Jared,
After 33 years as an electrical engineer for Chrysler (now retired), I
guess that I qualify as an "auto guy". To be honest, my area of
expertise was not charging systems but rather electronics and systems
engineering. But on numerous occasions I had to go to the charging
system experts to get questions answered as I was often confused by the
behavior of a modern charging system. I think that is perhaps true in
your case as well.
i won't pretend to have special, secret knowledge of Ford charging
systems, but it's my understanding that most modern charging systems are
pretty much the same, differing only in minor details.
You seem to believe that the charging system should keep the voltage
constant, but that is not true. The purpose of the charging system is
to maintain a healthy state of charge in the vehicle battery. It does
this by monitoring many parameters, voltage being only one. Even the
current going into or out of the battery is only part of the picture
because of variations in the current delivered by the alternator.
The charging system controls the current being delivered by the
alternator by controlling the current in the field of the alternator.
But there are limits to how much current the alternator can deliver,
based on how fast it is spinning (e.g., engine RPM). Few, if any
vehicles have alternators which can produce full current while the
engine is idling.
Probably the biggest mystery with modern charging systems are the
strategies employed to do its job. This is because the charging system
looks at the state of the vehicle electrical system and has to try and
predict what the electrical load requirements are coming so it can get
ready. Some of these strategies involve temperature, which might
indicate that the A/C system will be turned on soon. Also, the
performance of the battery itself it greatly affect by the temperature
in the engine compartment, which can be tens or hundred of degrees
higher than the outside ambient
Then again, on top of everything else, there is the wiring and batteries
that you've added to your vehicle. The charging system doesn't know
these have been added, it can only continue to do its job; that is to
monitor what it was designed to monitor and to maintain a healthy state
of charge in the battery.
I don't expect these generalized descriptions to be of much specific
help to you. My purpose in sharing this information was to illustrate
that there are many factors affecting the charging system; voltage being
only one. Expecting a constant, steady voltage level as a sign of
charging system health is simply not reasonable.
Reading through your note, I didn't see any voltage levels reported that
would seem unhealthy so I think you're good to go for your rover
operation. Just use common sense as to how you consume electricity and
monitor the voltage on your auxiliary batteries to watch for undercharge
conditions.
73, Dave, K8CC
On 6/5/2016 12:03 PM, Jarred Jackson wrote:
I finally ran a charging cable from my car battery (2012 Ford Edge) to the
auxiliary batteries in the back of the car. The system consists for a 100A fuse
mounted at the battery, cable to the rear of the passenger compartment, a
marine style manual disconnect switch and two 6V 210Ah golf cart batteries in
series. The plan is to disconnect the aux. batteries when the car is turned off
and when starting. I cant use 6m for anything other than local contacts when
the car is running, so often need to turn it off.
After getting all of this wired up yesterday, I was happy to see voltage climb
to 14V on the aux. batteries and everything looked good. I left the car idling
in the driveway and returned 20 minutes later to see voltage at 12.8V. Thinking
I popped the 100A fuse in the charging line, I checked under the hood and saw
the car battery at 12.9V and the fuse looked fine. I turned off the car and
turned it back on and voltage came back to 13.8V for maybe 10 minutes, then
dropped to 12.7V. At this point there is NO load on the aux. batteries at all
(the main fuse for the amp rack and radio gear is pulled). The mobile radio in
the car (simply plugged into the accessory port of the car) showed 12.4V.
This morning, the car has been idling for 30 minutes and voltage is good at
13.9V. The car battery is at about 14.1V and everything looks good. No change
in setup from yesterday. However yesterday was a hot day and the hood was
closed when idling (which is probably not a good idea for various reasons).
Today is cooler and the hood is open as I take measurements. Is it possible
that the voltage regulator doesn't like heat and simply keeping the hood
cracked open will solve this problem? Or maybe there is something else I dont
understand. A search of the internet says I need to replace my alternator. I am
not so sure.
Any rovers or car guys have any thoughts on the cause?
Thanks,
Jarred - KF2MR
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