Maybe if you get an ammeter going from 0 up to X value, can be measured in Volts and reflected as ammeter due the proportionally between volts and amps with a known resistance value ( Ohms law ). This can be measured getting just one power source and one device sucking it on the opposite side BUT if you ask me not with an ammeter reading Charge and Discharge with two power sources one on each side being one an acumulator and the other one a generator, with needle in center, because you can't read negative voltages. There is or there is not voltage, but never negative voltage able to sway the needle to the reverse side. Voltage is allways present in all the system without care where is going the current.

You have allways same voltage on all the system, but not necessarily current if there is not devices sucking it.

Our car ammeters are able to read what is coming or going from/to batt, and thats allways a positive flow, in one or other direction. An ammeter based on volts measurement won't be able to make that.

That's at least what I can see. I have a shunt ammeter in hands ( M body Lebaron ) and is exactly the same piece ( but smaller pieces ) than a full load unit with just the coil installed to amplify the fields able to move the needle, so is still magnetic device. Needle still mounted on a brass counterweight what will move in one or the other direction according to magnetic field variation given by the current flow.


Anyway, the diff ammeter design systems are not related to how to make efficiently work the charging system on our cars still keeping the stock system safe without need to bypass more than the weakness of terminals. Packard terminal weakness are there with ANY alternator you use, because no matter which one is the source ( Batt or alt ) if you car sucks 40 amps, will suck it from any source available. If your batt gets discharged, then your car will become on a maybe 60 amps sucker from alt and thats what we have to save with agood alt, to never get a discharged batt. This is so real, than our cars got melted those terminals with low capacity alts. The alt upgrade is just to keep safe the ammeter from loads coming and going simply eliminating the batt as a sucking device of the game. The bulkhead bypass OR doubling the paths will increase the handling capacity of the system to feed it, and still able to do it if batt gets discharged at certain point.

Is like a baby sucking milk! If is hungry, will cry and suck untill gets satisfied, no matter if from a boob or a bottle, maybe two bottles or both boobs. But it needs to get satisfied. If you have twins will be worst, so, keep safe from get the second baby sucking ( batt ) and will need less milk and less stress