How can I charge my trailer battery, off of my vehicle battery charging system?

[gonejeeping15]

When I say connector as stated above, I'm meaning wire guage of harness and the connector style that comes with it, what ever kind that may be in trailer standards. I don't know if a "7 pin" setup would have heavy enough wire to meet those amp requirements?

Doug

 

[Woods]

Found this, on another forum;

Run a 10 gauge wire from your positive battery post to a 30amp inline fuse, mount the inline fuse on your fender well (inside the engine compartment) then continue the wire all the way back to your wire harness on the back of the truck. When you run the wire make sure you avoid high heat areas such as exhaust manifolds and exhaust pipes. If you can find some wires running from the engine compartment to the rear you can secure your 10gauge wire to that using zip ties. Zip tie the wire to keep it out of the way and tight so it doesnt vibrate a hole through the insulation when you drive. You can tie it to the frame as well. Make sure you run it accordingly so that it doesnt interfere with your spare tire if you need to get it out. If you cant avoid a high heat areas wrap the wire with exhaust tape. You can wrap a few wraps of electrical tape around the wire in areas you are concerned about vibrating wear. When you get to the trailer harness in the rear of the truck put an appropiate wire end on it, say a male end and then you put a female end on the 10 gauge wire running from the positive battery post on your trailer battery. That way when you hook up your trailer lights you simply plug in the battery charging wire. Be sure to run a ground from your negative battery post on the trailer battery to the trailer frame.
If you didn't know,undo the battery clamps and fit the stripped end of the 10 gauge wire in between the clamps of the battery and the terminal posts. Auto Zone or any car place will have all you need.
I hope this helps and is understandable

This is a follow-up post;

One thing to remember, and I found this out the hard way, is that the battery charge wire coming from your truck harness was only designed to charge a small motorcycle battery for the trailer brake-away system. If your battery gets low and you are drawing any amps from it, it will melt the wire and could cause a fire. In addition to this, if your truck battery ever drains and it is plugged into the trailer the truck will try to draw its juice from the trailer battery, causing it to get overheated as well. I used to haul RV's for a living and it was common knowledge that the best way to get the job done was to run a heavy wire (8-10 guage) From the battery with an automatic reset 30 amp breaker, AND a switch on your dash so that you have the ability to turn the "charging system" off/on...


I'm going to run 8 gauge wire with a 30 amp circuit breaker. Will install a fuse on the trailer side, for good measure.

 

[evldave]

I'm going to run 8 gauge wire with a 30 amp circuit breaker. Will install a fuse on the trailer side, for good measure.

This should be great for charging a trailer battery no problemo. You should also run a separate 8ga ground wire as well, and fuse that. The trailer hitch itself doesn't act as a good ground conductor. The fuse on the ground is probably overkill, but it's only a couple bucks and the extra insurance might be worth it.

 

[Vince1]

Anderson plugs are a great solution, but I'm trying to avoid running heavy gauge wire.

When I looked into this I found:

1. If you aren't willing to run heavy wire, you are limited to trickle charging. In this case, why not just put a solar panel on top of your trailer for charging it's battery? They also make trickle chargers powered off your cigarette lighter outlet.

2. If you are going to run heavy wire, then an isolator will help protect your vehicle battery's charge.

I ended up going the solar route and it works great. Added benefit is it also charges when trailer is unhooked.

 

[Robert Bills]

A relatively simple solution is to mount a constant duty solenoid under the hood triggered by an "ignition on" hot lead. (easily sourced at almost any auto parts store - commonly used for lift gates, etc.) If you want to get fancy, use an on-off switch mounted in or under the dash so that the solenoid isn't powered even when the ignition is on unless you want it to be. I got extra fancy and used a lighted switch so that I know at a glance when the trailer battery charge circuit is on.

The charging wire runs from the tow rig battery through constant duty solenoid to the rear of your tow rig, and should be fused. I used 8 ga wire for this run to minimize voltage drop as much as possible. My charge wire then runs through my 7-pin connector and then to the trailer battery.

 

[UK4X4]

In no way do you need to put a fuse in the negative line on a DC circuit -

complete waste -won't do a thing

take a same size conductor from the rear of the vehicle frame to the trailer conector
on the other side depending if frame is part of the negative circuit either earth it or take directly to the battery

done

 

[pods8]

That's how I'm looking to do it. Have you found a DC to DC charger yet? I've found a cool trickle charger HERE, but it's limited to 1.5 amps. I'd like to find something that will run up to 18 amps (that's what my 12 gauge wire will handle). Have been considering a solar charger. Not even sure if I need a charger. If there's a way to limit the amps to 18, then I would just do that and let the Jeep regulator handle everything else.

If you want to go the DC-DC route here is a 7.5amp stage charger http://www.powerstream.com/DCC.htm You can either switch the power going to it off/on with a solenoid or use the remote input line off an ignition hot wire to turn it on and off (like an audio amp). If mounted close to you trailer battery it will correct for voltage drop as well.

Edit: I'm running one in my FWC to charge my batteries and provide isolation (I have the remote line off a switched ignition hot line so it's only on when the ignition is and I can also still manually turn it on/off in that case). If you aren't running the vehicle much in relation to the battery usage 7.5amps might be a little restrictive but for the most part I've found that it fits me pretty well (usually use less battery than the worst case I plan for and have multiple hours with the truck running for the places I'm coming/going). Most of the time my batteries are completely topped off when I get back and I don't need to plug in my shore charger to finish the job.

 

[VanIsle_Greg]

^ very kool item.

 

[red_5]

From my Conqueror build thread:

I had to build a wire harness for the truck with a 10ga power, 12ga brake control and an extra wire for a lighting relay to power the rear facing lights on the roof rack.(no factory brake control wiring or charge wiring for the trailer). I ran it through the firewall and parallel the truck's wire harness inside the pass compartment. All protected by circuit breakers @ the battery.

That was a real chore.

The 10ga is hot all the time, and I'm using a TOAD Charger installed at the rear of the truck (rather than on the trailer), taking power off the 10ga lead and protected by it's own 15A circuit breaker, from there to the 7-way trailer connector. I chose this option for two reasons A)It's automagic, sensing charging voltage on the vehicle side to turn it on B)It's deep cycle friendly, limiting charge current to 10A. On the trailer side, I installed a 2 wire harness directly to the battery.

This has been working great since I installed it. Zero issues.

http://www.lslproducts.com/ToadChargePage.html

 

[Woods]

this is perfect- am ordering asap - thanks for posting.

From my Conqueror build thread:


http://www.lslproducts.com/ToadChargePage.html

 

[pods8]

B)It's deep cycle friendly, limiting charge current to 10A

Considering it's just switch that turns on/off when the tow vehicle's charge system builds up a certain voltage it's really got no control over whether it's friendly to a certain battery type or not. The battery will see whatever voltage profile the tow vehicle puts out (less line losses) and voltage is the part that matters for "friendly charging". The battery will self limit the amount of current it takes on this type of charge system so that doesn't really matter too much (ie if it tries to pull higher amps then the line losses will build which will reduce the available voltage at the battery and thus reduce the motive force to put current into the battery thus the demand will reduce).

 

[Woods]

I partially disagree - Prior to finding this kit, I was going to run fused 8 gauge wire, directly from the vehicle battery to the trailer battery. I've found numerous examples of people doing this for years, without any problems. The concern that I had is if the trailer battery is run way down, the wiring may not handle the load when re-connected. This device eliminates this concern, as it limits the load to 10 amps. I agree that the device doesn't have some secret super designed patented algorithm that many charger manufacturers tout, but experiences from others indicate that these are not required. I can't count how many battery chargers I've had over the years (mostly RC chargers). I can tell you that not a single one stood above the rest as being any better or worse. Yes, my trailer batter may not last as long as it would with a $100+ charger, but it's only a $50 battery. This kit is less than 80 bucks and it includes about $30 worth of parts that I'd have to buy anyway. For $50 I'll buy this much peace of mind.

Considering it's just switch that turns on/off when the tow vehicle's charge system builds up a certain voltage it's really got no control over whether it's friendly to a certain battery type or not. The battery will see whatever voltage profile the tow vehicle puts out (less line losses) and voltage is the part that matters for "friendly charging". The battery will self limit the amount of current it takes on this type of charge system so that doesn't really matter too much (ie if it tries to pull higher amps then the line losses will build which will reduce the available voltage at the battery and thus reduce the motive force to put current into the battery thus the demand will reduce).

 

[pods8]

You didn't really disagree with me at all and I never commented on whether I thought anything of the unit itself. I only pointed out it was erroneous to think the device itself was friendly to a certain battery type. That is just marketing hype because if your charge system voltage itself doesn't happen to be friendly to the battery this device isn't going to do a thing about it, same as any other switch based device.


On the subject of wire gauge: There are some links that wire gauge failure shouldn't really be a concern on reconnection because voltage drop will self limit the current draw the battery seeks. The battery will only take current in if there is a higher voltage available that it's current resting state plus some overage, if you start pulling to much current through the wire the voltage available to the battery goes down and thus the motive to pull that current goes away too and it self regulates. The larger the gauge the higher this self regulation point will tend to be.

 

[Woods]

The statement that I disagreed with, is that this device is just a switch. It also limits amperage to 10 amps. That's the part where I get some peace of mind.

Are you saying that I need not be worried about limiting the amperage?

You didn't really disagree with me at all and I never commented on whether I thought anything of the unit itself. I only pointed out it was erroneous to think the device itself was friendly to a certain battery type. That is just marketing hype because if your charge system voltage itself doesn't happen to be friendly to the battery this device isn't going to do a thing about it, same as any other switch based device.


On the subject of wire gauge: There are some links that wire gauge failure shouldn't really be a concern on reconnection because voltage drop will self limit the current draw the battery seeks. The battery will only take current in if there is a higher voltage available that it's current resting state plus some overage, if you start pulling to much current through the wire the voltage available to the battery goes down and thus the motive to pull that current goes away too and it self regulates. The larger the gauge the higher this self regulation point will tend to be.

 

[pods8]

The statement that I disagreed with, is that this device is just a switch. It also limits amperage to 10 amps. That's the part where I get some peace of mind.

Are you saying that I need not be worried about limiting the amperage?

Lets lay it out, my truck for instance puts 14.4V out at the alternator when rev'd up (best case scenario, it's 14.1V at idle). Also lets say under 13V getting to your battery and there won't be any motive force to push amps in (probably need a higher number than that but we'll call this the worst case differential). So that is only a 10% voltage drop before nothing is driving amps into the battery, on a 12ga wire at 20' that is about 20amps. In reality you likely need a higher voltage at the battery to actually push some amps, lets say 13.7V instead of a 14.4V alt system. That means you can only have 5% voltage drop before there isn't any force pushing amps in, which on a 20' long 12ga wire is about 10-11amps... If you need 14V then it would only be 6amps when the truck is rev'd and only about 2 amps at idle.

I can't speak for the exact voltage numbers needed to push amps into the battery but you get the point, the system is self limiting. Usually people have the reverse problem in that they're using too small of a wire to keep the voltage up to push the amps they desire.

Make sense?