Cortina Ammeter Problems

[chris27]

Hi Guys

 

I am hoping someone out there is good with electrics....

 

I have a nice set of cortina clocks I am in the process of fitting ...

 

The ammeter supplied only reads up to 30 amps , however the sierra alternator is giving out aprox 60 amps.....

 

is there any way of converting the ammeter clock to read up to 60 amps ?????

 

could I use a resistor and if so what do I need????

 

many thanks

 

Chris

[ibrooks]

The ammeter goes in-line between the alternator and the battery - if you're getting 60 amps along there then stand by with the extinguisher. The 60 amp rating of the alternator is simply what it's capable of at full tilt. In practice it'll never get anywhere near that.

 

60 amps is what auntie Ford thought a Sierra might possibly need with every electrical toy that could be fitted to a Sierra being used at once plus a little safety margin - main-beam, fogs, brake-lights, heater, heated-rear-screen, electric windows going up and down (all 4), elecric mirrors being adjusted (both at once), heated mirrors (my Sierra had them) stereo at full blast, cigarette lighter and and..... We simply don't have most of that stuff.

 

What the ammeter actually measures is the current supplied to or drawn from the battery. This will initially be quite large (several whole amps at least) as the battery is recharged after starting the engine but will then be almost nothing as it comes back up to voltage. The next swing you may see will be a negative as lots of electrical equipment isused and briefly the current drawn exceeds that supplied by the alternator this will amount to a twitch from the needle because the regulator takes a measurable amount of time to react to an increase in demand. I used to see it in winter when the lights were all on along with the heater and the rear screen the needle would then twitch in time with the indicators as I signaled. In the Hood I suspect it'll be un-noticeable unless you're actually looking at the guage or there's something wrong somewhere (which is why you have the guage).

 

Iain

[Guest elgey7]

What you need if you really want to use that same ammeter with a 60 amp alternator is a thing called a SHUNT. Look it up on the web. Basically it is a very precise very low resistor capable of carrying the other 30 amps in parallel with the meter. Your gauge markings would be reading 30 for 60 amps of course.

You see your ammeter is normally a moving coil meter (cheap ones are moving iron) with a SHUNT across it which takes almost all of the current just leaving enough to deflect the coil & needle to the appropriate value proportional to the current passing the shunt. Many commercial vehicles have this shunt external to the meter/gauge However in the car world the shunt is usually inside the gauge.

It can be done, you need a 30 amp shunt. ( for a moving coil meter)

 

There are some cheaper ammeters, known as Moving Iron meters which are simply one or 2 turns of heavy wire moving a small lump of Iron on the bottom of the needle. As the current goes around the heavy coil it creates a magnetic field which deflects the Iron & so the needle attached. On this type you would need to add a resistor of the same value & current carrying capability in series.

Again it can be done.

 

But is it all worth it !

Regards

Colin