How accurate is accurate?

[Bigpeetee]

Buy a digital volt meter I and others have said to help resolve power issues in our beloved Motorhome.

For some time, I've been unsure of the leisure battery voltage at rest, even with solar panels or after a run, they never read 12.6+ volts always a little low.

Today I used a different meter and the voltage was higher, concerned, I gathered all my multimeters and tried on a fixed voltage

Results

1. 12.59
2. 12.69
3. 12.72
4. 12.92
5. 12.74
6. 12.74
7. 12.70
8. 12.78
9. 12.70

No 1 was the one kept in the MH, is obviously low reading, No 5 is my bench meter, I corrected to 2 decimal places.

No's 1 & 4 now have a sticker on saying inaccurate, but OK for general testing.

Just goes to show, that you can chase your own tail if the tester is out.

I know it's a sad test, and that I've got so many DMM's, actually got more, but they've not got batteries in!!

The cheap models that are in the acceptable range are as accurate as one costing 10 times the price. I don't get it calibrated nowadays.

PS, the leisure batt voltage was 12.71v after 12 hrs of no charge/load

 

[Deleted member 21686]

Pretty sad pete.

Ever thought of collecting stamps.

 

[Deleted member 21686]

Are you or were you a sparky?

 

[vwalan]

to be honest i use a battery alternator tester in the trailer .bought from aldi for 3.99 .gives a series of lights .cant be bothered with exact . it works for me . seems good enough .have multi meters but for ease these work for most things .

 

[Firefox]

The highest reading was only about 1.5% out from the mean, so still not too bad for low price kit. I don't know what the quoted accuracy of these meters should be but there will be a tolerance.

Battery state of charge versus voltage will depend on temperature as well so readings will vary over time of day too, but within 0.1v should be good for most purposes, and I prefer a figure to those coloured lights which are probably graduated on (say) 0.3v intervals if you have four or five of them

 

[Admin]

I am a sparky and have a Fluke test meter, before taking any reading you zero the meter and the meter is calibrated. This still is not a prefect reading.

 

[oldtech]

Buy a digital volt meter I and others have said to help resolve power issues in our beloved Motorhome.

The cheap models that are in the acceptable range are as accurate as one costing 10 times the price. I don't get it calibrated nowadays.

PS, the leisure batt voltage was 12.71v after 12 hrs of no charge/load

Hi Pete !

you certainly said THAT right.
I've worked in electronics all my life and when it comes to voltmeters , DVMs etc , " you pays your money and takes your choice "
Be thankful it's only DC you are measuring !!
When it comes to Pro quality meters for AC work ,the sky is the limit.
Of course , if your firm is paying , or it's tax-deductable ..... different story altogether
.......check out the prices for a top-of-the-range "True RMS" meter from a quality manufacturer eg Fluke

Looking at your list ( and leaving out No 4 ! ) then rounding up to the first decimal place , they are all within a very acceptable
percentage error ! ... for me , anyway ha ha !

I use one that cost a couple of hundred ( but rarely ! ) , a ten quid one ( all the time ) , and a large analogue one ( coz I can't
test Triacs any other way ! ) .... and also because watching a needle moving sometimes tells so much more than just numbers changing.

We could start a new thread ... " How many multi-meters does your Mrs let you keep in the house ? " :hammer:

Oldtech

 

[maingate]

I was installing and commissioning some kit in Oman and had an electrical problem which entailed climbing up a steel structure and clinging on while using a cheap clamp meter. While doing this, I managed to drop the meter, which broke on impact. After that, every time I walked past one of my workmates they said (in a loud voice) .......

Ding Dong, Avo falling. :mad1:

(Avon calling)

 

[Bigpeetee]

For the techies:

Again whilst in Oman, I was replacing the military telecom network.

In telecoms, you only earth the signal at either a separate earth point or at the building earth point to reduce noise.

On searching for the building earth we discovered that there wasn't one and as far as we could see, never had one, so we needed a good earth, very dry ground/rock etc.

The contractor came in and started boring a hole to insert the rod, it wasn't oil we struck, but the water table and we had a Gusher, that flooded the parade ground and started to run towards all kinds of buildings. Luckily the earth rod and whatever they put down the hole stopped it eventually.

Now we had a cracking earth and had to attach it to the building, no one volunteered, so eventually one of the Indian contractors was offered a large sum of money to do it (you couldn't switch off the whole army camp we were told) a length of bared copper was placed along side the building earth and fully clothed up and wearing a welding mask the said Indian was told to wrap the cable at a distance around the building earth.

There was one bl00dy great flash and half of the camp went off, luckily, the cable had welded itself to the building earth. It took weeks to resolve all the issues of actually having an earth.

In Salalah in the south, we had radio equipment that wouldn't talk to the telecoms equipment, only some 20 metres apart, yet both tested OK.

The earth potential difference was over 100v, a good length of cable and all was well.

One of our guys was up a tower aligning a comms dish, so the army (being trained by the Brits) decided to fire RPGs over the tower for a laugh.

A very expensive piece of kit fell about 100' and disintegrated!! And he literally sh*t himself, an irate Irishman took the smile off an officers face in one thump, said officer woke up some time later!!

 

[Bigpeetee]

Are you or were you a sparky?

Comms project manager.

I did a "Proper" apprenticeship, and the idea was they could send you anywhere in the world and you had to fix it, so Low voltage high current DC @50v, mains, engineering inc tin bashing, use of workshop machines, Filing etc as well as the electronics and or electro mechanical devices. We had to do the lot.

Spent 5 years in the R&D dept

Trouble with technology, when you get to mid 40's you're old, my last job running fibre optic networks around Europe and across to the states (480 terabit bandwidth across the pond) all disappeared with the dot com bubble bursting about 10 years a go. At 50 I was ancient!! Been repairing and installing sound and light systems since.

 

[oldtech]

It's a LIVE one !!!

Comms project manager.

I did a "Proper" apprenticeship, and the idea was they could send you anywhere in the world and you had to fix it, so Low voltage high current DC @50v, mains, engineering inc tin bashing, use of workshop machines, Filing etc as well as the electronics and or electro mechanical devices. We had to do the lot.

Spent 5 years in the R&D dept

Trouble with technology, when you get to mid 40's you're old, my last job running fibre optic networks around Europe and across to the states (480 terabit bandwidth across the pond) all disappeared with the dot com bubble bursting about 10 years a go. At 50 I was ancient!! Been repairing and installing sound and light systems since.

OOH !!! ... looks like we've got a LIVE WIRE of a topic here !!!

Reminds me of the Monty Python sketch about the Yorkshiremen ... and who had the toughest upbringing :lol-053:

So ... it appears that there are several members on here who have "made their bones" or "earned their stripes " in the
business of electronics / electrical engineering ... in some of the MANY different specialist fields of our trade.

Just to put in my "two penneth" , I once worked at Philips Radio / Data Comms when there was a little "clique" of old chaps
( mostly ex-RAF ) who ruled the roost when it came to RF electronics .... they did all the SINAD and final calibration
of radio sets that left the factory , then went all over the world ( all of the sets were badged with the trusty "Pye" brand name ).
And they wouldn't even talk to us "youngsters " with our fancy ideas about digital architecture and surface-mount technology.

I guess my point is this .... if we don't pause and take stock ,it can all take on a bit of a "trainspotter" / " anorack" aspect.
Next thing you know , we will all be meeting up somewhere ( probably a pub car-park ) , and getting our equipment out
........ to see who's got the biggest DVM ... ha ha ! ....:lol-061:

Having said all that , what's the betting that we will now get a deluge of members starting threads like " What is wrong with trainspotters"
and anyway , what about my earlier suggestion for a new thread ..... " How many DVMs will your Mrs let you keep in the house ? "
But let's try and keep it lighthearted !!! .....

.... Laugh ? .... I nearly voted .. !!!

All the best , fellow techies ... have a fab weekend !

Oldtech