Trailer battery charging while towing

Harvey51 wrote:
We had a new to us motorhome and it seemed like the batteries fully recharged from an hour or two of driving because the voltage went up to 12.6 a couple of hours after charging. We kept that up until the batteries no longer ran the furnace in the morning and had to be replaced.

Yes, it might "seem" like they are fully recharged after a few hours. But this is an illusion. Voltage reads higher for several hours after charging. Let it rest overnight (or better yet, for 24 hours) and then measure voltage - it will be way below 12.6, and will drop instantly as soon as you apply any load.

I benefitted from a similar thread a few years ago. We had a new to us motorhome and it seemed like the batteries fully recharged from an hour or two of driving because the voltage went up to 12.6 a couple of hours after charging. We kept that up until the batteries no longer ran the furnace in the morning and had to be replaced. It seems the voltage stays high for many hours after charging. A $25 eBay battery monitor made it possible to monitor the state of charge fairly accurately and just 100 watts of solar in addition to the engine charging keeps us going pretty well indefinitely in summer. Just fridge and LED lights.

ekirkland wrote:
Hey BCbigfoot, thanks. We pretty much camp/travel like you; camp 2-5 days at one spot as we take in the sights in the area, then move to the next spot; usually 2-5 hours done the road. Living in Alabama, we rarely camp in the open; only when we go out west every few years, so solar may not be best for us. I think a beefed up parallel charging system plus a generator (can use it tailgating too) will do the trick for us. Can you (or other guys here) give me more details on how to rig up a parallel charging system? What type connectors, battery isolator, and any other materials? Thanks to all!!!

Some of the better treads for this type of info is in the Truck camper area of this forum (Truck camper University section) here is a link to one of the best threads http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/23601503.cfm . You should be able to get 60 ft of 4 gauge welding cable, 2 fuses or breakers, lift gate connectors, ford style solinoid (continuous duty), for around 200$.

Hey BCbigfoot, thanks. We pretty much camp/travel like you; camp 2-5 days at one spot as we take in the sights in the area, then move to the next spot; usually 2-5 hours done the road. Living in Alabama, we rarely camp in the open; only when we go out west every few years, so solar may not be best for us. I think a beefed up parallel charging system plus a generator (can use it tailgating too) will do the trick for us. Can you (or other guys here) give me more details on how to rig up a parallel charging system? What type connectors, battery isolator, and any other materials? Thanks to all!!!

Hi Korbe,

It would be good to confirm the results with a temperature compensated hydrometer.

korbe wrote:

pianotuna wrote:
Hi Korbe,

What does the volt meter say 24 hours after you have arrived home? (assuming you do not plug in)

I believe it was tested the next morning after I used the batteries to level up. Do my results sound unrealistic?

ekirkland wrote:


Is there a portable solar charging system you can plug in and set outside on the ground instead of having to permanently mount it on the roof?

they all can be set on the ground.

Vague descriptions coupled to fragmented opinions makes not for great comprehension folks... :(

I would LOVE to see the pickup that has a factory wiring harness connected to a trailer wiring harness that could deliver TEN AMPS to trailer batteries. As many as I have measured 4-6 amps was overwhelmingly the bell curve. Lessee, charging a depleted to 50% pair of batteries maybe let's call it 5-amps, TWENTY HOURS would fill the batteries to say 85%. Remember, this is nothing more than a voltage regulated alternator doing the charging.

It's a pain, it isn't cheap, but 6 gauge preferably FOUR AWG running back to a truck semi trailer socket, then continuing on to the batteries would allow a decent 20-30 amp charge. Depends on the length. I took the conservative side.

Genuine circuit breakers on both ends of the positive cable. Not the garbage tin can type - All plastic with 1/4" studs.

Big rigs have ONE AUGHT cable running back to a group 27 to power electrohydraulic trailer life gates. mmmmm just a tad larger than six or four gauge.

OP, go to the nearest BIG RIG parts supplier. Kenworth, Peterbilt, International, White Freightliner. The 2 in 1 socket and plug is the hot setup. That way the cables stay neat and hookup mistakes are avoided.

Delcity.com has the 60 amp breakers, and terminals for the breakers, alternator connection, etc.

Check
skycraft.com for DLO diesel locomotive wire. Select 6 or 4 cable. The extra minimum lengths will be used for the ground cables.

Select preferably a twin outlet and twin plug. Then buy the cheapest garden hose you can lay your hands on. Cut the ends off.

The butchered hose with the cable stuffed through it cannot get any closer than a foot or so from any pickup exhaust parts. Use huge cable ties to secure.

Anything less than this is a pure waste of your time and money. Yank everything off when you go to sell the pickup.

The ground cable must positively run from the trailer batteries alongside the positive and preferable be connected to the engine somewhere.

From the school of hard knocks and doing exactly this for a living.

ekirkland wrote:
Some of the replies went right over my head. It sounds like some are saying a separate heavy gage charging wire with battery isolator is the way to go and some saying that's not such a good idea. What is a mechanically and electrically challenged person to do? I guess I have the options of parallel charging line with isolator vs. solar vs. generator. About the most I intend to dry camp is 3-5 days and then hit a campground with power to recharge on our next trip to Utah. I would imagine the batteries (2 ea. 24's) would be pretty depleted in that 3-5 day period. My present Jayco camper is new and we have not done any dry camping yet; only powered camping. With our previous Casita, we could do maybe 4 days with very frugal power usage on one battery. I'm trying to decide my best (maybe cheapest) means to extend battery power. Thanks for all the help.

Much depends on what type of camper/traveler you are. I tend to boondock/dry camp for a day or two then move on down the road, I tend to be more of a traveler than a camper, so adding a 4 gauge power wire to the camper batteries has been a big asset, more so than a generator or solar panels (I have both). However this changes if you are someone who likes to stop and dry camp for 4 days or more at a time, a generator or solar panels would be better. Time of year and area of country are other aspects to consider.

If you were to run 4 gauge pos and neg wires from tow vehicle to trailer batteries it would take approx. 3 hrs for the batteries to go from 50% to 90%+ charge. I typically get a initial 40 amp charge rate with a 35ft run of 4 gauge wire. My setup has two group 31 agm 12v batteries.

ekirkland wrote:
About the most I intend to dry camp is 3-5 days and then hit a campground with power to recharge on our next trip to Utah. I would imagine the batteries (2 ea. 24's) would be pretty depleted in that 3-5 day period.

Yes, 4-5 days to deplete 2*6V to 50% if you are good at conserving energy. Means - no microwave or other high-power devices.

ekirkland wrote:
I'm trying to decide my best (maybe cheapest) means to extend battery power.

SMK said this already - solar. FYI, his solar is far beyond mere "extending" the battery power - it provides enough energy to camp for any length of time. Mine too.

pianotuna wrote:
Hi Korbe,

What does the volt meter say 24 hours after you have arrived home? (assuming you do not plug in)

I believe it was tested the next morning after I used the batteries to level up. Do my results sound unrealistic?