charging batteries with truck

[pinesman]

Several years ago when the fifth wheel that I had at the time only had room for one battery, I carried 2 more in the back of my truck. I used 2 sets of good jumper cables with ring terminals on one end and winch connectors on the other end to supply extra battery power when dry camping. Fast forward a few years and my current trailer has room for 4 batteries so I do not use the cables like I used to. However, I got to thinking about using those same cables to charge my batteries using the truck. I would not be using it for hours to run everything
but just a little while to top off the batteries in the trailer. Has anyone done anything like this?

[SoundGuy]

pinesman wrote:
I got to thinking about using those same cables to charge my batteries using the truck. I would not be using it for hours to run everything but just a little while to top off the batteries in the trailer.

theoldwizard1 wrote:
Modern vehicle (after about 2000) charging system work TOTALLY DIFFERENT than the past. They drop the voltage down to about 13.2V within a few minutes of starting. That is much TOO LOW to charge such a large battery bank !

The solution being a DC > DC charger, one example being the CTEK 250SA. :B

[landyacht318]

I had nothing but issues with those 12v SAE connectors. Too hot to touch at a constant 25 amps with 10 gauge leads. And forever intermittent after such use.
Go with anderson powerpoles instead.

[landyacht318]

theoldwizard1 wrote:

landyacht318 wrote:
I found maxing out my alternator charging well depleted battery over thick copper when idling parked had my alternator quickly heat to 200 f+ degrees. But I can force.it.to seek and hold 14.7v.

What year, make and model vehicle and how do you force the alternator to seek and hold 14.7V ?

Mines just a dodge van with an externally regulated alternator. Tricked engine computer with a resistor and modified a transpo540hd regulator with an external potentiometer to choose any voltage i want it to seek and hold.

[theoldwizard1]

RoyB wrote:
Mine has these 2-pin connectors on it and I built up a lighter plug adapter so I can plug this solar panel into an always hot 12V Connector inside my truck... Great for trickle charging my truck start battery doing this...

That style connector has been around for a long time and they are quite robust. I don't like them for a couple of reasons.

• Frequently the two halves will not fully seat, leaving part of the metal exposed. Not tragic, but it just does not look right !
• You need two different halves if you are building something. Many times the wires are not color coded so you don't know if you have plugged in correctly or not

[Lwiddis]

If you aren’t fully recharging daily then your batteries will age fast. And not “some solar.” Do an energy survey of your amp hour use...or what you want to use...and start with adequate batteries, then at least one solar panel watt per battery amp hour. The total solar watts converted to amps determines the size of the controller.

[theoldwizard1]

landyacht318 wrote:
I found maxing out my alternator charging well depleted battery over thick copper when idling parked had my alternator quickly heat to 200 f+ degrees. But I can force.it.to seek and hold 14.7v.

What year, make and model vehicle and how do you force the alternator to seek and hold 14.7V ?

[theoldwizard1]

pinesman wrote:
I got to thinking about using those same cables to charge my batteries using the truck. I would not be using it for hours to run everything but just a little while to top off the batteries in the trailer.

Modern vehicle (after about 2000) charging system work TOTALLY DIFFERENT than the past. They drop the voltage down to about 13.2V within a few minutes of starting. That is much TOO LOW to charge such a large battery bank !

[landyacht318]

I found maxing out my alternator charging well depleted battery over thick copper when idling parked had my alternator quickly heat to 200 f+ degrees. But I can force.it.to seek and hold 14.7v.

The battery will accept 50% to 66% more amperage at 14.7 compared to 13.7, so actual charge rate will be determined ed by your vehicles voltage regulator.and 80%to100% charges still takes 3.5 hour at those higher. Voltages,so 'topping up' is delusional. And getting depleted batteries to 80% might fry your alternator, or just reduce its lifespan.

[ajriding]

Go solar as soon as you can, this solves a lot of problems. 200-300 watts will be plenty to keep them charged unless you use a lot of power camping. If you do use power use it early in the daylight so there is light left to charge back before dark.

Instead of fooling with jumper cables and risking sparks and possible damage to electronics consider beefing up your trailer charging system. The trailer wiring is insufficient.
Run a 2-pole plug from truck to trailer with heavy gauge wire, like your jumper cables gauge, and pull power off truck battery or the starter motor. A heavy duty solenoid can be a switch as you do not need truck power all the time while driving, and you do not want to use truck battery while parked or have to physically unplug trailer from truck.
etrailer.com has the 2-pole plugs at a good price, and they could even give you advice.

To give significant charge to that many batteries will take time. 30 mins will not do much, you may need hours, and really need the engine running at 1800rpm to have alternator optimized.
A generator will cost less in gas for sure.
Diesel engines are not meant to be run at idle for more than 10-15 minutes, they are not semis. I forgot if you said gas or diesel… You will do harm to a diesel unless you add a high idle switch.

Back to solar' that is the best option, even if all you do is have those portable ones out to the side.

Marine batteries are not true deep-cycle batteries, and if you run them flat too many times they will be gone. They can cycle 100-300 times maybe if I remember, where deep cycle can cycle into the thousands.

[pinesman]

OP here. When I retire and can spend more time on the road, I plan to get the smaller inverter generator and some solar panels. I have plenty of battery for a weekend of dry camping. I was just thinking about the once or twice (or maybe zero) times in a year that we would be able to get out for a longer time dry camping. I already have the cables so that would be no cost

[Lwiddis]

No question, 2oldman, solar needs a backup for those days but they are few.

[BFL13]

2oldman wrote:
Solar is a better solution.

Sometimes. 🙂

[2oldman]

Solar is a better solution.

[ppine]

No. Your trucks batteries and alternator are not reallly suited for charging your trailer batteries.
Get a solar panel and/or a quiet generator. Buy a long power cord for your trailer and you can run the generator in the back of your truck.

[RoyB]

I have been using one of those 10-watt Solar Panels sitting in the windshield area to trickle charge extra batteries when needed... When connected to my battery I can see my battery charge start out above 12VDC right away and will eventually creep up to 12.6-7 Volts

I think the MAX current is around 100MA or so which should not do any over charging of your battery...

This certainly makes a difference if you are sitting for a long period of time and not running the vehicle etc...


Google image

Mine has these 2-pin connectors on it and I built up a lighter plug adapter so I can plug this solar panel into an always hot 12V Connector inside my truck... Great for trickle charging my truck start battery doing this...


google image

I'm thinking this may be a great PLAN B thing to have around...

You can pick these 10W Solar Panels up from AMAZON for around $40...

Roy Ken