Ok, this may be worth repeating... I have a friend who is an electronic engineer genius that I always ask when I have questions like this. I believe him for the most part whatever he says. (he HAS taken advantage of my gullibility before) This isnt one of those times.. here goes..
Concerning how to properly shunt an ammeter:
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If you want to alter an ammeter to read a "Higher Current" ....... You'll have to lower the shunt resistor value. Current shunts are very low value resistors that are rugged and have to pass high currents at low voltages... The dude that says "use a stainless steel clamp" is correct. It doesn't make any difference the shape...it's the minute resistance value, and the ability of heat dissipation. The tread holes in the stainless clamp strap increases the surface area of the acting "resistor" and will better handle the current generated heat. If you have a "digital ohm meter" that can measure tenths of an ohm or "lower"...you can get a ballpark value of your 30 A meter's shunt by measuring the resistance between the two posts.... If you put another value of resistance (equal to the value you measure) across the posts it will in theory make the 30 A meter into a 60 A meter. Ni-Chrome wire is another way of making a LOW resistance shunt... You can use trial and error, and tin snips, too.
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But it doesn't stop there... THIS is what he said about the feasibility and logic on what meter to use...
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A simple way to describe an ammeter is to call it "a voltmeter measuring the voltage drop across a small fixed value resistor"! On my tractor restorations, I didn't install an ammeter, but purchased a "voltmeter" and used that to monitor the charge voltage coming out of the alternator. It actually gives you more information than an ammeter....... It gives you the state of battery charge before you "start", and tells you if the alternator or generator is putting out the proper charge voltage. Many times a generator or alternator has a defective voltage regulator that either over charges or under charges the battery. An ammeter only tells you the charge current......you have no idea what the voltage is coming out of the alternator or generator. An example....you could have a shorted cell in your battery. The ammeter will show your generator is "pumping out" 20 amps...... "You'll think"....man my electrical system is working great! Problem is: your
battery, with a shorted cell, is actually a 10 volt battery instead of a 12 volt, and the charging system is trying to overcome the short!! With a voltmeter, you would "see" the lower voltage and know the battery has a problem. Charge voltage is typically 14.5 volts. If your battery is fully charged, and you do not have any "load" on except for the ignition system.....you'll not pull much current, and the ammeter will be slightly above "0". With a voltmeter, you'll "know" everything is good because you'll see 14.5 volts with the engine running, and about 12.8V with it off and the "key on".
An 80 amp alternator is for a large "big rig" truck with "out the [censored]" clearance lights and loaded with bells and whistles...... Most pickup trucks and cars that have "heated seats", rear window defrosters, A/C, power seats and windows....etc......have 65 amp alternators. High output alternators are NOT for charging batteries. They power the high current demand options.
I recommend the voltmeter route because of the expense of the heavy gauge wire required from the alternator to the ammeter in the dash and back to the battery. Plus it's an electrical fire hazard! I put an ammeter in my '59 Chevy when I was in High School...... The wires shorted and about burned it up...
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This is not what I wanted to hear, but I know why I was thinking wrong. The battery is accepting the charge from the alternator. You aren't reading battery voltage alone. So, now I get to modify my gauge set. Woohoo!
