Trailer battery charging while towing

ekirkland wrote:
Probably a dumb question but how long would it take to charge a two-battery system while going down the road between campgrounds? I know it depends on how charged the batteries are to begin with. Would 2-3 hrs. fully recharge?

After adding a parallel charging circuit and upgrading the factory tow pkg charge line travel between CG's recharges our batteries. We usually travel 150 to 200 miles between CG's. I also added a solid state battery isolation system available at just about any RV parts store. Some vehicles already come with a relay isolation system as part of the tow pkg.

The best I could ever attain from traveling down the road charging my batteries from the the truck alternator system was a good trickle charge. Doing my OFF-ROAD camping if I don't get my batteries to at least the 90% charge state I cannot make it very long on performance and it will get dark on me pretty quick. Continuing to do the less than 90% charge state always harms my batteries.

Using my 2KW Generator in the mornings running my on-board smart mode converter/charger setup will take my 50% depleted batteries to their 90% charge charge in as little as three hours of generator run time.

Seems like everywhere we go here on the East side of the US all have generator run time restrictions in place making it difficult to planning when we can charge our battery bank...

The quickest way to safely charge my 50% depleted batteries is using 14.4VDC with the capacity of 17-20AMPS per battery in the bank. I can recharge my battery bank to its 90% charge state in three hours time doing this.

If you monitor the DC VOLTS being generated from the truck alternator setup when driving down the road you will see 14.4VDC when you first start up and the it drops to 14.2 in just a few minutes and then down to around 13.6VDC and eventually down to 13.2VDC. The Truck start battery being so close to the truck alternator will determine these readings based of how many DC amps the truck start battery is taking on coming from the alternator. Your trailer battery setup is to far away from the alternator to allow the truck start alternator electronics to determine its charge state. If all you have is 13.2VDC to 13.6VDC available from the truck alternator driving down the road it will take a good 12-14 hours to recharge a 50% charge state battery back up to it 90% charge state according to Progressive Dynamics.

Adding larger cables between the Truck Alternator and the Trailer battery bank will help the situation but you also need to keep the Alternator DC VOLTAGE up high around the 14.4VDC range for at least two hours before tapering back to the 13.6VDC ranges. The truck Alternator will also need to maintain a good 17-20AMPS per battery in your trailer battery bank at theses DC VOLTAGE levels if you want to recharge the batteries in a quick three hours run time.

This is asking alot from your Truck Start Battery system. It also goes against some of my golden rules of NOT messing too much with the truck charging system as this is my only way to get back home on haha... The truck's charging system is only designed to take care of the truck start battery...

If you really really want to do this and be successful then adding a separate Truck Alternator system setup just for charging the trailer batteries like the Fire Department Rescue Vehicles and other Emergency Vehicles have done...

Just some of my observations here...

Roy Ken

The bottom line: You should not rely on the vehicle 12v line to "charge" the batteries period. You should provide for another method for doing this such as plugging into shore power or a generator.

Clicky for Landyacht

Bill

ekirkland wrote:
Would 2-3 hrs. fully recharge?

Not even close. you'd be lucky to return 30AH to them in 3 hours of driving over the stock 7 pin charge path.

With high amperage applied, one can quickly return a battery to 80% charged, but that last 20% is going to take about 4 hours, and that is IF absorption voltage in the mid 14 range, is held for those 4 hours.

Your distant house batteries will never get to absorption voltage unless you drive for 24 hours. the voltage drop would never allow it until the batteries could not accept more than 2 or 3 amps.

Some solutions to faster recharging are an inverter hardwired to engine battery, feeding an household AC extension cord to a higher amp charger on the trailer.

One could beef up the original circuit, or better yet add A much thicker copper circuit between alternator and trailer battery through a Burly connector.

I achieved 100+ amps into a distant healthy group31 AGM battery over~30 feet total circuit length of 2awg and a '500 amp' winch connector.

Here is a 6awg kit ready to go which will drastically improve charging amps into depleted trailer batteries compared to just the 7 pin connector:

http://www.amazon.com/Keeper-KTA14128-Trailer-Harness-Connect/dp/B008N8IMI8/ref=pd_sim_263_1?ie=UTF8&refRID=147ND97WNXYBJX94R5M6


Thicker copper will allow one to get upto 80% much quicker, but that last 20% to a true 100% charge, is going to take hours, about 4, when the batteries are still healthy. If older and partially sulfated, expect absorption times to increase well beyond 4 hours until specific gravity maxes out at which point the flooded battery can be considered fully charged.

But they are just batteries and rented so perhaps 92% will give you an adequate rental contract.
I seek 100% asap, aoap, and this takes time at absorption voltage with no way to bypass the time required.

Most tow vehicles only provide a trickle charge at best.

ekirkland wrote:
Would 2-3 hrs. fully recharge?

With regular 7-pin connector, assuming a pair of 6V batteries discharged to 50% - No. Not even close.

pianotuna wrote:
If using the stock 6 or 7 pin connector 24 hours of towing might work.

The charging wire needs to be beefed up considerably. Even better is to add a 2nd external diode to the oem alternator.

While I agree that almost ALL OEM vehicle charging ckts need to have a larger dia wire I would think that your extra diode comment as generic and non specific as it is would help since any diode will have some voltage drop so the full alternator voltage will suffer when any diodes are in the charging ckt. This is why some of these battery isolators that use two diodes and generally a poor idea and result more often than not in poor battery charging.

Larry

Yes the tow vehicle alternate will supply a charge to trailer batteries when in transit.....

Limitations:
Gauge of charge line
Length of charge wire..truck and trailer


Tow vehicle is good to 'maintain' and provide a minimal charge on trailer batteries but a long days drive would be needed to actually charge a low trailer battery

When available it is best to plug in to electric source and let converter charge trailer batteries.

If using the stock 6 or 7 pin connector 24 hours of towing might work.

The charging wire needs to be beefed up considerably. Even better is to add a 2nd external diode to the oem alternator.