No offense taken.
Thanks for your comments. It was a mistake for me to say ”They are right on about the inability of a standard 7 way plug to charge a depleted battery.”
My mistake was to over generalize. I should have said that a 7 way plug will not meet my particular charging needs.
Below is the explanation of why the 7 way connector on my truck will not “adequately” charge my 225 amp hour lead acid, deep cycle battery, located in my trailer. I am only going to explain why my particular 7 way plug will not work for me.
A while back, I researched the pros and cons of using the power lead on my 7 way connector to charge my battery.
I determined I could not practically use my 7 way plug for two reasons:
1. The OEM wire would not carry enough current for my needs, and
2. After my starter battery becomes fully charged after a few minutes, my “smart” alternator will not charge the deep cycle battery.
Note: I think, but cannot remember without taking the time to research this forum, that flboy did not have this shut down problem with his truck. Maybe he will chime in.
First, the power wire to my 7 way plug is 12AWG. 12AWG is rated for 40 amps. My fuse box also has a 40 amp fuse.
My truck is 20 feet long, so I assumed that the power wire was 20 feet long. Actually, I think the wire is longer due to winding around to get from the front to the rear of my truck. It is another 10 feet from the 7 way connector to the deep cycle battery in the front of my trailer.
So, the 12AWG wire run is about 30 total feet.
The Renogy wire size calculator I use says that 14 volts, at 30 feet of 12 AWG wire, with a 3% voltage drop, will carry 3 amp hours (5 amps if the run is only 20 feet).
When my battery is discharged about 20% = down about 44 amps, my solar charger inputs about 25 amps at 14.3 volts, until the battery is about 90% charged at which time the battery will only accept about 6 amps at 14.6 volts, and then the amp hours continue to decrease as the battery gets full. When the battery is full, my solar charger floats the battery at 13.2 volts. So, it takes many more hours to top off the battery from 90% to 100% full using my solar charger.
If I was using 12AWG wire to input 3amp hours into my battery, it would take about 7 hours to push 21 amps into the battery, at which time the battery would only be 90% full. I can only guess how long it would take to top off the battery … perhaps seven more hours? (I really do not know).
Second, my batteries will not charge until at least 14.1 volts are pushed into the battery. My battery will not charge at less voltage.
My truck’s “smart” alternator will charge both my starter battery and my deep cycle battery at about 14.4 volts, until the starter battery is full (which only takes a few minutes after starting the truck because after starting the truck, the starter battery is only slightly discharged), then the voltage drops down to around 13.3 float volts. So, the alternator stops charging both batteries after the same short time.
So, I installed a DC to DC “smart” charger rated at 20 amp hours with 2 AWG wire to charge my deep cycle battery.
Conclusions:
1. A 7 way plug with standard wiring will charge a battery; but the number of hours to charge the battery depends on wire size and wire length. This is a matter of simple mathematics.
2. Some alternators will shut down charging early.
Note 1: My truck alternator is rated at 165 amps but can only safely out put a continuous 50% of rated capacity, otherwise the diodes in alternator will overheat and fail. After considering all OEM potential loads from my truck, my 165 amp alternator only has about 20 spare amps available to charge my deep cycle battery (I determined this by bench testing using my hand held amp meter).
Note 2: I would think that if someone were using a 7 way plug to charge the deep cycle battery without a separate “smart” charger, the battery would be charged with “unregulated” voltage which, in the long run, would damage the battery.