Quote:
Originally Posted by boywonder
Mike: Keep in mind that voltage drop through a wire is heavily dependent on current flow, that's why we run big fat cables when lots of current and/or long runs are present. When the batteries are topped up and you have a mouse-fart's worth of current flowing through a fire-hosed sized battery cable there should be negligible voltage drop from the cable resistance.
Ohm's law V=IR
say your cable has .01 ohms resistance.....
@100 amps .01R(100A)=1V drop
@10amps .01R(10A)=.1V drop
@1amp .01(1A)=.01V drop
|
Ahhhhh
.....AHA.....
......so should I correctly interpret what you are saying....
....are you indeed saying that
the .02v drop that is observed between the alternator and the starter battery is perhaps
totally normal?
If I follow you....
The starter battery / ignition (and associated under-hood / cab electrical systems)
are certainly drawing way more amps (when the van is running)
than is the house battery, which is sitting largely idle and only sucking enough amps to stay topped off.
So....continuing to try to follow you here.....
....
voltage drop / line loss in the lines to the low-amp-draw house battery would be almost negligible.....while
the lines to the higher-amp-draw starter battery would see a far more noticeable voltage drop, simply because of the necessary higher amperage that's flowing through them ----
......and due to how voltage, resistance, and current all interact via Ohm's law......?
Apples to apples example:
If two sets of cables are equally sized, of equal internal resistance measure for a given length (and each run is cut to be an equal run length), and are both given an alternator input of 14.5 volts....and then you attach an electrical device at the end of one line that pulls only 0.1amp, while at the end of the other line you place an electrical device that demands a draw of 10 amps....
you'll get 100 times more "line loss" or "voltage drop" in the line that's drawing 100 times more amperage.
So you could see
0.2v line loss in the branch that has 10 amps running, and then have only
0.002v line loss in the other branch. (And this second, tiny amount would be essentially invisible/un-measurable, at least with my voltmeter.)
So line loss of some degree is ALWAYS present. At least until we develop room-temperature superconducting wire.
This to me makes sense.
I might be totally misinterpreting what you are saying. But at this moment in time....it makes sense, haha....!
Finally ----
If I am reading you correctly.....
....
would 0.2V of "line loss" from the alternator to the starter/chassis battery seem
within the realm of normalcy/acceptability?