amp meter

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guesstimator - 29 Dec 2003 15:56 GMT

Hi everyone!

Just a quick one to understand what the amp meter should read under
normal operating conditions.

Meaning that i have an amp meter in my innocenty dash and i've no idea
what it isd actrually reading. It has -20 and +20 at the left hand
side and right hand side respectively and a 0 in the center.
I'm asking because at times it seems to read properly somewhere just
above the 0 and i have pretty dim lights (do not change through rev
range) and at other times, completely randomly the needle doesen't
budge from the +20 mark at wich point all lighting is much brighter.
Again the two states of "luminescence" appear to alternate completelly
randomly.
By the way the car is a 75 1.3 innocenti cooper export

Thanks everyone

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Graham - 06 Jan 2004 01:06 GMT

> Just a quick one to understand what the amp meter should read under
> normal operating conditions.

If the ammeter is correctly wired, it measure the current into or out of
the battery. When the battery is fully charged and the alternator is
supplying sufficient current for all electrical loads, it should read
zero Amps.

When the car is idling, especially with lots of electrical loads on, the
alternator will not provide enough current and it will indicate a
negative current, the battery is being drained.

When the car is first started, once running faster than idle it will
initially read positive current as the slight discharge of the battery
is replaced.

> Meaning that i have an amp meter in my innocenty dash and i've no idea
> what it isd actrually reading. It has -20 and +20 at the left hand
[quoted text clipped - 5 lines]
> Again the two states of "luminescence" appear to alternate completelly
> randomly.

Is it an aftermarket ammeter?

It may have been incorrectly fitted into the alternator output. If so,
when it reads zero, the alternator is not providing any charge, when it
reads 20 Amps, the alternator is supplying the current to the
headlights. The fault may lie with the alternator or the ammeter wiring.

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Shaun - 06 Jan 2004 12:20 GMT

> If the ammeter is correctly wired, it measure the current into or out
> of the battery.

What is the correct wiring for an aftermarket ammeter?

Shaun.

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Graham - 06 Jan 2004 14:18 GMT

> > If the ammeter is correctly wired, it measure the current into or out
> > of the battery.

> What is the correct wiring for an aftermarket ammeter?

The same as for an original equipment ammeter. Everything connected to
the positive terminal of the battery *except the starter motor cable*
should pass through the ammeter. That way it tells you whether the
battery is charging, discharging or holding it's own.

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Shaun - 06 Jan 2004 14:50 GMT

> The same as for an original equipment ammeter. Everything connected to
> the positive terminal of the battery *except the starter motor cable*
> should pass through the ammeter. That way it tells you whether the
> battery is charging, discharging or holding it's own.

Thanks.

So on a Mini it could be done by taking 2 heavy duty wires from the ammeter
to the solenoid, removing the permanent positive supply going off the
fusebox/ignition switch and connecting it to one of the ammeter wires, and
connect the other ammeter wire to where the solenoid permanent positive
terminal.

Shaun

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