Where's the shunt? - Team Camaro Tech
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post #1 of 17 (permalink) Old Sep 23rd, 07, 06:30 PM Thread Starter
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Where's the shunt?

Okay, the console ammeter in the Camaro hasn't worked since I got the car several years ago, and I'm not sure if it's even hooked up right. (Or if it's even hooked up!!)

I know that it should go from the fusable link on the horn relay to the gauge and then back to the fusable link at the junction block, but I don't even have a junction block anymore!!

My question is (as *Clara Peller would say), "Where's the shunt???" Is one of the fusable links the shunt? If so, which one? If it's the one on the junction block (which I'm missing), can I just add a resister to the wire going to the gauge? If so, what rating should the resistor be? If it's the one on the horn relay, do I need the other one? I'm SOOOO confused!!

* Clara Peller

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post #2 of 17 (permalink) Old Sep 23rd, 07, 09:38 PM
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Re: Where's the shunt?

I dont know how to hook up the ammeter, I think one goes to the juntion block by the batt as you said an the other is the horn relay maybe. Dont quote me

but I suggest that because it isnt working you get a volt meter, much easier to wire up and shows a much better picture of what is going on.

But I just noticed the Camaro Research Group thing in your sig, so nevermind, someone will have the right answers for you
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post #3 of 17 (permalink) Old Sep 24th, 07, 10:00 AM
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Re: Where's the shunt?

The shunt is the the wire connected between the terminal block and the horn relay. I forget what GM originally had in place there - 10 guage wire perhaps. 400bird is right - a voltmeter is a better way to go, but I'm not sure anyone has found a drop-in replacement for the factory ampmeter.

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post #4 of 17 (permalink) Old Sep 24th, 07, 02:23 PM Thread Starter
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Re: Where's the shunt?

Dave are you talking about the fusable links? There are two. One is at the horn relay (connecting the 14 gauge black/white wire from the ammeter to the horn realy fusable link), and the other is at the terminal block (connecting the 14 gauge black wire from the ammeter to the terminal block fusable link). Both are 20 guage orange.

I really can't see how this thing works! Both fusable links are the same so which one of these is the shunt?

Ed


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post #5 of 17 (permalink) Old Sep 24th, 07, 03:22 PM
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Re: Where's the shunt?

Ed, as was said, the "shunt" IS the 10 gauage factory wire that runs from the juncyion block by the battery to the horn relay. The "ammeter" is actually a millivolt meter, which is connected in parallel with that wire and measures the voltage drop across it.





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post #6 of 17 (permalink) Old Sep 24th, 07, 04:40 PM Thread Starter
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Re: Where's the shunt?

Okay guys, I think I'm getting a bead on this. I cut out all the non-related wiring in the Console wiring diagram and came up with the picture below. Take a look at my conclusion and tell me if I have it or if I'm still being thick!!

Ed



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post #7 of 17 (permalink) Old Sep 24th, 07, 04:53 PM
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Re: Where's the shunt?

let's cut out the horn relay resistance part, Ed, those 2 screws are on the same peice of steel, same point electrically, it's just used as a junction block.

Other than that detail, yes, you got it.





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post #8 of 17 (permalink) Old Sep 24th, 07, 05:35 PM Thread Starter
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Re: Where's the shunt?

Perfect. Thanks Jim.

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post #9 of 17 (permalink) Old Sep 24th, 07, 11:37 PM
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Re: Where's the shunt?

As you can imagine Ed, the ammeter isn't a highly calibrated peice of equipment. Variations in the 10 gauge wire resistance etc. can contribute to miscalibration. When guys upgrade thier charging system, they often replace that 10 gauge wire with an 8 gauge wire to handle the additional charging current. As a result, it's resistance decreases and the ammeter becomes less sensative.

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post #10 of 17 (permalink) Old Sep 25th, 07, 11:04 AM Thread Starter
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Re: Where's the shunt?

Dave, I agree that the ammeter is almost useless! I wish someone would come up with a Voltmeter that would fit in its place, or even a way to change the original ammeter to a voltmeter.

Ed


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post #11 of 17 (permalink) Old Sep 25th, 07, 12:50 PM
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Re: Where's the shunt?

Quote:
Originally Posted by bertfam View Post
Dave, I agree that the ammeter is almost useless!
While the voltmeter is better, the factory amp meter is not totally useless. The purpose of the ampmeter is to show the battery charging rate. The factory amp meter can be used with any amp alternator, but what is most important is the battery charge wire (wiring from the horn relay to the battery) and the alternator output wire (in terms of where its wired to) must be factory correct. Below is a copy of one of my posts on the chevelle board...


I don't think you understand how the factory amp gauge is supposed to work. The amp gauge only shows the battery's charge or discharge rate. Starting with a fully charged battery......In a amp gauge car, with the car not running start by turning on items in the car, high beams, fan blower on high, brake lights ect... the more thats turned on the farther the amp gauge will show discharge. With everything possible that was original to the car turned on, the gauge may be close to max discharge. Now turn everything off and start the car, the needle will move towards charge a little (not even to the first line) and may stay there for a min or 2, than settle close to the center mark, about a needles width on the charge side. While driving the car and everything working properly this is where the gauge will normally be. Now turn the car off, turn on the high beams and leave them on for 20-30 min or so to take some of the "charge" out of the battery, then turn them off and start the car. Now that the battery's charge is lower, the amp gauge will move farther towards the charge side. As the engine RPM varies, you might see the amp gauge vary the charge rate as alternator output changes with engine RPM (at idle it may be close to the center mark, at 2500 engine RPM, it may show a medium charge rate. As the battery becomes fully charged it will slowly settle close to the center mark, about a needles width on the charge side. Anytime you see the amp gauge on the discharge side with the engine running means either the charging system is not working or the cars current demand is greater than the alternators output, and you are just running off the battery. On factory high performance cars (Chevelle LS-6's, L-78's, Camaro Z-28's) these cars came with a larger deep grove alternator pulley. alternator output was lower than the the low perf cars at any given engine RPM, battery discharge at idle was sometimes a problem, especially if other accessories was turned on.

Quote:
Originally Posted by bertfam View Post
I wish someone would come up with a Voltmeter that would fit in its place, or even a way to change the original ammeter to a voltmeter.

Ed
This can be done. No one sells a factory look a like voltmeter, but you can have yours converted, but this is not a cheap option. There are some posts on the chevelle board on a member who had his converted.

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post #12 of 17 (permalink) Old Sep 27th, 07, 06:02 PM
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Re: Where's the shunt?

Quote:
Originally Posted by bertfam View Post
Dave, I agree that the ammeter is almost useless! I wish someone would come up with a Voltmeter that would fit in its place, or even a way to change the original ammeter to a voltmeter.

Ed
Ed, the factory gauge IS a voltmeter, NOT an ammeter, which is why it says "Battery" instead of "Amps". It's simply a sensitive voltmeter (galvanometer), wired in a parallel circuit; one lead senses the voltage at the horn relay junction buss, and the other lead senses the voltage at the junction block behind the battery, using the 10-ga. wire from the horn relay buss to the junction block as the shunt for the circuit. All the gauge does is measure the voltage difference between what it sees at the horn relay buss and what it sees at the junction block, and displays the difference - whether current is flowing TO or FROM the battery. The gauge carries no circuit loads at all.

An "ammeter", on the other hand (like in '53-'62 Corvettes), is in SERIES with all electrical loads, and is the power distribution point for the whole car, and is dangerous; that's why they disappeared almost 50 years ago.

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post #13 of 17 (permalink) Old Sep 28th, 07, 08:19 AM Thread Starter
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Re: Where's the shunt?

John I would like to argue this a little if you don't mind.



I don't believe this to be a Voltmeter in the true sense of the meaning. A volt meter (in automotive applications) only measures a positive output, starting at zero and going up. The meter in the console is more of a differenciator meter. Like you said, it measures the voltage difference of a circuit at two different points. I would agree that it's not an ammeter by the same defination you gave above.

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post #14 of 17 (permalink) Old Sep 28th, 07, 08:27 AM
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Re: Where's the shunt?

Ok, no argueing.

The facts: There is no such thing as an ammeter, except those things electricians use that place a coil around the wire being tested.

All automotive gauges are voltmeters, they in some way measure the voltage drop between two electrical points. The voltage drop is measured across a known resistance (shunt) and the gauge is calibrated per ohms law (voltage time resistance = amps) to display amperage.

The shunt can be internal to the gauge (the nasty ones John is talking about)
or external to the gauge (the ones used by the factory in our Camaro's.)





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post #15 of 17 (permalink) Old Sep 28th, 07, 09:48 AM Thread Starter
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Re: Where's the shunt?

Thanks Jim

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Last edited by bertfam; Sep 28th, 07 at 10:01 AM.
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