amp meter

[paulmac]

Hi all, fitting oil pressure, boost guage and amp meter 2 quattro, first 2 easy enough, amp meter, i need help with,all advise welcome, thanks in advance,paul.

[Phil Payne]

Originally Posted by paulmac

Hi all, fitting oil pressure, boost guage and amp meter 2 quattro, first 2 easy enough, amp meter, i need help with,all advise welcome, thanks in advance,paul.

What type is it? You can't actually _measure_ the amps flowing around inside an ur-quattro - there are just too many of them. Ammeters attach in different ways and display a derived implication.

[paulmac]

Hi phil,its a spitfire ammeter with a centrally postioned needle with 60 - and + on either side, 52mm dashmount, .

[Phil Payne]

Originally Posted by paulmac

Hi phil,its a spitfire ammeter with a centrally postioned needle with 60 - and + on either side, 52mm dashmount, .

Yeah, fine - but how does it work? Moving coil, hot wire? How does it tap in?

[Julian]

You've got to splice an ammeter in between the battery positive and all electrical loads except the starter. That's the way to see if the battery is being charged or discharged.

I've looked at the wiring diagram and I can't see an obvious way to do this on the urq. IIWY I'd ditch the ammeter and fit a voltmeter, that'll tell you much more about the electrical system health IMHO.

[Phil Payne]

Originally Posted by Julian

You've got to splice an ammeter in between the battery positive and all electrical loads except the starter. That's the way to see if the battery is being charged or discharged.

I've looked at the wiring diagram and I can't see an obvious way to do this on the urq.

Well, you can, and it's pretty easy. The rally fraternity have a range of battery terminals that have all sorts of little tweaks. Some have breaker functions with a cord or wire attached - pull it and the battery is disconnected. Some just have knobs you can turn. Quite often (RACMSA regulations) motorsport events require a breaker.

Some have calibrated resistances - usually a fraction of an ohm. Millivolts across that gives you current flow in amps. The ur-quattro voltmeter isn't actually that useful - on most cars, the ABS warning light will tell you about an alternator problem long before the voltage suffers.

IMO the most useful device is an alternator monitor. The alternator generates a/c at around 15 volts - a monitor will spot one leg of the rectifying bridge failing. Simple red light.

[Julian]

>Well, you can, and it's pretty easy. The rally fraternity have a range of battery terminals that have all sorts of little tweaks. Some have breaker functions with a cord or wire attached - pull it and the battery is disconnected. Some just have knobs you can turn. Quite often (RACMSA regulations) motorsport events require a breaker.

Yes, but where? I've got the wiring diagram here next to me. I can't find a wire to cut into that has current flow one way when the battery discharges, and the other way when subject to charge and _doesn't_ carry the main starter current - (that's a non starter!)

I've fitted several to cars with dynamos years ago, it was always obvious where you had to chop.

>Some have calibrated resistances - usually a fraction of an ohm. Millivolts across that gives you current flow in amps.

It doesn't matter if the ammeter has an internal or remote shunt, you've still got to splice into a wire - unless it's one of those current transformer types.

[Phil Payne]

> Yes, but where? I've got the wiring diagram here next to me. I can't find a wire to cut into that has current flow one way when the battery discharges, and the other way when subject to charge and _doesn't_ carry the main starter current - (that's a non starter!)

? The main battery lead. The starter current is a couple of hundred amps, agreed, but these things can deal with that. You're postulating the impossibility of ever fitting a charging gauge to any car - and lots have them.

> It doesn't matter if the ammeter has an internal or remote shunt, you've still got to splice into a wire - unless it's one of those current transformer types.

You can't use a current transformer on a DC line. You _can_ use a Hall effect device, but I'm not aware of anyone manufacturing one.

[rick]

In my personal opinion the ammeter has largely been made redundant, modern voltmeters are so accurate that they will give a accurate picture of the state of charge of the battery.

In the days of Dynamos yes a ammeter was very useful, I remember a escort I once had with a dynamo, if you used the spots for long the battery would start to discharge and a ammeter was useful to tell you to switch off something to let the battery charge for a bit!

I dont really see the point on a modern car.

On my rally car there is a tucked away voltmeter but large warning lights for alt and oil.

In reality when rallying you dont really get the chance to scan the dials!

[Julian]

>? The main battery lead. The starter current is a couple of hundred amps, agreed, but these things can deal with that. You're postulating the impossibility of ever fitting a charging gauge to any car - and lots have them.

Point me to one. I've never seen one designed for automotive use or fitted that will handle starter motor current. £10 says paulmac's won't.