I checked my truck tonight. I have 14.44 volts on the charging lead on my 7 way plug at the rear bumper. That wire has a 30a fuse from the factory. I emailed Redarc but haven't heard back yet. I assume that with 14.44 volts at the back of the truck, the DC to DC charger will work fine without running a heavier wire. The Redarc BCDC1225D (25 amp) just needs a minimum of 9 volts to work. I will let you know what I hear. I supposed I could almost get away with no additional trailer charger. Also, my truck does not have a smart alternator...which helps.
Best way to charge my trailer battery with current setup?
- Thread starter dgarber
- Start date
Member III
I do not have a DC to DC charger. I do not have a "smart" alternator in my tow vehicle and I also run a conventional deep cycle marine battery. With those two things, I felt no need to add the complexity of something like the Redarc. If I ever went to a Lith-ion battery in the trailer, then maybe, but those batteries have their own set of issues. The solar controller is intelligent enough to keep the trailer battery appropriately managed and I really like the way I can charge the trailer battery from both the tow vehicle and the solar. Solar also extends how long the trailer battery lasts without having to rely on the vehicle to charge it.
Member III
I assume that 14.4v is with it running. Depending on how long the wiring is you could get away with no Redarc. The trailer battery may never get to 100%, but that will also depend on the type of battery you have in the trailer. Redarc is fantastic stuff, but I do also find that lots of people out there over complicate their installations as its an easy trap to fall into. Its really all about the type and size of battery and the loads it will have to deal with. After that, it is just math and figuring out how to get it charged again. If you can keep it simple, just less of a chance of failures and problems.
The Redarc wiring diagram I included above is fused at 30a for the trailer connection. Since the truck lead is fused the same, it would make sense that the factory 12v charge feed would work.
Batteries are too expensive and too delicate to just dump 14+ volts into them, unregulated. These trailer charge circuits are only designed to "maintain" a battery that is already charged. They simply do not supply enough amps to "charge" a battery. If that works for you, so be it. But if the AUX battery is going to be used hard, and brought down to 50-70% regularly, I'd want a much more sophisticated charging system like Redarc or Renogy.
I will most likely go with the Redarc solution. My plan is to add solar in the near future and this would take care of that as well. It would be nice to be able to use the factory truck wiring to feed the Redarc. I may call them today if I don't get a response to my email.
Enthusiast III
The factory trailer wiring CAN NOT HANDLE 20+ AMPS SUSTAINED. You will burn it up. It is integrated in to the main chassis harness. It will cost several thousand dollars to replace. I know this because I have replaced one.
Run comoletely separate leads rated for the load, be happy.
Run comoletely separate leads rated for the load, be happy.
Member III
I utilize a Redarc BCDC 1220 in my trailer to maintain the battery. Although the 7 pin RV connector provides a 12 volt supply for charging a trailer's battery this is not an optimal solution. Using this charge line plus a DC to DC charger in a trailer is the best way to maintain the battery in the trailer. A DC to DC charger is a smart device that provides the proper voltage to intelligently charge the battery. Relying on the tow vehicle's charging system to manage the trailer's battery typically doesn't work. This is especially true of vehicles built after 2000. The tow vehicles charging system monitors the vehicles battery and when it is satisfied it is charge will drop the voltage from the 13.7+ volts typically used for batter charging to less than 13 volts (I've seen my truck drop as low as 12.3 volts) which is not adequate to charge a deep cycle battery.
So, in essence its a crap shoot as to whether or not your trailer battery will charge or not based on the tow vehicle's battery state. With a DC to DC charger you eliminate this variable because the smart charger will increase the voltage from the tow vehicle to charge the trailer battery.
Some vehicles have a "tow mode". I discovered my truck when in tow mode keeps the voltage at 13.7 volts instead of dropping it down. This is intended to allow the trailer battery to charge fully. However, this solution has the downside of not having the intelligence to drop the voltage when the battery is fully charged. This can shorten the life of both the tow vehicle and trailer battery.
None of this applies on older vehicles that always supply 13.7 volts. Vehicle manufactures started installing intelligent charging systems to prolong the life of vehicle batteries and decrease the load on the alternator to increase fuel efficiency. Maybe someday they will include an intelligent charging circuit with tow packages that is separate from the vehicles battery. Until then, DC to DC chargers are your best bet in a trailer.
If you choose to install a DC to DC charger insure your vehicle wiring can handle the model you choose. I chose the 20 amp Redarc because my vehicle's wiring is fused at 25 amps for trailer charging wire. Otherwise, running a dedicate line and utilizing an Anderson connector would be strongly advised.
-Curtiss
So, in essence its a crap shoot as to whether or not your trailer battery will charge or not based on the tow vehicle's battery state. With a DC to DC charger you eliminate this variable because the smart charger will increase the voltage from the tow vehicle to charge the trailer battery.
Some vehicles have a "tow mode". I discovered my truck when in tow mode keeps the voltage at 13.7 volts instead of dropping it down. This is intended to allow the trailer battery to charge fully. However, this solution has the downside of not having the intelligence to drop the voltage when the battery is fully charged. This can shorten the life of both the tow vehicle and trailer battery.
None of this applies on older vehicles that always supply 13.7 volts. Vehicle manufactures started installing intelligent charging systems to prolong the life of vehicle batteries and decrease the load on the alternator to increase fuel efficiency. Maybe someday they will include an intelligent charging circuit with tow packages that is separate from the vehicles battery. Until then, DC to DC chargers are your best bet in a trailer.
If you choose to install a DC to DC charger insure your vehicle wiring can handle the model you choose. I chose the 20 amp Redarc because my vehicle's wiring is fused at 25 amps for trailer charging wire. Otherwise, running a dedicate line and utilizing an Anderson connector would be strongly advised.
-Curtiss
Thx for this post, adds plenty of clarity. And the Redarc website is fabulous.
But after pricing it all out, I'm leaning to adding a second alternator and a dedicated/isolated electrical system for the trailer. Pricing out this option I'm pretty sure I will save money..... plus I get a second alternator which could be rerouted if the vehicles main alternator dies..... in the past 40 years the only time I needed a tow was when the alternator died and I failed to check the voltage gauge to see the dropping voltage before the truck died.
I'm liking the simplicity of an isolated system for the house.
everyone I talk to say power to charge a trailer battery needs a #10 wire, minimum
Member III
I love my lead acid batteries. Their not that picky. I also run a 4 gauge wire to the back of my tow rig then 10 gauge through the plug. The cord goes inside my trailer box where all my controls are. This keeps my wire length short. Typically a real low battery will draw 40 amps (2, 80 amps....). With the short pull of 10ga wire I run, I have no issue feeding my single battery. If I ran 2 then I would rethink it.
I am using a Renogy 20 amp DC-DC battery charger mounted in my trailer and it has solved my charging issue.
This is very simple , inexpensive and works . I've used a Toad charger for about 20 years and it works great. Both deliver a full 10 amps of real charging. Much cheaper than a Redarc.
Another similar unit is
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Automatic Battery Charger/Maintainer for Motorhomes
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Another similar unit is
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