regarding this thread:
http://forums.corvetteforum.com/show....php?t=1809697

I'm installing a replacement ammeter because the cool one I have is broken. The replacement is this model:

http://cgi.ebay.com/1-0-Digital-ANL-...QQcmdZViewItem

Before I went cutting and drilling, I decided to test the unit. Here's what's weird. When wired in-line between the Alternator and Battery (as shown in pic) It works fine.



However, when wired between the Battery and Sound system main power wire, the Amperage reads Zero. The voltmeter part works in both setups but either there's something strange up, or I have the the worlds most efficient sound system.

What am I doing wrong?

 

with the amps on and playing, or off?

 

Amps on, music playing (rather loud too)

 

Total up the fuse ratings on all the amps and take 5% of that as what you would expect when they're all cranked. That should be a ballpark figure. So if you have two amplifiers with 25 amp fuses that totals 50 amps. It would just be a guess depending on many other variables but I think 2.5 to 5 amps average draw would be about right.

If you're getting less than that, you probably just THINK that's the main sound system wire.

 

Total fuse ratings are in the ~100 amp range.

 

Then reread my last sentence.

 

There's only one blue (+) 4awg wire going through the car. Still, it doesn't make very much sense why it would work between the alt and the batt, but not between the batt and the amps.

 

Do you have it set for DC? Did you try it on the alternator again? Or anywhere else for that matter? I'm not familiar with that unit so I don't know what kind of settings if any. Range switches? Does it connect by inductive loop or does it actually wire inbetween? If it's an inductive loop unit, that picture tells me that the wire loop running underneath it may be causing interference.

 

I've been told on the12volt.com forum that these kind of combination voltmeter/ammeter units have common ground problems. Their accuracy is off drastically and they won't pick up currents lower than a certain size (I haven't seen this unit pick up anything less than 20 amps)

I've decided to try a deticated digital ammeter that uses a remote shunt and has a much more accurate processor. The seller has assured me this unit will work on automotive 12v systems and the electronics look alot more sturdy than the one I have now.

http://cgi.ebay.com/ws/eBayISAPI.dll...m=190159172490

The fun part will be fabricating a plexiglas mounting surface since the hole I cut for the original one is larger than the new one. I have cool plans in store for it though.

 

did you try reversing the leads?

 

Yes. Direction of current Flow has no effect on the reading.

 

RF,

I'm no "expert" but I know a little bit. Maybe I can help explain what is happening.

When your vehicle is running, there is a high demand for current from your alternator. All of the devices that require power (ignition system, radio, computer, sensors, etc...) are getting their required power from your alternator. Your battery is also another device that is receiving power from your alternator when your engine is running.

Basically, all of the current being delivered to your vehicle is being supplied by the alternator when your engine is running. Things are turning on/off, but the average load is there... simple enough, right?

Every device has a threshold of sensitivity. Some current sensing devices detect the changes in magnetic energy and relate it back as current flow. Others measure current by looking at the voltage drop across a known component... like a solid piece of brass for example. This is known as a shunt. Add a voltage meter across the brass, and you can now determine the current flow in that piece.

Another thing to consider is the reaction time of the metering device. Some simply cannot keep up with the changes in current flow... so they don't read correctly. Some are so sensitive, they need snubbing circuits to 'average' the input signal so you can get a good reading.

In your case, I think your overall load is so small/fast that it is below the sensitivity threshold of your ammeter. (DC to DC switching power supplies and low overall 'full current' duration.)

If you want, keep it connected to your system and connect a load back at your amplifiers. (Maybe a 12 vdc air compressor, or some fog lights, etc...) You should see that ammeter pick up with enough average load.

Let me know if this helps, or if you need me to clarify anything.

Mark

 

Mark: This seems to be the general consensious on other forums about this unit. It's just plain low quality. The new unit I'm planning has a faster and more accurate processor. It's accurate to +/-0.5% and has a 0.1 second resolution..... and lets not forget it's Blue (so cool )

Install on this guy will be in a few weeks.