Flummoxed by a small meter

[Simpo Two]

Yesterday I bought a small LCD multimeter for light duties, £4.99 from Mapiln.

However whilst the voltage side of the meter seems to work perfectly I can't get any reading from the current side. There are five ranges from 200 microamps to 10A and no matter which combination of range and socket I try (one does high current, the other low) I get a reading of zero. I'm a little hesitant to test it on mains, but certainly on batteries of 1.5, 9 and 12V the current is always zero. Am I doing something wrong or is it faulty?

[georgetaylor]

I suspect you are doing it wrong.
To measure current you must break the circuit and insert the meter into the circuit.
If you just put the probes across a voltage you will just blow the fuse in the meter as it will draw as much current as the battery/supply can muster.
Don't play with the mains if you are unsure!

[GarryA]

If you put a meter set up for current across a supply you will put a dead short on and probably blow the supply before the meter.

[Simpo Two]

Hmm, thought it might be something like that.

I bought the meter at the same time as a breifcase-style 13W solar panel to charge boat batteries.

How would I measure the current produced by the solar panel? Put it in the live line between battery and panel? But then you have the battery current coming from the other direction - milliamps from one side and two car batteries with a combined current of god-knows-what on the other. Which side wins?

ETA between the panel and batteries there's also a seperate charge regulator.

http://www.maplin.co.uk/module.aspx?moduleno=99760...

Edited by Simpo Two on Saturday 13th November 11:25

[GarryA]

Simpo Two said:

Hmm, thought it might be something like that.

I bought the meter at the same time as a breifcase-style 13W solar panel to charge boat batteries.

How would I measure the current produced by the solar panel? Put it in the live line between battery and panel? But then you have the battery current coming from the other direction - milliamps from one side and two car batteries with a combined current of god-knows-what on the other. Which side wins?

Current measured will be the load, just because car batteries are say 400A max output does not mean you will pick that up unless you attach a load to them i.e. a running starter motor.

P = IV

2 car batteries are 24v if the solar panel is 13W then I = P/V which is roughly 500mA.

[Simpo Two]

GarryA said:

Simpo Two said:

Hmm, thought it might be something like that.

I bought the meter at the same time as a breifcase-style 13W solar panel to charge boat batteries.

How would I measure the current produced by the solar panel? Put it in the live line between battery and panel? But then you have the battery current coming from the other direction - milliamps from one side and two car batteries with a combined current of god-knows-what on the other. Which side wins?

Current measured will be the load, just because car batteries are say 400A max output does not mean you will pick that up unless you attach a load to them i.e. a running starter motor.

P = IV

2 car batteries are 24v if the solar panel is 13W then I = P/V which is roughly 500mA.

The batteries are in parallel; it's a 12V system.

I hate electrons, they're too damn small to see!

[GarryA]

Well then you would say 0.9-1A but the spec sheet says 798mA tops, so if your batteries need charging thats what is will be.

[MOTORVATOR]

Pur your meter in line between the positive out of the charger and the battery positive. As Gary says you will only see the current coming from the charger (the batteries are not supplying current to the charger). depending on your battery condition (and the sun) you will see up to the 900 milliamps or whatever the max output is.

[GarryA]

Unless the batteries are attached to a load greater than what the solar can charge? Then you are going to see a discharge current.

O/P is this solar charger just clipped to the batteries? Or are the batteries disconnected from the supply (I mean totally isolated) when on charge by the panel?

[Simpo Two]

GarryA said:

Unless the batteries are attached to a load greater than what the solar can charge? Then you are going to see a discharge current.

O/P is this solar charger just clipped to the batteries? Or are the batteries disconnected from the supply (I mean totally isolated) when on charge by the panel?

I don't intend to run any devices from the panel because in normal use the batteries will have enough power between cruises. The panel is simply there to keep the batteries topped up, and principally during the winter lay-up (5 months on the bank with no mains power).

There's a batttery isolator as you see here, currently 'off'. Even when it's 'on' the only electrical things on the boat are four lightbulbs and a starter motor.

Here's the regulator connected to batteries by clips:



And here's the regulator:



By deduction from the curiously-worded Chinese instructions, both lights being on is good. If the panel is overcharging then one light goes off; if there's something drawing too much current (the setup has an option to connect another device) then the other light goes off.

I was trying to judge whether the panel was sending too little or too much power to the batteries ot keep them topped up.

Edited by Simpo Two on Saturday 13th November 12:06

[GarryA]

Cant see pics, anyway.....

It depends on the demand that you ask of the batteries, you can charge them at 1mA if you like although it might take a few weeks.

You need to look at the voltage of the batteries to see when they are charged.

Fully charged should be 12.6v perhaps dropping 0.1v in this crappy weather.

Flat would be about 11.9v

So you really need to leave the panel on for a bit and then check the voltage of the batteries, do not do this with the panel attached as it will fudge your readings.

[dilbert]

I have a cheap Chinese multimeter. It does work, but it doesn't work the way you would expect it to, or the way it says in the manual.

The meter appears to work like a Fluke, when you look at it, but it's actually much more basic inside. It's good for marketing. You think you're getting what you wanted when you see the picture. When you actually try to use it, it's something more basic.

I also have a Fluke, but I wanted a cheap second meter.

If it has high and low current inputs, try using the high current input for all ranges. If it's like my cheapo meter, then the low current input is not apparently connected, despite the markings on the case that indicate how and when to use it.

I just use the high current input for everything.

[xllifts]

You people scare the st out of me sometimes! If you don't know what your doing leave well alone!

People like you are the reason my and other trades peoples Liability Insurance is so high and the reason the H+S is so restrictive!

Get yourself on a electronics appreciation course and learn the basics rather than poke and see

[Poledriver]

xllifts said:

You people scare the st out of me sometimes! If you don't know what your doing leave well alone!

People like you are the reason my and other trades peoples Liability Insurance is so high and the reason the H+S is so restrictive!

Get yourself on a electronics appreciation course and learn the basics rather than poke and see

+1k

[Globulator]

Poledriver said:

xllifts said:

You people scare the st out of me sometimes! If you don't know what your doing leave well alone!

People like you are the reason my and other trades peoples Liability Insurance is so high and the reason the H+S is so restrictive!

Get yourself on a electronics appreciation course and learn the basics rather than poke and see

+1k

Nah, PH is all about being frustrated enough by a £2 multimeter to measure the current of the national grid with it to see what happens

[Simpo Two]

xllifts said:

You people scare the st out of me sometimes! If you don't know what your doing leave well alone!

People like you are the reason my and other trades peoples Liability Insurance is so high and the reason the H+S is so restrictive!

Get yourself on a electronics appreciation course and learn the basics rather than poke and see

Oh FFS, it's only a 12V battery.

Do you really think I'm going to pay someone to plug a mickey mouse solar panel onto a 12V battery? And who would do it anyway? If it was dangerous they wouldn't sell them.

Edited by Simpo Two on Sunday 14th November 00:26

[xllifts]

Simpo Two said:

xllifts said:

You people scare the st out of me sometimes! If you don't know what your doing leave well alone!

People like you are the reason my and other trades peoples Liability Insurance is so high and the reason the H+S is so restrictive!

Get yourself on a electronics appreciation course and learn the basics rather than poke and see

Oh FFS, it's only a 12V battery.

Do you really think I'm going to pay someone to plug a mickey mouse solar panel onto a 12V battery? And who would do it anyway? If it was dangerous they wouldn't sell them.

Edited by Simpo Two on Sunday 14th November 00:26

And that shows your ignorance its the amps that Kill you as little as 20a dc can kill whether its 12v DC or 240ac it'll be the amps that'll kill you. 100ma will stop your heart!
But you knew that anyway didn't you.

[Simpo Two]

I have also not been on a course on how to operate light switches which are mains and therefore very dangerous. I am frightened it may go wrong and I might kill myself; in fact you may be in the nick of time to save my life.

Lucky you turned up really. Please quote me for coming over in about 30 minutes to operate my bedside light for me.



If you can't contribute anything useful, save your 'industry outrage' for somebody else please.

Edited by Simpo Two on Sunday 14th November 00:48

[Poledriver]

Simpo Two said:

I have also not been on a course on how to operate light switches which are mains and therefore very dangerous. I am frightened it may go wrong and I might kill myself; in fact you may be in the nick of time to save my life.

Lucky you turned up really. Please quote me for coming over in about 30 minutes to operate my bedside light for me.



If you can't contribute anything useful, save your 'industry outrage' for somebody else please.

Edited by Simpo Two on Sunday 14th November 00:48

tt!

[xllifts]

Simpo Two said:

I have also not been on a course on how to operate light switches which are mains and therefore very dangerous. I am frightened it may go wrong and I might kill myself; in fact you may be in the nick of time to save my life.

Lucky you turned up really. Please quote me for coming over in about 30 minutes to operate my bedside light for me.



If you can't contribute anything useful, save your 'industry outrage' for somebody else please.

Edited by Simpo Two on Sunday 14th November 00:48

Its far from an Industry outrage, its a statement of how incompetent fools play with fire and then get burnt costing us trained professionals in the pocket!
Items such as test equipment should not be allowed for general public purchase to stop unskilled people meddling with stuff they have no knowledge on.

For a constructive comment

'you don't have a clue so leave it alone'

HTH