World's Worst DMM? - Page 1
Forum section: electronics / testgear

author: echen1024
author_rank: Super Contributor
timestamp: October 31, 2013, 02:26:22 am
content: For $1.91, is thishttp://www.ebay.com/itm/Digital-Multimeter-/291005261135?pt=LH_DefaultDomain_2&hash=item43c143e54f#shpCntIdthe world's worst multimeter? I would love to see someone zap it with 2.5k volts from an insulation tester.

author: IanB
author_rank: Super Contributor
timestamp: October 31, 2013, 02:38:03 am
content: I have a bunch of them. Harbor Freight Tools sells them in an appealing red color.They are crap, of course. But theycan also measure voltage accurately(the emphasis being oncan).If I wanted a DMM to give to a 5 year old to learn about batteries with, I would pick this one.

author: rolycat
author_rank: Super Contributor
timestamp: October 31, 2013, 02:48:05 am
content: Quote from: echen1024 on October 31, 2013, 02:26:22 amDefinitely not. I have owned a DT830B for ten years or more, and it is still working and giving reasonably accurate readings.The object to the left of this picture may qualify, though:All three meters are connected to a power supply set to 10V, as can be seen from the Fluke and DT830B displays.The analogue meter, however, thinks that it's just over 8V, despite having been cleaned up and adjusted.It's Japanese, an Eagle Products TK-25, which I liberated from my Dad when I was about 10. By comparison the DT830B is a masterpiece of precision engineering.(Edit: I have just spotted that you specified a DMM, but my first DMM was even worse in terms of build quality - it disintegrated many years ago.)

author: jwm
author_rank: Regular Contributor
timestamp: October 31, 2013, 02:50:10 am
content: I find them useful to rip apart and get a fairly decent 3 digit voltage controlled panel meter, depending on the layout you can just chop the PCB right below the lcd after probing out the voltage and power lines. you can then directly integrate them into power supply or whatever projects.

author: echen1024
author_rank: Super Contributor
timestamp: October 31, 2013, 03:03:03 am
content: AHhh yes. The Panel meter application may be a good idea.

author: johansen
author_rank: Super Contributor
timestamp: October 31, 2013, 04:51:34 am
content: you can chop the circuit board right below the lcd?!i had no clue. hmmon the other hand, a real panel meter for 5$:http://www.ebay.com/itm/YX-1000A-Voltmeter-Ammeter-Ohm-Multimeter-Battery-Leads-Electric-Pocket-Size-/251242439255a meter that won't go bezerk when emi exceeds some non zero valuethese don't look too bad.http://www.ebay.com/itm/Digital-DC-AC-LCD-Voltmeter-Ammeter-Multimeter-Tester-/180766330552too bad they need 9 v batteries.

author: retiredcaps
author_rank: Super Contributor
timestamp: October 31, 2013, 05:42:17 am
content: Quote from: echen1024 on October 31, 2013, 02:26:22 amIn Canada, there are very little auctions for multimeters on ebay.ca. The auction above is representative of our choices. I would get one for $1.91, but the shipping costs of $9.10 kills the deal.Some USA sellers ship to Canada, but at $30 ish shipping charges.

author: orin
author_rank: Frequent Contributor
timestamp: October 31, 2013, 06:51:47 am
content: Quote from: IanB on October 31, 2013, 02:38:03 amThe Harbor Freight versions will measure 10A without melting too... but best used to see if that AA cell found at the back of the bench is completely dead or not. Don't expect better than 1% accuracy.They eat 9V batteries if you forget to turn them off too; oh, I forgot, so do my Fluke meters.

author: Stonent
author_rank: Super Contributor
timestamp: October 31, 2013, 08:31:46 am
content: Quote from: IanB on October 31, 2013, 02:38:03 amHow the hell did you do that? On the half dozen or so HF meters I've had the trimmer appears to be just for looks doing nothing.I have red and yellow switched meters. The Red ones seem to be less glitchy though.

author: hedgewallace
author_rank: Contributor
timestamp: October 31, 2013, 09:39:47 am
content: Quote from: echen1024 on October 31, 2013, 02:26:22 amIt says it can test AC voltage, DC voltage, DC current, resistance, transistor and diode, which is pretty much the basics. But for $1.91, it seems pretty good. I wonder what the test leads are like? Probably best not to think about them...There seems to be heaps of these styles of meters on the market. I once owned a $10 cheapie from Jaycar (QM-1500) and the plastic coating on the test lead near the connector that plugs into the meter was stripped back after not much use. Definitely not safe.These kind of meters are designed for people who would only use them a few times, or not very oftern.

author: Stonent
author_rank: Super Contributor
timestamp: October 31, 2013, 10:11:15 am
content: Now that I'm not at work and can see the ebay link, the model number is the same as all the Harbor Freight special clones, but the design is different. The basic look is there but the straight transistor checker is new.

author: wraper
author_rank: Unknown
timestamp: October 31, 2013, 10:40:04 am
content: Quote from: mojo-chan on October 31, 2013, 09:16:56 amI don't understand why you hate that Rishabh so much. Leave it alone already, there was enough in the another thread.

author: Stonent
author_rank: Super Contributor
timestamp: October 31, 2013, 10:48:47 am
content: Oops, you said DMM.

author: ModemHead
author_rank: Frequent Contributor
timestamp: October 31, 2013, 01:28:29 pm
content: Quote from: Stonent on October 31, 2013, 10:11:15 amThere seem to be an entire universe of variations of this "830" style meter, with quality ranging from dangerous to passable. But they all share the same basic 7106 COB design. I once posted somewhere that the schematic must be printed on the back of every restaurant menu in Shenzhen.Some are well-dressed with different shapes and tool-maker brands. Dead giveaway is the two AC voltage ranges, 200V and anywhere from 500 to 700V, depending on the optimism of the one making the label.Pictures of the Harbor Fright variety, for those interested.

author: amyk
author_rank: Super Contributor
timestamp: October 31, 2013, 01:51:53 pm
content: They also comein kit form.I don't think any manufacturer has rated them any more than CAT II 600V.

author: johansen
author_rank: Super Contributor
timestamp: October 31, 2013, 06:11:17 pm
content: Quote from: ModemHead on October 31, 2013, 01:28:29 pmconsidering it goes to 1999.somewhere around here i might still have a photo of a not so cheap relatively unknown dmm reading -1999 volts. i then unclipped the leads, reversed them, and the meter blew up. (https://lh3.googleusercontent.com/-C-fKbwZtMAY/UnKcpjPv7tI/AAAAAAAAAi8/1mgLbpFHgDk/w867-h650-no/P1020420.JPG)I bought 5 of those cheap dmm's (behind the dmm in the photo).. I migtht hook the one remaining functional unit up to a 6KV transformer and see how high it goes before detonation. i'll be sure and video tape it. hmm. maybe friday afternoon pacific time.

author: rsjsouza
author_rank: Super Contributor
timestamp: October 31, 2013, 07:32:25 pm
content: It is probably not the worst, but I sawthis onethe other day and it looked really horrid.

author: Dongulus
author_rank: Regular Contributor
timestamp: October 31, 2013, 08:34:30 pm
content: Quote from: rsjsouza on October 31, 2013, 07:32:25 pmI ownthis onealso from Velleman and it's pretty awful, but about what you would expect for $10 on special at Fry's. I haven't used it in a few weeks and I've just remembered that I might have forgotten to turn it off. It's probably dead by now.

author: tocsa120ls
author_rank: Regular Contributor
timestamp: October 31, 2013, 09:23:10 pm
content: Quote from: amyk on October 31, 2013, 01:51:53 pm"Teaching kit"? What are you going to teach with that? Teach underage workers how to build multimeters (and probably mp3 players/clocks/etc)?

author: orion242
author_rank: Unknown
timestamp: October 31, 2013, 09:23:49 pm
content: Quote from: jwm on October 31, 2013, 02:50:10 amHey now, that's a great idea!

author: Lightages
author_rank: Unknown
timestamp: October 31, 2013, 09:31:01 pm
content: Maybe a great idea, maybe not. If they are unreliable and show incorrect readings as has been reported, perhaps you will get an incorrect reading and fry something with the incorrect output on your power supply or whatever you trust these things to show.

author: IanB
author_rank: Super Contributor
timestamp: October 31, 2013, 09:52:19 pm
content: The occasional incorrect readings seem to be caused by poor electrical contact on the rotary dial switch. If you remove the mechanical parts from the system the electronics seem to be quite reliable.

author: echen1024
author_rank: Super Contributor
timestamp: October 31, 2013, 09:53:29 pm
content: Quote from: Dongulus on October 31, 2013, 08:34:30 pmI got one on free special at frys. It's an AND 5526 rubbish.

author: orion242
author_rank: Unknown
timestamp: October 31, 2013, 10:01:15 pm
content: I want them nothing more than a backup volt / current meter for low voltage stuff.Basically a temp meter to backup my ADC readings while hashing out code on a project, aka sanity check. I'll stick to my 289s for any real measurements.

author: echen1024
author_rank: Super Contributor
timestamp: November 01, 2013, 12:16:16 am
content: That is true. SO these cheap meters do have their place...

author: Bored@Work
author_rank: Super Contributor
timestamp: November 01, 2013, 06:10:03 am
content: Quote from: echen1024 on November 01, 2013, 12:16:16 amYep, in the trash can.

author: retiredcaps
author_rank: Super Contributor
timestamp: November 01, 2013, 06:13:23 am
content: Quote from: orin on October 31, 2013, 06:51:47 amMost, if not all, cheap 830 meters like the three I have shown below have no auto power off. However, I measured the current consumption of the 830s when measuring DCV using a Fluke 87. As you can see it varies quite a bit even though I'm led to believe all 830s are more or less created the same.All figures below were recorded using min/max. I reported the max and rounded up.DT-830D - 1056uAM-830B - 968 uADT-830B - 298uAFluke 75 - 276.8uA (2,000 hour battery life on 9V battery)So if we estimate 1mA for the average 830, that should give around 400 hours of use assuming a 9V is 400mAh.On another forum where I participate, I estimate that 80% of the people asking for help have 830 variations. About once every two weeks, we get people with 830 meters reporting 10VDC readings on a 5V standby rail.Invariably, the cause of this bad reading is a 9V weak battery in the 830. However the 830 lcd, even though it has a low battery indicator, isnoton. Once we convince the user to put in a fresh battery, the 830 usually gives correct readings.BTW, the 2 yellows ones were non functional when I received them. I managed to "repair" them back to working order with advice/suggestions from modemhead. I spent a lot of time doing it, but I learned a lot about.QuoteI'm curious which model handheld Fluke multimeter eats batteries. I'm guessing the 233, 87IV/89IV/187/189, or 287/289. Most of the other models are in the 300-400 hour range. The current 28II is 800 hours on 3 AA batteries. Most of the modern ones have automatic power off.

author: BravoV
author_rank: Super Contributor
timestamp: November 01, 2013, 06:36:45 am
content: I own few of them although never use them anymore, starting from early version that is still using 7106 DIP package cramped into that small case and it looks horrid.@ModemHead or @retiredcaps, I think either of you should make a new thread for this popular 830 DMM, and inviting people to post their if they haven't dump it yet, I guess it will be fun to see how many variants out there.

author: Whales
author_rank: Super Contributor
timestamp: November 01, 2013, 06:41:41 am
content: Quote from: ModemHead on October 31, 2013, 01:28:29 pmAgree. I have one at the moment, alas current measurement has been fried by testing a transistor with too high a HFE. Indeed!Here is another 'good' DMM:Runs off a A23 12v battery. Drains in hours of standby timeHas no notification when battery is low -- readings just start fluctuating like the probes are not connected properlyBlew the current fuse in it a few years ago, before I properly understood ohm's law. Hence the foilHad to severely crimp the banana sockets so they actually kept contact with the probe plugsNo continuity buzzerShort probe leads

author: BravoV
author_rank: Super Contributor
timestamp: November 01, 2013, 06:47:01 am
content: LOL ... love that "UNFUSED!" label there.

author: rsjsouza
author_rank: Super Contributor
timestamp: November 01, 2013, 10:48:52 am
content: Quote from: BravoV on November 01, 2013, 06:36:45 amBravoV, checkthis other threadwhere people posted internal pictures of a range of 830 clones throughout the years.

author: amyk
author_rank: Super Contributor
timestamp: November 01, 2013, 10:57:37 am
content: That's thehttp://www.cem-instruments.com/en/pro/pro-490.htmlIf I remember correctly, the '830 design originated from a multimeter kit in the 80s that used the same '7106 and had the same set of ranges.Here's one from 1996:http://www.tequipment.net/pdf/Elenco/m-1005k.pdf

author: Dark Prognosis
author_rank: Regular Contributor
timestamp: November 01, 2013, 11:25:31 am
content: The probes on the HF red one are utter shit and the black probe broke near the meter for absolutely no reason on me. I noticed the wire inside had about 3 or 4 strands and that was it. I don't see those as handling 10 amps of current at all so I replaced them with some 30 to 40 year old probes that are real rubber and the points will stick you and make you bleed. I think the probes came from a VOM I found that was DOA.As far as the uses I use it to measure 3 things...batteries (has a nice battery position), resistors, and LEDs (using the diode tester it will make them light dimly if they are good). I would be so afraid to measure 10A of any real voltage on it.

author: Napalm2002
author_rank: Regular Contributor
timestamp: November 02, 2013, 01:03:15 am
content: The worlds worst dmm is the one that u need and don't have

author: BravoV
author_rank: Super Contributor
timestamp: November 02, 2013, 01:58:16 am
content: Quote from: rsjsouza on November 01, 2013, 10:48:52 amRafael, I'm aware of that thread, its just the title is not what I'm expecting, since you're the thread creator, maybe renaming it to something like ... "Post your 830 clone and teardown" or something similar ?

author: orin
author_rank: Frequent Contributor
timestamp: November 02, 2013, 02:37:52 am
content: Quote from: Dark Prognosis on November 01, 2013, 11:25:31 amI wouldn't measure 10A with pointy-ended test leads anyway unless I wanted to make sparks and potentially burn the end if one slipped. I used something like 14 gauge stranded wire leads with banana plugs at the meter and Anderson power poles at the other end. As for voltage, 50V DC, high side, but the meter didn't know that and I didn't tell itThe power supply however (a switching 500W 50V supply), did not last - junk capacitors and a PTC thermistor that let the magic smoke out. I fixed it, but short of an active load and some extensive testing, I'm not putting it back in service.

author: ModemHead
author_rank: Frequent Contributor
timestamp: November 02, 2013, 03:25:55 am
content: Quote from: BravoV on November 01, 2013, 06:36:45 amI've become a multimeter snob and I wouldn't want anyone to think I'm recommending these things. For anything other than the scientific study of how to make stuff dirt cheap.

author: Whales
author_rank: Super Contributor
timestamp: November 02, 2013, 04:09:23 am
content: FYI, I wrapped my fuse in aluminium foil because I could not find any of these official replacements:EDIT: Woops! Source:http://hackaday.com/2013/11/01/hackerspacing-in-europe-hack42-in-arnhem/

author: Huluvu
author_rank: Regular Contributor
timestamp: November 02, 2013, 07:16:09 am
content: Quote from: Whales on November 02, 2013, 04:09:23 amomg ...... spit all the coffee around and still laughing

author: Stonent
author_rank: Super Contributor
timestamp: November 02, 2013, 08:38:19 am
content: Quote from: Huluvu on November 02, 2013, 07:16:09 amI sent that to one of the maintenance guys at work and he got a kick out of it.

author: Dark Prognosis
author_rank: Regular Contributor
timestamp: November 02, 2013, 12:45:08 pm
content: Quote from: orin on November 02, 2013, 02:37:52 am