5 Digit Accurate Volt Meter

[sshibly]

I am just getting into Li batts and my el cheapo meters are lying to me.

I read that some volt meters are more accurate than others.

What is an accurate volt meter on amazon or ali?

How does one use a voltage reference module?

 

[snoobler]

These cells are 3.2V. 1% accuracy is 0.032V. Most meters report 0.00V accuracy. .01V accuracy is 0.3% of the measured value.

0.3% accuracy is more than enough. Many meters report .001V, which is 0.03% accuracy on these cells. 5 digits is pretty absurd unless you're engaged in scientific efforts where 5 digits matters. In the case of this forum, it's rare that more than 0.00 digits would be meaningful.

A voltage reference is a name given to a device that supposedly has a very accurate voltage to which meters can be checked and calibrated. Expensive ones are probably pretty accurate. Cheap ones are less so. I bought a cheap one one. When my Fluke read exactly the correct voltage to .000, I was confident the reference was accurate enough to calibrate my other meters to it.

 

[boondox]

Take a look at the Fluke 115 if you want to step up to a decent meter. It is a poor man's Fluke but still much better than a cheapie. However, for just about anything solar related you can get by with a < $50 meter. One thing about the Fluke is I trust the safety rating , CAT III I think. You will never need a 5 digit meter, as Snoobler said that is lab grade gear. I do have voltage, resistance and capacitance standards and the truth is I don't need them and occasionally use them just to make me feel cool.

 

[Factory400]

I have a Fluke 87 from the mid-90's that does most of my solar work. It is durable. It is trustworthy. It has literally traveled the planet and worked in all sorts of exotic locations. It was chose for it's reliability and it has delivered. Accuracy - is probably about 10x what is needed for almost all solar related things.

In general, however, you want your measurement instrument to be about 10x higher precision than what you need as a final result so that works out perfectly.

I also have a 6.5 digit Keithley DMM for my lab bench. It is brutally accurate and amazing, but it is also big, heavy, expensive, and requires AC power to work.

The Fluke is great.

 

[RCinFLA]

For low cost the Uni-T 61E gives 22,000 count (more decimal points) and 0.05% accuracy. They are about $60.

For LFP cells, if you want to estimate state of charge from open circuit cell voltage you need better then 5 mV accuracy. That requires meter in 0.1% accuracy range. Many of the cheap DVM's do not meet their claimed accuracy spec. I have checked six of Uni-T 61E bought over several years span and all were better then their spec.

Only negative is they are not super resistant to ESD static discharge damage.

 

[sshibly]

These cells are 3.2V. 1% accuracy is 0.032V. Most meters report 0.00V accuracy. .01V accuracy is 0.3% of the measured value.

0.3% accuracy is more than enough. Many meters report .001V, which is 0.03% accuracy on these cells. 5 digits is pretty absurd unless you're engaged in scientific efforts where 5 digits matters. In the case of this forum, it's rare that more than 0.00 digits would be meaningful.

A voltage reference is a name given to a device that supposedly has a very accurate voltage to which meters can be checked and calibrated. Expensive ones are probably pretty accurate. Cheap ones are less so. I bought a cheap one one. When my Fluke read exactly the correct voltage to .000, I was confident the reference was accurate enough to calibrate my other meters to it.

Snoobler:

Yes Sir, 3.65v up to the 100th decimal is what I am looking for.

I bought a UNI-T that David P suggests,

This unit lists:
DC Voltage - 600V +/-(0.7%+3)

Boondox:
The Fluke 115 lists:

Accuracy

0.5% + 2

What is the +3 vs +2 above?


I am going to wait for a deal on the Fluke 115, I could not find a deal right now.

Also, I want to put a volt meter/gauge on the battery with a switch to display the volts. I could not find an accurate waterproof volt meter with a LCD display, bright is good too as it is going to outside on the boat.

 

[sshibly]

I have a Fluke 87 from the mid-90's that does most of my solar work. It is durable. It is trustworthy. It has literally traveled the planet and worked in all sorts of exotic locations. It was chose for it's reliability and it has delivered. Accuracy - is probably about 10x what is needed for almost all solar related things.

In general, however, you want your measurement instrument to be about 10x higher precision than what you need as a final result so that works out perfectly.

I also have a 6.5 digit Keithley DMM for my lab bench. It is brutally accurate and amazing, but it is also big, heavy, expensive, and requires AC power to work.

The Fluke is great.

Factory, Nice, I will peek at craigslist for used Flukes too,

Please post a pic of your Keithley DMM, I used a variety many many years back in the lab in college

 

[sshibly]

For low cost the Uni-T 61E gives 22,000 count (more decimal points) and 0.05% accuracy. They are about $60.

Only negative is they are not super resistant to ESD static discharge damage.

RC,
I bought this unit, it in the snail mail.

I need 2 hand held units and 4 panel display that just display volts. I want to have a boat bag with the cheapo units, in Michigan stuff tends to walk off truck beds or even open garages unfortunately.

Fluke units - the features and the variations of model is mind numbing.
What features should I look for in picking a model?

 

[Zil]

I have one of these. https://shop.marinehowto.com/products/sterling-power-dc-ac-amp-clamp-volt-meter

 

[RCinFLA]

RC,
I bought this unit, it in the snail mail.

I need 2 hand held units and 4 panel display that just display volts. I want to have a boat bag with the cheapo units, in Michigan stuff tends to walk off truck beds or even open garages unfortunately.

Fluke units - the features and the variations of model is mind numbing.
What features should I look for in picking a model?

You will typically use DC volts, ohms/continuity, likely AC volts. Having freq is good to check generator's rpm settings. Capacitance is good for AC motors run and start capacitor testing.

Other thing you need to get is a clamp-On AC/DC amp meter. Make sure it has DC amps as many just do AC current. Depending on your setup make sure it can read your maximum amperage needs and still be able to check lower amperage. Having startup AC surge peak reading is good to check motor startup current so you know what your inverter or generator may face when trying to startup an air conditioner, pump, or air compressor. The DC amperage capability is good for spot checking battery load and charge current and balance if you have parallel battery packs.

Recommending a particular clamp-on is not so easy. I have four of them. One for lower currents (40 amps), one for higher currents (600amps). One is just so-so for accuracy as it tries to do low current and high current and does neither with good accuracy. Last one I found by chance that happens to measure AC surge current pretty accurately. Many clamp-on's AC surge read significantly lower then actual surge current because their sampling rate is too slow.

 

[RCinFLA]

I recently bought a kick around AnEng AN870 20,000 count DVM for about $30. It claimed 0.05% accuracy but I did not hold out much faith.
I did check its calibration and was surprised to find it was 0.02% off.

It feels a little cheap. Its calibration is stored in a serial eeprom so a lot more hassle to re-calibrate. The UT-61E has a ten turn pot for DC voltage calibration so very easy to recal. Of course you need a good reference to recal it to.

	Calibration check
Meter	2.0480v Ref.	deviation		5.0000v Ref.	deviation
UNIT61E #1 (22,000 count)	2.0482	0.010%		4.999	-0.020%
UNIT61E #2 (22,000 count)	2.0487	0.034%		4.999	-0.020%
ANENG AN870 (20,000 count)	2.048	0.000%		5.001	0.020%

For measuring 3.5v cell there is not much advantage of a 22,000 count over a 6000 count as both will have three digits pass decimal, however higher count meters usually have better accuracy specs.

 

[Hedges]

Snoobler:

Yes Sir, 3.65v up to the 100th decimal is what I am looking for.

I bought a UNI-T that David P suggests,

This unit lists:
DC Voltage - 600V +/-(0.7%+3)

Boondox:
The Fluke 115 lists:

Accuracy

0.5% + 2

What is the +3 vs +2 above?


I am going to wait for a deal on the Fluke 115, I could not find a deal right now.

Also, I want to put a volt meter/gauge on the battery with a switch to display the volts. I could not find an accurate waterproof volt meter with a LCD display, bright is good too as it is going to outside on the boat.

0.7% of reading + 3 counts of the least significant digit. 0.5% of reading + 2 counts of least significant digit.

If you have a 3 1/2 digit meter (reads up to 1.999), your 3.xxV cell is going to be displayed as 03.45 or 3.45, so 0.5% + 2 counts means 3.41 to 3.49V, a bit over +/-1%
You're not going to get 0.3% accuracy (no additional digit counts beyond that) unless at least 4.5 digit meter and 0.1% accuracy spec.
Meters often have multiple digits beyond their accuracy rating, which at least lets you use the percentage and not worry about least significant digit counts.

A meter may be stable for a while, but drifts with temperature and time.
A boss told me my circuit was 0.02% accurate according to his 6 1/2 digit meter and I had to get it to 0.001% (10 ppm).
I told him his meter's accuracy spec was barely sufficient to say 0.02%, and to measure 10 ppm we had to get a 1 ppm accurate, 8 1/2 digit, $10,000 DMM. And we had to keep the room temperature within +/- 2 degrees during testing. Only then would the DMM perform well enough to reliably say if my circuit achieved 10 ppm while cycling +/-20 degrees in a thermal chamber. (I did achieve 20 ppm, though not 10 ppm.)

"up to the 100th decimal" Is that like Google?

 

[myself]

The Fluke 1xx units aren't officially sold in the US. They're great units, but be aware that they're graymarket here. (I've verbally abused Fluke over this, I think it's the dumbest decision in business.)

I can recommend the Aneng AN8008 or any of its derivatives. But never trust a meter -- hit up VoltageStandard.com or DMMCheckPlus.com and get yourself a calibrated reference, they're super cheap. Store it somewhere, and check ALL your meters against it once in a while.

 

[sshibly]

A lot to digest here, I am reading and rereading the post, my EE is very rusty.

Cell voltage in the range of 0 to 5 volts
Batt voltage in the range of 10v to 15 volts

LSN - ah ha, that makes sense.

Yes, source of reference is something I am used to. I reload my 300 PRC and I do it once a year or so. I have reference weight and diameter gauge to first confirm the scale and digital calipers [el cheapo ones]

 

[sshibly]

It took me a bit of thinking and watching a few youtube videos [I think I have watched more youtube than my kids in the last week, lol]

This slow brain finally grasped the concepts.

Digits - Resolution
Accuracy = x.xx %..

Here is what I came down with in terms of need:

Bench meters - I have the UNI-T and a cheapo off amazon

Fixed volt display [waterproof] with on/off switch, which I can mount on battery box, [Bought a few off Riden, but they are not waterproof]

Little bitty LCD volt displays to hook up to each cell to watch em during my testing.

 

[HRTKD]

The Fluke 1xx units aren't officially sold in the US. They're great units, but be aware that they're graymarket here. (I've verbally abused Fluke over this, I think it's the dumbest decision in business.)

I can recommend the Aneng AN8008 or any of its derivatives. But never trust a meter -- hit up VoltageStandard.com or DMMCheckPlus.com and get yourself a calibrated reference, they're super cheap. Store it somewhere, and check ALL your meters against it once in a while.

I'm in the process of buying the cheapie reference unit from voltagestandard.com. Better to know your meter is off, than to assume it's right.

 

[sshibly]

I'm in the process of buying the cheapie reference unit from voltagestandard.com. Better to know your meter is off, than to assume it's right.

I bought one off ebay, voltagestandard is the cat's ...man, if you were close by we could swing by
He will check calibration for free if you mail to him and pay for postage, not sure if he does this till.
I paid $20 for ref unit of feebay.

 

[HRTKD]

$35.xx for the 5v cheaper version, including shipping. Not bad.

 

[Cal]

For low cost the Uni-T 61E gives 22,000 count (more decimal points) and 0.05% accuracy. They are about $60.

For LFP cells, if you want to estimate state of charge from open circuit cell voltage you need better then 5 mV accuracy. That requires meter in 0.1% accuracy range. Many of the cheap DVM's do not meet their claimed accuracy spec. I have checked six of Uni-T 61E bought over several years span and all were better then their spec.

Only negative is they are not super resistant to ESD static discharge damage.

This meter is upgraded to E+.

Just ordered 61E+ This will be an upgrade from my almost 40 year old Fluke 77. I've been borrowing a Fluke 87III meter for 4.5 digit accuracy, which I need to return.

RS232 communication is replaced with USB. Very nice.

 

[HRTKD]

I received my voltagestandard 5v test device. I checked three of my meters.
Cheap no-name meter: 5.02v
20 year old Sperry: 5.00
Fluke 325: 5.0 (precision is only one decimal place)