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Unread 09-20-2012, 09:38 AM   #1
Dr. Marneaus
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How to charge a trailer battery?

My camper has a deep cycle marine battery on it. The camper is currently wired with a 4 pin harness. There is an additional 5th wire there, just chilling, that runs to the batt for purposes of charging. Ithas 2 lights, a heater with a fan, and a few wall outlets from the inverter. No fridge or anything, and the lights are little. So, should be pretty low power usage.

I have a 1973 wagoneer. It has a regular car battery. It has a 4 pin harness.

I would like to charge the trailer battery somehow, while on trips, without a wall to plus a charger into.

Options seem to be as follows:

1. charge from the vehicle. Ideal because I can just hook up and drive while charging. However, of the trailer battery is near depleted, this can be dangerous as it'll be pulling 30 amps to recharge, which could affect the battery in the truck. I'd likely have to run a battery isolator, or a switch in line to choose between which battery is getting charged to avoid any potential issues.

2. Solar. I can make the investment now to set up a solar system with a charge controller so the camper not only will charge on its own free of the truck, but it'll also maintain the battery and always be ready to go.

3. Generator. Generators are loud and expensive and need their own gas. Or I can get a fancy Yamaha inverter/generator but those cost more than I paid for the camper.

The two obvious routes would be charging from the truck, somehow, or solar.

Am I missing any options, am I being overly cautious in the ideas about charging from the truck and it's not really necessary to do it 'right' with a circuit breaker, isolator or switch, and fat wire?

I feel like Id I do it the right way I'd end up spending just as much as I would on a harbor freight solar setup, with less benefit.

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Unread 09-21-2012, 12:29 PM   #2
Mickey_D
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You can get an inexpensive isolator from O'Reilly's that'll do great.

Your idea of the HF solar panels is a good one (I love solar) but I will be the first to admit that trying to keep solar panels clean on the roof of a trailer that's used offroad is going to be a PITA. I don't remember the exact numbers but I believe a single layer of fine dust reduces a panel's efficiency by up to 50% or some crazy thing like that.

Granted, a single 45W panel is probably going to exceed your requirements living where you do, so a twin set running at 50% will still be fine.
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Unread 09-25-2012, 04:25 PM   #3
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Bump... I'd like to also have a trailer with a battery.
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Unread 09-25-2012, 05:00 PM   #4
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seems one of the more commonly suggested things is to run a 40 amp circuit breaker on a line that then goes to a relay that is wired to ignition.

Idea is the circuit breaker will kick off if the battery tries to draw too much amperage from the charging system, and then after it cools itself down, it'll reset (most of my accessories are run on curcuit breakers under the hood).

The idea of the relay is that it will only be sending power to the baattery when the trucks ignition is on, thus preventing the battery from draining the truck when its not running.

People seem to suggest a minimum of 10AWG wire.
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Originally Posted by revelc View Post
Having a Full Size Jeep is likehaving a hot wife. When you take her out in public it turns heads, they can insight jealousy, you could look at them all day, they require a lot of attention, cost a lot to get them to do what you want them to do, but when they're not happy you'll be cussing, throwing things, and constantly weighing how much you'll lose if you divorce her.

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Unread 09-26-2012, 02:01 PM   #5
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I do a combination of things.
My GC uses the 7 pin plug, power from the battery when the car is running. Charge the battery before the trip and the tow maintains/tops off as needed.

Change anything that draws power to as low an amp draw as possible. LED or at least fluorescent lights etc. Use a heater w/o a fan so it's not pulling juice. The odds of completely discharging a battery are pretty low even on a longer trip.

Use a solar panel as well. Even at reduced efficiency as long as the sun is shining you're getting something. With low discharge it shouldn't take too much to keep the battery up.

My last camper had a regular furnace and fridge. We used it during trips but I also carried a generator and jumper cables. The cables came in handy when my hunting partner forgot that the engine running the generator needs weird things. Like oil. Or they seize up. My camper now hasn't been out more than overnight but this hunting season will likely change that
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Unread 09-26-2012, 06:13 PM   #6
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My 5th-wheel has 2 deep cycle batteries that charge off of my Chevy pickup when driving, as well as solar and a generator. The downside to solar is that, unless you get one of the more expensive solar panel controllers, the solar will overcharge and eventually cook the batteries. I added an inline fuse on my solar panels, and pull it when the trailer is in storage for extended periods of time.

The charging circuit is nothing more than a hot lead from the battery of the pickup. Unless I'm misunderstanding your question, it should be as simple as running a hot lead from the battery to a 5-pin (or more) connector and run that same pin to the positive side of the trailer's batteries. Your tow vehicle's alternator and regulator will handle the rest.

Electricity always follows the path of least resistance, so it will charge the trailer batteries without affecting your Wagoneer's battery. If both batteries are full then the regulator should back down the amperage.

The only concern about having a charging circuit is that you have 2 different types of batteries - deep cycle in the trailer, and standard in the Jeep, and they have different capacities. That's not a problem when the engine is running and the alternator is charging, but when you shut down the battery with less charge (usually the trailer) will continue to draw from the other battery. To solve this, you can either unplug the trailer when you park, or install a relay on the charging circuit (on the tow vehicle) so that it's only connected when the Jeep's ignition is turned on.
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Unread 09-26-2012, 06:15 PM   #7
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I like the idea of the circuit breaker, and as well to use low amp draws.

Indy, good story about the generator and oil.

Personally I don't plan to have a regular (propane) heater or fridge on a small popup trailer (thinking of a Quicksilver 6.0) that I want to haul into the woods. I mainly would like to have an electric heater for cold mornings or just run an electric blanket overnight to run off of the trailer's battery.
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Unread 09-26-2012, 10:02 PM   #8
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Quote:
Originally Posted by MPond View Post
My 5th-wheel has 2 deep cycle batteries that charge off of my Chevy pickup when driving, as well as solar and a generator. The downside to solar is that, unless you get one of the more expensive solar panel controllers, the solar will overcharge and eventually cook the batteries. I added an inline fuse on my solar panels, and pull it when the trailer is in storage for extended periods of time.

The charging circuit is nothing more than a hot lead from the battery of the pickup. Unless I'm misunderstanding your question, it should be as simple as running a hot lead from the battery to a 5-pin (or more) connector and run that same pin to the positive side of the trailer's batteries. Your tow vehicle's alternator and regulator will handle the rest.

Electricity always follows the path of least resistance, so it will charge the trailer batteries without affecting your Wagoneer's battery. If both batteries are full then the regulator should back down the amperage.

The only concern about having a charging circuit is that you have 2 different types of batteries - deep cycle in the trailer, and standard in the Jeep, and they have different capacities. That's not a problem when the engine is running and the alternator is charging, but when you shut down the battery with less charge (usually the trailer) will continue to draw from the other battery. To solve this, you can either unplug the trailer when you park, or install a relay on the charging circuit (on the tow vehicle) so that it's only connected when the Jeep's ignition is turned on.
to the best of my knowledge the issues arise when theoretically you are charging two low batteries (truck and trailer) or when you are constantly charging a drained battery.

Maybe a modern tow rig with a modern charging system is capable of just that, but i'm not going to rely on my 40 year old wiring and weak-arse alternator, haha.

If i wire it up i'll be going the route of the circuit breaker and the relay.
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Quote:
Originally Posted by revelc View Post
Having a Full Size Jeep is likehaving a hot wife. When you take her out in public it turns heads, they can insight jealousy, you could look at them all day, they require a lot of attention, cost a lot to get them to do what you want them to do, but when they're not happy you'll be cussing, throwing things, and constantly weighing how much you'll lose if you divorce her.

The Beast Build Thread: Marns '73 Wagoneer Thread ----- The Camper Build Thread: Marns 1980 Jayco JayFinch6 Build Thread

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Unread 09-27-2012, 05:58 PM   #9
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A break-a-way battery charger. it trickle charges at about 5 amps, and stops when battery is full.
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Unread 09-27-2012, 06:50 PM   #10
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Quote:
Originally Posted by Dr. Marneaus View Post
My camper has a deep cycle marine battery on it. The camper is currently wired with a 4 pin harness. There is an additional 5th wire there, just chilling, that runs to the batt for purposes of charging. Ithas 2 lights, a heater with a fan, and a few wall outlets from the inverter. No fridge or anything, and the lights are little. So, should be pretty low power usage.

I have a 1973 wagoneer. It has a regular car battery. It has a 4 pin harness.

I would like to charge the trailer battery somehow, while on trips, without a wall to plus a charger into.

Options seem to be as follows:

1. charge from the vehicle. Ideal because I can just hook up and drive while charging. However, of the trailer battery is near depleted, this can be dangerous as it'll be pulling 30 amps to recharge, which could affect the battery in the truck. I'd likely have to run a battery isolator, or a switch in line to choose between which battery is getting charged to avoid any potential issues.

2. Solar. I can make the investment now to set up a solar system with a charge controller so the camper not only will charge on its own free of the truck, but it'll also maintain the battery and always be ready to go.

3. Generator. Generators are loud and expensive and need their own gas. Or I can get a fancy Yamaha inverter/generator but those cost more than I paid for the camper.

The two obvious routes would be charging from the truck, somehow, or solar.

Am I missing any options, am I being overly cautious in the ideas about charging from the truck and it's not really necessary to do it 'right' with a circuit breaker, isolator or switch, and fat wire?

I feel like Id I do it the right way I'd end up spending just as much as I would on a harbor freight solar setup, with less benefit.
I'd put in a small isolator (figure about half of your alternator's rating should do - your 73SJ should have a 55A Motorola, unless you've changed it...) and run a charge lead out by the trailer plug (probably using an Anderson SB50 - but I like Andersons.) A solar panel on the trailer proper to keep the battery topped off would also be helpful - mostly for between trips.

For that charge rate, 10AWG wire should be plenty (and can easily be put into an SB50 - other connectors may present a difficulty.) Fuse it at the isolator's rating just after the isolator for safety's sake.
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Unread 09-28-2012, 01:44 AM   #11
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Quote:
Originally Posted by Dr. Marneaus View Post
to the best of my knowledge the issues arise when theoretically you are charging two low batteries (truck and trailer) or when you are constantly charging a drained battery.

Maybe a modern tow rig with a modern charging system is capable of just that, but i'm not going to rely on my 40 year old wiring and weak-arse alternator, haha.

If i wire it up i'll be going the route of the circuit breaker and the relay.
Interesting... I haden't considered the age of your alternator as an issue.

If I were in your shoes, I'd compare the cost of replacing the alternator with a modern one (along with a modern regulator), and a fresh wire run to the charging circuit at the trailer plug, vs. the cost of the suggested add-ons. I'd be more comfortable with a new (modern) alternator on my tow rig than trying to make an older system work with breakers, isolaters, etc...

Don't get me wrong - those things are good ideas, but if you're not confident in your alternator / regulator then I'd be worried about that before anything else.

Just my $0.02 - I haven't spent much time thinking about towing with a 40-year-old truck.
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Unread 09-28-2012, 05:16 AM   #12
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Quote:
Just my $0.02 - I haven't spent much time thinking about towing with a 40-year-old truck.
Haha. You got a good one there Pond.

The heater is the problem. You can't run a heater off a battery unless its for a Easy Bake oven. A little heater will use around 300- 500 watts. Like leaving 4 sets of car headlights on.
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Unread 10-03-2012, 11:55 AM   #13
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Well found out my heater doesn't work anyway so....there goes that issue haha. No I think it just needs a new thermocouple. We used the camper mostly just for sleeping this trip. Had the lights on for maybe a combined 2 or 3 hours. So it shouldn't have barely touched the battery. Ill check voltage here soon. I think ill just pick up a regular battery charger to use in the meantime.
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Quote:
Originally Posted by revelc View Post
Having a Full Size Jeep is likehaving a hot wife. When you take her out in public it turns heads, they can insight jealousy, you could look at them all day, they require a lot of attention, cost a lot to get them to do what you want them to do, but when they're not happy you'll be cussing, throwing things, and constantly weighing how much you'll lose if you divorce her.

The Beast Build Thread: Marns '73 Wagoneer Thread ----- The Camper Build Thread: Marns 1980 Jayco JayFinch6 Build Thread

Gone but not Forgotten: 97 TJs Build Up.

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Unread 10-04-2012, 06:08 PM   #14
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you live in the land of the sun my man... drop an appropriately sized solar kit on the roof of your rig/trailer and the battery will simply charge itself. You can hook the truck up for trickle charge easy enough via a solenoid isolator, some fuses and some phat wire.

Solar has gone way up in efficiency and way down in cost. If I were you, I would do some research on what fits for your needs.
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