Float voltage for Firefly batteries

[FlyingScot]

Originally Posted by hellosailor

Scott-
" a Fluke 365 true RMS meter. Weirdly the Fluke, despite it's price and quality, only reads down to .1 volt. It's more of a clamp on meter with removable jaw. As best as I could estimate there is a 0.05v difference between"
Nothing weird about that, but it does touch on the often ignored issue that when you are trying to get picky about 12VDC charging, you need ACCURATE instruments, not just PRECISE ones.
Fluke rates that meter as being accurate only to 2% on DC scales, with an additional possible error of 5 LSD (least significant digits). Even though the rated resolution is 0.1V, that means if the true voltage is 12.05VDC, the meter could display anywhere from 12.10 volts to 12.00 volts--and it would still be "just" off by those last 5 floating digits. And that's without accounting for the fact that 12.05 volts could be shown as 11.81 to 12.30 volts, simply because of the 2% accuracy limit of the meter.
Add them up, and that meter could read 11.76 to 12.35 volts, and the real voltage would still be 12.05. While most Fluke meters will easily exceed their specs, there are other models that would be more accurate, and many that are also factory certified and calibrated. Without vaguely annual calibration--you can really trust any meter once you start getting into tight measurements.
I'm sure that if you contacted Fluke and said "I want a factory calibrated meter that shows me DC voltage to four digits without any error" they'd find you a FIVE digit model at a considerably higher price, and tell you to put a piece of tape over the rightmost digit because even the best meters do have some float (usually 2-3 digits) on the LSD.

Fluke is arguably the most respected brand of meters, but they still don't make a model that carves numbers in stone.(G)

Great points.

I admit I didn't fully research before buying. One of the reasons I paid up for the Fluke is that I thought I didn't need to research so carefully.

Are you sure about the 2%? This doc shows 1% + 5
https://dam-assets.fluke.com/s3fs-pu..._umeng0000.pdf

Maybe you confused DC Current vs DC Voltage?

I have a Fluke 76 that is rated at 0.3% + 1 on the .01 resolution for the 40v range. I've had it for 22 years now. This level of accuracy (assuming it still is) would be about much better than the 365 model.

I should have taken it to the boat this last trip for these measurements.

[hellosailor]

Chris-
Could be my reading glasses need recalibration, I know my eyes are certainly out of calibration and no longer under warranty as well. But from a Fluke PDF "3805299_0000_ENG_A_W.pdf" if sure looks like 2% on DC voltage to me.

Your older Fluke (it isn't old enough to qualify for "ancient and venerable" status yet) might be the better choice, but after 22 years I'd be surprised if it hadn't drifted somewhat. It can always be amusing (ahem) to hook up different meters and see just how widely they disagree. Despite the fact that you can roll your own calibration source without robbing any banks, somehow, those don't seem to be available at "consumer" prices from any of the usual online sources. And the folks (including Fluke) who will take your meters in an recalibrate them to real standards....ouch.

[FlyingScot]

Originally Posted by hellosailor

Chris-
Could be my reading glasses need recalibration, I know my eyes are certainly out of calibration and no longer under warranty as well. But from a Fluke PDF "3805299_0000_ENG_A_W.pdf" if sure looks like 2% on DC voltage to me.

Your older Fluke (it isn't old enough to qualify for "ancient and venerable" status yet) might be the better choice, but after 22 years I'd be surprised if it hadn't drifted somewhat. It can always be amusing (ahem) to hook up different meters and see just how widely they disagree. Despite the fact that you can roll your own calibration source without robbing any banks, somehow, those don't seem to be available at "consumer" prices from any of the usual online sources. And the folks (including Fluke) who will take your meters in an recalibrate them to real standards....ouch.

I copied this from labeled pages 14/15 (PDF page # 18/19). I changed to Bold for what I'm looking at.

Specifications
Electrical Specifications
AC Current
Range .................................................. ...200.0 A
Resolution........................................ .......0.1 A
Accuracy .................................................2 % ±5 digits (45 – 65 Hz)
2.5 % ±5 digits (65 – 400 Hz)
Crest Factor ............................................2.5 @ 125 A
1.55 @ 200 A
Add 2 % for C.F. >2
DC Current
Range .................................................. ...200.0 A
Resolution........................................ .......0.1 A
Accuracy .................................................2 % ±5 digits
AC Voltage
Range .................................................. ...600.0 V
Resolution ...............................................0.1 V
Accuracy .................................................1 .5 % ±5 digits (45 – 400 Hz)
DC Voltage
Range .................................................. ...600.0 V
Resolution ...............................................0.1 V
Accuracy .................................................1 % ±5 digits
Resistance
Range .................................................. ...600.0 Ω/6000 Ω
Resolution ...............................................0.1 Ω/1 Ω
Accuracy .................................................1 % ±5 digits

This is from the link I posted which I got directly from the Fluke website. Dated 2010.

[hellosailor]

The file I got from them is only two pages long, it is the sales(?) brochure not the owner manual. But if I convert the locked PDF file to OCR the plain text version of the specs says:

Fluke 365 Range Resolution Accuracy
AC current 200 A 0.1 A 2 % ± 5 digits
DC current 200 A 0.1 A 2 % ± 5 digits
AC voltage 600 V 0.1 V 2 % ± 5 digits
DC voltage 600 V 0.1 V 2 % ± 5 digits <<<<<<<<<-----------
Resistance 6000 Ω 0.1 Ω 1 % ± 5 digits

You'd have to ask Fluke, or perhaps Congress, to investigate and see which of those files has been tampered with, by the Russians, Chinese, North Koreans, Iran....or perhaps just Fox News?

[FlyingScot]

Anyone make a 50v dc measuring device that is accurate and low cost?


I would rather not...but a Fluke 28-II may be my next meter. +/- 0.05% + 1 and IP67 rating.
Over $500 with certificate.

[FlyingScot]

Since I hate not knowing, I splurged and bought a Fluke 87V with NIST certificate. I also bought a $19 meter which can be purchased right now for under $13. Notice the extra digit on the 87V.

Older Fluke 76: 12.30 VDC
New certified Fluke 87V: 12.308 VDC
Dirt cheap: 12.35 VDC



I’m away from the boat so I’m using a sealed LA powered portable air compressor for the test.

[a64pilot]

Try the test a year from now, and on a hot day, and a cold day.
I suspect the cheap one will have varied more by then, and be more susceptible to temp changes.

[john61ct]

Or maybe will randomly become **more** accurate 8-)

[SoonerSailor]

I have been amazed at how well modern DMMs hold their accuracy over time. The many dirt cheap models now available may not hold up as well, but they usually seem to start off with rather impressive accuracy. Time will tell.

BTW, if you want a reasonable price voltage standard go to voltagestandard.com

[john61ct]

Ooh good stuff. What a great forum this is

[FlyingScot]

I couldn't resist the $13 price for the meter and bought a second one.
It's almost perfectly matches the NIST 87V. They both would swap the final digit back and forth (12.33 and 12.34).

[john61ct]

Order 20, send back the inaccurate ones 8-)

[hellosailor]

Scott-
I did calibrate my "free" red meters to match my good meter, all set to a 10.0000 volt calibration source. (Yes, that's more zeros than the meters can show.) It is just a matter of turning a trimpot that's usually obvious to spot in a meter.
Do I think they'll *stay* dead on? Hellno. But then again, I can compare them to the calibration source in the future, and we'll see how far they do or don't drift. If your two cheapies agree with each other in two years..."One giant step for mankind".(G)

[rgleason]

Low Cost Precision Voltage References
Nuts and Volts - September 2007
Store shop.voltagestandard.com