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-   -   Ammeter reading +15amps running (http://www.clubcobra.com/forums/superformance/141678-ammeter-reading-15amps-running.html)

tortuga 11-10-2018 06:26 PM
Ammeter reading +15amps running
 
Gauge reads Zero when ignition is off, fans take it down like they should but not as far as usual, system voltage 12.4 off, ~13.8 running, all connections on ign switch good, batt connections tight, optima red top battery couple years old..
Almost like the null has moved when running? The farthest down I can get it with ALL loads idling at about 950 is about +7 amps...

Battery cranks it right up.

Anyone had similar issue?

spdbrake 11-10-2018 07:18 PM
Quote:
Originally Posted by tortuga (Post 1453759)
Gauge reads Zero when ignition is off, fans take it down like they should but not as far as usual, system voltage 12.4 off, ~13.8 running, all connections on ign switch good, batt connections tight, optima red top battery couple years old..
Almost like the null has moved when running? The farthest down I can get it with ALL loads idling at about 950 is about +7 amps...

Battery cranks it right up.

Anyone had similar issue?
Trying to make sure I'm following you. When you stated your "fans take it down like they should but not as far a usual" do you mean they're adding Amps to the total reading but not as much as your used to seeing?
Then when you stated "The farthest down I can get it with All loads idling at about 950 is about about +7 amps..." I assume down being a highest Amp reading?

If your seeing +7 Amps on the Ammeter with (Headlamps,running lights, Fans, Elec fuel pump?) that appears to be extremely low. I'd suspect the resistor in the Ammeter to be faulty.

tortuga 11-10-2018 08:43 PM
The more I think about it I am starting to suspect the meter, the battery went to full in about 10 mins on the AGM charger, voltages are all normal, alternator is just about new etc etc.
my DVM has a current setting but is it ok to put it in series where the ammeter usually lives to check? Doing the dash reach around it's got two healthy wires on it that carry system current?

Thanks spdbrake

spdbrake 11-10-2018 10:51 PM
Yes you can use your multimeter. Most are only rated at 10amps though. It should be marked. Worst case is you'll blow the glass fuse in the case.

Blas 11-12-2018 09:15 PM
You might want to check the wire connectors on the back side of the AMP meter. Even if they look good, check the crimp on the wires. I have seen the wires just pull right off the connectors.
Blas

cycleguy55 11-13-2018 09:13 AM
Quote:
Originally Posted by tortuga (Post 1453759)
Gauge reads Zero when ignition is off, fans take it down like they should but not as far as usual, system voltage 12.4 off, ~13.8 running, all connections on ign switch good, batt connections tight, optima red top battery couple years old..
Almost like the null has moved when running? The farthest down I can get it with ALL loads idling at about 950 is about +7 amps...

Battery cranks it right up.

Anyone had similar issue?
Is this not the reason many have given up on ammeters and replaced them with voltmeters?

"...a voltmeter logically provides far more useful information about alternator system performance compared to the ammeter."

https://www.hotrod.com/articles/hot-...ical-system-2/

BTW: Does your ammeter have a range sufficient for your alternator (e.g. +100/-100 amp range for 70 amp alternator)? Is ammeter wired with a shunt, or does all current flow through ammeter?

HTM101 11-13-2018 09:44 AM
During one Cobra ride I smelled an electrical melt odor, it was my amp gauge failing. So what did I do next, I installed another amp gauge. Several years later I noticed the replacement amp gauge was headed toward failure. I finally decided to permanently ditch the amp gauge and replaced it with a volt meter.

cycleguy55 11-13-2018 10:12 AM
Quote:
Originally Posted by HTM101 (Post 1453833)
During one Cobra ride I smelled an electrical melt odor, it was my amp gauge failing. So what did I do next, I installed another amp gauge. Several years later I noticed the replacement amp gauge was headed toward failure. I finally decided to permanently ditch the amp gauge and replaced it with a volt meter.
As I've seen in a number of articles, there's a reason auto manufacturers replaced ammeters with voltmeters - and idiot lights (far more common). Regardless, OEM ammeters have pretty much gone the way of the dodo.

Blas 11-13-2018 10:29 AM
Just for grins, what output alternator do you have installed?
Blas

cycleguy55 11-13-2018 10:59 AM
Quote:
Originally Posted by tortuga (Post 1453759)
Gauge reads Zero when ignition is off, fans take it down like they should but not as far as usual, system voltage 12.4 off, ~13.8 running, all connections on ign switch good, batt connections tight, optima red top battery couple years old..
Almost like the null has moved when running? The farthest down I can get it with ALL loads idling at about 950 is about +7 amps...

Battery cranks it right up.

Anyone had similar issue?
Properly wired, with the ammeter between the alternator and all loads, an ammeter measures the total current flow - not the 'net' from the battery. See the diagram here: https://www.fwmurphy.com/uploaded/do...00-02-0207.pdf

A 7 amp reading at 12 volts is 84 watts, but of course 12 volts is really a nominal value so probably in the range of 90-100 watts. Regardless, how much power does your ignition system draw? MSD 6 series are about 1 amp/1,000 RPM, while 7 series are slightly higher. Ignition coils draw 3-7 amps.

7 amps at the ammeter at idle doesn't appear unreasonable.

Gaz64 11-13-2018 02:24 PM
Quote:
Originally Posted by tortuga (Post 1453759)
Gauge reads Zero when ignition is off, fans take it down like they should but not as far as usual, system voltage 12.4 off, ~13.8 running, all connections on ign switch good, batt connections tight, optima red top battery couple years old..
Almost like the null has moved when running? The farthest down I can get it with ALL loads idling at about 950 is about +7 amps...

Battery cranks it right up.

Anyone had similar issue?
I think everybody is reading this thread incorrectly going by Steve's opening statement.

I read it as +7 amps, (positive) not negative, at idle.

HTM101 11-13-2018 05:17 PM
Quote:
Originally Posted by Blas (Post 1453835)
Just for grins, what output alternator do you have installed?
Blas
I believe it was 55 amps.

Blas 11-14-2018 09:01 AM
Just checking. So many put 100 AMP+ alternators on these cars which have wiring and gauges designed for half that output. Not that anything should ever pull that combined load.
Blas

HTM101 11-14-2018 01:56 PM
Quote:
Originally Posted by Blas (Post 1453893)
Just checking. So many put 100 AMP+ alternators on these cars which have wiring and gauges designed for half that output. Not that anything should ever pull that combined load.
Blas
Back in the days of running the amp gauge, I can't remember seeing the needle ever indicate more than 30 amps.

I've replaced the 55 amp alternator with an arc welding unit, LOL. This one's rated at 70 amps.


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