ebay panel voltmeter accuracy and a question..

[BruceDanforth]

It IS woefully inaccurate but you get away with it in this use case because the battery has low internal resistance. Nobody has said it is a waste of money.

This conversation is hillarious!

You could supply all the proof and common sense in the world, and the naysayer(s) will STILL try and argue that your 12v meter for measuring whether a light is on or off is *WOEFULLY* inaccurate and a waste of £8! And if you don't understand where you're completely wrong, I'm not going to tell you!

 

[GHA]

It IS woefully inaccurate but you get away with it in this use case because the battery has low internal resistance. Nobody has said it is a waste of money.

It's so obviously being discussed to be used on a boat that it doesn't even need to be said. Measure it or calc it, for 8 quid it's bang on.

 

[BruceDanforth]

People were just trying to tell you the limitations of cheap measuring gear as you seemed to be showing an interest in electrical things. You might understand in time as you learn more.

It's so obviously being discussed to be used on a boat that it doesn't even need to be said. Measure it or calc it, for 8 quid it's bang on.

 

[GHA]

People were just trying to tell you the limitations of cheap measuring gear as you seemed to be showing an interest in electrical things. You might understand in time as you learn more.

the concept of a voltage divider really isn´t all that complex.

Anyway, would the circuitry for powering the meter and the backlight not effect the overall impedance more than the input impedance?

 

[Rivers & creeks]

This conversation is hillarious!

You could supply all the proof and common sense in the world, and the naysayer(s) will STILL try and argue that your 12v meter for measuring whether a light is on or off is *WOEFULLY* inaccurate and a waste of £8! And if you don't understand where you're completely wrong, I'm not going to tell you!

It has been fun reading.

You can't read.

As a response it has all the rapier wit, intellectual depth and insight of "you are you mean"

 

[BruceDanforth]

Just bolt it to your bulkhead it will work fine.

the concept of a voltage divider really isn´t all that complex.

Anyway, would the circuitry for powering the meter and the backlight not effect the overall impedance more than the input impedance?

 

[GHA]

Just bolt it to your bulkhead it will work fine.

I know that already, it was a genuine question, would the led backlight and power circuitry have a bigger effect on impedance than the meter input?

 

[BruceDanforth]

There only appear to be 2 wires going into it so they are one and the same.

A good meter will have a FET input stage or something to really limit the amount of current flowing into it.

I know that already, it was a genuine question, would the led backlight and power circuitry have a bigger effect on impedance than the meter input?

 

[VicS]

I know that already, it was a genuine question, would the led backlight and power circuitry have a bigger effect on impedance than the meter input?

Id expect the meter itself to have a very high impedance and draw very little current although I was surprised to discover that my cheap Maplin multimeter has an input impedance of only 1 megohm and so takes 12 microamps at 12 volts. Maybe better meters have higher impedances ???

Id expect the electronics to take more current.

However since you cannot separate the two with these self powered panel meters the difference is academic.

Id expect the back light to take significantly more current than the above and there fore perhaps affect the reading but only when measuring voltages on circuits which themselves have fairly high resistances.

Id not expect the meter electronics or the backlight current consumption to have any relevance when monitoring your boat electrics. in fact for troubleshooting the high impedance/ low current consumption of digital meters can make a fool of you. A test lamp often more useful or appropriate

 

[nigelmercier]

... in fact for troubleshooting the high impedance/ low current consumption of digital meters can make a fool of you. A test lamp often more useful or appropriate

Or indeed both. I've got a set of test leads with stackable 4mm plugs, so I can plug in a second set with crocodile leads and a bulb.
BTDTGTTS!

 

[BruceDanforth]

High end dvm's will have a switch to put the unit into a low impedance mode when there is a risk of 'ghost' voltages. Mine doesn't - I have a lightbulb.

 

[John_d_Smith]

Hi I've just bought a usb scope. Nice little unit and only £10. Look at picaxe website.

 

[Rigger Mortice]

Hi I've just bought a usb scope. Nice little unit and only £10. Look at picaxe website.

Have you used it yet? I'd be interested to hear what you think of it.

The Picaxe system suits me. The programming is easier.