because i need to vent somewhere, if somebody wants to share their multimeter pain then feel free too, if nobody replies thats fine too.
So today i was working on a little rgb led lamp project (im only a beginner so yea, no jetpacks or hoverbikes just yet) and i needed power, so after a little looking around online i noticed half the ppl making a similar project these days just cut the charging plug of a phone charger and use that, and i happen to have like 3 drawers full of old random chargers etc.
So i cut one, make a nice split with heat shrink tubes (whats with all chargers of the past years using some teeny tiny coax? wish they'd still have plain ol' usb cables) and then figure i should test it before soldering it in, i hook up the multimeter, nothing.
So i shrug, pick another charger, cut it, heat shrink, blabla, test, and its giving me random outputs between 10-16volts, while its a 5v charger
Shrug again, cut another, clean it up, test it, this one does absolutely nothing again.
This goes on for like 7 chargers until i literally lost it, stomped on the multimeter till it started beeping, and pull a oscilloscope out of a cabinet.
I pretty much already gave it away in the title, but yea, to my amazement, 'suddenly' all chargers deliver a steady 5v too the oscilloscope, and it turns out the problem this whole time was the damned multimeter...
So there, i hate multimeters now, spent like 4h going back and forth between a load of chargers, pulling my hear, and re-reading every tut on multimeters i could find because i was convinced i must be measuring wrong or something.
Lesson learned: 'Normal price' multimeters (€30-40 range) are terrible, and its much better to just take the extra few mins to set up a scope, or even just shell out €150ish for a real proper multimeter.
Venting complete ;D one last tip for any reader, avoid the Velleman DVM850BL, it looks alright and the brand is actually pretty good from what i've heard, but yea, fml and this thing.
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Thank you for your information that you've shared. It's really helpful for me.
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Never had any issues with cheap multimeters being unreliable, generally fine for most low-voltage, not ultra-high precision stuff. Also, scopes aren't any good for accurate voltage measurements due to their low resolution.
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Fluke 17B should be around €100. And mine passed through without customs.
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Many inexpensive meters are just fine if you do not use them outside of their intended application. I trouble shoot all sorts of things with an old $20 meter- you often do not need a lab meter, and no worries if it walks off. I did replace the junk plasitc leads with some spare silicone leads however ...... Just do not use a cheap meter to measure 460 three phase on an industrial machine, if it does not have the correct safety category rating!
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I always test mulitmeters (and any test equipment, such as a non-contact voltage sensor) on a known source - especially if the measuring is safety related. Cheap meters often have very poorly made leads. You can easily test resistance/continuity of the leads themselves before making measurements. Any test instrument, no matter how well made, can have damaged leads, low battery etc.- you need to learn to confirm its operation first. I have seen good oscilloscopes have leads with damaged connectors, ruined compensation adjustment, because someone careless turned the tiny cap too far etc. Also, learn about meter safety ratings/classes and do not use them for measurements they are not designed for.
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Yeah I'm normally a cheapskate but I got a Fluke 287 and the pain of the expense faded over time.. it's been useful, reliable, robust and accurate every day.
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could of tested a battery first... ;-)
william...
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Lol... thanks for the giggles, good read.
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Didn't see anyone mention checking to see if there was a blown fuse in the device. Had mine for little over 10 years and still works like a champ, Sun Equipment DMM-1230. But when I started out, I was careless with the settings and blew a few fuses. Was also going to electronic classes so blowing fuses also affected the grade so learned quick to get extra fuses.
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multimeter can be exhibit a kind of anomalous behavior sometimes.... but its best u v an extra to get rid of unnecessary variables
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I think you should never really trust anything in the lab. I've been had by bad batteries, bad cables, broken meters, bad components, etc. In grad school, a lab-mate spent several weeks "debugging" software crashes on a huge code base. We eventually tested the RAM in his PC with MemTest86, and guess what - bad stick of RAM; it was not a software problem at all.
Stay skeptical and mistrust everything your senses and instruments tell you until everything makes perfect sense.
But, don't take my word for it ;-)
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1.Es cosa de locos los valores que te dan algunos
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My fluke 87 has never let me down. Expensive but worth every penny in the long run.
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I prefer the really cheap $5 multimeters; you NEVER trust them, so you end up doing sanity checks.
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Um, there is another explanation. Most of those cheap chargers actually give you anything between 10-15V when not loaded. They only give around 5V when you actually draw the current they were specified for from them. Lots of people fried their Arduinos that way.
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Hmm ok thats some very good details to have lol, ty for that, i did play with that idea a couple of times during the above, because for some chargers it almost seemed like they 'tried to connect' (voltage spikes with a clear pattern) and then stopped giving voltage.
Currently using a 'Delta Electronics, Inc.' AC adapter, that seems to be a super generic usb charger (like, i have 5 from a bunch of different devices, all same spec) and for as far as i can tell with the oscilloscope it does what it says on the plug, 5v and nothing more, ever, any chance you know/could guesstimate if this would be safe to use?
Pic of the chargers label:
imgur.com/4W56WD3.jpg (its a bit big so therefor no embed)
Thanks in advance, whatever your awnser, and thx again for that tip about cheap chargers. :)
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Try them under a load, for example a 50Ohm 0.5W resistor should use 100mA on 5V and would be about the maximum watt limit. Or take some 100Ohms and play with different values, in parallel or series.
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I really don't know. You would have to find out what load you are going to have, and measure the voltage with an equivalent resistor connected to the charger to simulate that load — that should give you an idea of what to expect.
Of course, a faulty multimeter is a possibility too. Personally I sometimes get some crazy readings when I forget to set the mode (AC/DC) right for the thing I am measuring.
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@davedarko Good idea, ill give that a go
@Radomir Dopieralski Fair enough, ill see if i can figure that out
Thanks both! :)
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