Amps and volts

notjustair

Well-known Member
I was moving tractors today to grind feed and had a thought. That's dangerous in and of itself.

Why did the industry (auto and machine) move away from amp (ampere) gauges to volts?

When things were 6 volt (and for a while after the switch to 12) amp guages were king. The tractors I have here that are that old have amp guages. I fire them up and watch the oil and amp guages to make sure everything is working. On the newer tractors I do the same but wait to see the volts come up.

The only thing I have seen have both were the school buses I drove (Ford). For whatever reason they had an amp guage as part of the factory cluster and then a volt meter added on separate (a Ford unit not the body builder). Those always had both but that was the only thing. The last new vehicle I remember having an amp guage was a conversion van - 1982 model.

Did the switch come as people quit doing their own repairs/maintenance and no longer understood how amps work? I find that when I have an amp guage I watch it like a hawk. The grain truck is an example. It is 12 volt with a generator so I watch to make sure it picks up when I pull away from a stop. With an alternator there isn't much fluctuation but that truck runs from -15 amps to +15 amps at night with every stop or turn.

What are your guesses, boys?
 
Considering how much the average motorist understands about the technical workings of a new automobile probably the best thing would be to go back to the old idiot light.
 
Both are nice. An amp gauge assures charging. A volt gauge assures appropriate charging. If a battery is being over charged the amp gauge will not indicate the fact. Jim
 
probably had to do with costs; ampere meters in the automotive field requires wire size to and from the meter of enough wire size to carry the charging current. it also means that amount of current is present in/under the dash and poses a danger in the event of wire failure. voltage however, at 13-14 volts requires smaller wires. in addition, voltmeters requires less physical size and components than ampere meters.
 

I actually prefer a volt meter. That way you can tell right away if the alternator / voltage regulator are putting out too little voltage: (less than 12.6 volts) to keep the battery charged, or too much voltage: (over 13.5-14 volts) to boil the electrolyte out of the battery.

Myron
 
I think it has to do with the change from mechanically regulated generators to alternators.

The old generator/mechanical regulator setup let the regulator sense battery voltage and sort of "throttle" the charging voltage off the battery voltage. The chargning voltage was not very much higher than the battery voltage. And when the battery voltage got to a certain point, it stopped charging altogether. At this point the ammeter read zero.

So, in a real-world senario, did it charge the battery up, or is the generator just not charging any at all?

In the alternator/regulator setup the charging voltage was pre-set in the regulator, because the current generated in the alternator"s field is usually a much higher AC voltage. And the regulator will keep the system voltage at the pre-set voltage, usually around 13.5 to 14.5 volts.

So at a glance the operator will always know if his alternator/regulator is charging or not. If the voltmeter reads 12.6 or below, he has a problem. 13 to 14.5 or 15 and he is good to go.
 
(quoted from post at 21:08:30 04/20/14) I was moving tractors today to grind feed and had a thought. That's dangerous in and of itself.

Why did the industry (auto and machine) move away from amp (ampere) gauges to volts?

When things were 6 volt (and for a while after the switch to 12) amp guages were king. The tractors I have here that are that old have amp guages. I fire them up and watch the oil and amp guages to make sure everything is working. On the newer tractors I do the same but wait to see the volts come up.

The only thing I have seen have both were the school buses I drove (Ford). For whatever reason they had an amp guage as part of the factory cluster and then a volt meter added on separate (a Ford unit not the body builder). Those always had both but that was the only thing. The last new vehicle I remember having an amp guage was a conversion van - 1982 model.

Did the switch come as people quit doing their own repairs/maintenance and no longer understood how amps work? I find that when I have an amp guage I watch it like a hawk. The grain truck is an example. It is 12 volt with a generator so I watch to make sure it picks up when I pull away from a stop. With an alternator there isn't much fluctuation but that truck runs from -15 amps to +15 amps at night with every stop or turn.

What are your guesses, boys?
oesn't any one ever learn anything? It is always the money! When industry went from 10 or 20amperes to 100+ amperes, it became readily apparent that a voltmeter was cheaper than an ammeter.
 
Pete black pretty much hit the nail on the head. The old tractors only put out 20 amps. New ones put 80-100 amps and more, maybe even 130. If an amp gauge is used all that power flow has to be routed to the amp gauge in the dash and then distributed out to various functions. I can envision a lot of dash fires happening. Jim
 
(quoted from post at 22:21:45 04/20/14) Pete black pretty much hit the nail on the head. The old tractors only put out 20 amps. New ones put 80-100 amps and more, maybe even 130. If an amp gauge is used all that power flow has to be routed to the amp gauge in the dash and then distributed out to various functions. I can envision a lot of dash fires happening. Jim
ope, it is money. Plenty of installations are perfectly safe at thousands of amperes. It just has a cost.
 
An ammeter does not need to have very heavy wire running to it if a shunt is used to handle the largest part of the current. In some battery chargers we used in the fork lift business, the current was way over 100 A when the charging started but they used 12 or 14 gauge wire from the shunt to the meter.

I agree that voltage tells the story.
 
The only way you can really know what is going on with the charging system is to have both. You can have proper voltage, and a battery that is not taking a charge. You can also have amps flowing, but the voltage is too low, so the battery won't be fully charged.

As other have said, a amp meter requires the full amount of current to flow through it or an external shunt. Volt meters are easily wired with small gauge wires. Lights are cheaper yet since they don't need a meter movement.

If there is only one gauge, I feel that an amp meter gives the most useful information to the driver/operator. Voltage can be estimated by the brightness of lights. I have both in my cars with generators that also have two way radios, factory amp and add on voltage.

Some makes of cars and trucks with oil pressure gauges (Ford comes to mind, I had one. Add on gauge read lower at hot idle), don't really read anything but a switch. The gauge is either in the "normal" range or "low". Lets hem sell a gauge package without the expense of a real sending unit.

Josh
 

OldFarmTractor,
Yep, you know instantly if your voltmeter reads way low that either the charging system isn't working, or something is pulling so much amperage that the charging system can't keep up with it.

IMO, a much better indicator of the health of the electrical system.

Myron
 
(quoted from post at 19:11:36 04/20/14) I think it has to do with the change from mechanically regulated generators to alternators.

The old generator/mechanical regulator setup let the regulator sense battery voltage and sort of "throttle" the charging voltage off the battery voltage. The chargning voltage was not very much higher than the battery voltage. And when the battery voltage got to a certain point, it stopped charging altogether. At this point the ammeter read zero.

So, in a real-world senario, did it charge the battery up, or is the generator just not charging any at all?

In the alternator/regulator setup the charging voltage was pre-set in the regulator, because the current generated in the alternator"s field is usually a much higher AC voltage. And the regulator will keep the system voltage at the pre-set voltage, usually around 13.5 to 14.5 volts.

So at a glance the operator will always know if his alternator/regulator is charging or not. If the voltmeter reads 12.6 or below, he has a problem. 13 to 14.5 or 15 and he is good to go.




ok, now i understand why when i got my 9n it had a volt meter instead of an amp meter. it had been converted to a 12 volt system. some ... day... i gotta look and see why it don't work. it's probably just a hokey connection, when i first got it, the guy couldn't figure out why sometimes it would start and other times not, after all he had just put a new battery in it. when i got it home i traded out a less hokey positive battery terminal and wire and discovered the wire coming from the start button wrapped around the screw kinda sorta, i put a crimp on terminal on it and she fires right up every time.
 
Amps is the amount of current flow and volts is pressure. Therefore the volt meter is like an oil pressure gauge and you know if the system is working.
 
(quoted from post at 00:29:17 04/21/14) Amps is the amount of current flow and volts is pressure. Therefore the volt meter is like an oil pressure gauge and you know if the system is working.
Tim (Ga),
The analogy is simple when expressed in other terms: [b:eb2a2be6f3]voltage[/b:eb2a2be6f3] is like [b:eb2a2be6f3]pressure[/b:eb2a2be6f3] in a water line.
[b:eb2a2be6f3]Amperage[/b:eb2a2be6f3] is like the [b:eb2a2be6f3]flow[/b:eb2a2be6f3] expressed in GPM.

Myron
 
A lot of it is cost savings during manufacture. Volt meters are cheaper to make; plus the older tractors used Generators (low Amperage) while the newer tractors use Alternators (high Amperage 80-100+). Higher Amperage requires heavier gauge wiring - more Copper & with the high price of Copper, more expense. So if they can save a couple of $$ per tractor, times 100,000 tractors, that adds up pretty quickly.
 
Back in the days of low-output generators and simple electrical systems, ammeters made a lot of sense: plus means "good", minus means "bad". This is easy to see if you have a 15 or 30 amp meter. But the meter needs to be able to handle the maximum alternator output, and it's pretty difficult to tell a slight charge from a slight discharge on a 60 amp ammeter. Many vehicles today have 130 amp alternators; a 130 amp full-scale ammeter is pretty much useless.

Higher alternator capacities also made it less practical to install an ammeter in the dash. The shunt needs to be large and the alternator-to-battery cable needs to be heavy gauge. Ammeter-equipped vehicles built in the late sixties used remote current shuts, but this adds a complexity and expense to the charging system.

I think another factor was the popularity of imported cars in the seventies; Japanese and European manufacturers had already made the switch to voltmeters and the introduction of these cars to the US helped gain acceptance for voltmeters. In the end, the only reason to stick with ammeters was that drivers were familiar with them. Once they got used to seeing volmeters on imported vehicles that reason wentt away.

In my opinion, the voltmeter is a far better diagnostic tool than an ammeter. Add to that the simplicity of installing a voltmeter and it wins hands-down.
 
Id guess they changed cuz a Voltmeter is easier and cheaper. An ammeter registers the direction and flow of current while a Voltmeter registers the Voltage or Electromotive Force (EMF) across say the battery terminals. BOTH provide good diagnostic information. I have BOTH in my RV, the ammeter shows how many amps are being pumped into my battery bank for charging or out of it when discharging. The Voltmeter keeps me abreast of the state of charge in my battery bank. Actually I watch it more then the ammeter if Im dry camping and running strictly off my battery bank. When my solar panels are pumping and my charge controller is regulating I may settle in at say 13.8 volts while at night it may drop down to 12.6 or 12.4 etc subject to lights and the furnace and water pump use. HOWEVER if it ever dropped to 12 volts (which it doesnt since I now have 4 golf cart batteries and 460 amp hrs of storage) Id be thinking about firing up my Genset so the Xantrex Truecharge2 Smart Battery Charger can replenish my batteries.

VOLTMETER MAY BE CHEAPER WHILE BOTH SERVE A DIFFERENT PURPOSE

Hope this helps

John T
 
A Voltmeter is every bit as useful as an Ammeter in monitoring and troubleshooting an electrical system, if you understand the relationship.

In a nutshell:

More Volts = More Amps

Less Volts = Less Amps

14-15V tells you that the system is producing a normal amount of current to power the tractor's electrical system and charge the battery.

It can go above 15V if the battery is really dead, but if it pegs the needle, the regulator isn't working and you'd better shut down ASAP to avoid boiling the battery dry.

When you see <13V, the alternator isn't charging properly either, and needs help soon, before the battery dies.
 
It is a heck of a lot easier to wire in a volt meter
because it carries NO charge current. An amp meter
must carry ALL the charge current unless it is
shunt-wound. It would take some awful big wire to
hook up a 150 amp alternator to a amp meter in the
dash.
 
As we learned back in the day at Purdue University School of Electrical Engineering,

An "ideal" Ammeter would be ZERO OHMS

An "ideal" Voltmeter would be INFINITY OHMS

John T
 
Out of all the responses i like t.r,k.'s the best.

"If the voltmeter reads 12.6 or below, he has a problem. 13 to 14.5 or 15 and he is good to go. "


An Amp meter reads alternator output and a alternator not putting out current (Amps) can mean 2 things

- 1.) the battery is charged (your OK) or

- 2.) the alternator isn't working (your in trouble or will be soon).

So, how do you know if your ok or not.

With a volt meter -- 12v your in trouble 13v your ok
 
not true concerning volts/amps relationship.
volts is measured across a circuit, amps is
measured in a circuit. you can have volts with no
amps but you cannot have amps with no volts.
 
I suspect there are more people who misunderstand volt readings then current readings. A voltmeter can tell you when a system is overcharging whereas an amp meter cannot. Amp meter can show a lot of current flow but can't tell you if it's over-volting or not. A voltmeter can also tell you if a battery is dangerously low when you first turn the key on.
 
(quoted from post at 22:21:45 04/20/14) Pete black pretty much hit the nail on the head. The old tractors only put out 20 amps. New ones put 80-100 amps and more, maybe even 130. If an amp gauge is used all that power flow has to be routed to the amp gauge in the dash and then distributed out to various functions. I can envision a lot of dash fires happening. Jim

It would just have a shunt out by the battery and small sense leads going going to the meter inside.
 
One volt = 6.25X10 to the 14 power of electrons to pass a given point.

One Amp = the amount of push to get the volt across that point.

Anyway that's the was my basic electrical course puts it.

Walt
 
(quoted from post at 19:05:02 04/21/14) One volt = 6.25X10 to the 14 power of electrons to pass a given point.

One Amp = the amount of push to get the volt across that point.

Anyway that's the was my basic electrical course puts it.

Walt
inda close, but no cupie doll!

The ampere is a measure of the amount of electric charge passing a point in an electric circuit per unit time, with 6.241×10*18 electrons (or one coulomb) per second constituting one ampere
 

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