To all of you who understand all this, my congratulations. Electricity
is as mysterious to me as the Horse Nebula.
Jo Ann
-----Original Message-----
> So does the vehicle's regulator "protect" the battery ?
In the modern vehicle, yes. In the 70s and earlier vintage vehicle, not
so well. Modern voltage regulators work much better for longer battery
life.
> I'm guessing
> that the length of the cable from vehicle generator/alternator to the
> trailer battery is enough to drop the charge voltage down to where the
> trailer battery doesn't get enough voltage to boil it.
As the battery reaches full charge the current goes towards zero. If the
voltage is right the charge current does go to zero, and with a small
current, any wire that would charge at a decent rate (10 or 20 amps)
won't drop the voltage at all with just a few milliamps of current. The
size and length of the wire will limit the peak charging current.
> In effect, a
> trickle charge.
A trickle charger that has no voltage limit will boil a battery as dry
in a few days as a humongous battery booster with no voltage limit
(though the booster can do the deed in a lot less time).
> Unless someone has rewired it with a fat cable.
>
> Always willing to learn,
> Daisy
>>
>> The Univolt has no effect on battery charging from the tow vehicle.
>> But
>> it will overcharge from shore power.
The Univolt is out of the circuit because it has diodes to block current
leaving the battery and the charge line from the tow vehicle goes almost
directly to the battery.
In vintage vehicles we had to add a battery isolator package,
essentially two big diodes to separate the batteries yet let the
alternator charge them both. Today's tow packages generally are simpler
with just a relay to connect the trailer battery to the vehicle battery
when the engine is running. That may be accomplished by the ignition
switch or the computer. A reliable way to do that is to power the relay
coil through a switch that closes when the engine has oil pressure, a
sure sign the engine is running. A surer sign than the ignition switch.
Might take adding a bit of plumbing at the oil pressure sensor to add a
second switch that operates the opposite of the oil light switch. I'm
sure I've posted a suitable NAPA number on this forum in the past two or
three years.