Battery Charge Time

[MTRancher]

On a recent trip in our 2004 Wilderness 5th wheel, we ended up dry camping for a couple of days. According to our meter we used 1/3 of our battery power. I have two deep cycle marine batteries installed in the camper. The trip home was 4 hours, and in that time frame the meter still indicated 2/3rds charged. What's the average charge time for batteries when charging from a running vehicle. Both batteries charge fine when plugged into 110 and charging from the converter. Thanks in advance for your replies!

 

[Carl L]

On a recent trip in our 2004 Wilderness 5th wheel, we ended up dry camping for a couple of days. According to our meter we used 1/3 of our battery power. I have two deep cycle marine batteries installed in the camper. The trip home was 4 hours, and in that time frame the meter still indicated 2/3rds charged. What's the average charge time for batteries when charging from a running vehicle. Both batteries charge fine when plugged into 110 and charging from the converter. Thanks in advance for your replies!

It all depends on your alternator in the truck and the wiring back to your RV batteries.  Most alternators are designed to charge one vehicular starting battery and to generate 50-60 amps at charging voltages.  You are adding 2 deep cycle batteries to the poor liddle rascal's chore.    You can buy heavy duty alternators running up to 150 volts.  But before that, check the gauge of the wiring back to your trailer.  It should be fairly heavy.  If it isn't, consider upgrading it.

 

[Tom]

You can buy heavy duty alternators running up to 150 volts.

Typo Carl - that was 150 amps, right? But we knew what you meant 

 

[Gary RV_Wizard]

I'd say you experienced a normal charge rate for your set-up.

It takes a long time to get that last 20-30% of charge into the batteries - the charge rate slows down as it gets closer and closer to "full charge".  And as Carl says, you vehicle's charging wasn't designed to handle extra batteries, especially if it was servicing other electrical loads while you drove (e.g. fans running, stereo playing, etc.).

And chances are the charge line running back to the trailer is of limited size. It should be at least 10 gauge, but even that isn't "big" when  the batteries are gulping down the amps after dry-camping for a couple days.

Last, the "gauge" you are looking at is probably not very accurate anyway.

Just leave the rig  plugged in for at least 36-48 hours  and its own charger will bring the batteries up "full".

 

[Jim Godward]

I generally recomend at least a No. 8 wire to the batteries all the way from the alsternator.? Actually, you should use 2 wires from the batteries, one directly to the battery isolator and the other to a vehicle ground close the isolator.? '

I agree with Gary, what you experienced is about right and the generic battery indicator is not adequate for good battery management. There are some good indicators but they are pricey so are not usually included in an RV as delivered.

 

[MTRancher]

Thanks for the input; I was surprised the charge rate was that slow; but it's nice to know it sounds about right.
I appreciate the answers, thanks again.

 

[Carl L]

Typo Carl - that was 150 amps, right? But we knew what you meant?

Naah, 150 volts.  Why mess around with wimpy 12 volts when you can get a big charge with a 150 of those rascals.

Sheesh.

 

[Gary RV_Wizard]

10 gauge wire sounds big, but still can deliver only about 30 amps continuous. 8 gauge is much better, as Jim suggests. Overkill for most situations, but just right if you frequently boondock and then recharge while driving.

Whether charging by driving or using the rigs own charging system, fully re-charging a battery that is down to 50% or less will always take 48 hours [or more].

 

[Ron]

I don't think # 8 wire could be considered as overkill given the distance from the alternator to the load, in this case the trailer batteries being charged.  In this case I would think #8 wire would be the minimum size wire to use.

 

[rickst29]

It all depends on your alternator in the truck and the wiring back to your RV batteries.  Most alternators are designed to charge one vehicular starting battery and to generate 50-60 amps at charging voltages.  You are adding 2 deep cycle batteries to the poor liddle rascal's chore.    You can buy heavy duty alternators running up to 150 volts.  But before that, check the gauge of the wiring back to your trailer.  It should be fairly heavy.  If it isn't, consider upgrading it.

That's not the most important problem. It depends even more on the Alternator's controller, which (in virtually ALL modern vehicles) will test Battery Voltage under the hood using a "Sense" wire - and then drop Voltage, according to the estimated "State of Charge" which it sees up front - basically, the SOC of the TV battery, ignoring the Trailer batteries completely.

In my own SUV, the Alternator output is "tuned down" to just 13.8V after a few minutes. (That basically runs the engine, and the dashboard, the stereo, and applies a "float" charge to the Battery.) Even if there wasn't any "Voltage Drop" on the wiring path back to the trailer batteries, 13.8V is not going to charge batteries in a reasonable amount of time - they simply won't absorb much power at that voltage.
- - - - -
The key step is installing some kind of "Voltage Booster" at the end of the Bargeman cable (within the Trailer), and then using some kind of "intelligent charge controller" to reduce the Voltage according to trailer battery State of Charge. Expensive "single box" devices, by Redarc and Ctek, do it all - although the somewhat cheaper Ctek has no adjustments to compensate for different battery types (AGM, etc.). You could build your own, using 3 components: A 12V->24V Boost converter (high amperage and waterproof, $60-90); a Solar Charge Controller (negative ground, 3-stage or better, $40-$60) and a pair of tiny 12V batteries, wired in series to "smooth" current and voltage spikes coming from the Solar Controller (when it operates in "PWM Mode"; about $30 for two batteries.) An array of high-speed ceramic capacitors might replace the batteries, but I think that batteries would do a better job.

If your TV wiring is already #10 (or better), this would provide up to about 20A for the batteries and Fridge in the Trailer. To go higher, you could upgrade to an MPPT controller, or buy a "bigger" boost Converter - or a 40A Redarc machine.

 

[kjansen]

Have your trucks fuse box checked.  My Chevy did NOT have a fuse in the box that would charge the 5er batteries when running down the road.  I was told the factory puts blanks in that space.