Swapping Ammeter to Voltmeter
Thread Starter
Le Mans Master
Joined: Jan 2001
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Swapping Ammeter to Voltmeter
Well, I either fried my ammeter or blew some fusible links to it. Since I have to go back in there I was thinking of swapping over to a Voltmeter. Any suggestions on the forum? Go with a voltmeter from a later model? Or some aftemarket unit that looks similar?
Race Director
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From: North of Toronto - Ontario
The 77 vette voltmeter is the only year with the word "VOLTS" and an orange needle
Afterwards they went to the little image of a battery and a white needle
Easy to sway in, minor adjustment needed to get it to fit in stock place.
I've also seen references to a mid 80's (or was it mid 70's) gmc truck gauge fitting fairly close
Mooser
Afterwards they went to the little image of a battery and a white needle
Easy to sway in, minor adjustment needed to get it to fit in stock place.
I've also seen references to a mid 80's (or was it mid 70's) gmc truck gauge fitting fairly close
Mooser
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From: Plano TX
Can't tell what year you have but if it's 68-71 you have green numerals instead of the white 72-up used. So a later gauge will look off.
I checked with "corvette instrument service" (can't post link as per forum rules) and they say they can convert the 68-71 ammeter to volts and screen print the volt numbers with the correct green color. They also modify the metal back plate as the connector is different. They can also convert the mech oil pressure gauge to electric.
Note: I haven't used them, I just checked into it a while back.
I checked with "corvette instrument service" (can't post link as per forum rules) and they say they can convert the 68-71 ammeter to volts and screen print the volt numbers with the correct green color. They also modify the metal back plate as the connector is different. They can also convert the mech oil pressure gauge to electric.
Note: I haven't used them, I just checked into it a while back.
Race Director
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From: North of Toronto - Ontario
Team Owner
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From: Crossville TN
You cannot just replace the ammeter with a voltmeter...you will get no reading. One of the leads (it doesn't really matter which one) can be used as the 'positive' lead for the voltmeter; the other terminal needs to run to a good frame or battery 'negative' connection.
Melting Slicks
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Usually the first winding breaks/burns right at the post. It's a simple fix to unwind one coil and solder it back to the post.
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Roger at "Corvette instrument services" did mine for my 71...VERY reasonable and it tuned out nice.
Richard
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Depending on how the ammeter is shunted, normally you'll need to connect the two leads that were going to the ammeter together and then either tap into that connection for your positive or find a better location closer to where the meter was originally connected. The voltmeters had calibration resistors attached to the back and vary slightly depending on where they were connected in regards to the battery / alt.
Either way not a big deal to hook up
Mooser
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Le Mans Master
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My gauges were white on black ...
when I bought it (1984!?! really?) ...so that 77 voltmeter should work.
I'll get in there and see what went wrong. If it's just a fusible link, then I may just repair it. I could always get one of those cool voltmeters that attach to the battery.
Now if I can just get going...it should be easy. I can also look to see if I screwed up the ammeter itself while redoing the stereo.
Thanks for all the input. As a former electrical operator I prefer all kinds of instrumentation.....ammeter, voltmeter, wattmeter, varmetter(Vars....but for what? on a car?? heheheh).
I'll get in there and see what went wrong. If it's just a fusible link, then I may just repair it. I could always get one of those cool voltmeters that attach to the battery.
Now if I can just get going...it should be easy. I can also look to see if I screwed up the ammeter itself while redoing the stereo.
Thanks for all the input. As a former electrical operator I prefer all kinds of instrumentation.....ammeter, voltmeter, wattmeter, varmetter(Vars....but for what? on a car?? heheheh).
Team Owner
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From: Crossville TN
Both the voltmeter and the ammeter provide useful information about the electrical system. IMO, an ammeter is MORE useful; but that's because I know how to interpret its movements. Most autos these days have voltmeters. Not because they are better, but because most folks don't know how to interpret an ammeter.
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From: San Jose CA
Both the voltmeter and the ammeter provide useful information about the electrical system. IMO, an ammeter is MORE useful; but that's because I know how to interpret its movements. Most autos these days have voltmeters. Not because they are better, but because most folks don't know how to interpret an ammeter.
Team Owner
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From: Crossville TN
Those two 'pick-up points' are located a specified distance apart, along the same run of wiring that carries nearly all of the current drawn from the battery/charger system. The distance is important, because that specific length of that size wire has the resistance required to act as a "shunt" resistor for the ammeter circuit. The ammeter is, in fact, a millivoltmeter that is measuring the voltage drop across that 'shunt' resistance in the circuit wiring. Then, the dial face on the ammeter just calibrates that reading into 'amperes' (amps).
The difference in voltage between those two 'pick-up points' is very small....which is why you can't use those two leads to connect a voltmeter into the system. Both leads would measure close to 12 vdc and the difference between them would be a very small fraction of one volt.
The difference in voltage between those two 'pick-up points' is very small....which is why you can't use those two leads to connect a voltmeter into the system. Both leads would measure close to 12 vdc and the difference between them would be a very small fraction of one volt.
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From: mount holly NC
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The other terminal on the ammeter connects to the alternator.
Current flowing into or out of the battery determines which way the needle moves.
Technically it's not an ammeter it's a galvanometer and that's why the gauge just says "Battery".
Last edited by Peterbuilt; Jun 1, 2013 at 07:29 PM.
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From: Farragut,TN
Both the voltmeter and the ammeter provide useful information about the electrical system. IMO, an ammeter is MORE useful; but that's because I know how to interpret its movements. Most autos these days have voltmeters. Not because they are better, but because most folks don't know how to interpret an ammeter.
I would rather have the ammeter also.
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From: Farragut,TN
Le Mans Master
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As Pete stated-the Vette (pre 77) has a pseudo ammeter anyway...so it really doesn't matter how good you can "interpret it"...
FYI-
Reprinted from Autometer-
"Which is better for monitoring a vehicle's electrical system - a Voltmeter or an Ammeter?"
Short answer:
A voltmeter, by far.
Electrical guru Mark Hamilton of M.A.D. Enterprises points out that amperage is a measure of current flow, so an ammeter is actually a "flow meter" that's intended to measure current flow to the battery (under normal conditions) or discharge from the battery (in the case of alternator system failure). On a typical flow meter, all output must be directed through the device to obtain an accurate reading. In the ammeter's case, that means all the alternator output used to recharge the battery must first be routed through the ammeter under the dash. Which requires a heavy-gauge cable and presents a possible fire hazard. And the ammeter itself must be able to handle all this current flow, so it must have a higher current rating than the alternator's maximum rated output.
All this might be worth the hassle if the ammeter produced reliable information. But the ammeter can only measure the amount of current output to the battery for recharging purposes: When the alternator recharges a "low" battery, the ammeter indicates a high charge rate; with a fully charged battery the voltage regulator reduces alternator output, and the ammeter is supposed to indicate a very low charge rate. But how can you really tell the regulator has reduced alternator output because the battery is fully charged? Maybe a diode in the alternator rectifier failed, or the alternator belt slipped after it warmed up, just as if the battery were fully charged. Or maybe the meter indicates a medium charge rate most of the time-does the battery want this much or could the voltage regulator be overcharging the battery?
On the other hand, a voltmeter works like a fuel pressure gauge-but instead of measuring fluid in psi, the voltmeter measures electrical system pressure in volts. Just like a fuel pressure gauge, a voltmeter only needs to tap into a circuit; all the fuel (or electricity) does not have to detour through the gauge itself. Voltmeter installation is easy, quick, and safe: It hooks up to a fused, ignition-switched "off/on" source and does not require any modification of the circuit used to recharge the battery or any part of the alternator/regulator system. In short, the voltmeter installed at the dash will be a stand-alone circuit.
The voltmeter directly measures the result of charging-system performance. With normal alternator/voltage-regulator function, battery voltage is maintained at 14.0 to 14.5 volts-and this is reported directly by the voltmeter. In the event of alternator-system failure, voltage will be low and continue to drop as the battery discharges. In the event of an "overcharge" condition, the voltmeter will climb above its normal zone. In summary, there is no chance for misinterpreting a voltmeter's readings as can happen with an ammeter.
FYI-
Reprinted from Autometer-
"Which is better for monitoring a vehicle's electrical system - a Voltmeter or an Ammeter?"
Short answer:
A voltmeter, by far.
Electrical guru Mark Hamilton of M.A.D. Enterprises points out that amperage is a measure of current flow, so an ammeter is actually a "flow meter" that's intended to measure current flow to the battery (under normal conditions) or discharge from the battery (in the case of alternator system failure). On a typical flow meter, all output must be directed through the device to obtain an accurate reading. In the ammeter's case, that means all the alternator output used to recharge the battery must first be routed through the ammeter under the dash. Which requires a heavy-gauge cable and presents a possible fire hazard. And the ammeter itself must be able to handle all this current flow, so it must have a higher current rating than the alternator's maximum rated output.
All this might be worth the hassle if the ammeter produced reliable information. But the ammeter can only measure the amount of current output to the battery for recharging purposes: When the alternator recharges a "low" battery, the ammeter indicates a high charge rate; with a fully charged battery the voltage regulator reduces alternator output, and the ammeter is supposed to indicate a very low charge rate. But how can you really tell the regulator has reduced alternator output because the battery is fully charged? Maybe a diode in the alternator rectifier failed, or the alternator belt slipped after it warmed up, just as if the battery were fully charged. Or maybe the meter indicates a medium charge rate most of the time-does the battery want this much or could the voltage regulator be overcharging the battery?
On the other hand, a voltmeter works like a fuel pressure gauge-but instead of measuring fluid in psi, the voltmeter measures electrical system pressure in volts. Just like a fuel pressure gauge, a voltmeter only needs to tap into a circuit; all the fuel (or electricity) does not have to detour through the gauge itself. Voltmeter installation is easy, quick, and safe: It hooks up to a fused, ignition-switched "off/on" source and does not require any modification of the circuit used to recharge the battery or any part of the alternator/regulator system. In short, the voltmeter installed at the dash will be a stand-alone circuit.
The voltmeter directly measures the result of charging-system performance. With normal alternator/voltage-regulator function, battery voltage is maintained at 14.0 to 14.5 volts-and this is reported directly by the voltmeter. In the event of alternator-system failure, voltage will be low and continue to drop as the battery discharges. In the event of an "overcharge" condition, the voltmeter will climb above its normal zone. In summary, there is no chance for misinterpreting a voltmeter's readings as can happen with an ammeter.
Team Owner
Joined: Jan 2006
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From: Crossville TN
So, I present my opinion on which is better, and you feel obligated to contest it. Interesting. I also find it interesting the you have no opinion or your own, but chose to present someone else's "opinion". So, is that "opinion" supposed to carry more weight than mine?
From my point of view, everyone has opinions. I guess you are just confrontational by nature....
From my point of view, everyone has opinions. I guess you are just confrontational by nature....
Race Director
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From: Florida
The only reason why ammeters were changed to voltmeters is because of cost involved.
Most drivers can't read a volt meter let alone decipher an ammeter.
A lot of voltmeters on vehicles today don't even have any type of readable scale, just makes a buyer feel better by having a couple more "gauges".
Airplanes still use both, they usually want to know what's really going on.
And what to do with a battery that that reads 14.2 volts on a voltmeter while the engine is running, but after sitting for 15 minutes won't start the car. Still shows ample 12.6v, but doesn't have the reserve CA after the surface charge dwindles.
You really need both, but in reality the alt idiot lite is enough for 99.9% of the population. They take it in for service when it stays on or the car won't start.