Voltmeter

[cleverdicky]

But aren't we discussing the merits of a fuse in a circuit used as a voltage measuring device on a 12v DC battery, where the current needed for said device is only going to be a few 10's of miliamps at the most.

NOT a high current, high voltage circuit even if is at 10% or less of maximum load.
A fuse is a protection device, it is NOT part of a circuit and should be sized according to the design of the equipment used and the normal current it will carry. A voltage measuring device or meter will not be using a high current or anything like the maximum rated for the fuse. It is measuring VOLTAGE NOT CURRENT, and so will not need to carry any current, and will not offer any significant resistance.

 

[Miffy]

As Above, lets get back on topic as we have deviated too far.

 

[television]

I think it is a bad idea to add 20ma to the drain on this car this making 75ma or more, plus reading the voltage gives little indication of the state of the battery, any significant change read it will be too late

 

[Alex Crow]

Getting back to the original idea, an amp meter would be better, and will not add anything to the ma draw at all.

 

[television]

Getting back to the original idea, an amp meter would be better, and will not add anything to the ma draw at all.

You cannot wire it in Alex unless you have a master battery switch that would shunt out the meter when the car was in use

 

[Alex Crow]

You cannot wire it in Alex unless you have a master battery switch that would shunt out the meter when the car was in use

No Malcolm, the OP wants to measure the load when locked.

A voltmeter is not a good measure, when the thing you really want to know is the current...

 

[television]

No Malcolm, the OP wants to measure the load when locked.

A voltmeter is not a good measure, when the thing you really want to know is the current...

If you read my post above I have already said that a voltmeter is useless, and I am quite aware of what he wants to do thank you very much.

And again you cannot wire an ammeter in without a shunt over it when you want to use the car. A battery isolator is the only way it can be done, as I have already said in answer to your post above.

I hate it when people try and make out that I have said something different to what I have,, its all there in the post above.

 

[cleverdicky]

Sorry, but just as a reminder for everyone This is the OP's first post that started this debate

Advice please?
I am fitting a voltmeter (not digital) to my A Class.
I want it across the battery to provide a rough check all the time as directly as possible and I will be able to check the voltage without opening the car doors for example.
The meter internal Resistence is 600 ohms (12V/600 say 20ma)
What size line fuse would be reasonable?
Thanks

A it happens, you can use and leave in circuit a zero centre ammeter in parallel to a shunt. Ford Capris, and many other cars had them left in circuit.

http://en.wikipedia.org/wiki/Ammeter

 

[television]

Sorry, but just as a reminder for everyone This is the OP's first post that started this debate




A it happens, you can use and leave in circuit a zero centre ammeter in parallel to a shunt. Ford Capris, and many other cars had them left in circuit.

http://en.wikipedia.org/wiki/Ammeter

With a shunt no meaningful measurement could be done as a meter with FSD of 100ma or 200ma is needed

 

[Alex Crow]

I hate it when people try and make out that I have said something different to what I have,, its all there in the post above.

Brilliant

 

[television]

I think it is a bad idea to add 20ma to the drain on this car this making 75ma or more, plus reading the voltage gives little indication of the state of the battery, any significant change read it will be too late

Brilliant

Well did I say it was not a good idea or not, you can see it in the above post that I have quoted here. It just is not nice talking down to people as though they no nothing on the subect

 

[Alex Crow]

...It just is not nice talking down to people as though they no nothing on the subect

I agree with you there Malcolm, and I make sure I never talk down to people as though they no (sic) nothing on the subject.

 

[television]

I agree with you there Malcolm, and I make sure I never talk down to people as though they no (sic) nothing on the subject.

If you are referring to me sticking to my guns on this thread, I have probably used more fuses and repaired more things than anyone else on here where voltages are critical, Am I supposed to agree with things that are not true or possible.

It has been shown in the charts that there is no measurable value that is of any use to anyone, and just the natural resistance of that strand of wire.

AGC-12 32V - - 0.0070
AGC-14 32V - - 0.0062
AGC-15 32V - - 0.006
AGC-20 32V - - 0.004
AGC-25 32V - - 0.003
AGC-30 32V - - 0.002
AGC-35 32V - - 0.0014
AGC-40 32V - - 0.0019

Am I supposed to agree with wrong info, you do not, and I will not.

Its a shame that you cannot separate one issue from another as this thread had got back on topic.

You commented that an ammeter is better, but as you well know its not that easy without a battery switch to shunt the meter, so your post was not very practical was it.

 

[Alex Crow]

Personally, when checking for quiescent load, I use an ammeter.
I do not feel a voltmeter is of much use for this, which you agreed with.
You yourself say that an ammeter is the thing to check for untoward battery drain, and have in the past recommended the CPC low range clamp meter, for which I am grateful (a very useful tool, well worth the £50 or whatever it cost me).

So why do you say 'You commented that an ammeter is better, but as you well know its not that easy without a battery switch to shunt the meter, so your post was not very practical was it.'?

Moving on, and I would rather not respond, but you force me...
I certainly did not disagree with the vaues for fuse resistance that you quote above - sounds good to me.
Nor do I disagree that an ammeter that could be fitted permanently (would need to cope with approx 700A max) would be useless, as it would not have the resolution to read the ma range we want (understood).
And yes, having the isolator fitted (to go with a very low range ammeter) would be impractical.
I also like threads that are 'back on topic', which is exactly where I was going with the ammeter suggestion, which you agree with?!

I really would rather not have this silly spat Malcolm, and am not really sure what you feel we disagree about on this one?

Or, was it just because I said 'No Malcolm, the OP wants to measure the load when locked'?
Sorry if that got up your nose, it was not intended to, but how else could I have said it?

 

[drmw]

Come on guys - it does this forum no good when spats develop - particularly between two long standing and well respected members.

Time out on this one please.

Thank you in advance

 

[television]

Personally, when checking for quiescent load, I use an ammeter.
I do not feel a voltmeter is of much use for this, which you agreed with.
You yourself say that an ammeter is the thing to check for untoward battery drain, and have in the past recommended the CPC low range clamp meter, for which I am grateful (a very useful tool, well worth the £50 or whatever it cost me).

So why do you say 'You commented that an ammeter is better, but as you well know its not that easy without a battery switch to shunt the meter, so your post was not very practical was it.'?

Moving on, and I would rather not respond, but you force me...
I certainly did not disagree with the vaues for fuse resistance that you quote above - sounds good to me.
Nor do I disagree that an ammeter that could be fitted permanently (would need to cope with approx 700A max) would be useless, as it would not have the resolution to read the ma range we want (understood).
And yes, having the isolator fitted (to go with a very low range ammeter) would be impractical.
I also like threads that are 'back on topic', which is exactly where I was going with the ammeter suggestion, which you agree with?!

I really would rather not have this silly spat Malcolm, and am not really sure what you feel we disagree about on this one?

Or, was it just because I said 'No Malcolm, the OP wants to measure the load when locked'?
Sorry if that got up your nose, it was not intended to, but how else could I have said it?

I am deeply sorry Alex if I have over reacted on this, its been a rotten thread as far as I am concerned, people just do not understand the implications of having a fuse with significant measurable values. Some of the answers just wound me up.

I really am so sorry

 

[Alex Crow]

By the way Malcolm, I received through the post a package of goodies this week - self solder heatshrink sleeves.
Enigmatically this gift came with no real identifying marks, other than the name at the bottom of the note - Malcolm.
I will assume it was you, and thank you very much, you are truly a kind and helpful person Malcolm, thanks!

Or, is the invoice to follow?

 

[television]

By the way Malcolm, I received through the post a package of goodies this week - self solder heatshrink sleeves.
Enigmatically this gift came with no real identifying marks, other than the name at the bottom of the note - Malcolm.
I will assume it was you, and thank you very much, you are truly a kind and helpful person Malcolm, thanks!

Or, is the invoice to follow?

Yes I sent them, I do not use the self solder part, so do a small solder joint then slide over and heat shrink, they are much stronger than standard heat shrink offering a better protected joint. I used them in RF applications where components were added.
As I will snuff it one day it just seems a waste to let some of these things be thrown away, just trying to empty my place a bit. I have at least 10,000 transistors that no one wants

 

[Alex Crow]

Well thanks again then.

I am pleased to hear you prefer to do a solder joint first, that would be my way as well, they are tricky otherwise.

And now we are many miles OT, my bad.

 

[television]

I think the main point with them is that when you heat shrink the solder bit sticks to the original joint and the sleeve cannot slide off