Volt meter (1 Viewer)

hilldweller

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Just how can they do this at this price ? No idea of quality but it seems worth sticking one across the batteries maybe with a simple Push-On switch.

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Feb 27, 2011
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Just how can they do this at this price ? No idea of quality but it seems worth sticking one across the batteries maybe with a simple Push-On switch.

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Saw these a couple of weeks ago and was really tempted.

I wonder if you could get a shunt and calibrate one of these meters to do amperage as well?
 
Feb 27, 2011
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found one...

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50Amp one here cheaper
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Destination Unknown

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This is the type we have fitted to the rig. Volt meter via 3 way switch which shows volts from Chassis/Leisure/Leisure (spare)
Also fitted same design but amp meter via shunt, shows what we are using from leisure.
Again only a few quid each.
 

Jim

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How they can make them, ship them 8000 miles, then the maker, seller and eBay still make money, it beggars belief. :Eeek:
 

stcyr

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We've got one of these wired into the solar gubbins... found it very useful in letting us know when to cut down on consumption... :thumb:
 

magicsurfbus

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I've got a couple of those voltmeters that fit into the 12v ciggie lighter sockets - one on the dashboard and one on the leisure battery circuit. Very handy because they're portable.

What's also useful is the little digital display thermometers with sensor - I fitted one to the MH fridge's front panel. Trouble is the readout in Southern France in August is frightening. We had one day where it didn't go below +16 degrees inside the chiller compartment, although the icebox remained frozen.

I've also got one fitted on the house fridge so I can see if the lodger's been leaving the fridge door ajar ;-)
 
Jan 24, 2010
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found one...

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50Amp one here cheaper
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youll need to use a Isolated DC-DC converter for these, if you use the same source as it is measuring it will probably just short out or just not work at all

Alternativly take the 12v from the hab battery or vice versa if your measuring the hab battery
 
Feb 27, 2011
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youll need to use a Isolated DC-DC converter for these, if you use the same source as it is measuring it will probably just short out or just not work at all

Alternativly take the 12v from the hab battery or vice versa if your measuring the hab battery

I don't follow you?

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Jan 24, 2010
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Basically this amp meter needs a power source which is not directly from the same circuit you are measuring the amps or it won't work or will short out.

for measuring the hab battery, don't take the power for the meter from the hab battery unless you are using an isolating dc-dc converter.

Ooops ....just noticed in my previous post I should have typed..alternativley take the 12v from the Van battery or vice versa if you are measuring the van battery
 
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johnp10

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Being able to monitor amps used is obviously useful.
Battery voltage can be measured at the control panel or with a multi meter.

At the risk of indulging in muppetry............
I'm no electrical wizard, so have I got this amps measuring business right?

I have 2 leisure batteries totalling 185 amps, so I would need a device rated at say 200 amps?

The shunt would be spliced into the (+) outlet from the leisure batteries to the control panel?

The power source cant be taken from the leisure batteries?

Power source from the vehicle battery is ok, as the device would only draw milliamps?
From fag lighter ok, or hard wired?

Can a similar bit of kit be spliced into the AC circuitry, or is that unecessary?
 
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Basically this amp meter needs a power source which is not directly from the same circuit you are measuring the amps or it won't work or will short out.

for measuring the hab battery, don't take the power for the meter from the hab battery unless you are using an isolating dc-dc converter.

Ooops ....just noticed in my previous post I should have typed..alternativley take the 12v from the Van battery or vice versa if you are measuring the van battery

I still don't follow you. Why should it short? I don't follow your logic.

The shunt is in series (usually on the negative terminal) then you connect the supply as normal. No short there....

This is exactly as it should be.:Confused:

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Feb 27, 2011
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Being able to monitor amps used is obviously useful.
Battery voltage can be measured at the control panel or with a multi meter.

At the risk of indulging in muppetry............
I'm no electrical wizard, so have I got this amps measuring business right?

I have 2 leisure batteries totalling 185 amps, so I would need a device rated at say 200 amps?

The shunt would be spliced into the (+) outlet from the leisure batteries to the control panel?

The power source cant be taken from the leisure batteries?

Power source from the vehicle battery is ok, as the device would only draw milliamps?

Can a similar bit of kit be spliced into the AC circuitry, or is that unecessary?

No you just need a shunt that is capable of carrying your usage at maximum. I have 500AH of battery and a 100Amp shunt. Never seen it go above 35 amps when charging and never about 15amp discharging.

The shunt is usually on the negative terminal. Disconnect everything from the negative terminal of the battery. Connect one side of the shunt to the battery terminal then reconnect everything back to the other side of the shunt.

You can power the meter from the same battery. Not sure what bungy is on about here but hopefully we will get an answer soon and clear up my confusion:thumb:

forget the AC side not necessary.
 

johnp10

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Thanks Grommet.
Sounds easy enough.
So....that will monitor how many amps being used at any given time?
 
Feb 27, 2011
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Thanks Grommet.
Sounds easy enough.
So....that will monitor how many amps being used at any given time?

And also how quickly you are getting charge in. for instance from a solar panel or main charger.

It's like a really rudimentary NASA battery monitor without the cumulative count/% left readings..

Wait for Bungy just in case I am missing something.

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Jan 24, 2010
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Im talking about the meter shorting btw .....as most amp meters at the cheap end of the scale dont allow for a common ground between what is being measured and the dc supply that powers the meter. These are also generally used in multimeters etc so generally expect a seperate power supply

The wiring diagram on the both that are listed show two distinct circuits, one for the shunt and one for the power. So assuming they are correct....they need a seperate supply to what is being measured

Also need to be aware of where the shunt needs to be for the particular meter, most are designed to be in the - side, to eliminate common mode voltage....which the first one listed is. But some are designed for the + side. The second listing doesn't say which it is so may be worth checking with the seller on both counts to be sure.
 
Feb 27, 2011
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Im talking about the meter shorting btw .....as most amp meters at the cheap end of the scale dont allow for a common ground between what is being measured and the dc supply that powers the meter. These are also generally used in multimeters etc so generally expect a seperate power supply

The wiring diagram on the both that are listed show two distinct circuits, one for the shunt and one for the power. So assuming they are correct....they need a seperate supply to what is being measured

Also need to be aware of where the shunt needs to be for the particular meter, most are designed to be in the - side, to eliminate common mode voltage....which the first one listed is. But some are designed for the + side. The second listing doesn't say which it is so may be worth checking with the seller on both counts to be sure.


I don't see how a common ground could cause a short. Can you point me at an internal circuit diagram that explains what you mean please?
 
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Oct 14, 2007
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How they can make them, ship them 8000 miles, then the maker, seller and eBay still make money, it beggars belief. :Eeek:

Jim,

Sadly It's a very simple answer, Child Labour.

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hilldweller

hilldweller

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Ooops ....just noticed in my previous post I should have typed..alternativley take the 12v from the Van battery or vice versa if you are measuring the van battery

And the two batteries don't share a common ground so both +12Vs effectively identical !

It looks to me like the ground is common to power and the shunt so the +12V should be fine to power it. The input will only go to an op amp, inside a micro, so it's common mode rejection should cope with any small differences, which on such a shunt will be tiny.
 

Techno

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I bought this too, great Chinese price. Now my Baraldi cooker hood is controllable
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Jan 24, 2010
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I don't see how a common ground could cause a short. Can you point me at an internal circuit diagram that explains what you mean please?
I don't have an internal circuit diagram for the meters hence the warning - lessons learnt and all that...but there are lots of examples on line...this pdf has a very detailed description ., bit of an old one but does go into what I think your after
Just to clarify - im not saying the meter will cause a short across the batteries...its the meter its self that can short out and die a death of a thousand wigglies

UPDATE - Just found this lot...http://www.datasheets.org.uk/500--digital+Ammeter+circuit-datasheet.html
update again - forget that - you have to pay for them!!

And the two batteries don't share a common ground so both +12Vs effectively identical !

the two batteries are normally isolated from each other by charging systems etc - so don't actually function as one battery so are, for the purposes of the meters, Isolated supplies ::bigsmile:

It looks to me like the ground is common to power and the shunt so the +12V should be fine to power it. The input will only go to an op amp, inside a micro, so it's common mode rejection should cope with any small differences, which on such a shunt will be tiny.

It all depends on the meters design...if it has been designed to work that way - then no issues, but if it has not it will at best display incorrect info or more likely just not work. and at worst the meter will burn out

this one for example doesnt need a separate supply Link Removed where as this one, from the same seller, does
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The simple fact is that some require a isolated supply and some dont, hence why I said its worth checking with the seller -

So you can either buy one that doesn't need an isolated supply...or buy one that does and use a isloated supply, or just give it a go and accept that it may not work

forgot to add that if your going down the route of installing an Amps one and volts one... you'll definatley need a isolated supply

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johnp10

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Wonderfully confused now.

In simple terms:
Monitor the leisure batteries through a shunt (in + or - ?) and take the feed for the meter from the vehicle battery (minimal amps drain)......all safe, should work....yes?
 
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Jan 24, 2010
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Wonderfully confused now.

In simple terms:
Monitor the leisure batteries through a shunt (in + or - ?) and take the feed for the meter from the vehicle battery (minimal amps drain)......all safe, should work....yes?

sorry for the confusion::bigsmile:

from my point of view....yes it should, you could also add a switch into the circuit to turn the meter on an off, which will help with the battery drain. Shunt should be inline in the -ve wire from the battery, and as close to the battery as possible.

Make sure you get one that can cope with 12v power supply, or you will need a DC voltage converter to drop the 12v down to whatever the meter needs...which just adds complexity and cost.

Best bet is to get one that can accommodate a range, most of them have a range from 4.5v upto, and beyond 15v - one of these would be ideal

One thing - dont expect them to overly accurate(+- 2-3%)...a good guide line but not a precision info...to get very accurate needs shielded wire and some other bits and bobs!! but again all dependant on the design of the thing...
 
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Thanks for the information Bungy. I will look into it in more detail later when I get some time. I will take your word for it though.

I have set up meters before using a shunt and not taken this into account (both v and a meters) and never had a problem.

I am struggling to imagine a circuit with a fault mode caused by using the same supply but you have obviously experienced this...

My practical experience of electronics comes from being a radio ham, having a tv/VCR repair round (many moons ago) as well as my hobby electronics from 20 years ago. It is all well out of date now so I will bow to more current knowledge on this.

A quick fix for the would be to use a PP3 (9v) battery and a momentary push action button to turn it on.

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Apr 27, 2008
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I have bought the odd cheap meter and would suggest checking against a known accurate meter. So for example a volt meter I bought reads nearly 10% low, which is no problem as long as it is known, and for a lot of purposes it really doesn't matter though it might if it was even further out.
 
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hilldweller

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the two batteries are normally isolated from each other by charging systems etc - so don't actually function as one battery so are, for the purposes of the meters, Isolated supplies ::bigsmile:

As long as the two battery system negatives are connected together, ours is, then as far as the +12V is concerned the meter will not know the difference between either 12V. You cannot consider either to be isolated.
 
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hilldweller

hilldweller

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forgot to add that if your going down the route of installing an Amps one and volts one... you'll definatley need a isolated supply

I've been tossing this round my head all night.

Why ?

I can't work it out.

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