After serious thinking Interloper wrote :
"Harry Bloomfield" wrote:

Remember the old type charge / discharge ammeters, where used a couple of
turns of cable which used to sometime be fitted to vehicles ? I have one
fitted to the tractor mower which is not marked + and - and I'm sure it
reads the wrong way. The needle goes left when on charge, I seem to
remember the norm is to move to the right.

Can anyone remember, before I take steps to correct it?

The usual orientation for a charge/discharge ammeter is with the quiescent
needle pointer resting at 12 O'clock (needle pivot at 6 O'clock); the
negative (-) discharge sector to the left (anticlockwise) and the positive
(+) charging sector to the right (clockwise).

Some ammeters (like yours) rather unhelpfully are not marked + and -.
However, they are usually colour-coded (blue or green sector for charging;
red sector for discharging), or annotated 'Charge' and 'Discharge' or simply
'C' and 'D'. Doesn't your ammeter have any of these legends or markings?

There are some versions of these ammeters designed to be mounted the other
way up, with the quiescent needle pointer resting at 6 O'clock. If your
ammeter is actually mounted upside-down (as has already been suggested), then
the needle would appear to read the wrong way. However, there must be some
lettering on your ammeter ('Amps' or 'A', or the manufacturer's name) that
would be inverted if the ammeter has been mounted the wrong way up.

This one has the pivot at the bottom and points to 12. There are no
markings apart from 30 amp at either end and a 15amp marker. It kicks
left slightly (or did) when the starter solenoid engaged, then with the
engine running, would show around 5amps. No marks to indicate which
side was which at all.

When you say, "The needle goes left when on charge...", is that when charging
from an external battery charger, or when charging from an engine mounted
alternator? If the latter, then your alternator could be faulty and not
generating enough output to meet demand.

No, when the engine is running it went to the left - which seemed wrong
to me.


Check the wiring diagram (if you have one!) to see where in the circuit the
ammeter has been located. Also check the ammeter connections to see if it
has been connected reverse polarity.

Its in series with everything, apart from the starter main feed - just
the ignition circuit the interlocks and alternator really. The lights
rather oddly, are run from a separate output of the alternator.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk