[DeTomaso] Amp gauge

Sat May 19 22:22:51 EDT 2012

I don't use either.  It is just one more damn gauge to watch.  If I suspected a discharge, I would unhook the battery after starting the car.  If it dies, the alternator isn't working.

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On May 19, 2012, at 9:23 AM, John Taphorn <jtaphorn at kingwoodcable.com> wrote:

> Yes, you can use a shunt; however, your gauge will no longer be 
> accurately reading the quantity of charge/discharge without 
> recalibration.  It is about as useful as an idiot light at that point.  
> Idiot light on, you are discharging, idiot light off you are charging.  
> I haven't heard of anyone using a shunt recalibrating their amp gauge.
> 
> As I see it.  The real challenge to the amp gauge is connecting the 
> larger gauge wire or running additional wiring to it's backside as 
> owners ramp up the potential amperage output of their new high output 
> alternators to accommodate the higher draw of additional accessories.  I 
> have found it extremely difficult to get larger gauge wires safely 
> connected to the amp guage's limited real estate on the backside.
> 
> Frankly, I would prefer an accurate amp gauge; However, I run a 
> voltmeter for the aforementioned limitations.
> 
> JT
> 
> On 5/19/2012 8:42 AM, shawkins777 at comcast.net wrote:
>> I fall into the ammeter more usefull information side, you can limit the current through the dash with a properly sized shunt/gauge.
>> 
>> Steve
>> 
>> 
>> ----- Original Message -----
>> 
>> From: "Kirby Schrader"<kirby.schrader at gmail.com>
>> To: MikeLDrew at aol.com
>> Cc: guson at home.se, detomaso at realbig.com, "mikael hass"<mikael_hass at mail.tele.dk>
>> Sent: Friday, May 18, 2012 2:25:54 PM
>> Subject: Re: [DeTomaso] Amp gauge
>> 
>> Gee, Mike,
>> 
>> I knew how an ammeter worked before you were even born! No need to tell me.
>> :-)
>> The GT40 _was_ wired wrong and Superformance sent out a wiring 'fix'.
>> 
>> If you want both, by all means do so!
>> There has been many a thread on this forum since it started back in
>> the mid-90's.
>> 
>> Up to you what you use. I used to be a 'dyed in the wool' ammeter fan.
>> I have converted to voltmeters.
>> 
>> Kirby
>> 
>> On Fri, May 18, 2012 at 12:45 PM,<MikeLDrew at aol.com>  wrote:
>>> In a message dated 5/18/12 9 41 35, kirby.schrader at gmail.com writes:
>>> 
>>> 
>>> 
>>> I disagree and can not at all see how this approach is valuable...
>>> That's the way my GT40 came 'incorrectly' wired.
>>> As you turned things on (fans came on, A/C compressor, etc. etc.),
>>> the ammeter kept climbing as it measured all the loads. Do you really
>>> care?
>>> I suppose for bragging rights. Look at me!!!! 83 amps!!! Woohoo!
>>> 
>>> 
>>> That's not how an ammeter is designed to work, and as you said, your car was
>>> wired *incorrectly*.
>>> 
>>> If the car is shut off and you start adding loads (turning on lights, fans
>>> etc.) then the ammeter registers in the negative, not positive.  When the
>>> car is turned on and the alternator is charging, ideally the charge should
>>> be slightly higher than the load, so that the gauge indicates slightly
>>> positive.  When you first start the car, if your battery is weak, it will be
>>> drained quite a bit, so the ammeter will reflect a high state of charge for
>>> a minute or two as the charging system rapidly returns the battery to a
>>> fully charged state, and then it will come down to show a slight charge
>>> (ideally).  If your idle speed is too low, you might show a slight discharge
>>> at idle with all your components (lights/fans etc.) running.
>>> 
>>> Sounds like your car had both the supply AND the loads wired on the same
>>> side of the ammeter?  That would deliver crazy readings for sure.
>>> 
>>> My point is that it's senseless to take high-load components and wire them
>>> outside of the ammeter so that the ammeter never registers their draw when
>>> running.  It's like partitioning your fuel tank so that the fuel gauge only
>>> registers part of the fuel you have on board.  Doing so guarantees that
>>> you'd never know exactly how much fuel you have.  What would the point of
>>> that be?
>>> 
>>> An ammeter will instantly indicate a charging system failure because the
>>> needle will displace into the negative side, which is easily apparent.  A
>>> voltmeter is much more subtle; it will show 12.5 or 13 volts when all is
>>> good, and will ALSO show 12.5 or 13 volts if your alternator fell out of the
>>> car, because it's just showing the state of charge of the battery.
>>> 
>>> The common fallacy is that the voltmeter tells you about your alternator.
>>> It doesn't tell you JACK about your alternator, it only tells you about the
>>> state of your battery.  An AMMETER is the only gauge that tells you about
>>> your alternator, because it instantly informs you as to whether it is
>>> charging the battery, or if the battery is being discharged.
>>> 
>>> Over time, if your alternator clatters onto the roadway, your voltmeter will
>>> drift imperceptibly lower as the battery drains, but at a glance it will
>>> still look healthy.  When it gets to 11.5 volts or whatever, you'll sputter
>>> to a stop with a 'dead' battery.
>>> 
>>> It would be ideal to have both a voltmeter and an ammeter, but given the
>>> choice I'd take an ammeter any time.
>>> 
>>> Mike
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