In a message dated 98-10-30 11:01:31 EST, Bary Schwartz wrote:
> And the vote is in. I have just removed any doubts as far as I am
> concerned about which gauge is more useful. And the winner is. . .the
> ammeter!!
Barry,
I would have to agree with you wholeheartily on that! There are advantages
and disadvantages with each, but for pure functionality, the ammeter is the
clear winner. One of the major disadvantages of the ammeter is their near un-
availability in aftermarket gauges, or of sufficient range for use with high
output alternators. I would use one in my TR6/Ford V8 conversion, but one was
not available to match the other gauges. For some Triumph owners, Smiths makes
a -50 - 0 - + 50 amp meter that will match nicely, but for most, it's either a
-30 - 0 - + 30 ammeter or a voltmeter.
> After having had to do a little work on the radiator and
> shrouding after the trip home from Triumphest, I was checking the car for
> leaks and noticed the gauge showing a 10 amp drain while idling. Every
> thing was working fine before the radiator work, but the alternator
> apparently decided to take a dump. It was VERY apparent that I had a
> problem, and quick confirmation with a DIGITAL voltmeter showed that I was
> not charging.
Just out of curiosity, what was the voltage reading you got? Not wanting the
readers to get the idea that the voltmeter is worthless, I can't help but
think you would have noticed the drop in voltage on the voltmeter. Admittedly,
it's easier to spot that the ammeter is no longer on "zero" than it is to
notice that the voltage has dropped a volt or two on the voltmeter.
> As a side note, after the always futile conversation with the counter
> person (the car has a GM alternator, and non stock motor, so I can't tell
> you what car it goes in JUST GIVE ME A FRIGGIN 63 AMP ALTERNATOR FOR A 1975
> GM VEHICLE (gun pointing at his head, crazed look in my eyes, OK just
> kidding)!!!!)
Next time, try asking for a model # 7127. That has been the model # on all
three of the last GM units I bought, from different stores. It may not work
at any given store, but it's worth a try.
> I noticed that after I told him " OK, OK it goes in a
> Spitfire, BUT. . ." the screen showed both the Lucas unit and an AC Delco
> unit. Could this be a GM direct bolt on replacement that fits, or is it a
> Lucas type built under licence by Delco??
According to the TRF catalog, the AC Delco was used on "...an unknown number
of Triumph models prior to 1973." From the illustration in the catalog, it
doesn't appear to be the same as yours, and, as far as I know, The 7127 or
equivelent was not produced till somewhere in the mid '70s. TRF also says in
their catalog that these alternators are very scarce, and parts are hard to
come by, so you probably wouldn't have gotten one anyway, listed or not.
Later, Barry wrote:
> >Is an ammeter wired differently, and are there particular locations which
> >are better than others for such wiring? I assume it is, and there are,
> ****************************************
> Yes, most ammeters are wired in series with positive side with the entire
> load of the car, minus the starter running through it.
I know what you are trying to say, but that's not quite right. As long as the
alternator is working as it should, NONE of the cars electrical load will be
going through the ammeter. If you look at your wiring diagrams, you will
notice that the connections for the electrical loads are connected to the
alternator on the SAME side of the ammeter as the alternator. If the
alternator is supplying the current, as it will if everything is as it should
be, the current for the car will bypass the ammeter. The only current flowing
through the ammeter will be the charge/discharge current from the battery.
When the alternator fails to supply sufficient current for the loads, the
battery will take over; under this condition, the ammeter will show a
discharge. If the battery is low, the alternator will charge it, and the
ammeter will show a charge. I have a JPG diagram showing this if anyone is
interested.
You're right, in that the entire load CAN run through the ammeter, and the
wiring will have to be sized to handle it, but under normal conditions, none
of it will.
As you may well expect, there are exceptions to the above, given that we are
talking about Triumphs! On an early TR6, for example, the horns and the
courtesy lamps are wired directly to the battery (only Triumph knows why!). If
you blow the horn on one of these cars with the engine/alternator running, it
will show up on the ammeter as a CHARGE!
> Being wired in series, the wires
> have to be capable of handling the entire load of the running car with all
> accessories running which means quite heavy gauge wires running to the
> gauge.
With the exception of loads that are switched via underhood relays, all of the
car's current HAS to run through the interior anyway, voltmeter or ammeter.
Current to the headlights, for example, have to go through the interior
headlight switch unless you are using relays. The only current that doesn't
HAVE to go inside is the charging current of the battery. The discharge
current of the battery will have to go through the car, as it must follow the
same path as the alternator current to the loads, but not the charging
current. The discharge current from the battery is limited to the total load
of the electrical equipment in the car, but the charge current is limited by
the battery condition and the capacity of the alternator. If your battery is
completely dead and you have a 63 amp alternator, your charge current could be
as much as 63 amps minus whatever loads are on.
For that reason, I put a warning In my alternator conversion instructions to
monitor the ammeter if you are trying to recharge a flat battery with the
alternator. Adding a large alternator will not increase the current demands on
the wiring from what it was before the conversion, except that charging
current can easily exceed the wiring capacity.
>From a practical standpoint, though, there will be several extra inches of
high current wire under the dash with an ammeter, plus there will be at least
two more exposed terminals, all of which increases the hazard level a bit over
the voltmeter.
> Voltmeters on the other hand just have to have current capabilities
> of the gauge itself, maybe half an amp if that, and as such have only very
> small gauge wire requirements. Plus, with an ammeter the wires are always
> hot or have current running through them, even with the ignition off, so
> careful routing is required. As for location, anywhere that it is clearly
> visible is all that is required -
Very true, plus the voltmeter will be fused if it is wired to one of the green
wires, which it should be. The ammeter leads are not fused, and they have the
entire current capacity of the battery available to them in case of a short.
If your battery has 600 cranking amps capacity, that is the amperage available
to the ammeter wiring!
A good battery will produce about 12+ volts, and a good alternator, running
above idle, will produce about 14+ volts. As long as you are getting a voltage
reading of around 14 volts, you can be reasonably sure that the battery is
being charged, but not 100%. You could easily have a bad connection to a
battery post, such that the battery is not getting much charge at all, but
still see a good reading on the voltmeter. An ammeter, on the other hand,
tells it like it is. If there is a bad connection to the battery, the ammeter
will show it as a low or zero charging current.
Of course, it is still up to you to interpret the ammeter reading. Is it zero
because the battery is fully charged? Or because the battery isn't taking the
charge for some reason? If you haven't driven your car for a while, the
battery will be low and the ammeter will show a fairly heavy charge for a
while, gradually tapering off as you drive the car and the battery gets fully
re-charged. The ammeter reading won't get to zero, but it will get to be so
small that it doesn't show on the meter. A zero reading at the beginning of
your trip means something is wrong; at the end of your trip, it means
everything is alright.
If I were in charge, all cars would come with ammeters, properly wired and
installed, but till then, run what cha brung! Either one is OK, as long as
you know and understand what either is telling you.
Dan Masters,
Alcoa, TN
'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
http://www.sky.net/~boballen/mg/Masters/index.html
'74 MGBGT---3000mile/year driver, original condition - slated for a V8 soon
'68 MGBGT---organ donor for the '74
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