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Big Clive's "Trashy" meter, unboxed ( Duratool D03047 multimeter )

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Fungus:

--- Quote from: joeqsmith on April 23, 2023, 09:04:07 pm ---Right, you wrote " Seems to me like a 2000 count meter should be able to display 2000V."   There was no mention of range until now.    Still, on the back of the meter it states "5. Read the manual before use.".  You seem to have been missed this as there is no mention of a 2kV range.

--- End quote ---

Right... but then you posted a picture of a "250V" meter happily displaying 1100V:


I was just wondering where it stops measuring, it seems like a reasonable question to me.

It's a 2000 count meter so 2000V seems like a possible limit.

(unless it freaks out earlier)

Gyro:

--- Quote from: Fungus on April 24, 2023, 04:31:45 am ---
--- Quote from: joeqsmith on April 23, 2023, 09:04:07 pm ---Right, you wrote " Seems to me like a 2000 count meter should be able to display 2000V."   There was no mention of range until now.    Still, on the back of the meter it states "5. Read the manual before use.".  You seem to have been missed this as there is no mention of a 2kV range.

--- End quote ---

Right... but then you posted a picture of a "250V" meter happily displaying 1100V:


I was just wondering where it stops measuring, it seems like a reasonable question to me.

It's a 2000 count meter so 2000V seems like a possible limit.

(unless it freaks out earlier)

--- End quote ---

These 3 1/2 digit dmms are all based on clones of the Intersil ICL7106, which has been around for decades. The chip basically has a +/-200mV input and display capability which you scale with voltage divider networks for the desired ranges. There is no intelligence in there - there are no dedicated pins for overrange, to enfoce a reading limit etc. The only way to decode the display values going to the display would be a bunch of XOR gates monitoring the LCD segment and backplane drives.

There is no way to limit the display at 250V, it will carry on displaying up to the 2000 digit reading if nothing on the board breaks down first (which it does). The manufacturers have cost reduced the meters to the point where they can't take anything like the maximum display reading without breaking down, and semsibly provided indications on the range switch and warning label. This isn't restricted to 3 1/2 cheapies, many dmms would probably display 2kV, 4kV, or 6kV (depending on IC display counts) but are limited to 1kV on the front panel labelling, instructions, and internal protection / breakdown.

There are two alternatives for the manufacturer. Either delete the 250V range altogether and provide a the maximum range at 200V, or provide the higher range and clearly indicate that it is rated for 250V max (as they have done). I know which alternative most buyers would prefer - and so is what they sell.

joeqsmith:

--- Quote from: Fungus on April 24, 2023, 04:31:45 am ---
--- Quote from: joeqsmith on April 23, 2023, 09:04:07 pm ---Right, you wrote " Seems to me like a 2000 count meter should be able to display 2000V."   There was no mention of range until now.    Still, on the back of the meter it states "5. Read the manual before use.".  You seem to have been missed this as there is no mention of a 2kV range.

--- End quote ---

Right... but then you posted a picture of a "250V" meter happily displaying 1100V:

I was just wondering where it stops measuring, it seems like a reasonable question to me.

It's a 2000 count meter so 2000V seems like a possible limit.

(unless it freaks out earlier)

--- End quote ---

I had posted that picture prior to your asking.   The 1100ish volts isn't a magic number.  It's where that particular power supply folds back with that load.  A different power supply was required to reach the 2kV you had asked about.   The counts will have nothing to do with when the hardware fails.  All of the meters shown held up beyond their maximum ranges. 

floobydust:
If there is e.g. 1mm PC board spacing (creepage and clearance), question is what (voltage) use are people here comfy with?

rsjsouza:
Good testing Joe. The older versions of the M830B-type meters can take a beating but not the newer ones.

Over the years I did several tests on those meters, obviously noting the erosion in quality and materials. However, on my channel I recently tested the Hypertough TD35235J (All-Sun EM830) that is sold at Walmart stores, has third party certification and it is quite well built for the price of $12.99 on US eBay: eBay auction: #294500510119

In my lower voltage tests (up to 280Vac) I was able to damage only the 1.5 and 9V battery testers (I forgot about the load resistors). Overall, it works quite well.

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