I have 2 comments or suggestions. As Dave suggested, the voltage of the
alternator will vary depending on the state of the battery in order to
control the charge current. If you are running fairly low power, less
than 30 Amps, you can get a voltage booster/regulator from MFJ or the
original designer whom I can't remember. It will provide a constant
voltage to the rig no matter what the battery voltage is down to
something like 10.5 volts. Also I used a battery combiner from Boat US
that allowed charging from the automotive system but isolated it when
the alternator is not at a charging level (or off). This small device
will handle up to 80 Amps. I powered my amps with this up to 400 watts.
Also use an appropriate size wire for the current and distance, #4
worked fine for me.
73 and good luck roving, Jim K3LFO
On 6/6/2016 3:55 AM, David Pruett wrote:
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
_______________________________________________
VHFcontesting mailing list
VHFcontesting@contesting.com
http://lists.contesting.com/mailman/listinfo/vhfcontesting
_______________________________________________
VHFcontesting mailing list
VHFcontesting@contesting.com
http://lists.contesting.com/mailman/listinfo/vhfcontesting
--
Jim Erickson
---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus
_______________________________________________
VHFcontesting mailing list
VHFcontesting@contesting.com
http://lists.contesting.com/mailman/listinfo/vhfcontesting
|