Hi. My experiences trying to directly charge (via DC) extra batteries from
automotive electrical systems during my amateur radio activities have not been
very favourable over the last 10 years or so.
My current approach is to run a 120 VAC power inverter from the vehicle
electrical system (with the engine running) and in turn run a battery charger
from the inverter.
I typically turn the engine, inverter and charger off during weak signal work
due to RFI.
I also like having the vehicle electrical system more or less isolated from
batteries that run the radios. My thumb rule is to only run the inverter /
charger combination when the engine is running. I once had to jump start my
truck in an out of the way location from one of the radio batteries and as a
result I'm very hesitant to pull any power from the truck battery when parked
with the engine off.
Your experiences may vary from mine.
73
Mark S
VE7AFZ
Sent from my iPhone
> On Jun 5, 2016, at 12:19 PM, Alan Larson <wa6azp@gmail.com> wrote:
>
> From Jarred:
>> I finally ran a charging cable from my car battery (2012 Ford Edge) to
> the auxiliary batteries in the back of the car.
>
>> . . . 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.
>
> Apparently this is common on newer cars - they want to save energy in any
> way they can, so charge is cut back
> once the battery is recharged from starting. From what I have read, some
> even measure the current out from the
> battery to know how much to put back in.
>
> This can present a problem if you are connecting the aux batteries to the
> starting battery, and taking power from
> them. The charge system cutting back when "enough" energy has been
> supplied to the starting battery won't put
> enough in to make up for running the radio from the aux battery system. In
> some cases, the current sensing is in
> the *negative* lead to the battery.
>
> Beware of the voltage drop in the wire to the rear batteries, as it can
> reduce the charge voltage so they don't get
> fully charged in reasonable time. You may need a separate charger for the
> radio batteries in the back of the car.
>
> Alan
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