Unless you’re running lithium batteries, most deep-cycle batteries can be discharged down to about 50 percent. I revisited this problem in-depth in my article, A Geek’s Guide to Murder Your Battery. Smart alternators can take a long, loooooong time to charge RV house batteries! There’s also the argument that modern-day “smart” variable-voltage alternators are programmed to run only when necessary to charge your vehicle’s starter battery.
#TOW READY BATTERY ISOLATION SOLENOID FULL#
At best, it functions as a trickle charger.Įven if you’re using good ol’ wet lead-acid batteries in your RV, you’re not out of the woods! With enough voltage loss, an alternator/regulator can’t even charge a typical lead-acid battery up to full capacity.
That’s why many people say a trailer connection “maintains” a battery it doesn’t truly charge it. Translation: Best-case scenario, most tow vehicles cannot charge your house batteries more than 80 percent! That’s not high enough to charge an AGM battery during the absorption phase. Charging voltage should jump up to 14.5 to 14.8 volts for the duration of charging.Ī typical automotive regulator has a maximum voltage setpoint of 14.0 to 14.5 volts. When your battery hits about 80 percent state-of-charge, a smart 3-stage charge would enter the absorption or the acceptance phase. The big difference is that AGM batteries are charged at a higher voltage during the absorption phase. It works (kinda), but it’s not recommended. That means it’s programmed to charge a flooded lead-acid starting battery from a shallow discharge of 5-20 percent.īut if you read my ultimate guide to RV lead-acid batteries, then you know that RV batteries are usually AGM deep-cycle batteries routinely discharged down to 40-50 percent.ĭeep-cycle AGM and flooded starting batteries are similar in construction but not the same! And they aren’t charged using the exact same algorithm.Ĭharging an AGM battery with the charge profile of an automotive starting battery is like using a straw to eat soup. The job of your car’s voltage regulator is (you guessed it!) to recharge the car’s battery and power the car’s electrical systems. Think of the regulator as the electrical traffic controller. Your voltage regulator might be an internal component to your alternator, an external component, or part of your Engine Control Unit (ECU). Your voltage regulator controls the output voltage from your alternator. But the truth is that by itself, the alternator is kind of dumb. I’ve been referring to the “alternator” as if it was the solo star of the show. The smaller and longer the wires, the longer it will take your battery to charge – if it charges at all! To some degree, a system self-regulates by decreasing the amperage, which decreases the voltage loss. If voltage drops at the battery to less than 12.9 volts, you won’t charge the battery! You need at least 2.15 volts per cell, or 12.9 volts for a “12V battery,” to get a meaningful charge.ġ2.9 volts is the minimum “trickle charging” voltage for most lead-acid batteries. It’s outside the laws of battery chemistry. Our voltage at the receptacle (where we plug in our trailer) is now just 12.5 volts.Īnd no lead-acid battery can be fully charged at 12.5 volts. Now, let’s try it again with a 14GA wire. Good news! We only lost 0.3 volts! That’s just 2.3 percent! Using this handy-dandy calculator, what’s the voltage drop of an 8GA copper conductor after 25 feet at 13.8V and 10A? In other words, how much voltage would be lost running an 8GA wire from your alternator about 25 feet back to the 7-way receptacle? The longer and smaller the wire, the worse the voltage drop (voltage, remember, is the electromotive force, the pressure, that “pushes” electricity through a conductor).
You see, wires lose voltage due to resistance. But here’s one scenario where size matters! If you’re not getting any power from your umbilical cord, confirm the receptacle is wired correctly!) (Actually, in some cases, there isn’t! If your 7-way receptacle was installed aftermarket or by a previous owner, there’s no guarantee that anyone fished that wire. A wire runs between your alternator and your 7-way plug.
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