On Saturday, January 7, 2023 at 11:22:49 AM UTC-8, Fred Bloggs wrote:> On Saturday, January 7, 2023 at 2:16:50 PM UTC-5, Ed Lee wrote: > > On Saturday, January 7, 2023 at 11:10:02 AM UTC-8, Fred Bloggs wrote: > > > On Saturday, January 7, 2023 at 1:42:05 PM UTC-5, Ed Lee wrote: > > > > On Saturday, January 7, 2023 at 10:14:06 AM UTC-8, John Larkin wrote: > > > > > On Sat, 7 Jan 2023 09:34:02 -0800 (PST), Fred Bloggs > > > > > <bloggs.fred...@gmail.com> wrote: > > > > > > > > > > >On Saturday, December 31, 2022 at 1:19:58 PM UTC-5, Ed Lee wrote: > > > > > >> But not immediately. I tested 400V occasionally, but couple of them died while testing 12V. I am wondering it 400V weaken the meter. > > > > > >> > > > > > >> The old CenTech meters are 1000V, but the new models are 250V. Why even bother to have 50V more than the next range of 200V. Perhaps it's just same design with new label, when they got enough reports/complaints. > > > > > >> > > > > > >> I am wondering if it's worth picking up some of the older 1000V models off ebay. > > > > > > > > > > > > You blew out some nominal protection like this: > > > > > > > > > > > >https://www.vishay.com/docs/29072/ptccl.pdf > > > > > > > > > > > >This is a quiescently low ohm resistor in series with measurement input. Schematics show a voltage clamp shunt to COM after the PTC. > > > > > PTC+TVS can help but isn't generally reliable. The combo still has > > > > > failure modes. > > > > > > > > > > For signal-level stuff, depletion fets are good current limiters. I > > > > > knew the guy who designed some nice Fluke benchtop DVMs and he used > > > > > long strings of jfets as HV current limiters in the ohms sections. > > > > > > > > > > The world needs a really good 2-terminal bulletproof current limiter. > > > > > > > > > > > >If the meter comes on and presents a normal display but doesn't produce any readings, your PTC is open. If the meter is dead and produces a haywire or no display, you've blown their processor chip, which means the voltage clamp failed, was missing, or never worked. Apparently the PTC will fail from overvoltage. It should fail open. Hard to imagine the voltage clamp being overstressed. The PTC is easy to spot. You might take a look at it. And if an issue with the CenTech brand, you might buy a handful and replace the garbage in your working meters with better PTCs. > > > > The failed cenTech meters come on with display but no meaningful readings. I don't see any PTC. There are glass fuses. One failed open but another one intact. > > > > > > > > I got an auto ranging meter. I will measure 400V with a 4:1 resister divider. I only need to know between 90% to 100% of 400V anyway. > > > > > > > > https://www.ebay.com/itm/295076537933 > > > Does that even measure current? > > No, voltage and resistance only. I can probably calculate I=V/R. I still have a few cenTechs for measuring current. BTW, the failed meters still work with High Amp (HA) mode, with a separate lead connector. > > > Can you read that display in bright sunlight? > > Yes, display is large and good, even has back light at night. > > > This one looks more standard and is a lot of meter for the money: > > > https://www.protechtrader.com/Digital-Multimeter-Autoranging-DMM-with-Test-Leads---Checks-Voltage-ACDC-Volts-ResistanceOhms-Current--10-Amps-15s500-MA-Diode-Transistor-NPNPNP-Battery-Tester-Meter-with-ONOFF > > > > > > Then there's this, same as the above: > > > https://www.harborfreight.com/7-function-digital-multimeter-63759.html > > > > > > These meters are not bad for field work convenience. > Check to be sure the display is not some pain in the ass that you have to activate and it only stays on for 3-seconds or something. Dunno what kind of display it is but some of them draw a LOT of current, closer to 100mA than 10mA, hence the quick timeout.Auto-off after 15 minutes. Definitely not keeping back light on too long. Or the 2xAAA batteries won't last.
HV damages meter?
Started by ●December 31, 2022
Reply by ●January 7, 20232023-01-07
Reply by ●January 8, 20232023-01-08
On Saturday, January 7, 2023 at 11:31:33 AM UTC-8, Ed Lee wrote:> On Saturday, January 7, 2023 at 11:22:49 AM UTC-8, Fred Bloggs wrote: > > On Saturday, January 7, 2023 at 2:16:50 PM UTC-5, Ed Lee wrote: > > > On Saturday, January 7, 2023 at 11:10:02 AM UTC-8, Fred Bloggs wrote: > > > > On Saturday, January 7, 2023 at 1:42:05 PM UTC-5, Ed Lee wrote: > > > > > On Saturday, January 7, 2023 at 10:14:06 AM UTC-8, John Larkin wrote: > > > > > > On Sat, 7 Jan 2023 09:34:02 -0800 (PST), Fred Bloggs > > > > > > <bloggs.fred...@gmail.com> wrote: > > > > > > > > > > > > >On Saturday, December 31, 2022 at 1:19:58 PM UTC-5, Ed Lee wrote: > > > > > > >> But not immediately. I tested 400V occasionally, but couple of them died while testing 12V. I am wondering it 400V weaken the meter. > > > > > > >> > > > > > > >> The old CenTech meters are 1000V, but the new models are 250V. Why even bother to have 50V more than the next range of 200V. Perhaps it's just same design with new label, when they got enough reports/complaints. > > > > > > >> > > > > > > >> I am wondering if it's worth picking up some of the older 1000V models off ebay. > > > > > > > > > > > > > > You blew out some nominal protection like this: > > > > > > > > > > > > > >https://www.vishay.com/docs/29072/ptccl.pdf > > > > > > > > > > > > > >This is a quiescently low ohm resistor in series with measurement input. Schematics show a voltage clamp shunt to COM after the PTC. > > > > > > PTC+TVS can help but isn't generally reliable. The combo still has > > > > > > failure modes. > > > > > > > > > > > > For signal-level stuff, depletion fets are good current limiters. I > > > > > > knew the guy who designed some nice Fluke benchtop DVMs and he used > > > > > > long strings of jfets as HV current limiters in the ohms sections. > > > > > > > > > > > > The world needs a really good 2-terminal bulletproof current limiter. > > > > > > > > > > > > > >If the meter comes on and presents a normal display but doesn't produce any readings, your PTC is open. If the meter is dead and produces a haywire or no display, you've blown their processor chip, which means the voltage clamp failed, was missing, or never worked. Apparently the PTC will fail from overvoltage. It should fail open. Hard to imagine the voltage clamp being overstressed. The PTC is easy to spot. You might take a look at it. And if an issue with the CenTech brand, you might buy a handful and replace the garbage in your working meters with better PTCs. > > > > > The failed cenTech meters come on with display but no meaningful readings. I don't see any PTC. There are glass fuses. One failed open but another one intact. > > > > > > > > > > I got an auto ranging meter. I will measure 400V with a 4:1 resister divider. I only need to know between 90% to 100% of 400V anyway. > > > > > > > > > > https://www.ebay.com/itm/295076537933 > > > > Does that even measure current? > > > No, voltage and resistance only. I can probably calculate I=V/R. I still have a few cenTechs for measuring current. BTW, the failed meters still work with High Amp (HA) mode, with a separate lead connector. > > > > Can you read that display in bright sunlight? > > > Yes, display is large and good, even has back light at night. > > > > This one looks more standard and is a lot of meter for the money: > > > > https://www.protechtrader.com/Digital-Multimeter-Autoranging-DMM-with-Test-Leads---Checks-Voltage-ACDC-Volts-ResistanceOhms-Current--10-Amps-15s500-MA-Diode-Transistor-NPNPNP-Battery-Tester-Meter-with-ONOFF > > > > > > > > Then there's this, same as the above: > > > > https://www.harborfreight.com/7-function-digital-multimeter-63759.html > > > > > > > > These meters are not bad for field work convenience. > > Check to be sure the display is not some pain in the ass that you have to activate and it only stays on for 3-seconds or something. Dunno what kind of display it is but some of them draw a LOT of current, closer to 100mA than 10mA, hence the quick timeout. > Auto-off after 15 minutes. Definitely not keeping back light on too long. Or the 2xAAA batteries won't last.If you are going to be working on HV circuits (>240 V) ONLY use DMMs with a CAT certification (which cheap Chinese meters don't have). https://www.fluke.com/en-us/learn/blog/safety/multimeter-guide
Reply by ●January 8, 20232023-01-08
On Sunday, January 8, 2023 at 5:52:35 PM UTC+11, Flyguy wrote:> On Saturday, January 7, 2023 at 11:31:33 AM UTC-8, Ed Lee wrote: > > On Saturday, January 7, 2023 at 11:22:49 AM UTC-8, Fred Bloggs wrote: > > > On Saturday, January 7, 2023 at 2:16:50 PM UTC-5, Ed Lee wrote: > > > > On Saturday, January 7, 2023 at 11:10:02 AM UTC-8, Fred Bloggs wrote: > > > > > On Saturday, January 7, 2023 at 1:42:05 PM UTC-5, Ed Lee wrote: > > > > > > On Saturday, January 7, 2023 at 10:14:06 AM UTC-8, John Larkin wrote: > > > > > > > On Sat, 7 Jan 2023 09:34:02 -0800 (PST), Fred Bloggs <bloggs.fred...@gmail.com> wrote: > > > > > > > > > > > > > > >On Saturday, December 31, 2022 at 1:19:58 PM UTC-5, Ed Lee wrote:<snip>> If you are going to be working on HV circuits (>240 V) ONLY use DMMs with a CAT certification (which cheap Chinese meters don't have). > https://www.fluke.com/en-us/learn/blog/safety/multimeter-guideWhich doesn't tell you much. "The latest UL standard for electrical test instruments is UL 61010B-1, which is a revision of 3111-1. It specifies the general safety requirements, such as material, design, and testing requirements, and the environmental conditions in which the standard applies. UL 3111-2-031 lists additional requirements for test probes. The requirements for hand-held current clamps, such as the current measuring portion of clamp meters, are included in UL 3111-2-032. UL standards are gradually being harmonized with similar international standards, such as those published by IEC. Until this is completed, there may be significant differences between each group's standards. For example, IEC 61010-1 2nd Edition includes requirements for voltage-measuring instruments in CAT IV environments. UL 61010B-1 doesn't." What Flyguy might be saying - if he knew what he was talking out - is that there are safety standards for multimeters. In the US they are published by the Underwriter Laboratory. There are also international safety standards. https://www.nema.org/standards/international/the-iec-and-nema The International Electrotechnical Commission (IEC) headquartered in Geneva, Switzerland is the top level body. A chinese multi-meter might well not conform to an American Underwriters Laboratory standard, but will probably conform to the relevant IEC standard, which isn't going to be much different. A cheap chinese meter might be truly cheap and nasty, and correspondlngly dangerous, but anybody who sold it to you would risk being sued if it was. It's more likely to be cheap because it was produced in high volume, rather than because the manufacturer cut any corners. I've ran into one American instrument that didn't meet their published specifications, which is a slightly different kind of problem - it wasn't certainly wasn't cheap. -- Bill Sloman, Sydney
Reply by ●January 8, 20232023-01-08
In article <fcb22892-2d93-4046-bcdc-1d9ed5f410adn@googlegroups.com>, bill.sloman@ieee.org says...> > A chinese multi-meter might well not conform to an American Underwriters Laboratory standard, but will probably conform to the relevant IEC standard, which isn't going to be much different. > > A cheap chinese meter might be truly cheap and nasty, and correspondlngly dangerous, but anybody who sold it to you would risk being sued if it was. > > It's more likely to be cheap because it was produced in high volume, rather than because the manufacturer cut any corners. I've ran into one American instrument that didn't meet their published specifications, which is a slightly different kind of problem - it wasn't certainly wasn't cheap. > > >Meters are rated for certain usages. That is where the CAT number comes into play. The cheap meters may be rated for home low voltage/current usage. Others rated for higher voltage /current. I have a couple of $ 300+ meters and some of the 'free' Harbor Freight meters. None of the $ 10 to $ 50 meters. I worked with some 480 volt circuits that had fuses up to 300 amps. No way would I use any meter that I did not know it was CAT rated for the service. I would use the China meter on my home electronics that may have 500 volts in them but the current was an amp or less, but no way on a 240 volt+ circuit that had over a few amps, especially 100 or more amps supply. If you had ever seen any Fluke or other safety films where the less expensive meters had been set on the ohms or current ranges and put across the high amp circuits no one would even think about using the meters that are not CAT ( or maybe some other standard) rated for the application. As far as the sueing, all they have to say is the meter was used outside of its ratinng.
Reply by ●January 8, 20232023-01-08
...> A cheap chinese meter might be truly cheap and nasty, and correspondlngly dangerous, but anybody who sold it to you would risk being sued if it was.Even for the old model with HV 1000V range, there is a warning label at the back "Do not test voltage over 250 volts". Defendant counters that plaintiff did not read the warning label, If the item was given out free, there is no damage.
Reply by ●January 8, 20232023-01-08
On Sunday, January 8, 2023 at 6:41:15 AM UTC-8, bill....@ieee.org wrote:> On Sunday, January 8, 2023 at 5:52:35 PM UTC+11, Flyguy wrote: > > On Saturday, January 7, 2023 at 11:31:33 AM UTC-8, Ed Lee wrote: > > > On Saturday, January 7, 2023 at 11:22:49 AM UTC-8, Fred Bloggs wrote: > > > > On Saturday, January 7, 2023 at 2:16:50 PM UTC-5, Ed Lee wrote: > > > > > On Saturday, January 7, 2023 at 11:10:02 AM UTC-8, Fred Bloggs wrote: > > > > > > On Saturday, January 7, 2023 at 1:42:05 PM UTC-5, Ed Lee wrote: > > > > > > > On Saturday, January 7, 2023 at 10:14:06 AM UTC-8, John Larkin wrote: > > > > > > > > On Sat, 7 Jan 2023 09:34:02 -0800 (PST), Fred Bloggs <bloggs.fred...@gmail.com> wrote: > > > > > > > > > > > > > > > > >On Saturday, December 31, 2022 at 1:19:58 PM UTC-5, Ed Lee wrote: > <snip> > > If you are going to be working on HV circuits (>240 V) ONLY use DMMs with a CAT certification (which cheap Chinese meters don't have). > > https://www.fluke.com/en-us/learn/blog/safety/multimeter-guide > Which doesn't tell you much.It tells you everything you need to know to make a purchasing decision. This IS NOT a designer's guide, Bozo.> > "The latest UL standard for electrical test instruments is UL 61010B-1, which is a revision of 3111-1. It specifies the general safety requirements, such as material, design, and testing requirements, and the environmental conditions in which the standard applies. UL 3111-2-031 lists additional requirements for test probes. The requirements for hand-held current clamps, such as the current measuring portion of clamp meters, are included in UL 3111-2-032. > > UL standards are gradually being harmonized with similar international standards, such as those published by IEC. Until this is completed, there may be significant differences between each group's standards. For example, IEC 61010-1 2nd Edition includes requirements for voltage-measuring instruments in CAT IV environments. UL 61010B-1 doesn't." > > What Flyguy might be saying - if he knew what he was talking out - is that there are safety standards for multimeters. In the US they are published by the Underwriter > Laboratory.I am WELL AWARE of UL and other testing labs.> > There are also international safety standards. > > https://www.nema.org/standards/international/the-iec-and-nema > > The International Electrotechnical Commission (IEC) headquartered in Geneva, Switzerland is the top level body. > > A chinese multi-meter might well not conform to an American Underwriters Laboratory standard, but will probably conform to the relevant IEC standard, which isn't going to be much different.Pure SPECULATION by Bozo completely UNVERIFIED by ANY facts whatsoever. But, why am I not surprised coming from Bozo?> > A cheap chinese meter might be truly cheap and nasty, and correspondlngly dangerous, but anybody who sold it to you would risk being sued if it was.LOL! Just TRY suing a Chinese company - just TRY!!> > It's more likely to be cheap because it was produced in high volume, rather than because the manufacturer cut any corners. I've ran into one American instrument that didn't meet their published specifications, which is a slightly different kind of problem - it wasn't certainly wasn't cheap.No, Bozo, they cut ALL KINDS of corners: https://www.youtube.com/watch?v=iGUiZT6kLDk Notice that this meter has NO certification marks. And for GOOD REASON: it would NEVER pass.> > -- > Bozo Bill Sloman, Sydney
Reply by ●January 8, 20232023-01-08
John Larkin <jlarkin@highlandsnipmetechnology.com> wrote:> On Sat, 7 Jan 2023 01:04:32 -0000 (UTC), antispam@math.uni.wroc.pl > wrote: > > >Ed Lee <edward.ming.lee@gmail.com> wrote: > >> But not immediately. I tested 400V occasionally, but couple of them died while testing 12V. I am wondering it 400V weaken the meter. > > > >High voltage can destroy resistors, but this seem to be quite fast. > > > >> The old CenTech meters are 1000V, but the new models are 250V. Why even bother to have 50V more than the next range of 200V. Perhaps it's just same design with new label, when they got enough reports/complaints. > > > >Lot of folks live in countries where line voltage is 230V. So 50 volts > >makes a lot of difference. > > > >> I am wondering if it's worth picking up some of the older 1000V models off ebay. > > > >I know nothing about CenTech meters. But I have several "DT830B" > >meters. Available schematics shows 3 resistors in series for 1000V. > >My oldest one have 2 resistors. Newest one have single resistor. > >Standard miniature resistors are rated for 250V, one can get > >better ones, but I doubt that one can get cheaply 1000V capable > >ones. Still, meter is marked as 1000V DC, 700V AC (the same > >as old meters). > > They eliminated 0.2 cents worth of resistors. Ignore temperature and > voltage coefficient effects. Maybe some of that is mathed out? > > Chinese product prices ratchet towards cheap, and the specs ratchet > deep into the lies region. Chinese amps and volts and per cent are > about 10:1 off from SI standards.Well, the cheap "DT830B" were surprisingly accurate. I have used 4 to measure the same voltage. IIRC the differences were in last digit and did not exceed 2 counts. They were bought from different sources at different times, so it is unlikly to be the same error on all. And they agreed with better meter. Newest ones seem to have larger errors, but still well withing specs. AFAICS biggest problem with cheap meters are test leads, they tend to fail rather quickly. Second problem is main switch, which is formed from part of PCB. It seem to degrade with use. And failing switch can produce all kinds of wrong results. -- Waldek Hebisch
Reply by ●January 8, 20232023-01-08
On Sun, 8 Jan 2023 19:02:15 -0000 (UTC), antispam@math.uni.wroc.pl wrote:>John Larkin <jlarkin@highlandsnipmetechnology.com> wrote: >> On Sat, 7 Jan 2023 01:04:32 -0000 (UTC), antispam@math.uni.wroc.pl >> wrote: >> >> >Ed Lee <edward.ming.lee@gmail.com> wrote: >> >> But not immediately. I tested 400V occasionally, but couple of them died while testing 12V. I am wondering it 400V weaken the meter. >> > >> >High voltage can destroy resistors, but this seem to be quite fast. >> > >> >> The old CenTech meters are 1000V, but the new models are 250V. Why even bother to have 50V more than the next range of 200V. Perhaps it's just same design with new label, when they got enough reports/complaints. >> > >> >Lot of folks live in countries where line voltage is 230V. So 50 volts >> >makes a lot of difference. >> > >> >> I am wondering if it's worth picking up some of the older 1000V models off ebay. >> > >> >I know nothing about CenTech meters. But I have several "DT830B" >> >meters. Available schematics shows 3 resistors in series for 1000V. >> >My oldest one have 2 resistors. Newest one have single resistor. >> >Standard miniature resistors are rated for 250V, one can get >> >better ones, but I doubt that one can get cheaply 1000V capable >> >ones. Still, meter is marked as 1000V DC, 700V AC (the same >> >as old meters). >> >> They eliminated 0.2 cents worth of resistors. Ignore temperature and >> voltage coefficient effects. Maybe some of that is mathed out? >> >> Chinese product prices ratchet towards cheap, and the specs ratchet >> deep into the lies region. Chinese amps and volts and per cent are >> about 10:1 off from SI standards. > >Well, the cheap "DT830B" were surprisingly accurate. I have >used 4 to measure the same voltage. IIRC the differences >were in last digit and did not exceed 2 counts. They were >bought from different sources at different times, so it >is unlikly to be the same error on all. And they agreed >with better meter. Newest ones seem to have larger >errors, but still well withing specs. > >AFAICS biggest problem with cheap meters are test leads, >they tend to fail rather quickly. Second problem is >main switch, which is formed from part of PCB. It >seem to degrade with use. And failing switch can >produce all kinds of wrong results.Why buy cheap junk test equipment? Why buy cheap junk anything?
Reply by ●January 8, 20232023-01-08
On 2023-01-08 20:44, John Larkin wrote:> On Sun, 8 Jan 2023 19:02:15 -0000 (UTC), antispam@math.uni.wroc.pl > wrote: > >> John Larkin <jlarkin@highlandsnipmetechnology.com> wrote: >>> On Sat, 7 Jan 2023 01:04:32 -0000 (UTC), antispam@math.uni.wroc.pl >>> wrote: >>> >>>> Ed Lee <edward.ming.lee@gmail.com> wrote: >>>>> But not immediately. I tested 400V occasionally, but couple of them died while testing 12V. I am wondering it 400V weaken the meter. >>>> >>>> High voltage can destroy resistors, but this seem to be quite fast. >>>> >>>>> The old CenTech meters are 1000V, but the new models are 250V. Why even bother to have 50V more than the next range of 200V. Perhaps it's just same design with new label, when they got enough reports/complaints. >>>> >>>> Lot of folks live in countries where line voltage is 230V. So 50 volts >>>> makes a lot of difference. >>>> >>>>> I am wondering if it's worth picking up some of the older 1000V models off ebay. >>>> >>>> I know nothing about CenTech meters. But I have several "DT830B" >>>> meters. Available schematics shows 3 resistors in series for 1000V. >>>> My oldest one have 2 resistors. Newest one have single resistor. >>>> Standard miniature resistors are rated for 250V, one can get >>>> better ones, but I doubt that one can get cheaply 1000V capable >>>> ones. Still, meter is marked as 1000V DC, 700V AC (the same >>>> as old meters). >>> >>> They eliminated 0.2 cents worth of resistors. Ignore temperature and >>> voltage coefficient effects. Maybe some of that is mathed out? >>> >>> Chinese product prices ratchet towards cheap, and the specs ratchet >>> deep into the lies region. Chinese amps and volts and per cent are >>> about 10:1 off from SI standards. >> >> Well, the cheap "DT830B" were surprisingly accurate. I have >> used 4 to measure the same voltage. IIRC the differences >> were in last digit and did not exceed 2 counts. They were >> bought from different sources at different times, so it >> is unlikly to be the same error on all. And they agreed >> with better meter. Newest ones seem to have larger >> errors, but still well withing specs. >> >> AFAICS biggest problem with cheap meters are test leads, >> they tend to fail rather quickly. Second problem is >> main switch, which is formed from part of PCB. It >> seem to degrade with use. And failing switch can >> produce all kinds of wrong results. > > Why buy cheap junk test equipment? > > Why buy cheap junk anything? >Because cheap isn't always junk and junk isn't always cheap? Sometimes it's kind of hard to tell. Jeroen Belleman
Reply by ●January 8, 20232023-01-08
On a sunny day (Sun, 08 Jan 2023 11:44:32 -0800) it happened John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote in <l57mrhtf7f160aol86iru5r7o2h6hqmnc0@4ax.com>:>Why buy cheap junk test equipment? > >Why buy cheap junk anything?Why buy your stuff? I am happy with my cheap meters, other Chinese made equipmnet I have so are thousands if not millions others, Your definition of 'junk' is so vague that your own stuff may fall into it. A SANE person looks at it case by case. If it works its OK. Take my Tecsun PL600 radio, it is so good that I would have be proud if I had designed it and build it, but could not have made it for the about 35 (at that time) dollars it was on ebay. You could not have designed it. And my Baofeng, And my digital mutimeters And my satellite receivers. Nothing is perfect. Yes the test leads of the multimeters seem to be made of plastic that eventually breaks, But I have 4, so .... 3 for what I payed for coffee and pie plus a tip last week in the city (10 Euro == 10 dollars). You self overrated 'merricans need to produce cheaper and better to compete. Had to repair my washing machine and my dryer several times because the power supply design sucks! Pestering others with sanctions put you on level with the mafia that you really are now war mongering in the world to sell your weapons crap (F35 etc). End of the world? Even the Mafiosi get locked up eventually. Keep asking for it. Some of your cars are junk, and you know it. Not even mentioning that one made by who was once the richest man in the world... thousands for a battery fix..
