Charging Trailer Batteries

Robert Franzke

SILVER Star
Joined
Apr 3, 2017
Messages
1,136
Location
Plano Texas
I have a little Bantam T3-C trailer I restored that I pull behind my FJ60:

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I want to add a battery setup to it that I can use to power things while I am at camp. I don't really know much about how that's done. Here is what I want to be able to do:

1. When towing the trailer, I want the batteries charged by the tow vehicle using the 12V hot lead in my 7-way connector.
2. When at camp I want to be able to charge batteries using a solar panel when A/C power is not available while at the same time using them
3. When at camp I want to be able to charge batteries using A/C power when available while at the same time using them
4. When the trailer is sitting not used at home, I want to be able to plug in the batteries to A/C power to trickle charge and maintain the batteries
5. When at camp I want to be able to use the batteries to run either A/C devices or DC devices as use demands without having to switch between A/C and DC
6. When at camp have USB ports available for electronics
7. Would like a meter of some sort to tell me when the battery charge level and current load, etc.

I am not really sure how to achieve this without cobbling together a bunch of devices. The way this could be done I think is by using a combination of an inverter charger with USB ports, a Solar charge controller, maybe a trickle charger for use when sitting at home, and a tow vehicle battery charger like this:


I am not sure how all these would work together. Can I just add the output (charging side) side of each of these devices to a battery and have each one charge the battery depending on which one is being used? Or do I need some sort of voltage sensing switch to prevent the charging voltage of one device to impact the others while they are all connected to the same battery, or does it not matter. Is there an all in one device that can do this sort of thing or am I stuck building a custom charging setup to do what I want to do. The trailer is quite small as you can see so not a lot of space for this stuff. I would like to put it all under the trailer somehow in a weather proof box. Thanks in advance for any ideas on how I can achieve this.
 

ntsqd

technerd
Joined
Apr 26, 2007
Messages
5,874
Location
Upper So. CA
 
 
I have a distrust of "Overland" specific products. I tend to go with deep ocean marine intended products over all else. My reasoning is that deep ocean travelers need reliable components much more than anywhere else other than in space. Their products have been extensively tested where I'm not convinced that any "Overland" hardware's testing comes anywhere close to being as rigorous. Most RV stuff are toys in comparison to marine hardware.

With two batteries connected to each other you need some sort of circuit protection at both ends of the circuit. This is really important and frequently overlooked. I use manual reset Series 285 breakers because I can kill the circuit with them if I need to for maintenance or whatever. Not sure exactly who makes them, but frequently they're found under the Blue Sea label. Can use Maxi fuses too.

Max wire gauge in your 7 pin connector is 10 ga. Sounds big until you do the voltage drop calculation for the whole charging circuit length, which includes the length of the ground path. Then it's not so big if you are wanting much more than a trickle charge from the alternator. To give you an idea I decided that I wanted an 80A charging capacity to our pop-top camper's batteries with a less than 3% voltage drop. Most of the time it will never go that high, but I wanted to make sure that in an extreme circumstance that it safely could. To do that over the ~35' total circuit length called for 6 ga. cables.
I'd call 3% voltage drop the maximum tolerable because there is not a lot of margin available between the alt's output voltage and a battery's minimum charge voltage. Assuming that you can't live with whatever the 10 ga. option gives you I'd look into the Anderson SB connectors for your charging wires/cables.

Alternately you can use a DC-DC converter to step up the voltage sent back to the trailer. Volts X Amps = Watts, so if you bump up the volts you don't have to send as many amps and that means that you can use a smaller wire without penalty. An FJ60 shouldn't be a problem, but for some late model trucks this is the best way to charge a trailer battery with causing the ECU to go nuts over the power being used 'somewhere'.

Solar is awesome, but much above a couple amps and you'll need something that will control the charging. The less expensive solar charge controllers are the PWM type and they don't have as good of an efficiency as the most expensive MPPT type. Some charge controllers can take more than one input. If you go with the DC-DC converter one of these would be a good choice. If the solar can be deployed when the trailer is in storage you may not need the AC trickle charger.

To monitor the battery you really need a battery monitor. In the pop-top camper world the old std is Bogart Engineering, and the new std. is Victron. In blue water marine stuff Xantrex looks to be the name of choice. Any of these will do what you need.

To get AC from a battery you'll need an inverter. There are two types, semi-sine wave & pure sine wave. Semi's are less to much less, but sensitive electronics probably won't like them. Inverter's are not terribly efficient and they draw when on even if the device plugged in isn't running.

There are a lot of ways to get USB power from a battery. Simplest is something like the Blue Sea dual USB charging port.

Not a problem to have multiple charging methods connected at the same time. It is best if they can all go thru the charge controller because those have a multi-step charging function. this promotes the best battery life. Unfortunately you probably can't do that. Partly why if you can use the solar to the float the battery while in storage I think it's best to do so.


EDIT: Suggest that you investigate using advanced chemistry batteries. The benefits over a lead-acid are great and this can be done with Nissan Leaf batteries off of ebay if you're so inclined.
 
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ntsqd

technerd
Joined
Apr 26, 2007
Messages
5,874
Location
Upper So. CA
 
 
I thought someone else would reply by now. Good to get a variety of inputs.

Just reading a thread on another forum I was exposed to something that I didn't know existed. There are some interesting combined capacity units made by CTek, Redarc, and Victron that might better fit your needs. I don't know much about them, and I'll guess that they are not optimal in every aspect of their functions, but they may simplify your installation.
 
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