Trailer Charging by Vehicle

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Trailer Charging by Vehicle

Postby oside trailer » Thu Nov 13, 2008 1:01 am

I'm running two 6 volt batteries to power the 12v circuits in my trailer and want to be able to charge the batteries with my truck in a pinch.

It seems ridiculous to get a separate power inverter to run from my truck's 12v socket (lighter) in order to plug-in my charger/converter to recharge the batteries.

Is there a more direct method? I'd like to avoid alligator clips if possible...
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Postby del » Thu Nov 13, 2008 1:47 am

Run a wire from the battery to the trailer connector (six or seven pin connectors have a pin for this). Add a relay so it only charges when the car runs, and a circuit breaker.

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sounds easy enuff...

Postby oside trailer » Thu Nov 13, 2008 7:08 am

thanks del -- will a 20A in-line fuse work for a circuit breaker?
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Re: sounds easy enuff...

Postby del » Thu Nov 13, 2008 11:07 am

oside trailer wrote:thanks del -- will a 20A in-line fuse work for a circuit breaker?
An inline fuse will work, but when it blows you need to replace the fuse. An RV supply or auto part store should carry the circuit breaker. I believe (I did this a year ago) I used a 30a circuit breaker and 8 gauge wire. There needs to be a circuit breaker (or fuse) near the battery in the trailer also.

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Postby jimqpublic » Thu Nov 13, 2008 12:21 pm

Use big wire! With two golf car batteries you can get a good charge rate but only if you don't have much voltage drop. I ran 6 AWG stranded wire when I wired my car. Copper is very expensive though so 8 might be a more economical choice. Most RV places install 10 AWG or smaller (bigger number) and then everyone complains they don't get much charge. I do have a standard 7-pin RV plug and cable on the trailer, so part of my wire run is 10 AWG.

I used a continuous duty relay tripped by the car accessory circuit and a 30 amp self-resetting circuit breaker in the car. In the trailer I used a 50 amp stereo fuse (with gold plated terminals).

For long drives and shallow depth of discharge just about any wire gauge will keep the battery topped up. When you want to get a lot of charge in a short time you need big wires.

The other, very simple option for occasional use when camped is to just let the car idle and use jumper cables. Don't expect to recharge the battery in a short time, but you can probably pump 20 to 30 amps across. High idle or a stick wedged on the gas pedal to get the RPM's up around 1500 will help a lot.
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4 pole to 7 pole

Postby oside trailer » Thu Nov 13, 2008 12:43 pm

ok, now the question becomes how to convert my truck's 4 wire trailer wiring to accomodate a 6 or 7 pole connector that has a hot lead.

i see there are adapters for this online:

http://www.etrailer.com/pc-A~37175.htm

but where does the "red" wire need to be connected to get its juice? is there an OEM wiring harness i can tap into, or does this need to come from the battery?

factory wiring seems way too small for effectively charging in this manner.
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Postby vrooom3440 » Thu Nov 13, 2008 12:57 pm

One caveat when adding the "BIG" power wire is to make sure that you are not sending more charge current than the battery can take. I have seen 10g advocated for the battery connection in a car just as a current limiter of sorts.

And as a bit of background, you need circuit protection (fuse or breaker) on *both* ends of the power wire as effectively both ends are hot. A short anywhere along the wire can be fed from the power source on either end.

With respect to hooking up to the car... while you can hook up to the battery this is less than optimal. For one there can be corrosive fumes in that area, especially as the car battery gets older. This degrades your wire and terminal. Yuck. It also is not the true source of electrical power when the car is running. And one of the cardinal rules is generally to hook up as close to the source as possible. This means the alternator.

The alternator will have a large power wire coming off the back. THIS is the true source of electrical power when the car is running and it is sized appropriately to that heavy lifting (the battery feed wire may very well be a bit smaller). It will likely use a bolted connection to handle high current. Follow this cable and it's other end will be a good place to connect your new power feed wire. In modern cars it will probably be a power distribution box with fuses and stuff inside. It will likely have a bolted connection for the alternator power cable here too.

If you really want to run monster cable... check auto stereo install shops as a wire source. Might even find a high power amp install kit in the auto parts store to cannibalize for 8g cable and an inline fuse.
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Postby jimqpublic » Thu Nov 13, 2008 5:08 pm

I'll add that I spent way more money and time wiring up my car than really makes sense. I probably should have bought a small generator instead.

Many 12 volt electrical problems are related to high resistance caused by poor electrical connections and corrosion. When I wired the car I used marine grade cables and terminals. The cables are all pre-tinned, all end connectors are crimped and soldered, then bolted to terminal lugs. I ran wiring from the alternator output lug direct to my breaker and relay. I also ran a secondary ground from the alternator frame back to the trailer connector.

The trailer tow lights run through relays so they only draw sense current from the car lighting circuit. Plus they are all fused so no short in the trailer can damage the car's electrical system. If I were to do that part again I would have swapped the trailer tow lights to LED and avoided any potential for overloading the car's lighting circuit.

If you already have a "flat four" trailer plug you can buy an adapter from E-trailer. Make sure you attach the extra ground wire to the car's chassis.
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under the hood

Postby oside trailer » Thu Nov 13, 2008 8:38 pm

i looked under my hood and found that there are already two hot leads with inline fuses that are connected to the alternator terminal in the fuse box -- one is for a stereo amplifier, but i'm not sure about the other one... it may have something to do with the SnugTop camper shell on the bed.

i could just ditch the amplifier and use that as my power source since it's already wired (with good auto AV wiring, and plenty of extra). the aux lead off of the adapter on eTrailer looks like it's only 12g though so i'm probably losing whatever benefit gained once it's attached to the connector anyway.

jim q.p.: to your point, i'm not sure it's all worth it when i could simply hook up the jumper cables in an emergency and get some extra juice that way... although it concerns me that i might fry the trailer electrical system.

suddenly the idea of getting some additional charge while DRIVING to the camp site seems like it might not be worth the hassle
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Postby TheBizMan » Thu Nov 13, 2008 8:39 pm

I just bought a wiring setup from this site:

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

It contains wire, connectors, breakers and everthing for running a charge line.
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cooler is the culprit

Postby oside trailer » Thu Nov 13, 2008 10:40 pm

once upon a time, in a thread long, long ago, the topic of my Waeco CDF-40 was the center of much debate. the model was discontinued, but essentially the link below is the current equivalent:

http://www.waeco.com/en/252_483.php

this is the only thing i truly care about powering and i need it to last in desert conditions for as long as food takes to spoil.

lights in my trailer will long outlast the fridge, which shuts off automatically when there's insufficient amperage. the only thing that puts more of a drain on my battery is the 750w power inverter i'm running that powers some home electronics (what do you expect?)... but that's primarily during girlfriend camping.

the fridge is only good for about 2 days out in the desert heat on its own. i'm trying to toy with the settings but the slider controls are only so precise. as you might guess, there's plenty of sun (and frequently wind), but not an AC outlet in sight. my goal is to outlast ice (or dry ice) and a conventional cooler for as long as possible.

solar anyone?

[sidebar: one technique that has been successful is to wait for the last 2 days of camping before turning the fridge on -- it's less convenient but a life-saver when all the ice has melted]
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Postby TheBizMan » Thu Nov 20, 2008 7:56 pm

TheBizMan wrote:I just bought a wiring setup from this site:

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

It contains wire, connectors, breakers and everthing for running a charge line.



Got the setup and installed it in about 5 hours. The longest time was to run the wire from the truck battery to the connector on the back bumper. I'm no good when it comes to getting under the truck. Could only work for 10-15 minutes at a time. The trailer part went fast. When the last connection was made I started the truck and guess what IT WORKS!! The trailer battery was fully charged, after being down to 10%, in about 20 minutes. The $90 cost is a lot less then a $800 generator and this was easy to install.
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Re: cooler is the culprit

Postby Steve F » Thu Nov 20, 2008 8:16 pm

oside trailer wrote:once upon a time, in a thread long, long ago, the topic of my Waeco CDF-40 was the center of much debate. the model was discontinued, but essentially the link below is the current equivalent:

http://www.waeco.com/en/252_483.php

this is the only thing i truly care about powering and i need it to last in desert conditions for as long as food takes to spoil.

lights in my trailer will long outlast the fridge, which shuts off automatically when there's insufficient amperage. the only thing that puts more of a drain on my battery is the 750w power inverter i'm running that powers some home electronics (what do you expect?)... but that's primarily during girlfriend camping.

the fridge is only good for about 2 days out in the desert heat on its own. i'm trying to toy with the settings but the slider controls are only so precise. as you might guess, there's plenty of sun (and frequently wind), but not an AC outlet in sight. my goal is to outlast ice (or dry ice) and a conventional cooler for as long as possible.

solar anyone?

[sidebar: one technique that has been successful is to wait for the last 2 days of camping before turning the fridge on -- it's less convenient but a life-saver when all the ice has melted]


I also run a Waeco, mine is the 50lt. I have a 100AH AGM battery in the camper with a 30w Monocrystalline solar panel that I put on the roof if parked in the sun. To keep mine running pretty much forever I put the fridge in the jeep during the day when I'm out exploring (this has a second battery as well and is charged while driving) and then put the fridge on a table next to the camper when in camp for convenience (running off the camper battery). The solar recharges the camper during the day and is ready to go for the next night. I've only had to go 5 days like this so far but it was no problem and may be an option for you :)

Cheers
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Found the Culprit

Postby oside trailer » Sat Dec 13, 2008 9:26 pm

So, it wasn't my Waeco that was causing the problem -- it was a set of amplified computer speakers that I had connected to the AC inverter (note the one plug in the powerstrip below).

my stereo has no amplifier so stealing my PC speakers from the house seemed "better" than buying an amp or different stereo for the trailer.

WRONG

My fridge, lights, and everything else will run for days without recharging... but anything on the 110 side of the inverter is just a deal-breaker when it comes to battery life.

Will be switching to a 12V amp wired directly to the battery and some cheap car speakers as soon as budget will alllow.

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Re: Found the Culprit

Postby 2bits » Mon Dec 22, 2008 11:57 pm

oside trailer wrote:....anything on the 110 side of the inverter is just a deal-breaker when it comes to battery life.


Yessir you hit the nail on the head there!
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