jacksonchuck
Member
Does any one know of a source for a 12V voltmeter that would fit neatly in place of the model A ammeter?
Voltmeter in a Model A
- Thread starter jacksonchuck
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jrelliott
Well-known member
Question why do you want an voltmeter? You cannot simply substitute an voltmeter for an amp meter as both are measuring different things. The voltmeter only takes a few milliamps to go to full scale and the current going through an amp meter in a correctly wired vehicle can be close to 20 Amps. This amount of current will fry the volt meter. There is a shunt in the back of the amp meter so only a small amount of current flows through the actual meter and the majority flows through the shunt.
MrTube
Well-known member
You would simply connect the two ammeter leads together and of course insulate them somehow. Next you would run a connection from those leads to the volt meter and another from the volt meter to the chassis.
SLPreston53
Senior Member
to answer the "why a volt meter" question, some of us run alternators, and conventional wisdom says a volt meter is a better way to monitor than an ammeter.
bettlesr
Senior Member
Here is a picture of the voltmeter I have in mine. I bought a 1-1/2" meter and changet the bezel to one off of a stock ammeter. I ran wires out of the back and connected them to ground and the ignition switch. The switch was rewired to break the hot wire to the ignition coil and an accessory relay. Sorry, I don't remember where I bought it.
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Mike V. Florida
Well-known member
With an ammeter I know if my points are opening and closing when I start my engine, I know if my generator is charging, if my brake lights are working, and can tell if I have a filament out or completely out in my headlight/s.
What does the volt meter tell you?
Amazon has one,
http://www.amazon.com/Auto-Meter-2356-Electric-Voltmeter/dp/B00062YVSY?tag=atomicindus08-20
You can search on, Auto Meter Autogage Gauge, their part number is 2356
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MrTube
Well-known member
George Miller
Well-known member
Pete
BANNED
Actually, a voltmeter will tell you more than an ammeter IF you know how to interpret the readings AND you have a radio quality voltmeter.
A 2 inch radio quality meter can be had with .1 volt resolution.
This is close enough to tell if your points are working when you start.
It will tell you battery condition at rest. It will tell you battery condition while charging. It can also be used to analyze certain electrical problems.
It will indicate charging system problems.
It will tell you approximate charge rate.
The voltmeters sold for automotive use are a waste of time and money unless you have an extra hole in the dash that needs filling. Their accuracy is probably plus or minus 20% if you are lucky.
A 2 inch radio quality meter can be had with .1 volt resolution.
This is close enough to tell if your points are working when you start.
It will tell you battery condition at rest. It will tell you battery condition while charging. It can also be used to analyze certain electrical problems.
It will indicate charging system problems.
It will tell you approximate charge rate.
The voltmeters sold for automotive use are a waste of time and money unless you have an extra hole in the dash that needs filling. Their accuracy is probably plus or minus 20% if you are lucky.
As explained to me:
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 7.0 to 7.56 volts (for 6 volt battery with alternator) 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.
I use a Datel Voltmeter. It's digital. I glue a magnet to it and wire it to the battery and cutoff switch. When driving its right there to see. When "showing" I hide it up under the gas tank. That way original ammeter still in circuit.
[/URL][/IMG]
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 7.0 to 7.56 volts (for 6 volt battery with alternator) 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.
I use a Datel Voltmeter. It's digital. I glue a magnet to it and wire it to the battery and cutoff switch. When driving its right there to see. When "showing" I hide it up under the gas tank. That way original ammeter still in circuit.
Mike V. Florida
Well-known member
As explained to me:
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 7.0 to 7.56 volts (for 6 volt battery with alternator) 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.
I use a Datel Voltmeter. It's digital. I glue a magnet to it and wire it to the battery and cutoff switch. When driving its right there to see. When "showing" I hide it up under the gas tank. That way original ammeter still in circuit.
[/URL][/IMG]![IMG_2695_zpsed6d310e.jpg](http://[URL="http://s13.photobucket.com/user/6mmbr/media/IMG_2695_zpsed6d310e.jpg.html"][IMG]http://i13.photobucket.com/albums/a254/6mmbr/IMG_2695_zpsed6d310e.jpg)
Best of both worlds.
steve s
Well-known member
Thanks for the nice explanation. I am wondering whether ANY of the voltmeter advantages apply to a generator? It seems to me that the voltmeter became important when voltage regulators were added. If so, wouldn't they also be informative for folks who have added voltage regulation to their generators?
By the way, the pressure gauge analogy for voltmeters is handy, but, like all analogies, has limitations. While absolute pressure readings make sense, voltage (which is really an energy measurement) is always a relative, or difference, quantity--it is the energy difference between two places. A pressure gauge can be simply tapped into a system at one point, but a voltmeter has TWO wires that must be connected to two different points.
Steve
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mralternator
BANNED
The “local” and “online” experts may tell you, that you need to add a “shunt” to your original amp gauge when you upgrade to a modern alternator type of charging system. You do not and here is why….
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An amp gauge does not measure alternator output it measures the amount of current going into or coming out of the battery.
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The advantage of the alternator is the ability to provide an output at idle and low rpms (something the generator could not do) to keep the lights bright and the battery fully charged. The total electrical load of the vehicle remains the same as it was before.
The total amount of amperage passing thru your dash gauge will be the same or less with the alternator because the alternator is keeping up with the electrical load at all times. With the battery always fully charged at all times no large amounts of current will be flowing into or out of the battery as before.
Upgrading to 12-volts…
Now suppose you decide to upgrade to 12-volts and install a 12-volt 60-amp alternator, so you can add a modern stereo and air conditioning. What happens to the total electrical load then?
The total electrical load becomes half of what it was originally because of the electrical rule that says when you double the voltage the amperage load will be reduced by half. So our 36 amp electrical load becomes 18 amps on 12 volts. Do you think you can run air conditioning and a stereo on the remaining 18 amps? Absolutely!
You have plenty of reserve output from the alternator (40 amps, 60 minus18) and the only current that will flow thru the amp gauge in the dash is what is needed to keep the battery fully charged just as before. The alternator will take care of the additional electrical load with no affect on the amp gauge or battery.
-------------------------------------------------
An amp gauge does not measure alternator output it measures the amount of current going into or coming out of the battery.
------------------------------------------------
The advantage of the alternator is the ability to provide an output at idle and low rpms (something the generator could not do) to keep the lights bright and the battery fully charged. The total electrical load of the vehicle remains the same as it was before.
The total amount of amperage passing thru your dash gauge will be the same or less with the alternator because the alternator is keeping up with the electrical load at all times. With the battery always fully charged at all times no large amounts of current will be flowing into or out of the battery as before.
Upgrading to 12-volts…
Now suppose you decide to upgrade to 12-volts and install a 12-volt 60-amp alternator, so you can add a modern stereo and air conditioning. What happens to the total electrical load then?
The total electrical load becomes half of what it was originally because of the electrical rule that says when you double the voltage the amperage load will be reduced by half. So our 36 amp electrical load becomes 18 amps on 12 volts. Do you think you can run air conditioning and a stereo on the remaining 18 amps? Absolutely!
You have plenty of reserve output from the alternator (40 amps, 60 minus18) and the only current that will flow thru the amp gauge in the dash is what is needed to keep the battery fully charged just as before. The alternator will take care of the additional electrical load with no affect on the amp gauge or battery.
mralternator
BANNED
And do NOT forget the most important part of adding a voltmeter. a Volt meter will drain a battery, analog meter slightly, digital meter more, .where an amp meter will not, So don't forget to have the Volt meter on a circuit that is turned off at key off or a individual switch