Is It An Amp Gauge Or A Volt Meter? - Team Camaro Tech
Electrical & Wiring Troubleshooting electrical.

Reply
 
LinkBack Thread Tools Display Modes
post #1 of 18 (permalink) Old Dec 31st, 05, 08:29 AM Thread Starter
Gold Lifetime Member
Larry
 
Join Date: Oct 1999
Location: Alamogordo, NM, USA
Posts: 987
Is It An Amp Gauge Or A Volt Meter?

I know this is going to open a can of worms, but I really need to know why there seems to be discrepancy in how the 1st gen "amp gauge" is designed.

My experience so far is that it is truly an ammeter. Others have said it is a milivolt meter. I can see how it could work both ways. But the gauges I have tested are bonafide ammeters.

Could there have been possibly two designs?

A while back, I contacted American Autowire about this. Here's their response: (The first few sentences are what's really relative to this subject)

Hi Larry,
The amp gauge is a true amperage gauge! It is not a voltmeter in any way shape or form, period. The gauge is wired in parallel to the charging circuit and is battery live at all times. It reads the rate of charge from the alternator in relation to the rate that is being used by the operating system. That is why when you first start your car, the rate of charge can be upwards of 20-30 amps and after a relatively short time, the meter will approach zero. This is due to the fact that the system has leveled off and is charging what is being utilized. As the cars circuitry started becoming more complex in the mid 70's, the OEM's went over to a voltage meter which simply measures the amount of voltage in a system at any given time. The AMP gauges were found to be a fire hazard due to the higher output of the alternators. The hook-up on the voltmeter was real simple as all that was needed was a fused 12 volt ignition feed on one side and ground on the other. Hope this helps.

Donny


Don Bock, Tech
American Autowire
150 Heller Place #17 West
Bellmawr, New Jersey 08031
(856) 933-0801 – phone
(856) 933-0805 - fax
[IMG]cid:3214811410_736907[/IMG]
Visit our new Website!
www.americanautowire.com

69-er is offline  
Sponsored Links
Advertisement
 
post #2 of 18 (permalink) Old Dec 31st, 05, 08:36 AM
Gold Lifetime Member
Jim
 
Join Date: Dec 1999
Location: Yorkville, Illinois USA
Posts: 22,121
Re: Is It An Amp Gauge Or A Volt Meter?

Quote:
Originally Posted by 69-er
I know this is going to open a can of worms, but I really need to know why there seems to be discrepancy in how the 1st gen "amp gauge" is designed.

My experience so far is that it is truly an ammeter. Others have said it is a milivolt meter. I can see how it could work both ways. But the gauges I have tested are bonafide ammeters.

Could there have been possibly two designs?

A while back, I contacted American Autowire about this. Here's their response:

Hi Larry,
The amp gauge is a true amperage gauge! It is not a voltmeter in any way shape or form, period. The gauge is wired in parallel to the charging circuit and is battery live at all times. It reads the rate of charge from the alternator in relation to the rate that is being used by the operating system. That is why when you first start your car, the rate of charge can be upwards of 20-30 amps and after a relatively short time, the meter will approach zero. This is due to the fact that the system has leveled off and is charging what is being utilized. As the cars circuitry started becoming more complex in the mid 70's, the OEM's went over to a voltage meter which simply measures the amount of voltage in a system at any given time. The AMP gauges were found to be a fire hazard due to the higher output of the alternators. The hook-up on the voltmeter was real simple as all that was needed was a fused 12 volt ignition feed on one side and ground on the other. Hope this helps.

Donny


Don Bock, Tech
American Autowire
150 Heller Place #17 West
Bellmawr, New Jersey 08031
(856) 933-0801 – phone
(856) 933-0805 - fax
[IMG]cid:3214811410_736907[/IMG]
Visit our new Website!
www.americanautowire.com

Larry, an ammeter (ALL ammeters) are really millivolt meters that work by inserting a small, known resistance in series with the circuit, and displaying the voltage drop across that resistance.

The confusion comes in because when we think of an ammeter, we think of one with THE RESISTANCE INSIDE THE METER, with really big wires running to and from the point of connection. All The General did is take the resister out of the meter and put it somewhere else.

The ammeter is a millivolt meter that reads the voltage drop across the wire from the battery to the horn relay.

There's no such thing as an ammeter, there is no direct way to measure amps.

meters (analog) work by generating a magnetic field in a coil to move the pointer, and the strength of the magnetic field depends on the voltage, not the current.





To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.



To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
New website for my vert is coming together. Do ya like the slide show on the home page?
JimM is offline  
post #3 of 18 (permalink) Old Dec 31st, 05, 09:12 AM
Gold Lifetime Member
Jim
 
Join Date: Dec 1999
Location: Yorkville, Illinois USA
Posts: 22,121
Re: Is It An Amp Gauge Or A Volt Meter?

Quote:
Originally Posted by 69-er
I know this is going to open a can of worms
...
Quote:
Originally Posted by JimM
meters (analog) work by generating a magnetic field in a coil to move the pointer, and the strength of the magnetic field depends on the voltage, not the current.
You're right about the "can of worms" Larry. As I walk around thinking about my reply, I'm wondering about the validity of the statement above. It seems as I think about it, that the current thru a coil does in fact affect the it's magnetic field, as both a starter solenoid and a little bosch relay have 12 volts across the coil, but the starter solenoid can move a lot more iron... perhaps my statement is true referring to a guage, which actually has 2 coils in a push /pull arrangement?...
Or maybe the strength of the field is more a function of wattage, and it's responding to both voltage and current?





To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.



To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
New website for my vert is coming together. Do ya like the slide show on the home page?
JimM is offline  
 
post #4 of 18 (permalink) Old Dec 31st, 05, 09:14 AM Thread Starter
Gold Lifetime Member
Larry
 
Join Date: Oct 1999
Location: Alamogordo, NM, USA
Posts: 987
Re: Is It An Amp Gauge Or A Volt Meter?

OK, that makes sense. I never could find a how an ammeter was actually constructed. My books from college didn't help in that respect either. The resister that would be installed in the gauge is now the red 10 gauge wire between the junction block and the horn relay. Your explaination and of JohnZ on the milivolt meter measuring the voltage drop across the wire has always made sense.

But...

Can you explain this...

I can connect my factory amp gauge to a 9 volt battery and the needle deflects about one needle's width. If it were a milivolt meter, wouldn't 9 volts peg the needle? Then, when I connect another 9 volt battery in parallel, the needle deflects another needle's width. It's what you would expect in an ammeter. (Doubling the amps) If it were a voltmeter, (and just assuming it could measure 9 volts without pegging), it shouldn't move at all because the batteries are wired in parallel. (Same voltage, more current)

That's where the discrepancy comes into play.
69-er is offline  
post #5 of 18 (permalink) Old Dec 31st, 05, 09:18 AM Thread Starter
Gold Lifetime Member
Larry
 
Join Date: Oct 1999
Location: Alamogordo, NM, USA
Posts: 987
Re: Is It An Amp Gauge Or A Volt Meter?

Quote:
Originally Posted by 69-er
I can connect my factory amp gauge to a 9 volt battery and the needle deflects about one needle's width. If it were a milivolt meter, wouldn't 9 volts peg the needle?
BTW, if I connect the gauge to a 12 volt battery, the needle pegs violently! Now, if 9 volts only moves the needle as described above, 3 more volts shouldn't peg the needle. It acts like an ammeter.

Larry
69-er is offline  
post #6 of 18 (permalink) Old Dec 31st, 05, 09:27 AM
Gold Lifetime Member
Jim
 
Join Date: Dec 1999
Location: Yorkville, Illinois USA
Posts: 22,121
Re: Is It An Amp Gauge Or A Volt Meter?

lol, we were posting at the same time, check my other reply above.

As for your last, the meter's internals should have very low resistance. The 9 volt battery is only capable of a few milliamps (regardless of the resistance, even thru a direct short), while the car battery can push 300 amps + thru a dead short.

If you take my last post into account, that the magnetic field produced in the meter is a function of both the voltage and the vurrent thru the coil, it makes more sense. Still kinda esoteric and out there.

I will definitely stand by the statement that ALL meters measure ONLY voltage drop, and how you use it and what readings you see are all a matter of interpretation and the application of ohms law to the circuit with the meter in it.





To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.



To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
New website for my vert is coming together. Do ya like the slide show on the home page?
JimM is offline  
post #7 of 18 (permalink) Old Dec 31st, 05, 09:38 AM Thread Starter
Gold Lifetime Member
Larry
 
Join Date: Oct 1999
Location: Alamogordo, NM, USA
Posts: 987
Re: Is It An Amp Gauge Or A Volt Meter?

Quote:
Originally Posted by JimM
As for your last, the meter's internals should have very low resistance. The 9 volt battery is only capable of a few milliamps (regardless of the resistance, even thru a direct short), while the car battery can push 300 amps + thru a dead short.
That's why my gauge acts like an ammeter. A car battery can supply more amperage compared to a 9 volt battery. That's why the 12 v pegs it and the 9 v doesn't. A volt meter would just deflect the needle a little more to show that it is reading 12 v instead of 9 v.

I am so confused! I really need to decide, because my diagrams describe the amp gauge sharing the current load of the red wire like American Autowire described to me about 20 years ago along with their current description of it being a "true" ammeter.

I should do more experiments with an actual charging system setup.

Larry
69-er is offline  
post #8 of 18 (permalink) Old Dec 31st, 05, 10:08 AM
Senior Tech
Mark
 
Join Date: Sep 2000
Location: Shrewsbury, MA, USA
Posts: 6,509
Re: Is It An Amp Gauge Or A Volt Meter?

If you continue connecting that stock "ammeter" across battery terminals you will be buying a new one pretty soon. They are 1V range millivolt meters with +.5V on the (+) side of the guage, and (-.5V) on the (-) side of the gauge.

Look at these posts:

https://www.camaros.net/forums/showth...ight=millivolt
https://www.camaros.net/forums/showth...ight=millivolt
https://www.camaros.net/forums/showth...ight=millivolt
https://www.camaros.net/forums/showth...ight=millivolt

Mark Canning
1969 Indy Pace Car
350/300HP RPO Z11

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Mark C is offline  
post #9 of 18 (permalink) Old Dec 31st, 05, 10:25 AM
Senior Tech
 
Join Date: Mar 2002
Location: Austin, TX, USA
Posts: 5,277
Re: Is It An Amp Gauge Or A Volt Meter?

Larry, as you are discovering there are two types of amp meters. All the ones I am familiar with on GM cars work as Jim described - they measure the tiny voltage drop accross the charging wire between the battery junction block and the horn relay. The wire acts as an external "shunt". But, as in your case, some route system voltage through the amp meter itself because the "shunt" is internal to the meter. I've only seen that type used on farm equipment and a few older cars.

Here is a good way to tell which is which. Use a volt-ohm meter starting on the highest scale (if it is an analog volt-ohm meter). Place it accross the meter terminals. If you see the meter defelect and some resistance, the meter is an external shunt type. If you see little or no deflection, set the meter to a lower scale (if it is an analog volt-ohm meter). You'll probably be reading near 0 ohms resistance between the terminals if it is an internal shunt type amp meter.

The external type meters are better IMHO because they don't lengthen the charge wire. Also, they dont' route hot power through the firewall via a heavy guage wire (fire hazzard). On the other hand, the external shunt type depend on the charge wire having a known amount of resistance. If you were to upgrade your charging system to say a CS130 alternator, you'd probably want to up-size the charge wire. As a result, the external shunt ampmeter will likely read too low, though it would still give you a visual indication of charge / discharge.

Dave
========================
68 Coupe, 350 w/ Edelbrock Performer RPM heads, cam, intake, 700R4, Dave's small body HEI
dnult is offline  
post #10 of 18 (permalink) Old Dec 31st, 05, 10:35 AM Thread Starter
Gold Lifetime Member
Larry
 
Join Date: Oct 1999
Location: Alamogordo, NM, USA
Posts: 987
Re: Is It An Amp Gauge Or A Volt Meter?

No, I only momentarily touched the terminals to the 12 v battery. Even so, I'm sure it didn't help its life span. I know what it does when I do that, so I won't be needing to torture the gauge anymore.

I'd like to mention a couple quotes from Mark:

"These gauges are essentially 1 volt range millivolt meters. +0.5 volts deflects the gauge one way -0.5 Volts deflect it the otherway. They indicate trends, and were never intended to provide indication of a specific amount of current flow".

"The full span of the meter is probably about 5 or 10 millivolts. If you run battery voltage through the meter to ground you can figure on buying a new gauge".

As I stated earlier, I can connect a 9v battery to the gauge and it deflects about a needle's width. If it's a milivolt meter, then it should peg the needle. Also, why are the windings in the gauge so heavy? A typical volt meter needs only extremely smaller gauge wiring to do the job.

See why I am confused?

Larry

Larry
69-er is offline  
post #11 of 18 (permalink) Old Dec 31st, 05, 10:47 AM Thread Starter
Gold Lifetime Member
Larry
 
Join Date: Oct 1999
Location: Alamogordo, NM, USA
Posts: 987
Re: Is It An Amp Gauge Or A Volt Meter?

Quote:
Originally Posted by dnult
Larry, as you are discovering there are two types of amp meters. All the ones I am familiar with on GM cars work as Jim described - they measure the tiny voltage drop accross the charging wire between the battery junction block and the horn relay. The wire acts as an external "shunt". But, as in your case, some route system voltage through the amp meter itself because the "shunt" is internal to the meter. I've only seen that type used on farm equipment and a few older cars.
I also mentioned that possibility of different types of gauges.

I went to a Chevelle sight, Team Chevelle I believe, and looked at a diagram of a mid 60's chevelle. It showed what looked like a shunt that a milivolt meter connected to. The shunt performs the same function as the red 10 gauge wire in our Camaros.

I am missing something here. Only one person, Donny at American Autoworks, has shared my view of how this system works. Could it be my style of gauge was used in different GM applications, and that it is not a Camaro gauge?

I will post a couple of pictures in a few minutes for all to see what I have.

Larry
69-er is offline  
post #12 of 18 (permalink) Old Dec 31st, 05, 10:47 AM
Gold Lifetime Member
Jim
 
Join Date: Dec 1999
Location: Yorkville, Illinois USA
Posts: 22,121
Re: Is It An Amp Gauge Or A Volt Meter?

I'm not sure confusion is needed Larry...

Just keep the important facts in mind.

This is a shunt type meter. It does not install in series with the electrical system. A failure of the meter will not cause the car to have no power.

The accuracy of the meter depends on the resistance of the shunt. Changing the resistance by altering the size or length of the wire from the horn relay to the junction block in front of the battery will change the reading of the meter.

The last point would be that regardless of the alternator used, it's really not required to upgrade that wire. I suppose if the battery were completely dead the wire could get really hot, but that hopefully won't happen. Regardless, the pigtail from the battery terminal is a fusable link to protect that circuit. The upgraded alternator can supply a bigger load, and the wires feeding that load should be upgraded to handle the current, but the wire from the horn relay to the battery really only keeps the battery charged and supplies power if the charging system is not operating.





To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.



To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
New website for my vert is coming together. Do ya like the slide show on the home page?
JimM is offline  
post #13 of 18 (permalink) Old Dec 31st, 05, 10:59 AM
Super Moderator
Bess-68's rule
 
Everett#2390's Avatar
 
Join Date: Sep 2000
Location: Va Beach VA
Posts: 31,651
Garage
Re: Is It An Amp Gauge Or A Volt Meter?

I believe Dave (dnult) has hit the nail on the head! All aftermarket ammeters are internal shunt gauges and OE gauges are external shunt.

A shunt, a calculated amount of resistance, is used to handle the majority of the current flowing and the meter is connected in parallel with the shunt used. A small amount of current passes through the gauge coil, whether the current is forwards or backwards, the meter will indicate as a discharge or a charge.

To indicate the correct amount of current flowing, the coil current draw at full scale is needed to determine the the size of the shunt used, whether internal or external. The wire resistance of the pigtails attached to the ammeter posts are used in conjunction with the meter coil resistance to determine the miniscule amount of current needed for full scale deflection on an external shunt ammeter. For aftermarket ammeters, only the coil's resistance is used to determine the full scale deflection.

I hope what I explained made sense..........

Give a man a rescued dog for the health of both their souls. May 2017 ROTM Winner - Thank you!
'
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
CUBS - 2016 World Series Champions - Thank you, Joe Madden … enjoy your next chapter.
Everett#2390 is offline  
post #14 of 18 (permalink) Old Dec 31st, 05, 11:03 AM Thread Starter
Gold Lifetime Member
Larry
 
Join Date: Oct 1999
Location: Alamogordo, NM, USA
Posts: 987
Re: Is It An Amp Gauge Or A Volt Meter?

Makes sense to me. In fact, I want to agree with all of you. I just need to clear up why I apparently have something that's incorrect.

Here's pics of my gauge:

http://www.myimagehosting.com/album_...aKnA&f_id=3309

See how the windings appear to be larger than a typical voltmeter would have?

Larry
69-er is offline  
post #15 of 18 (permalink) Old Dec 31st, 05, 11:12 AM Thread Starter
Gold Lifetime Member
Larry
 
Join Date: Oct 1999
Location: Alamogordo, NM, USA
Posts: 987
Re: Is It An Amp Gauge Or A Volt Meter?

Quote:
Originally Posted by Everett#2390
I believe Dave (dnult) has hit the nail on the head! All aftermarket ammeters are internal shunt gauges and OE gauges are external shunt.
So I'm sure, Everet and Dave, aftermarket gauges are still milivolt meters, measuring across the internal shunt?

Larry
69-er is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Team Camaro Tech forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address.
NOTE we receive a lot of registrations with bad email addresses. IF you do not receive your confirmation email you will not be able to post. contact support and we will try and help.
Be sure you enter a valid email address and check your spam folder as well.



Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome