Where's it all go? I've not owned a petrol engined car since everything became electronic - mine have all been diesels, and a lot of that is still rather mechanical. I know that there are electrical valves for the common rail fuel injectors, but the rest is done by a high-pressure pump driven by the engine. My petrol-engined classic car has an alternator that is only 34A. The ignition took about 1A and that was all there was.

I have common rail diesel vehicle and one pump duze diesel vehicle also. Yes I observe a much lower current draw from the pump duze engine. I think on the common rail diesel the piezo injectors requires about 200-500V to operates, but provides the capability of multiple injections in one cycle (e.g. post injection for after treatments of exhaust gas). For some reason the manufacturer have fitted a 120 amp alternator on the pump duze engine ... probably due to the bigger battery => bigger starter.

 

Just to try to simplify things a bit more...

The alternator is grounded to the engine which is then grounded to the rest of the body and also connected to the battery. The ground connection between the battery and the engine is solely used to start the engine, charge the battery, and absorb electrical noise (there's probably a better way to say that part).

The power wire between the alternator and the battery on the other hand carries all current produced by the alternator to the battery and then it is distributed from there through the normal positive battery terminal connection. You will see a much higher current on the positive wire between the alternator and battery because of this.

As previously stated the readings are totally normal.

 

Where's it all go?

I think you know the answer. But for those who might not - the alternator is capable of producing so many amps. The electrical system will only draw what it needs. If the battery is being charged then the bulk of the current will go to that aspect of the operation. The rest of the current will be drawn by the auto electrics, be they fans, lights, injectors, pumps etc. What isn't used isn't produced.

The alternator is grounded to the engine which is then grounded to the rest of the body and also connected to the battery. The ground connection between the battery and the engine is solely used to start the engine, charge the battery, and absorb electrical noise (there's probably a better way to say that part).

I think you said that pretty well.

 

I think you know the answer. But for those who might not - the alternator is capable of producing so many amps. The electrical system will only draw what it needs. If the battery is being charged then the bulk of the current will go to that aspect of the operation. The rest of the current will be drawn by the auto electrics, be they fans, lights, injectors, pumps etc. What isn't used isn't produced.
I think you said that pretty well.

What I meant was that 35A was a lot more than I was expecting to run a fuel pump, fuel injectors and six spark plugs.
I‘m intrigued now. I’ll measure it on my car when I get home (if it’s not raining, I’m only so much intrigued)

 

@Ian0
You should know that when you have a circuit that requires 1 amp you need a power supply capable of producing AT LEAST 1 amp. A 2 amp supply would be better even though your circuit is going to draw 1 amp. The alternator is a power supply for the auto electrics and for recharging the battery. Even if you have a 120 amp alternator, the electrics are only going to take what they need. A 120A alternator might be something you see on a camper. Kids are crazy about 120A alternators because of their stereo BOOM BOOM systems they put in their cars. And for that extra kick they use high capacity capacitors with extremely low ESR so that when the base note hits it hits hard. But between tracks when there's no music or other sounds the current draw is very small.

 

@Ian0
You should know that when you have a circuit that requires 1 amp you need a power supply capable of producing AT LEAST 1 amp. A 2 amp supply would be better even though your circuit is going to draw 1 amp. The alternator is a power supply for the auto electrics and for recharging the battery. Even if you have a 120 amp alternator, the electrics are only going to take what they need. A 120A alternator might be something you see on a camper. Kids are crazy about 120A alternators because of their stereo BOOM BOOM systems they put in their cars. And for that extra kick they use high capacity capacitors with extremely low ESR so that when the base note hits it hits hard. But between tracks when there's no music or other sounds the current draw is very small.

Consider that if that 1200 watt audio amplifier were 100% efficient it would draw 100 amps at full output. So certainly the thundering audio systems need huge power.
And even a normal current production car is so full of useless toys that all draw power most of the time. And the big screen to provide all of the distractions so that the driver won't get bored paying attention to driving.

 

In the US almost every vehicle sold in the last 20 years was built with an alternator rated at over 100A. Some models are closer to 35 - 40 years since they had a sub 100A alternator from the factory.

 

@Ian0
You should know that when you have a circuit that requires 1 amp you need a power supply capable of producing AT LEAST 1 amp. A 2 amp supply would be better even though your circuit is going to draw 1 amp. The alternator is a power supply for the auto electrics and for recharging the battery. Even if you have a 120 amp alternator, the electrics are only going to take what they need. A 120A alternator might be something you see on a camper. Kids are crazy about 120A alternators because of their stereo BOOM BOOM systems they put in their cars. And for that extra kick they use high capacity capacitors with extremely low ESR so that when the base note hits it hits hard. But between tracks when there's no music or other sounds the current draw is very small.

so many panels and covers that I couldn’t get a current clamp anywhere near the alternator.

 

In measuring current to and from the battery, if you put the clamp on meter around the single ground wire to the engine block , but then only around one of many going to the positive battery terminal , how would you expect to get a similar reading..

Also, if there is not a second wire from the battery negative to the body ground, the electical design is JUNK!!
For anything close to reliability there needs to be a DIRECT connection between the battery ground and the vehicle body ground. In addition there should be a direct wired connection between the battery negative and the wiring harness ground wires. But that one may be at the junction block.. (Certainly this is a harsh accusation of some auto makers, but they deserve it. Cheating on a ground connection reduces reliability.)