Multimeter wrong voltage reading

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lfb
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Multimeter wrong voltage reading

I’ve bought a multimeter today. Decided to check my 18650s voltage and got 4.3v on all of them. I thought that this could be an issue with my liitokala Lii-100, but when I’ve tested voltage of batteries charged inside other flashlights with built-in charge, I’ve got 4.3v too. So I think I have a multimeter problem. Before this I accidentally measured CA voltage using CC scale. Could this have damaged the multimeter? Just to mention, it’s a yellow cheap one (3 dollars).

Robin Dobbie
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Maybe go to an auto parts store and spend $10 – $15 on a meter. Maybe check it in-store with their shop meter. Then maybe you can calibrate the $3 jobber. Maybe.

edit: apparently I’m old now because autoparts stores meters are $20 – $25. And they’re not really worth that. If I was going to spend $25, I might as well get the Harbor Freight one that’s kinda nice. https://www.harborfreight.com/11-function-digital-multimeter-with-audibl...

Of course they have the one that looks like what you have for $7, and like I said, it’s not terrible(mine, anyway). But the leads kinda are terrible. Had to repair them because the wire is so thin and breaks. Just get the $23 one.

jeff51
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I’d suspect the cheap meter. A meter should cost more than an 18650. Crown
But I’ve had cheap meters that were spot on.
Got any primary cells to measure?
Or got a buddy with a better meter?
All the Best,
Jeff

zoulas
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You really need three meters to test them against each other. If you only had two and the readings were different, you would not know which one to believe.

Robin Dobbie
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What if all three are different?! Shocked

GhostJoe
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Robin Dobbie wrote:
What if all three are different?! Shocked

Take an average…

zoulas
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Robin Dobbie wrote:
What if all three are different?! Shocked

This method was used by sailors to test GPS’s. If two were right that was the one to go with. The possibilities of having three bad DMM’s with all different readings is very low. This is using statistics to your advantage.

lfb
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jeff51 wrote:
I’d suspect the cheap meter. A meter should cost more than an 18650. Crown
But I’ve had cheap meters that were spot on.
Got any primary cells to measure?
Or got a buddy with a better meter?
All the Best,
Jeff

Thanks for attention, Jeff. I’ve read 1.64v from a brand new alkaline AA. How much it’s supposed to be?
lfb
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Robin Dobbie wrote:
Maybe go to an auto parts store and spend $10 – $15 on a meter. Maybe check it in-store with their shop meter. Then maybe you can calibrate the $3 jobber. Maybe.

edit: apparently I’m old now because autoparts stores meters are $20 – $25. And they’re not really worth that. If I was going to spend $25, I might as well get the Harbor Freight one that’s kinda nice. https://www.harborfreight.com/11-function-digital-multimeter-with-audibl...

Of course they have the one that looks like what you have for $7, and like I said, it’s not terrible(mine, anyway). But the leads kinda are terrible. Had to repair them because the wire is so thin and breaks. Just get the $23 one.

I think I’ll mentally calibrate it for now Big Smile . If I need, I get a good one in the future.

zoulas
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But guys, make no mistake, Chinese DMM’s are only for reading up to two significant figures, in other words 10.21 volts. If you want to know past the 1, you have to get a Fluke.

jeff51
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lfb wrote:
jeff51 wrote:
I’d suspect the cheap meter. A meter should cost more than an 18650. Crown
But I’ve had cheap meters that were spot on.
Got any primary cells to measure?
Or got a buddy with a better meter?
All the Best,
Jeff

Thanks for attention, Jeff. I’ve read 1.64v from .brand new alkaline AA. How much it’s supposed to be?

I just measured a few. Several at 1.59x
The highest I got was 1.605
Looks like you meter is reading high.
All the Best,
Jeff
kennybobby
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Your meter is reading too high, but it may be damaged also. What is the CA and CC measurements and scale that you mentioned?

Is this meaning AC and DC, that you used the AC scale to make a DC measurement, or vice versa? That would not normally damage a meter, but it might have if you were measuring the mains AC line voltage using the DC scale.

Now i used to think that i was cool,
drivin' around on fossil fuel,
until i saw what i was doin',
was drivin' down the road to ruin. --JT

iamlucky13
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If you have some way of checking the voltage of the battery in the meter, that could be the issue.

Most digital multimeters use a fixed reference that is about 6V. If the battery voltage falls below six volts, they start reading high. Since the meter is new, that would mean a bad battery.

If this is the case, the inaccuracy should start getting progressively worse.

For what it’s worth, at a previous workplace, we kept a mix of both high quality (Fluke) and low quality (Centech / Harbor Freight) multimeters. They wanted us to use the cheap meters when not doing critical work to save money. All of them got calibrated and certified. They all consistently measured within the accuracy specified on the box, which to be sure, was tighter on the Flukes.

Looking up the current cheap Centech on Harbor Freight’s site, they specify +/- 1% and +/- 2 digits (they don’t actually clarify if that is % of reading or % of range – if unstated, it should be the more restrictive % of reading). So if the battery is exactly at 4.2V, this meter would be in-spec if I was using the 250V range setting (which only displays 1 decimal place, if I remember right), it is within spec to 4.4V (within 2 digits).

If I turn it down the dial to the 20V range and get 3 decimal places, it now should not read higher than 4.244 V (4.2 + 1% + 2 digits).

Note that battery voltage can vary because they are allowed tolerances, too. When a manufacturer says to charge a battery to 4.2V, they know the charger will not have perfect accuracy, so they usually mean something like +/- 0.05V. Such a battery can acceptably be as high as 4.25V (I think in reality, most charger manufacturers bias their chargers a little bit low to avoid concerns).

lfb
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kennybobby wrote:
Your meter is reading too high, but it may be damaged also. What is the CA and CC measurements and scale that you mentioned

Is this meaning AC and DC, that you used the AC scale to make a DC measurement, or vice versa? That would not normally damage a meter, but it might have if you were measuring the mains AC line voltage using the DC scale.

Just forgot to translate. That’s exactly what I’ve done, measured the mains AC line voltage using the DC scale.

lfb
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iamlucky13 wrote:
If you have some way of checking the voltage of the battery in the meter, that could be the issue.

Most digital multimeters use a fixed reference that is about 6V. If the battery voltage falls below six volts, they start reading high. Since the meter is new, that would mean a bad battery.

If this is the case, the inaccuracy should start getting progressively worse.

For what it’s worth, at a previous workplace, we kept a mix of both high quality (Fluke) and low quality (Centech / Harbor Freight) multimeters. They wanted us to use the cheap meters when not doing critical work to save money. All of them got calibrated and certified. They all consistently measured within the accuracy specified on the box, which to be sure, was tighter on the Flukes.

Looking up the current cheap Centech on Harbor Freight’s site, they specify +/- 1% and +/- 2 digits (they don’t actually clarify if that is % of reading or % of range – if unstated, it should be the more restrictive % of reading). So if the battery is exactly at 4.2V, this meter would be in-spec if I was using the 250V range setting (which only displays 1 decimal place, if I remember right), it is within spec to 4.4V (within 2 digits).

If I turn it down the dial to the 20V range and get 3 decimal places, it now should not read higher than 4.244 V (4.2 + 1% + 2 digits).

Note that battery voltage can vary because they are allowed tolerances, too. When a manufacturer says to charge a battery to 4.2V, they know the charger will not have perfect accuracy, so they usually mean something like +/- 0.05V. Such a battery can acceptably be as high as 4.25V (I think in reality, most charger manufacturers bias their chargers a little bit low to avoid concerns).


I’ll check battery voltage tomorrow, but it has a low battery indicator, so I think it’s not the battery. The readings were between 4.30v and 4.32 from different chargers, so I think it’s more likely to be a wrong reading.

#update
I’ve measured the multimeter battery and got 9.80v.
Also measured 12v power supply and got 12.50v. I’m constantly getting 3-5% error, way more than 0.5% 2dgts of specs. Overload protection spec for DC voltage also says 1000VDC/750VAC, so it should not be damaged by measuring AC on DC scale.
Probably it’s just a defective multimeter.

sarge12
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zoulas wrote:
But guys, make no mistake, Chinese DMM’s are only for reading up to two significant figures, in other words 10.21 volts. If you want to know past the 1, you have to get a Fluke.

Yes my fluke 89 IV is very accurate, but it is 600 bucks new. Other flukes are cheaper and still very accurate. The 89 IV fluke has data logging features and other bells and whistles. Any fluke with true RMS will be fairly accurate. and amp draw can be checked on the 89 IV using the meter leads between the battery negative and the ground on the tube while swithing to turbo. Basically the meter is wired in series with the light. For accuracy the true root means squared…RMS…is much more accurate. This mainly applies to ac voltage calculations, but any fluke meter with that feature will have more refined voltage reading circuits for DC volts as well. The accuracy specs for all readings will have much lower error rates.