When did they stop using AMPS and switch to VOLTS

Not to worry. I'll never run any wire, just spent the better part of the day installing flooring in a freshly wired '32 Rordster with about 5 miles of wire in it, just got me spooked looking all all that stuff all day.

 

Fair dinkum you blokes.....

Ammeters are just a nowhere instrument IMO.


Why run a heavy gauge wire from gen, to reg, to gauge, back to battery?
By the time the volts get to the battery, they've dropped.
Yes, no - one mentioned "VD"

no; not the disease, it's voltage drop.

Like a previous post said, you can compare it to water in the pipe.

Take your water meter for example out front of your house.

If you turned the tap off at the meter, it's like disconnecting the battery (stay with me here)

The "pressure" on the supply side is like you voltage.

Higher water pressure is like higher voltage, OK?

Now, if you went inside and turned on the laundry tap (no flow just yet, right?)

So that's like trying to turn on your headlights when the battery's still disconnected OK?


So., leave the tap (headlight switch) on.

Go back outside, and turn on the tap at the meter (re connecting the battery)
look at the water meter. What's it do? starts ticking over, right?

Your water meter is mow measuring the flow of water going from the water supply side (battery) through the pipes (wires) and out the tap, down the sink (through the headlamp filament, to ground) still with me?

So, voltage is like pressure, or potential.
Current is the flow.
Power (watts) is volts x amps (pressure x flow = volume)

So, as an analogy, you stick a 55W headlight globe in where there used to be a 35 watt globe.

This means we now draw more current with the globe.
This would be like the laundry tap opening up from 1/2 to full, fight?

So what now happens at the water meter?

The pressure drops off a little, as the flow is now great.

Same applies for the car.
Voltage drops off when current flow increases.
P=VI
So if you had a 55 watt globe at 12 volts (nominal)
55/12 = 4.58 Amps.

When the car is running, the alternator (or generator) voltage is set by the regulator to usually max out at 14 volts.

At 14 volts, the globe only draws 3.93 Amps (work it out fellas.)55/14=?

To stop getting long winded, I would stick a voltmeter in the dash anyday before an amp meter.
1. I'd only need small gauge wires from a fused Ign source to the meter, and from meter to GND
2. this is cheaper!
3. why risk losing all charging activities if a meter went bung? (if the volt meter died, that's all that dies, not the charging system)
4. All regulators have the facility to run an idiot light for charging indication
5. No risk of burning your hard earned, if the heavy wires were to have a problem with sheet metal.
6. If I had an Amp meter, it would show the charge when lights, fans/wipers (high draw) is on - a voltmeter can do this too you know.


Another example
gauge of wire for indicators/stop lamps/instruments = small, right?
why?
low current draw
(dont forget, you only have 12 - 14 volts to play with)
starter motor cables - why so big?



Starter motors suck the juice. So, to get all that current to flow to the starter motor, you need big cables. Cross sectional area of a conductor will determine its ability to transfer current flow.

Ever seen a car where the earth strap from block to chassis was missing?

you turn the key to "start" and all that current going through the starter motor needs to find a way to get bak to the -ve side (GND) to complete the circuit; so, all the small earth wires, accelerator cables, all get fried, because they're small guage, and cant handle the flow.

I think I better stop now.

 

A modern car has far more big, heavy current wires in it than the old ones ever did.

An ammeter is nothing more than a voltmeter calibrated in amps which measures the voltage drop across a resistor inside of it.

If you want an ammeter but don't want the heavy wires get an ammeter with a remote shunt resistor. That means you are moving the otherwise internal resistor to some other location. Then you can use small wires to go the the gauge.

A small wire that shorts to ground will start a fire just as easily as a big one.

 

only if its not fused.

 

Yes, this is true. But, you don't use a 30 amp fuse to feed a bundle of wires that will each handle only 5 amps without melting.

 

Just remember that even with a volt meter there is still the same amount of amperage running through the system. The only difference is that it no longer runs into the cabin and up through the dash. That wire can still burn your hotrod down if it is not prtected.

The first industry wide change that I'm aware of was the introduction of the "idiot lights" in the early 50s. One of the first things any self respecting hotrodder did in the 50s was to add the under the dash 2 gauge panel that we all remember...oil pressure and ammeter. When you add a new toy like that you will be constantly admiring it and get used to it. When it's gone you miss it.

When I got started, all the old cars had ammeters. I never heard of any epidemic of burning cars that forced the factories to change. This was not a Pinto gas tank deal. I'm sure it was probably a financial consideration. 16 gauge wire is cheaper than 10 ga wire. multiplied by a million cars that can add up to a lot of profits. Yeah I'm cynical.

If you grew up with amp gauges like me you probably got used to them and what they can tell that a volt meter can't. You get used to checking it as you get out of the car to see if you left the lights on or your brake light switch is stuck. A small thing you say but it has saved my bacon a few times. You'll come back to a dead battery with a volt gauge.

If you believe all the hype about a volt gauge please put the same fusible link in the charging wire that you need with an amp gauge. Either style gauge needs that fusible link or master fuse.

My comments are directed for cars that fit the HAMB profile and not the streetrod luxocruisers with all of their electrical accessories. The tube radios of the 50s used more juice and worked fine with amp meters, than the solid state radios of today.

My problem is I have never seen a 1940s or 50s "winged" SW voltmeter. So I use a fusible link to protect the wire and the pricey ammeter. One of those newfangled alternators burnt my wiring up and ate my not too pricey 2" SW ammeter so my cars now get the fusible link to prevent any problem.

I can't pinpoint when the modern volt ga became standard equipment but it was long after what I consider the golden age of hot rodding.

 

Wish I would have had this on the shelf when I was in the rebuild bussiness.I'm sure some of my do it yourself customers would have bought it. I love these electrical threads.

 

Mudgy, I'll reread your post tonight. Once the electrical fire starts, and you kill the battery in most cases does it go out by itself or is it all over? Wouldn't a battery kill switch on the dash or within reach of the driver be a smarter thing to have than one buried in the trunk or under the floorboards? The wiring will be the very last thing done on my project, if in fact it ever gets close to looking ,like a finished vehicle, seeing it burn to the ground it not something I want to deal with, heavily insured or not.

 

Both meters will tell you if charging is good.
As for flat batteries, thats a no brainer. Run all the circuits through the key, fed to relays for hi power circuits.
Key off = whole car off. Dead easy.

 

Northern Lights?

I really have learned something from this thread...I need to take Electrical Engineering classes...

 

When wiring race cars, the battery isolator (wherever located) was hooked up to a bowden cable, so marshals could kill the supply quickly at an incident (the big red "E" in the white circular symbol)

Heavy circuits (alternator, injection, headlamps) usually use a fusible link.
All else is dealt with by the fusebox. Individual circuits are protected, and rated at about 150% maximum demand.

most problems come from the addition of circuits installed by that guy "Eddie the expert" - we've all met one.

Once ther is a fire, cutting the battery supply won't guarantee it's gonna go out. All this does is stop further potential for re ignition. Once there's flames, that's when you have to use that extinguisher you installed. And you did add an extinguisher didn't you?

On board extinguishers have at least 2 x points of exit
engine bay
driver's tub.

hope this helps.

Just personal preference, I'd chuck a VM in any day, regardless of historical importance.

Maybe I'm on e of these street rodders...at least I have no blinkers on, and am willing to test anything new - what Hot Rodders did in the day too you know.

 

Yes, this is one solution. Also, a lot of folks will convert older generator charging systems to alternators,and add a bunch of accessories that increase the current that has to flow through the ammeter. Sometimes this results in the ammeter actually having more current flow through it that it was designed for, resulting in a pegged needle, and raising the risk of an issue due to overload. One solution is to run a small gauge wire in parallel with the ammeter circuit, from the voltage regulator BAT terminal or alternator output directly to the battery. This diverts some of the current flow from the ammeter, and makes it read more normally, although the amperage indicated on the meter will be less than it actually is.

The biggest problem with the Mopars mentioned so frequently in this thread really wasn't the ammeter, but the firewall connector. The connections for the ammeter + and - wires were woefully undersized. Many times you will find that the plastic on the connector surrounding these terminals is melted due to the current flowing through them.

 

There's nothing wrong with an amp guage, All those amps are still running around inside your wiring harness whether you are monitoring them or not. A cheap ass amp gage designed to measure 30 amps ain't gonna get it if you hook it up to a 100 amp alternator. Wire it up with a wire sized to handle only 15 amps and you may as well get out the hot dogs...

 

All sound a bit confusing to me. How's there going to be a fire, with all that water flowing out of the wires? (By the way, that water theory is about the best way of explaining volts and amps that I've ever heard) I've never looked at a gauge to see if I've left my headlights on..I can usually tell, because it's a lot lighter in front of the car than behind it . If the charging system's not working, then it won't start, or the lights are dim, or some other easily worked out evidence is usually in front of you, so hook up a test gauge and find the fault, or push or jump start the thing. Just put a Fuel Gauge and a Speedo in it, maybe a Tacho might be handy as well.

 

Ha ha. At least you kinda get it now, right?

look at a basic flashlight. You got battery power, and a switch, and a bulb.

Just like a car, all DC circuits need a positive, and a negative to work.

B+ goes to one side of a switch, the other side of the switch goes to one end of the bulb filament, the other side of the filament goes back to _ve Battery.

That's the simplest explanation.


Can I hear that penny drop?

 

Nope, although they look like they may be a volt gauge. They are and amp.

 

My '79 Dodge D100 had a amp gauge that shorted out and almost burnt up my truck.
My friend installed a voltage gauge and I've had no more problems.

 

I hate voltmeters in the dash. I understand the problems with the heavy wire, fire danger from the high current and the cost of the heavy wire to wire a amp meter in the dash. Dad had a mid 70 Dodge pickup that burn the firewall plug where the amp meter wires connected. The main problem was the terminals were not heavy enough to carry the current. Volt meter WILL leave you on the side of the road because it is hard to notice the SLOOOOOW decline of the battery voltage if the alternator dies. The alternator die on my wife's 1993 Cougar. She did not notice the volt meter was low. I luckily did one Sunday morning. A amp meter on the other hand, one get used to the heavy and then tapering charge every morning after starting a vehicle. The first time a AMPMETER does NOT lay over after the engine starts, YOU KNOW you have a charging system problem.
If you remember almost all dash gauges disappeared starting in the sixties with the appearance of the idiot lights. Gauge started to reappear with the invasion of the Japanese cars in the late 70's early 80's because they still had gauges.
The way to run a amp-meter on these cars and truck of today is to use a shunt type Amp-meter. A shunt is a heavy block of copper that you run the vehicle electrical system current through. When current is running through this shunt a small voltage drop is developed. You can then read this voltage and correlate it to current. You can have a shunt with 300 AMPS running through it that might develop 1 volt of voltage drop. You then use a volt meter as to read the one volt full scale but you calibrate the scale on the meter in amps. The meter needs to be of the type that zero is in the center and it read negative voltage to the left and positive voltage to the right. Why you do not see this today is the bean counter will say it cost to much.

Kent

 

A VOLTMETER measures the rate of charge, measured in volts. In a 12VDC system, a normal charge is 13.8VDC. A voltmeter simply needs a power supply (off the fuse box, for example) and a ground to function.

An AMMETER measures the amount of charge in amperes. If the needle is in the middle, or points towards the "charge" slightly, it's good. Problem is, in most cases, there is the line coming directly off the alternator to the gauge itself, then back out the bulkhead. Forty and fifty year old wiring is going to have issues here, mainly burning up the gauge and then the car itself when the gauge stays pegged to the "charge" side! I know, as a lifelong owner of '50s, '60s and '70s Mopars.

 

Bob let's simplify this; a push truck, mag, manual choke[to kill the engine], don't drive it at night or in the rain or cold, practice your hand signals and hum to your self. no wires!

 

Perfect solution in my eyes!

 

Voltmeter is a check of the generator or alternator.You're battery goes flat,jump start,then a voltmeter is on the battery to make sure the 6 volts is getting 7.2 ish and 12 volts 14.4 ish.
An amp meter can show a charge on 6 .2 volts on a 6 volt system so long as the battery voltage is less than the generator. So you jump your slow cranking engine figuring the battery is low,the amp meter sees a charge,you drive off only to have a discharged battery next time you crank it.
Actually you need both gauges in the dash? Do aircraft have both gauges?

 

Thank you, my point exactly...which one is going to get hotter/ be more prone to arc?

 

i like it!

 

I've had two electrical fires in old cars due to ampmeters.
Im more of a fan of voltmeters.

 

This is not quite accurate; alternators produce a/c voltage that is rectified to d/c with diodes. A generator also produces a/c but the current is rectified by the brushes and commutator. I am sure someone will jump all over me here, but do your research and you will see.

 

An Ammeter tells you how much current is flowing period. It doesn't tell you how much the generator is producing or how much the accessories are using, only if the generator is producing more or less current than the accessories are using. When the Ammeter reads 0, it could be because the battery is fully charged, the generator can't put out enough current to charge the battery and supply the accessories or the battery won't take a charge. A voltmeter helps diagnoses the charging system. You check battery voltage with the key on before starting the engine. Then you check again after the engine starts to see if the voltage goes up and stays up.

It was in the late 1960s when the change started. We used a voltmeter plugged into the cigarette lighter to help diagnose charging system and battery problems.

 

I really do miss my old Riley 4Port, four plug wires and ONE wire on the car to run the kill switch. Body and paint is a lot more fun than mysteries of electrisity.

 

that was a cool car! body and paint is a lot more fun than the mysteries of spelling.

 

I think the voices in his head would eliminate the need to hum.