I'll agree with that. They do that because they use fairly cheap ammeters.



A better (and far safer) way to do it if you absolutely MUST have an ammeter would be to use a remote shunt ammeter where the meter shunt is out near the alternator instead of inside the ammeter. This way you run little tiny (and fused) wires for the meter.



I don't think anyone actually makes an automotive meter that is externally shunted but it would work MUCH better.



A volt meter or an idiot light is probably the best bet nowadays.....




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1955 F-600/272/E4OD// Disclaimer: No animals were injured while test driving my F-600 except the ones I ran over intentionally!

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This post was created using OpenSuSE Linux x64 and Firefox

D'Arsonval movements are used in all mechanical meters; how they are connected makes all the difference.  Meter movements are no more ammeters than volt meters; they are tiny DC motors acting against a coiled spring. 

Ammeters and load meters both use a shunt, a set resistor in series with the load but in parallel with the meter movement, which lowers generator voltage further.  Any series resistance in the charging path is not good.

A volt meter is connected in parallel with the battery potential, it draws nothing, and has zero affect on the charging system.  If a wire comes loose there is no consequence.

Some folks regard the GEN light as a 'test' light because it comes on when you turn the key, and it goes out when the engine starts.  Others regard it as an 'idiot' light, probably because it will indicate a thrown belt.  That little light bulb does far more:

There is a small separate wire connected between your GEN light and regulator (terminal A).  When you first turn the key on, the GEN light shines.  ***IMPORTANT***  The power going through the GEN light comes from the key switch, goes through the regulator, and excites your generator's armature (producing magnetism).  That's how the regulator senses the key is ON.  When the key is turned off and the generator stops motion, the regulator's cutout relay opens so sustained field power won't drain your battery .  When the generator overcomes battery voltage (charges), the GEN light has equal voltage on both sides, so it goes out.

Expect charging failure if your GEN light bulb burns out.  If you don't have a GEN light, there is a resistor, instead.  I hope this helps.  - Dave Dare

Royal Oak, Michigan (Four miles north of Detroit, and 12 miles NORTH of Windsor, Canada).  That's right, we're north of Canada.

Ford 292 Y-Block major overhaul by simplyconnected

Actually ALL (D'arsonval) Meters are ammeters. They ALL measure current. There are no "volt" meters per se' .......But I digress..... (My Wife says I ALWAYS digress......as such she never asks me what time it is.....After 20 years.....she know how to build a clock!!! )



A load meter is simply an ammeter that measures the "load" on the source of power (in this case the gen/alt)



It's frequently used in airplanes to tell the total load on the primary source of power. It's useful to know the load on the gen, because if one or more components start drawing too much power and the total load exceeds the capability of the generator, it will discharge the battery (the emerg source of power).



The old ammeters tell you basically the same thing when they go "negative" indicating that the either the engine is at idle and the generator is not putting out sufficient power or you have exceeded the rated output of the generator by turning too many accessories on. (lights, heater fans, A/C clutches, radiator fans, booming stereos , etc)



A Loadmeter is placed in the output line from the GEN/ALT. It only indicates the current provided by the GEN or ALT. Then you have to know what is rated output (35A, 50A, 60A, etc.... and monitor the gage to see it that "MAX" is exceeded.)



The old + & - ammeter is probably a better choice since you don't have to know what the rated output of the gen is. You only have to keep the gage in "positive territory" to know it's working correctly. But then, a GEN light is pretty much the same thing....


















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1955 F-600/272/E4OD// Disclaimer: No animals were injured while test driving my F-600 except the ones I ran over intentionally!

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This post was created using OpenSuSE Linux x64 and Firefox

Taken in context and using modern alternators, is it reasonable to run UN-fused #6AWG (or bigger) copper to your dash just to feed an amp meter?  I still agree with Cereal.  Some alternators output in excess of 130 amps in a passenger car.

When charging systems were simple, and only used 35-amp alt/gen's, an amp meter made more sense.  Instead, a volt meter will show the system is charging, just as well.

Royal Oak, Michigan (Four miles north of Detroit, and 12 miles NORTH of Windsor, Canada).  That's right, we're north of Canada.

Ford 292 Y-Block major overhaul by simplyconnected

I'm not so sure I would agree with that. It might be good to know how much current everything is "drawing" (Ammeter) or how much current the GEN/ALT is providing (Loadmeter)....... Both meters are electrically identical. Ammeters usually will measure current in both directions (I.E. charge/DIScharge) where a Loadmeter is usually marked to measure current in one direction.



Alternatively, a voltmeter will tell you if the alternator is working..... but it will not tell you how many AMPs it's providing to either charge the battery or power the accessories or both.......(unless you draw more current than the ALT is rated at.....then the voltage will drop accordingly)



(by the way, your battery only provides current to start the engine. The GEN/ALT provides ALL the power once the engine is running (unless at idle it cannot provide enough current for everything)





Cheers,





Rick














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1955 F-600/272/E4OD// Disclaimer: No animals were injured while test driving my F-600 except the ones I ran over intentionally!

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This post was created using OpenSuSE Linux x64 and Firefox

Most of those gauges can be bought separately, and you can put them in any order you wish.  A volt meter is the easiest to wire.  One post goes to chassis-ground and the other post goes to any wire that is hot when the key is on.  Volt meters don't need big wire because they draw under a half amp.  If the volt meter is wired backwards, simply switch the leads.  They work on positive or negative ground systems.

Ammeters don't tell the whole story and must be kept away from the starting circuit.  Most go to +/-30 amps.  That was ok when we had 35 amp generators, but far too small for more modern alternators (which start at 50 amps; many go over 130 amps).

12-volts applied to a 12-volt battery would have no current flow.  So the charging circuit needs to output more than 12-volts (and it does).  A running engine should show 13.5-volts at the battery.  When it is shut off, battery voltage slowly creeps down to 12 and levels off there.  Since your starter used battery power, the charging circuit pumped 20-amps (at ~14-volts) back in, until your battery got up to 13.5-v.  Then your regulator stopped all charging.  Very normal in most all cars.

Hope this helps.  - Dave

Royal Oak, Michigan (Four miles north of Detroit, and 12 miles NORTH of Windsor, Canada).  That's right, we're north of Canada.

Ford 292 Y-Block major overhaul by simplyconnected

Yes, I've heard it said that a Volt Meter is the better way to go, & I won't argue that point. (even though I'm not sure of the correct way to wire one in) However, most of the after market under dash triple guage sets, sold for years, came with an Amp Guage, & that was what was on the car when I got it. There are many still in service, so that is why I posted on the subject...

Paul

While not really a fan of "idiot lights" (I DID install an oil pressure gauge), if you use a trickle charger to keep the battery up in a car not driven frequently, the GEN light will let you know when the brushes are gone. In our modern world, where most everyone with the know-how to properly adjust a regulator has gone to his reward, the glowing red light in my Bird is likely adequate?

6 VOLTS/POS. GRD. NW INDIANA

 Paul, I agree with you for this reason; most 'modern' alternators output over 100-amps!  What size meter lugs do we need for that?  I think most owners just want to see their system charge to 14-volts.

Royal Oak, Michigan (Four miles north of Detroit, and 12 miles NORTH of Windsor, Canada).  That's right, we're north of Canada.

Ford 292 Y-Block major overhaul by simplyconnected

Another lesson to learn from this is to get rid of the amp gauge and use a voltmeter. In my opinion, a volt meter will show you more about the charging system than an amp gauge will. I know others will disagree with me on this.



I have a 48 Ford that I built some 25 years ago. I first used an amp gauge and always had electrical/battery problems. When I got rid of the amp gauge, zero electrical/battery problems.

54 Victoria 312;  48 Ford Conv 302, 56 Bird 312
Forever Ford
Midland Park, NJ