DC Wiring Layout for LiFePO4 Trailer Battery Charging

[jrob4267]

Hello everyone,
Looking for some help with my daughter’s trailer that I’m helping with. This is my first time installing a dc system in a camper.

The objective is to have a dc system that when connected to her vehicle will charge the trailer’s battery, but will work independently when camping. It will not cross connect to an shore power system, even though the trailer came with an isolated shore power system already installed and due to cost she did not want to combine them at this point. Maybe in the future.

What I need help with is connecting everything in my list in the battery compartment. I have a 7 pin harness to a junction box on the tongue that I have run a power and ground line to the battery compartment. The components (already purchased) I have are:


100ah LifePo battery
100ah battery terminal fuse block
Shut off switch
Smart shunt
Dc-dc battery charger
DC 12 circuit fuse panel


At this point I have already run all the interior lights and charging ports lines with a dedicated ground and power from each fixture back to the dc fuse panel in battery compartment. I ran a good ground (white) from trailer frame to junction box and then a power (black) and ground (white) into battery compartment.

My question is how to hook up each component in the system between junction box power and ground that I fed into battery compartment and fuse panel and in what order/series.

I am not an electrician and my terminology will be wrong at times for sure. Basically I know enough to be dangerous! I don’t want to damage any components by installing them incorrectly. If your instructions could be tailored to a novice without all the electrical terms, I would be grateful. Thanks in advance,, even if you just read my post and not respond. Hopefully someone else can learn from this thread too.

 

[GTS225-TNT]

Let's back up a bit. You're on a teardrop board, where many of the subject matter were hand-built by their owners. You did not mention exactly what kind of "camper" you're talking about. If it's a factory-built teardrop, it may already have some of the gear you're looking at installing.

Let's determine exactly what you're starting with first, if you would.

Roger

 

[jrob4267]

I thought the board was teardrop and tiny travel trailers? If not, I can go elsewhere. The trailer is an old lark trailer. Don’t know year but it’s small!

 

[jrob4267]

Everything was taken out of it so no wiring except some ac wiring that was after market by former owner

 

[GTS225-TNT]

It is a teardrop and tiny trailer board, but you hadn't mentioned much about what you're working on. Now we know.......you're starting from scratch.

The objective is to have a dc system that when connected to her vehicle will charge the trailer’s battery, but will work independently when camping. It will not cross connect to an shore power system, even though the trailer came with an isolated shore power system already installed and due to cost she did not want to combine them at this point. Maybe in the future.

This gives me the impression that she plans on a lot of boon-docking, independent of shore power connections.

What I need help with is connecting everything in my list in the battery compartment. I have a 7 pin harness to a junction box on the tongue that I have run a power and ground line to the battery compartment. The components (already purchased) I have are:


100ah LifePo battery
100ah battery terminal fuse block
Shut off switch
Smart shunt
Dc-dc battery charger
DC 12 circuit fuse panel


At this point I have already run all the interior lights and charging ports lines with a dedicated ground and power from each fixture back to the dc fuse panel in battery compartment. I ran a good ground (white) from trailer frame to junction box and then a power (black) and ground (white) into battery compartment.

My question is how to hook up each component in the system between junction box power and ground that I fed into battery compartment and fuse panel and in what order/series.

OK.......T'were me, I'd fasten that battery down, and if possible, hard-mount the disconnect switch right to the positive post. Barring that, attempt to mount the switch inside the battery compartment so that the unswitched wires are as short as possible.

Running dedicated grounds is good, and bonding the chassis ground with the j-box is good, too. (A pic of this junction box would help things a bit.)
You used incorrect wire colors for what you're building. DC circuits are supposed to be red for 12+, and black for 12-. Your current color choices are correct for 120V AC systems.

This 7-pin harness you mentioned.....you mean a trailer connection plug?

I typically work from the power source out to the branch circuits, and you've started with the branch circuits first. Not a big deal, just different.

Have you already terminated each circuit to a fuse location on your fuse panel? If so, I'd think about how you did it, and if all your lights are on one fuse, maybe split that into two fused circuits. That way, if something goes bad, she won't lose ALL her lighting at once. Maybe share a lighting circuit with a USB/power port circuit. The idea is to keep from crippling the camper completely.

I assume you used LED lighting all around? If not, I think I'd change that, in order to conserve battery power as much as possible. She might want to use a power hog, like a little fan or something.

I am not an electrician and my terminology will be wrong at times for sure. Basically I know enough to be dangerous! I don’t want to damage any components by installing them incorrectly. If your instructions could be tailored to a novice without all the electrical terms, I would be grateful. Thanks in advance,, even if you just read my post and not respond. Hopefully someone else can learn from this thread too.

I think I can accommodate you, even if our philosophies may differ. I'm a retired industrial maintenance electrician, with quite a bit of experience with DC up to about 90 volts, and AC all the way to 480V, 3-phase, so I do have some idea of what I talk about.

Roger

 

[jrob4267]

Thanks for response. I wasn’t doubting your experience but didn’t want to have an overly long post.

Each circuit is on its own fused lug except the two dimmable lights which are together and are the red wires on fuse panel. There are 4 light/usb charging combo lights, one usb charging port, 2 lights that are switched on fixture, and one shunt.

The junction box has all the exterior trailer lights are wired in, I have not connected brakes yet due to waiting on a brake controller.

I have no idea what a power hog is and all lights are LEDs inside and out.

Planning on short wires to battery to shutoff switch after placing 100 ah fuse on battery terminal. Probably 6-8” from terminals.

 

[Rich796]

" DC circuits are supposed to be red for 12+, and black for 12-. Your current color choices are correct for 120V AC systems. "

This is not always true, especially with RV trailers. There have been a couple of different standards over the decades. And sometimes they are manufacturer dependent.

It is very common for RV 12v accessories to come with black and white leads.

7 pin trailer plugs also run either a black or red + battery power. And white as the - ground.

My own vintage-ish camper is wired with White + positive, and Red - Negative, from the factory.

 

[jrob4267]

Should I place shunt/smart volt meter between shutoff and battery or between shutoff and fuse panel?

 

[Rich796]

If you place the shunt after the disconnect. The trailer battery will be completely disconnected from anything you may need to work on. When switched off. And it will not have any parasitic losses from the meter, potentially.

A power hog, is a high amperage/wattage device. Uses alot of power.

Your DC/DC charge controller may not work for you unless its adjustable. The lipo battery will need different bulk and float voltages. Than a common lead acid battery. Just check to make sure its compatible.

Edit, you may not really need the power shunt/monitor. Your battery has a smart lable on it. Which means it should be Bluetooth accessible. And will probably provide all of the same information as the shunt. Unless you prefer a stand alone gage also.

 

[Tony Latham]

after placing 100 ah fuse

Yowsers.

Remember, a fuse protects the wires, and that's what it should be rated at. Unless you're running 2 AWG to the fuse box, it's doing nothing.

The cable from my battery to the fuse box is 12 AWG, and it's protected by a 15-amp fuse.

Tony

 

[GTS225-TNT]

Thanks for response. I wasn’t doubting your experience but didn’t want to have an overly long post.

Reasonable.....but being as I'm just another internet "voice", I thought I should qualify myself a bit. 'Course, ANYBODY can make the same claims I did.

Each circuit is on its own fused lug except the two dimmable lights which are together and are the red wires on fuse panel. There are 4 light/usb charging combo lights, one usb charging port, 2 lights that are switched on fixture, and one shunt.

Sounds good at this point.

The junction box has all the exterior trailer lights are wired in, I have not connected brakes yet due to waiting on a brake controller.

OK.....so I assume the only connection to the rest of the DC system will be the 12vdc "hot" tap from the towing vehicle?

I have no idea what a power hog is and all lights are LEDs inside and out.

Answered by others. But, to add a bit of detail.....something with a motor load, like a fan, or maybe a small electric heater. Both of those would pull quite a bit of power.

after placing 100 ah fuse on battery terminal.

Like Tony, I caught that notation, too. Care to clarify? Do you mean 100 amp fuse? (The "AH" notation represents a mathematical product of amps multiplied by time.) Either way, as Tony suggested, you'll only need a 15 or 20 amp fuse, maximum.

Roger

 

[jrob4267]

you may not really need the power shunt/monitor. Your battery has a smart lable on it. Which means it should be Bluetooth accessible. And will probably provide all of the same information as the shunt. Unless you prefer a stand alone gage also.

Not the case, there is no Bluetooth on this battery and therefore will need a shunt and monitor to see capacity and usage.

Answered by others. But, to add a bit of detail.....something with a motor load, like a fan, or maybe a small electric heater. Both of those would pull quite a bit of power.

No plans for “power hogs” except when plugged into shore power.

" DC circuits are supposed to be red for 12+, and black for 12-. Your current color choices are correct for 120V AC systems. "

This is not always true, especially with RV trailers. There have been a couple of different standards over the decades. And sometimes they are manufacturer dependent.

This is the wire I had on hand and trying to save $$$ use what I have. And if I keep consistent throughout I feel comfortable with it.

OK.....so I assume the only connection to the rest of the DC system will be the 12vdc "hot" tap from the towing vehicle?

Yes

Like Tony, I caught that notation, too. Care to clarify? Do you mean 100 amp fuse? (The "AH" notation represents a mathematical product of amps multiplied by time.) Either way, as Tony suggested, you'll only need a 15 or 20 amp fuse, maximum

Noted

Your DC/DC charge controller may not work for you unless its adjustable. The lipo battery will need different bulk and float voltages. Than a common lead acid battery. Just check to make sure its compatible.

Charger is compatible with LifePo batteries

If you place the shunt after the disconnect. The trailer battery will be completely disconnected from anything you may need to work on. When switched off. And it will not have any parasitic losses from the meter, potentially.

Will do

So actual connections I need to implement from what has been suggested so far are:

1. Hot tap and ground from junction box to charger, with separate ignition wire connecting to truck fuse block or alternator for charging when running vehicle

2. Charger to battery

3. Battery to shut off switch

4. Shut off switch to shunt/monitor

5. Shunt/monitor to fuse panel

Is this correct?

 

[GTS225-TNT]

Sounds like you've got it. I do implore that you take abundant precautions with wires passing through walls. It doesn't take long for that vinyl coating to get rubbed through and create a hazard.

Roger

 

[jrob4267]

Thanks

 

[jrob4267]

Like Tony, I caught that notation, too. Care to clarify? Do you mean 100 amp fuse? (The "AH" notation represents a mathematical product of amps multiplied by time.) Either way, as Tony suggested, you'll only need a 15 or 20 amp fuse, maximum

After doing some more research and your suggestions, I’m more confused. You are saying I only need a 15-20amp fuse instead of 100amp on battery terminal. Correct? AI is saying I need a 40 amp inline blade fuse before truck and trailer batteries and 100 amp on battery. And an additional 40 amp inline to protect wire from harness to trailer junction box. This seems excessive.

My dc/dc charger documentation suggests an inline fuse tap on vehicle for IGN wire for charging of trailer battery while driving.

I worked on wiring yesterday and had an issue with the battery terminal 100amp fuse. Every time I connected it, I lost all power to my fuse panel. I tried multiple times with same result. Don’t know if it’s a bad terminal or fuse or I installed it incorrectly. It is an Amazon purchase and they are not always reliable.

At this point, no fixtures are connected except the battery monitor and I removed 100amp fuse. I have no plans to connect any fixtures or connect trailer harness to vehicle until I get this sorted out. Also, battery cut off switch is off currently, except when I test for voltage at any location beyond battery compartment.

Could someone give me a definitive answer on what are the recommended number of fuses, locations and type of fuse connection/fuses that will work with the components I have listed for my project.

I understand everyone has different opinions, but I’m looking to protect my components but not go crazy with protecting a $2 part that in all real world scenarios has a .02 percent chance of blowing.

I do fiber optics for a living and this stuff makes my brain hurt!! After this, I’ll probably stick to tiny wires!! What we do for our kids! Thanks in advance.

 

[GTS225-TNT]

OK.....the fuse and sizing. A fuse is intended to protect the wiring from a power source to it's intended load. That fuse should be sized to the wire's ampacity, or slightly over, not to the power source"s supply ability. The idea is to pop the fuse, should that conductor somehow come into contact with a grounded material before it gets to the intended load. It's a fire prevention thing, more than anything else. And, let's face it, a camper is a rolling earthquake while it's being towed.

Here's why......if you run a 10-gauge wire, with a 25-amp capacity, and protect it with a "recommended" 100-amp fuse, if that wire should become abraded at a metallic, electrically-grounded wall, then it will ground out, and that 100-amp fuse will let 100 amps through your 25-amp wire. That will heat up the wire, and cause the vinyl coating to start to burn, at least until the copper conductor melts through and opens the circuit.

So, no matter what "artificial intelligence" might say, go by the old-school, REAL intelligence and documented experience practices. (I suggest you avoid A.I. entirely, but you do you.)

Now, as far as fuses from Amazon, you can do better. I've heard horror stories of Chinese Amazon fuses NOT blowing at all, let alone when they should have. Might it be internet lies? Maybe, but it only takes once for the disaster to happen.

Roger

 

[GTS225-TNT]

You are saying I only need a 15-20amp fuse instead of 100amp on battery terminal. Correct?

Correct. Do you actually think ALL the loads, combined, in the camper will need 100 amps? Even my old 5th-wheel, 30-foot camper only had a 30-amp primary fuse.

AI is saying I need a 40 amp inline blade fuse before truck and trailer batteries and 100 amp on battery. And an additional 40 amp inline to protect wire from harness to trailer junction box. This seems excessive.

And it is excessive. While I applaud the safety margin that "artificial intelligence" is trying to observe, in practice it's far too much. I highly doubt even commercial over-the-road trucks have that many fuses in the harness from the cab to the trailer plug. The 40-amp between the tow vehicle and the trailer isn't bad, as that will protect your vehicle wiring, should bad things happen in the harness, but that 100-amp fuse after the battery is FAR too much. As I said above, size the fuse between the battery and the camper to the supply wire's ampacity.

My dc/dc charger documentation suggests an inline fuse tap on vehicle for IGN wire for charging of trailer battery while driving.

Hmmmm. Interesting.....it sounds like your 12-to-12 charger is engineered to interrupt the circuit from your alternator to the camper's battery while the ignition is off. That's a good thing......it'll keep the camper from draining your tow vehicle's battery if left hooked up at the campsite.

I worked on wiring yesterday and had an issue with the battery terminal 100amp fuse. Every time I connected it, I lost all power to my fuse panel. I tried multiple times with same result. Don’t know if it’s a bad terminal or fuse or I installed it incorrectly. It is an Amazon purchase and they are not always reliable.

The way you typed that out suggests you had power at the panel before you plugged in the fuse. If not, then I'd ohm-check your fuse. Then isolate that supply wire, and ohm check it with the fuse in place. Could be the fuse, could be the fuse holder.

At this point, no fixtures are connected except the battery monitor and I removed 100amp fuse. I have no plans to connect any fixtures or connect trailer harness to vehicle until I get this sorted out. Also, battery cut off switch is off currently, except when I test for voltage at any location beyond battery compartment.

Might I suggest you connect up that battery charger to the towing harness, but not to the camper's battery? Then do a voltage test, with the vehicle off, to see if you have about 14 volts at the output side of the charger. (You shouldn't.) Then, start the vehicle, and perform another voltage test. You should then have whatever the tow vehicle's charging output normally is. (About that 14vdc.) If you get what's expected, then at least that part is correct.

Roger

 

[jrob4267]

I worked on wiring yesterday and had an issue with the battery terminal 100amp fuse. Every time I connected it, I lost all power to my fuse panel. I tried multiple times with same result. Don’t know if it’s a bad terminal or fuse or I installed it incorrectly. It is an Amazon purchase and they are not always reliable.

The way you typed that out suggests you had power at the panel before you plugged in the fuse. If not, then I'd ohm-check your fuse. Then isolate that supply wire, and ohm check it with the fuse in place. Could be the fuse, could be the fuse holder.

What I meant was that I had no power with everything hooked up, then I started removing components to determine what was causing no power beyond the battery. The battery terminal and fuse were the first things checked. Once I removed the battery fuse and holder, I had power to each fixture location. Then reinstalled the holder and got no power beyond it again.

Might I suggest you connect up that battery charger to the towing harness, but not to the camper's battery? Then do a voltage test,

Will do, but we have guests coming in on Monday, so, all work on trailer stops till they leave on Wednesday.

Hmmmm. Interesting.....it sounds like your 12-to-12 charger is engineered to interrupt the circuit from your alternator to the camper's battery while the ignition is off. That's a good thing......it'll keep the camper from draining your tow vehicle's battery if left hooked up at the campsite.

That is exactly what it is recommending. My alternator doesn’t have an ign lug, so I will be tapping the AC fuse as recommended in charger documentation.

So it seems you are recommending a 40 amp fuse between vehicle battery and tow harness, a inline fuse between vehicle battery and dc-dc charger, and a camper battery mounted 40 amp fuse sized to amperacity of output wire (43amps per wire documentation). And that’s it, correct?

With all that said, I just wanted to say thanks for your explanations and suggestions. It has been very helpful in straightening this all out. I will be back on once all recommended fixes have been installed and tested. Thanks again!

 

[GTS225-TNT]

What I meant was that I had no power with everything hooked up, then I started removing components to determine what was causing no power beyond the battery. The battery terminal and fuse were the first things checked. Once I removed the battery fuse and holder, I had power to each fixture location. Then reinstalled the holder and got no power beyond it again.

Sounds like a faulty fuse holder/fuse assembly to me.

Will do, but we have guests coming in on Monday, so, all work on trailer stops till they leave on Wednesday.

WHAT!? I thought I was the only one in the world that got interrupted during their project work.

That is exactly what it is recommending. My alternator doesn’t have an ign lug, so I will be tapping the AC fuse as recommended in charger documentation.

So it seems you are recommending a 40 amp fuse between vehicle battery and tow harness,

Yes.......that'll protect the tow vehicle's wiring and components. I highly doubt she'll ever see 40 amps for a charging rate to that camper battery, but the harness could get damaged.

a inline fuse between vehicle battery and dc-dc charger,

Yes.......that charger could fail and develop an internal short.
But.....hang on........this is sounding like a redundancy issue. That AC tap you're talking about......is that same wire supplying the DC-DC charger through the trailer harness?

and a camper battery mounted 40 amp fuse sized to amperacity of output wire (43amps per wire documentation). And that’s it, correct?

Basically correct. Now, 43 amps seems like still too much for a small camper's needs. I'd recommend a fuse sized for the camper load, or slightly above. It's more a process of adding the current requirements of everything in the camper, and installing a fuse slightly higher rated than the total load. Even then, it's highly unlikely she'll ever have EVERYTHING in the camper running at the same time.
It's still entirely OK to use "oversized" wire. It just adds un-needed expense.

With all that said, I just wanted to say thanks for your explanations and suggestions. It has been very helpful in straightening this all out. I will be back on once all recommended fixes have been installed and tested. Thanks again!

You're quite welcome.....Roger

 

[jrob4267]

a inline fuse between vehicle battery and dc-dc charger,

Yes.......that charger could fail and develop an internal short.
But.....hang on........this is sounding like a redundancy issue. That AC tap you're talking about......is that same wire supplying the DC-DC charger through the trailer harness?

No, separate. I will never use the back up lights on any trailer I have, so I’m repurposing that wire in the harness for this use, and so I don’t have to run another separate wire from vehicle to trailer junction

Thanks again
Jim