Kelvin 50LE Multimeter Review - Page 1
Forum section: electronics / general

author: retiredcaps
author_rank: Super Contributor
timestamp: December 04, 2012, 08:19:28 am
content: I'm hestitant to put this under the product review section and after you watchbothvideos you will understand why. 10 minutes total for both videos. And NO, it is not me doing the review or video.

author: ModemHead
author_rank: Frequent Contributor
timestamp: December 04, 2012, 03:23:13 pm
content: Gee, I didn't know the Centech ones are crap while the Kelvin ones are awesome. I guess my taste in multimeters is somewhat... uncalibrated.

author: saturation
author_rank: Super Contributor
timestamp: December 06, 2012, 12:45:17 am
content: Impressive looking at first, but its not unexpected.On voltage mode, at 1Mohm input impedance, current would be ~ 1mA at 1kV, 3.5mA at 3.5kV. You're looking at 1W to 12W of total power, not enough energy to make a dramatic failure. The overload protection seems to have worked as the meter survived going past 1kV but the meter eventually failed, this protection should also protect the ohms mode. Chances are the cracking sound heard was arcing inside the PCB or failure of some component from arc over leading to the DMM's failure.http://www.kelvin.com/Merchant2/merchant.mv?Screen=CTGY&Category_Code=ELEQKMCAT rating is to protect the user from electrical shock, not the meter from exploding. Once in kV range, one should scan the meter chassis and the test leads with a probe to check leakage of high voltage caused by dielectric breakdown.To see an explosion in volts mode, the meter would have to be attached to a CAT IV level circuit. This would apply the power more likely to cause an arc flash. In which case, the bench, loaded with equipment, wires and debris, is not the place to risk such a demonstration.In the current test, raising the current slowly to 5A will simply cause the fuse or equivalent to blow. What you don't want is arc over of the cut fuse or a fusible link, thus not breaking the circuit, so you need to test the voltage rating of the fuse as well. To test this in a US type home setting, you'd connect the DMM in amps mode to switched mains outlet, then turn mains on; it will put 120V 16A directly on the amp circuit and if the fuse doesn't work it will provide a more dramatic effect. This is a common error done by users, measuring voltage with the meter in current mode.Lastly, using a typical transformer will not provide the total power needed for an arc flash. Transformers are constant power, so even with 100:1 step up, I presume, the current is reduced proportionately. However, it adds safety because had the DMM leaked kV out of the chassis or leads, its not likely to use a users body as a ground path as the secondary windings intrinsically provide some level of isolation from mains. If kV did leak from something akin to a direct connection to mains, then it could electrocute the operator, using the operator as the ground path to earth.Conclusion? I don't think the test shown proved the meter is safe to use to meters rated ~1kV nor the results of current overload because the tests for those safety issues were not conducted.The drop test is convincing.

author: retiredcaps
author_rank: Super Contributor
timestamp: December 06, 2012, 01:28:12 am
content: Quote from: saturation on December 06, 2012, 12:45:17 amSaturation, thank you for your explanation. When I posted the link, my intention was not to make fun of the poster, but to try and learn what is actually going on with his tests. I'm trying to learn more about input protection so your explanation is appreciated.

author: retiredcaps
author_rank: Super Contributor
timestamp: December 06, 2012, 02:25:15 am
content: Also thanks to ModemHead who also gave me an explanation.

author: ModemHead
author_rank: Frequent Contributor
timestamp: December 06, 2012, 01:28:42 pm
content: The part where I got nervous was when he stuck the probes of the zapped, known-malfunctioning meter into the mains outlet to 'test' it, while holding it in his hands. There's a lot more energy available at that outlet than there is out of the transformer. Enough to create some fireworks, had the fault been serious enough.

author: saturation
author_rank: Super Contributor
timestamp: December 06, 2012, 03:17:23 pm
content: ... you're welcome, my comment was not implying anyone endorsed his methods. In my years at eevblog I don't think anyone has made an analysis of leakage current from DMM in high voltage mode. I think he had the right idea in mind but not the right technical implementation, except for his drop test; that meter did hold up well to physical abuse and for that alone, its a plus and I was impressed; thus the effort to discuss it here.Modemheads comments are also vital, that the videomaker took some safety precautions and yet risked others suggests there was some gaps in his knowledge, that can be serious with kV. Had the meter truly made a light show at high voltage, he was not complete covered and his face and elbows were exposed, also his father's desk was littered with items that could ignite and make matters worse.Compare to Dave's video of doing the same so long ago, the conditions and methods are proper, plus he made it fun:The high voltage shock is short and snappy, and the physical result is less the issue than that voltage leaping out of the meter chassis and into the users hands, thus giving them a potentially injurious but short lived kV shock. They can be lethal.My beef with cheap meters is not so much it doesn't work, aka measurement accuracy while new, but that it may fail unexpectedly as it ages, be it months or years, and when you need it most. Even if the safety is dubious, if you use it only for CAT 1 level and below 30V, most any meter, is safe to use. I once kept such a cheapie in my car for troubleshooting purposes, and found it reading erratically when I actually needed it and then died, and of course, I didn't have a backup because what can happen to an unused meter in a car? All it was subject to was heat, humidity, or severe cold every year and used only once. I subsequently bought a used Fluke 85 for $50 and replaced it and as expected, works every time.The video says he bought 10 pieces at $3 each, and by probability if I did the same and brought a few I could correlate them when needed to insure at least 2 were reading correctly, and replace whatever broke. Over years a few may die due to assembly defect, I'd still be ahead, but if there is a parts defect from a cheapo source, all can die literally the same year. So now, my $30, I must compensate for the cheapness by doing more brainwork, and carrying more stuff, a simpler solution is get a meter with a solid reputation. That's what we pay big names to do, do truly good QC, and what few rarely discuss: the operational temperature conditions of heat, humidity, vibration and shock that a portable device is subject too.Quote from: retiredcaps on December 06, 2012, 01:28:12 am

author: cnlohr
author_rank: Newbie
timestamp: December 07, 2012, 07:43:52 pm
content: I demonstrate at the beginning the transformer has more than enough umph to flash pretty hard... the whole Jacobs ladder. This transformer was also the same transformer a long time ago that blew my arm against a wall and knocked me out, when I came to, it took a while before the right side of my body started functioning correctly. It's NOT like a neon sign transformer. It's a seriously potent beast. I've been bitten by 125V countless times. The one time I got zapped by this transformer it was a serious zap. To say that there's less death coming out of the transformer is simply untrue.The point I was mostly defending is everyone was all uneasy about the putting a whole 1kV through the thing... And I wanted to point out that it's not a concern. The meters are designed plenty safe. And they aren't a piece of junk that's going to break and kill you as the price, and similar meters would indicate.I just haven't seen anything that would make me question the quality these meters. Your if's, maybe's, concern over cheap parts. Sure, it's dubious - but after owning these for over a year and having them beat up thrown around everywhere and not a single one broke (until I did these tests)Until I see some shred of evidence that would indicate the meter might kill me if measuring 220V or something practical, I intend to continue to use them for exactly that.You do pose some points though about the quality of the output that I could do more tests. I have seen them be off by around 20 or 30 mV at 10V as compared to a calibrated expensive meter... I'll toy with buying another box, and comparing the voltages warm and cold.

author: saturation
author_rank: Super Contributor
timestamp: December 07, 2012, 08:47:29 pm
content: ... It certain can, it would help if you specify the transformer winding specs to give us a better idea."Zaps" is far more potent to organic beings, you can get a jump with only 30V. What you describe is electrocution, which can occur far sooner than seeing some explosive like results from a DMM.Is the Kelvin LE double insulated? If not, it fails even if it passes an insulation test because if the chassis cracks with age or is dropped, the break will allow it to leak more easily [ instead of plastic+air as in insulator, you've replaced it with air]. Regardless, without leakage equipment to test for insulation resistance and leakage current:you can estimate leakage by using a DMM with a transconductance mode to test for >=10Mohm resistance from commons to anywhere on the case; this is the safest way to do it.... as the OP video shows another way could be put 500-1000V on the DUT on kV range, then simultaneously take another DMM, connect the ground to the negative rail of the transformer, and use the positive probe to pass over the meter's plastic case and try to measure any voltage leaking across the DUT. Likely areas to fail would be near the jacks & transistor test ports. Officially, you are looking for leakage current, but the high impedance voltmeter readings will clue you in to problem areas with less risk to an operator or risking a dead short. You should have 0 Volts in this quick safety test.Quote from: cnlohr on December 07, 2012, 07:43:52 pm

author: ciccio
author_rank: Frequent Contributor
timestamp: December 07, 2012, 09:06:11 pm
content: Funny, at 2:02 time in the above video there is a real good advice: connect BRAIN ....My teacher always told me: Never test anything with brain disconnected.Best regards

author: saturation
author_rank: Super Contributor
timestamp: December 07, 2012, 09:24:33 pm
content: I just got this from a friend, many look alikes to the Kelvin LE50 sold in Europe were tested by various electrical safety authorities, failed, and were then banned or withdrawn voluntarily. So caveat emptor, it could be the exact same model or lessons learned by the manufacturer, and later improved.EU model, tested in HungaryUS ModelQuite a large number of look alikes spanning the 5 years of the EU RAPEX archives, click link below then search for 'multimeter'.http://ec.europa.eu/consumers/dyna/rapex/create_rapex_search.cfm

author: saturation
author_rank: Super Contributor
timestamp: December 09, 2012, 07:57:42 pm
content: I was at a hardware yesterday and ran into this, General Tools is a reputable maker of low cost tools, and been around for almost 100 years in the USA. This model is very similar to the various 830 labeled DMMs that were withdrawn from EU sales but its a US version that is UL listed. As I've seen the Harbor Freight version but not the Kelvin version, I cannot compare the true model together, but here are the interesting differences.The entire meter is derated to CAT 1.The plastic case is much thicker and feels more solid.The upper limit of voltage ranges are markedly reduced.Transistor test jacks are removed.Retails for $25 vs $3.In the end, added safety features and certification increased the price over 8 fold.In the promo photo, the DMM is OFF, but reads 00.0, so clearly its been photoshopped.

author: T4P
author_rank: Super Contributor
timestamp: December 10, 2012, 05:19:05 am
content: http://www.all-sun.com/china_digital_multimeter/dt830_manufacturers.htmI think it's a ET-830 not the standard DT830

author: joeqsmith
author_rank: Super Contributor
timestamp: December 15, 2015, 03:20:41 am
content: I want one!