Your ammeter wouldn't have expired without some substantial amount of smoke
and the plastic part in the back would be burned, melted or at least
distorted. As was suggested, you've probably miswired it somehow.
If you test your ammeter with an ohm meter then it should probably not deflect
significantly, and it should read less than 1 ohm if it's in good condition
and the shunt is still in place.
If that does measure out properly then if you put a new 1.5V AA cell straight
across it (not for too long) you'll get probably about a 10 to 12 amp reading.
The wires you use to do this may get a little warm, and the battery definitely
will (that's why you shouldn't do it for long).
A 1.5V AAA battery will peak out at about 6 amps, but a 3V, CR2032 lithium
coin cell won't give you more than about 30 milliamps so you won't get too
much of a reading from one of those.
If the ammeter has much more resistance than 1 ohm then maybe the shunt is
burned out... if the needle moves when you test it with the ohm meter then the
shunt is toast but the meter movement itself may be OK. In that case do not
put a battery straight across the ammeter terminals, because you'll fry the
ammeter. You'd need to first find a replacement shunt.
Ammeters are kind of a hassle to wire when the alternator can supply a lot of
current... there is no real practical way to protect it from full-load
currents. As I've previously posted, a voltmeter is a better indication
instrument on an alternator equipped car.
Cheers
Theo
----- Original Message -----
From: Robin Young <robin02@mindspring.com>
Date: Thursday, September 3, 2009 5:48 pm
Subject: [Tigers] Amp Meter
To: Tigers@autox.team.net
> I recently changed form generator to alternator on my Mk
> 1. The amp meter
> quit working about the same time and collective wisdom concluded
> that the
> amp meter burned up from the higher current. I pulled it
> out today and
> thought I would take a look inside.....nothing is burned and
> there was no
> diode or anything else other than an electro magnet about the
> shape of a
> paper clip. Apparently the magnet is charged by the
> direction of current
> from either the battery or alternator and swings the needle
> depending on
> current. It seems that more current from the alternator
> would pin the
> needle positive but a failed alternator would just give a
> typical discharge
> of amps from the battery. Both of the eight gage
> wire ends sparked to
> ground (forgot to disconnect the battery). Do I really
> need to have the
> meter worked on or is there some other place I need to investigate?
> ........think I will repaint the needle while I
> wait. Robin Young
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