18 replies to this topic

[Roro92]

Hi everyone, 

 

I've been reading the topics about the wiring of an amp meter and it seems that anyone would agree about the danger that it involves. 

I actually already have a brand new amp-meter lying down my desk and I'd be happy to find a way to wire it in up my dashboard. I don't want to just screw it in the dash, I'd like to find a way to wire it in so the needles moves in some ways. 

 

I know I can appear like a poser, but I really enjoy the view of gauges and needles moving everywhere. 

 

SO, is there a way to bridge that amp-meter with anything that would make it seems to "work" ?

I've been thinking about it about can't find any idea by myself…

 

Thanks ! 

 

[Magneto]

Why not just wire it up properly to work?

[govig]

I know you have one sitting on the desk but a voltmeter is a better way to get (more or less) the same information in a car without the risk.

 

Ammeters were ok in dynamo days of say 15A charging. Some alternators are capable of 100A +.

[Roro92]

Govig : I already have a volt-meter (correctly wired up haha). It it has already proved its usefulness ! 

Magneto : I've read stories about cars catching fire and things like this. My alternator is the 70amp one, and my amp-meter only reads up and down to +/- 60 amp, therefore I ain't shure that it's safe enough ?

Edited by Roro92, 16 July 2016 - 11:21 AM.

[KernowCooper]

I'd leave the amp meter on your desk or open it up and see how the quality of the internals is, this may decide it for you. Rule of thumb on car electrics is always have a leeway of 30% so a 70amp system would need a amp meter 91amps. I never install anything running at its maximum capacity.

[tiger99]

Yes, derating, as it is called, is always a very good idea as it improves reliability.

The safety problem with the ammeter is that it goes in the unfused brown circuit, which is permanently live, and if it shorts a fire is inevitable. Also, extending the bunch of brown wires to the ammeter and from there back to the battery terminal at the starter solenoid is going to add voltage drop, with effects on charging and other things. That is why a voltmeter, which can take its signal from the switched ignition circuit via a fuse, is always used in modern cars.

Nevertheless an "ammeter" is possible, with some moderately simple electronics. You can get hall effect current sensors which will clamp around the bunch of brown wires near the solenoid, without electrical connection at that point. They produce a voltage output, which can be shown as amps on a suitably scaled voltmeter. Some electronics design capability is needed to make it work.

Similar devices with a measuring range of maybe 5 amps are useful for detecting failed light bulbs, but again some electronics design capability is needed.

Worth looking at, I think, if you are modernising your electrical system by adding some kind of computer.

Edited by tiger99, 16 July 2016 - 08:15 PM.

[Spider]

I don't know if there are available in the Auto World, but see if you can find a Meter that uses an external Shunt.

 

This has many advantages, not the least of which is you are not running huge cables to the Meter and back again. They are generally way more tolerant to overloads and even if the Meter does burn out, everything else still works.

 

The Shunt is basically a Resistor (of VERY low resistance), the circuit for current measurement is connected through that, then off either side of it, smaller signal wires are run to the Meter.

 

I have seen Digital versions for Cars.

[nicklouse]

 
I know I can appear like a poser, but I really enjoy the view of gauges and needles moving everywhere. 

Sorry but if that is your main driving force for a device that is not suitable for your car you would do better buying another useless guage that is safer and has a moving needle. Such as a Vacuum guage.

[JBW]

I've always removed ammeters from the cars I have bought with them already fitted, too much risk, always managed to sell them on Ebay though.

As said above a vacuum gauge would be far more use & the needle will move a lot if that's what turns you on.

[govig]

Clocks have needles that are always on the move too. Even when the motor isn't running.

 

I'd get a clock. When it packs up (Smiths ones always do eventually, usually at twenty past one) it will still be 100% accurate twice a day. No other gauge is 100% accurate.

[Roro92]

Hi mates,

Thanks for all your messages, I've learned a lot.

Two things first :
- I don't have no particular electronics design skills. I can handle the simplest kinds of work as I do really enjoy it but nothing more complicated.
- I already have a vacuum meter and I really like it ; I also already have a clock.

KernowCooper : I'll remember that rule of thumb of a 30% leeway.
My amp-meter is a brand new Smiths one, it doesn't really feel great as it is quite small and essentially made of cheap plastic... I wouldn't trust it now that I know how high is the power going through the meter.

Tiger : well I don't really have electronics design capabilities and I won't try to fit some kind of computerized things in my Mini. Not because I wouldn't be interested in doing it but because it's way too complicated for me as I do not have any technical knowledge... I can plug a wire between two objects but I can't do a lot more.

Tell me more about a "Hall effect current sensor" as I couldn't find a lot of things on Google. I quite understand the way it's supposed to work but I haven't find any to buy so it must be more complicated that what I figure.

Mike Spider : I've read a few things about shunted meters and you're right, they actually exist for the automotive market but they're designed to fit modern cars. My others gauges being Smiths ones with the classic chrome bezel, I don't want to fit a black plastic gauge next to them...
And trying to extract the mechanism of a modern shunted meter to install it in a vintage looking gauge is way ahead of my skills.

Thanks again for all the informations.
I know definitely think that the fitting of a working amp meter ain't that interesting given how dangerous it could be and how unnecessary it is... (Even though I really like unnecessary things...just not when they could cause a major failure).

Edited by Roro92, 17 July 2016 - 10:49 PM.

[Magneto]

If you're concerned about it, put a volt meter in - it will move too and it runs on low current, so no risk.

[gazza82]

When did Smith's go "plastic"? Yuk!

[timmy850]

The more unusual Smiths ones are:

External temp 

Oil temp 

Fasten Seat belts

Oil level 

There are a couple of old brochures here with them http://mk1-performan..._electrical.htm

[tiger99]

I didn't have time earlier to dig out info on a suitable sensor, but here is one of many:

 

http://www.lem.com/h...,instantaneous/

 

LEM are the leading company for such things, and are widely used in industry.

 

I have vague recollection that someone, somewhere did make a remote sensing ammeter, which would be a package of sensor, meter and all necessary electronics, but can't remember where I saw it..