Questioning my simple electrical in homebuilt camper trailer

[-handyman]

Hello everyone. I am in the late stages of building an offroad camper trailer, so I can take my family on some adventures.




Now that I've got most of the hard work done, I'm looking at my design for the electrical system inside the trailer. It's getting down to crunch time as we want to go on vacation yet this year, so I don't have as much time as I would like to over-research everything. I've read several threads and feel like I'm close, but there are still several things I am not sure about.

I am wanting to pull power off the 7pin connector hot 12V to charge a LiTime 100 Ah battery in the rear of the trailer. I would put the battery in a tongue box, but I want the flexibility of being able to haul a dirtbike up front on a carrier. After researching a bunch, I am leaning towards using the Redarc BCDC1212S which is a 12 amp DC to DC battery charger with a 40 amp solar charge controller built in. I also thought about using either the Victron 12/12-9 or 12/12-18 DC to DC with a Victron MPPT 100/30 or 100/50 solar charge controller, but thought the 9 amp was too little and 18 amp too much for the 10ish gauge hot 12V wire from the truck. I currently only have a EcoFlow 160 W portable solar panel, but some day after the littles are grown, I may take off the rooftop tent and mount solar panels on the roof rack.

Anyway, I will only be powering a few interior and exterior LED lights, a Maxxair fan, and a small water pump for an external shower. I do not have need for an inverter, and the 12V Dometic fridge will be inside the truck, powered by an EcoFlow River 2 Pro. So I feel that 100 Ah LiFePO4 battery will be plenty and should last several days without charging.

So here is a sketch of my proposed electrical diagram. All of these items (battery, fuse block, DCDC charger, smart shunt) will be mounted in the rear galley area of the trailer.



I'm just a mechanical engineer, so I have enough electrical knowledge to be dangerous. I would very much appreciate if you experts could take a look at this and let me know what should be changed or done differently. Here are some of my questions:

1. I ran all my 7 pin trailer wiring in the frame (which was a pain!) back to a junction block at the rear of the trailer to wire my taillights. I ran a 10 gauge 12V hot wire (which gives 14.3V at the rear of the trailer with the truck running), but stupidly only ran a 12 gauge ground (-) wire from the 7 pin. Now, at the 7 pin juncture box mounted at the front of the trailer, I used a 12 gauge wire jumper on the ground wire to a bolt welded to the frame of the trailer to ground the trailer frame. I did not use the frame as a common ground for my tail and marker lights, but ran a 14 gauge ground (-) wire back to the rear junction block. Would it be smart to run a wire from the junction block ground at the rear of the trailer to the frame in order to make sure I do not over tax the 12 gauge ground wire? I know there are such things as ground loops, but I'm just worried about that 12 gauge ground wire being heavy enough to return power from the DC to DC charger and the taillights too.
2. I am planning on using 4 gauge tinned copper wire from the battery (+) to a 30 amp Blue Sea systems breaker. From there, more 4 AWG wire to a Blue Sea 12 circuit fuse block. I have seen several diagrams where people put in a 300 amp MIDI fuse, then a battery switch , than a 30 amp or more breaker, then the fuse panel. Is it necessary to have a big MIDI fuse, then a battery switch? Can I just go straight to the 30 amp breaker and also use that as a battery switch? It seemed like the breaker (https://www.amazon.com/dp/B0055MV7AA) doubles as a switch, but I can understand if that is not ok.
3. After the fuse block, I've got 4 gauge (-) wire going to a bus bar with 4 gauge (-) going back to the battery through a Victron Smart Shunt. Should this ground bus bar have a wire that goes to the frame of the trailer? (Remember, I only have a 12 gauge wire going back to the 7 pin connector to starter battery negative.)
4. The Redarc DCDC charger has the 10 gauge 7 pin (+) wire coming into it. This wire is fused (40 amps) at the engine bay main fuse box. Does it need another fuse before it goes into the DCDC charger?
5. Do I use 4 gauge wire from the DCDC charger (+) to the battery (+)?
6. Do I use 4 gauge wire form the DCDC charger (-) to the bus bar (-)?
7. For the 160 watt solar panel, are 10 gauge wires heavy enough to run to the Redarc charge controller? I plan on using Anderson connectors to connect the solar panel.
8. Do I need a fuse and/or switch on the (+) cable from the solar panel?

Thank you for taking time to read this. I want to do it right to keep my family safe and keep from burning down all my hard work.

 

[HRTKD]

Welcome to the forum! Your camper looks great!

I'm not enthusiastic about combining a DC-DC charger with an MPPT solar charge controller. That's mainly based on what I've seen of the Renogy combination unit. Before putting in a device to charge from the tow vehicle, figure out how large your loads will be and how much the PV can put back into the battery. You may not need a DC-DC charger. I didn't need one on my system, still don't. But I have 640 watts of PV.

The Victron MPPT 100/30 or 100/50 solar charge controllers are likely overkill if all you have is a single 160 watt panel. Use the Victron MPPT Calculator to find the right solar charge controller for your PV.

For a LiFePO4 battery system, the usual recommendation for fuse and switch is like this:
Battery(+) -> Class T Fuse -> Switch -> Common Bus Bar(+)

To determine the size of your cabling, use a wire gauge calculator. My favorite one is here. Note that the cable distance is round trip, not one way.

10 gauge wire from the PV to the solar charge controller should be plenty. Use the wire gauge calculator. I bet you could get by with 14 gauge.

 

[-handyman]

Welcome to the forum! Your camper looks great!

Thank you!

I'm curious why you don't like the combined units...were there some problems with the Renogy ones? I would hope Redarc would be higher quality than Renogy.

From calculating my loads, it looks like max with everything running at the same time, which would never happen, is 50 amps at the most.
Fan - 5 amps
Puck lights - 1 amp
Porch lights - 2 amps x 2
Strip Lights - 23.5 amps max probably less
USB - 3 amps x 2
H20 Pump - 6 amps max
Galley Lights - 4.5 amps max probably less

Since I don't have hard mounted solar panels and don't plan on staying in the same place very long, that is why I am needing to charge while driving. Ideally, I would have hard mount panels on the roof rack, but the rooftop tent takes up space and I cannot block the fan further forward on the rack.

It looks like I only need about a 15 amp charge controller for my 160W panel, but if I ever added 200 more watts, I'd need a 30 amp controller.

I've been researching the T-type fuses. With only a single 100Ah battery, could I use an MRBF Terminal fuse instead? They have an interrupting capacity of 10,000 Amps vs T-type at 20,000 amps. I am unclear exactly how many amps this 100Ah Lithium battery can output with a dead short.

Thanks again for all your help.

 

[HRTKD]

Dead short should be 100 amps, limited by the BMS. However, many BMS have the ability to allow a surge. This is usually considered a feature, not a bug. So the dead short amount could be higher than 100 amps.

The Renogy DC-DC/MPPT had some odd limitations. For example, if the solar charge controller was producing power, no matter how little, then that limited the DC-DC charger to more than half of the total amps that the device could produce. If the device was rated for a total of 50 amps and the solar charge controller was contributing 5 watts then the DC-DC charger was allowed no more than 25 amps. I don't know if Renogy ever fixed that limitation.

Renogy had quality issues within the last 3 to 4 years, many of them documented here on the forum. Tech Support wasn't known for being very helpful.

Check the idle draw of the components you're considering. A device with a high idle draw can drain your battery faster than you think.

Supposedly the ABYC (American Boat & Yacht Council) was going to change their requirements to allow the MRBF on LiFePO4 batteries. I haven't kept up with if they ever did. Here's the forum discussion about the change: https://diysolarforum.com/threads/abyc-fusing-changes-re-mrbf-class-t.55134/

The amps for your strip lights seems quite high, especially if it is LED strip lights. Are you trying to get a tan from your LED lights?

LiFePO4 batteries can charge pretty quick. Much faster than lead acid batteries. Given your solar panel, you may not need much DC-DC charging.

A 160 watt solar panel would produce, at most, 13.3 amps. That would be wildly optimistic. When adding PV, it's best for the add-on panel to match the existing panel as closely as possible when looking at watts and amps. Otherwise, you may end up producing less power than expected. If you know you're going to add PV later, consider going with a 20 amp solar charge controller now.

 

[-handyman]

I do know the Redarc unit has green power priority, so that is probably what the Renogy unit is also doing. Since I won't be charging with solar while driving, that part doesn't really matter so much to me, but it definitely could be an issue with hard-mounted solar panels.

I thought idle draw was mostly from inverters, since I'm not planning on using one, I hope there would only be idle draw from the Victron Smart Shunt. Do DC to DC chargers and Solar Charge Controllers have some idle draw as well?

Yeah, the strip lights are LED...I thought that seemed way high as well. I'm planning on cutting down several strips to shorter lengths, but each 16.4ft strip draws 40 watts or 3.5ish amps, while the amber led strip draws 72 watts or 6 amps. So my calculation came from 5 full length strips of white and one of amber which is way more than I will actually use.

So would you suggest a Victron MPPT 75/15 if no additional PV? And a MPPT 100/20 if possible additional PV?

 

[HRTKD]

Do DC to DC chargers and Solar Charge Controllers have some idle draw as well?

Yes, even the solar charge controllers have an idle draw. Victron documents this in their datasheets for each product.

So would you suggest a Victron MPPT 75/15 if no additional PV? And a MPPT 100/20 if possible additional PV?

Yes.

With just one battery you could get away without using a shunt if you can access your battery using Bluetooth. The Victron smart solar charge controller will use the shunt voltage (which should be more accurate since it would be in closer proximity to the battery) to determine the charge voltage. So there are some benefits to using the shunt, even with just one battery.

 

[Scott SD]

I prefer Victron components. My thought is to add (2) 75/15 mppts, they are relatively cheap for what they do, to use with 2 portable arrays. Newpowa makes a compact 100w panel. I made a frame and used 3 for a ground array into a 75/15. It is a little cumbersome, 2 would be better. I like multiple mppts, it helps if you leave the trailer and have the arrays pointed in different directions. For the DC/DC, because you will have low solar production, use the 12/12-18 of your wire will support it. Even the 12/12-9 would give you something while traveling, for $65, why not.

 

[0truck0]

is a long post I didnt read all of it...

First off, your 100 amp/hr batt probably plenty for your limited time camping. Dont do any charging and you will prob be fine. Sounds like you have a week or two vacation for the year and prob just spending a few days camping anyway? These big systems that can recharge/maintain off solar and DC-DC charging are used by people out there for weeks and months on end. If all you do is a few days then the batt will last easily.

Your fan is prob as high as 3 amps and will be the biggest draw of what you listed. 3 amps on 100 amp hr batt will run 33 hours straight, 8 hrs a night for 3 days is 24x3=72 amp hours, and the rest you listed will run off the remaining amp hrs easily for 3 days. The clip fans are even less amp hours so do math accordingly. Add just a little solar and you can run indefinitely.

DC-DC is a great thing to have. 20 amps is plenty. I suggest to get one device for dc-dc and another device for solar charge controller, not an all-in-one device. Things will break, if one breaks you have a backup.

 

[Bluedog225]

My small needs trailer with tv, lights, fan, phone charging are all served by 100 ah lfp battery with a little 100/20 or so Victron mppt. I even put in a little Victron 12/1200 inverter and run most things off 120 volts now. It’s great.

Never have run out of juice. You have a few more things, like the pump. But I’d keep it simple and see how long you can stay out.

A little Bluetooth SOK would be nice so you can monitor. Can always add more solar deployable panels later if your mppt can handle it.

 

[HarryN]

Here is a slightly different layout of an electrical diagram that might make it easier to look at.

Just delete the items that are not needed for your build.

Run your chargers and loads in / out via the fuse block for anything up to 30 amps.

If you want to run power from the vehicle to the trailer, just use 120 vac - much safer and easier.

I would be tempted to put some solar panels on the side of the trailer - at least for transport. You can put them out in the sunshine on the ground when you get there to power stuff. A pair of 150 ish watt will cover most of your loads in the trailer.

Something simple like a bogart pwm solar charge controller will work for you.