48 Volt System Toy Hauler Build

[HRTKD]

Since I was remiss in documenting my 12 volt RV build, I'll begin documenting the new 48 volt build from the day that I received the cells.

The RV will be a 2025 Northwoods Desert Fox 27FS. This is a four season bumper pull toy hauler with a GVWR of 12,800 Lbs with a theoretical cargo capacity of 3,858 Lbs. My current toy hauler has a GVWR of 11,000 Lbs so this isn't a huge step up. The Desert Fox is on order, with an expected delivery of late August 2024. I chose this trailer because of Northwood's quality. The chassis is certified for off-road. No crappy Lippert frame on this beast. I requested a couple of deletions from the factory to make sure there is plenty of open space on the roof. It should come with 400 watts of PV on the roof installed at the front. I'll leave that in place for now and use the power from it to charge the OEM 12 volt battery on the tongue.

Designing a system for a trailer that I don't have is a little stressful. I found a 2024 model that they allowed me to crawl on/in/under and that gave me enough of a warm fuzzy on dimensions and obstructions that I think I'll be OK. (Famous last words

)

Why 48 volts? If you've read any of my past posts where the question of system voltage for an RV comes up you'll see that I almost always recommend sticking with 12 volts. For an RV, a 12 volt system is less complex, easier to understand and less expensive.

The main reason for going 48 volts is that I'm planning to put at least 1720 watts of PV on the roof. 2s2p of 430watt panels. A 48 volt system (instead of 12 volt) allows me to use a less expensive solar charge controller or depending how it's wired, just one solar charge controller.

The secondary reason is that I can put 16 cells in series (16s) and have explicit monitoring of all of them (as opposed to 2s8p) and have inverter communication with the BMS. No daisy chaining of communication or power cables.

Saving money by being able to use smaller cabling is not a factor in my decision to go 48 volts. Any savings from smaller cabling is easily eaten up by having to install step up and step down devices. I'm planning to wire the system as if it was a 12 volt system, mainly because I have plenty of that size cable leftover from my prior build.

 

[HRTKD]

This post details the components and supplies that were purchased.

I'll update this post as things change.

The Victron part numbers came from this Victron page. It's a European Price List but if you ignore the prices, it's a great list.

Description	Part Number	Qty	Vendor Price	Total
Victron SmartSolar MPPT 150/35 (2s2p PV)	SCC115035210	1​	162.75​	162.75​
MPPT WireBox for MPPT 150/35	SCC950200000?	1​	26.25​	26.25​
Victron Lynx Shunt VE.Can	LYN040102100	1​	313.5​	313.5​
Victron Lynx Distributor M8	LYN060102000	1​	177.75​	177.75​
Victron GX Touch 50 (not flush mount)	BPP900455050	1​	194.25​	194.25​
Victron Cerbo GX MK2	BPP900450110 or BPP900451100	1​	243​	243​
Victron Orion Tr 48/12-30	ORI481240110	1​	177.75​	177.75​
Victron Orion XS 12/12-50	ORI121217040	1​	289.5​	289.5​
Victron Quattro 48/3000/35-50/50 120V	QUA483021100	1​	1226.25​	1226.25​
Victron Battery Switch 275a	VBS127010010	1​	30.75​	30.75​
Victron Smart Battery Protect 48v - 100 amp	BPR110048000	1​	121.5​	121.5​
Victron MK3-USB	ASS030140000	1​		0​
VE.Direct cable 1.8m Right Angle (MPPT & Orion XS)	ASS030531218	2​	12​	24​
VE.Bus cable 1.8m (Quattro to Cerbo GX)	ASS030064950?	1​	9.75​	9.75​
Victron MC4 Y Connectors	SCA520500000	1​	22.5​	22.5​
Temperature Sensor (Lynx Shunt and Cerbo GX)	ASS000001000	2​	18​	36​
				0​
RuuviTag 4-in-1 Bluetooth Sensor	RuuviTag	3​	28.5​	85.5​
RuuviTag Silicone Case	RuuviTag Silicone Case	3​	3​	9​
LiFePO4 cells 3.2v 280 Ah	LF280K	18​	$ 76.00	1368​
JK Inverter BMS 150 amp, 2a bal	JK-PB2A16S15P	1​	$ 84.00	84​
JK 4.3" LCD Display Screen		1​	$ 22.00	22​
Luyuan 16s Battery Box		1​	$ 220.00	220​
Mission Solar MSE430SX9Z		4​
Low Profile Aluminum Strut
Lynx Shunt Fuse CNN 175amp	Littlefuse 0CNN175E.H	3​	$ 26.05	78.15​
Class T Fuse 175amp	Littelfuse JLLN175.XXP	3​	$ 58.06	174.18​
Lynx Distributor Fuses Mega 80 amp	Littelfuse 0998080.UX-2M8	5​	$ 12.00	60​
Lynx Distributor Fuses Mega 60 amp	Littelfuse 0998060.UX-2M8	8​	$ 12.00	96​
UltraHead-Dual Set of Heat Panels 52VDC, 0.8 amp, 8"x22"	AM-BAT822-52V-Set	2​	$ 149.60	299.2​
Mopeka Check Sensor	Mopeka Pro	2​	$ 46.00	92​
600VDC Din Rail Mount Two Pole Breaker - 30amp	MNEPV30-600-2PP	1​	$ 55.76	55.76​
150VDC Din Rail Mount Single Pole Breaker - 40 amp	MNEPV40-150-1PNP	3​	$ 23.01	69.03​
150VDC Din Rail Mount Single Pole Breaker - 5 amp	MNEPV5-150-1PNP	1​	$ 23.01	23.01​
Distribution Box DIN Rail ABS Clear Cover	MTHT-8WAY	1​	$ 17.50	17.5​
Red: Temco 12 AWG, 100'				0​
Black: Temco 12 AWG, 100'				0​
TEMCo 30 amp 6 pairs (m/f)				0​
6 AWG black/red 25' each				0​
120x120x25mm low speed fan (Cooler Guys)	840556091929	2​
3Pin Splitter Wiring Harness 42/50 (Cooler Guys)	840556104537	2​
120Mm Steel Mesh Filter Grill, Black (Cooker Guys)	840556087601	2​
Kapton Tape				0​
				5808.83​

 

[HRTKD]

The shipment from Shenzhen Luyuan Technology. From order time to delivery time it was 40 days. That's pretty good. Everything arrived in great shape. Amy and her crew do a fantastic job of packaging to ensure that there is no in-transit damage.



The terminals look good. There might be one outlier or it could be how the cell is sitting on the tailgate. Could just be the photo.

	Before Top Charge
Cell	Internal Resistance	Voltage	Difference From Avg
1​	0.24​	3.2949​	-0.0001​
2​	0.22​	3.2951​	0.0001​
3​	0.24​	3.2950​	0.0000​
4​	0.22​	3.2948​	-0.0002​
5​	0.21​	3.2948​	-0.0002​
6​	0.20​	3.2950​	0.0000​
7​	0.21​	3.2950​	0.0000​
8​	0.20​	3.2953​	0.0003​
9​	0.21​	3.2950​	0.0000​
10​	0.21​	3.2951​	0.0001​
11​	0.20​	3.2950​	0.0000​
12​	0.20​	3.2951​	0.0001​
13​	0.20​	3.2949​	-0.0001​
14​	0.21​	3.2950​	0.0000​
15​	0.21​	3.2947​	-0.0003​
16​	0.21​	3.2950​	0.0000​
17​	0.19​	3.2949​	-0.0001​
18​	0.19​	3.2948​	-0.0002​
Avg	0.21​	3.2950​
Min	0.19​	3.2947​
Max	0.24​	3.2953​

Busbars connected to nine cells, getting ready for top balancing. Don't use just one screw for each terminal. I did it that way, then checked the resistance along the entire line of busbars. Then added a second screw to each terminal and rechecked the resistance. I don't have the numbers but they were different enough to justify the second screw.


Power supply set to 3.4 volts without being connected to the cells.


Shut off the power, connected to the cells, then turned the power back on and let it rip. I'm not using the cables provided with the power supply. I made my own cables that do NOT have an alligator clip. 14 awg for the cable may be a bit light. It's what I had on hand. I swear I made a set of these cables once already, but darn if I can find them. The Banana plugs probably can't handle many amps either.


I then checked the voltage at every cell, touching the probes to the cell terminal surface not the busbars.


Just for giggles I shot a couple pictures with my Flir One Edge Pro.


Different picture, zoomed in on the bottom right of the above picture. This is the terminal where one of the power supply leads connects.

I haven't had my Flir camera very long, so I'm learning how to use and figuring out what it's telling me.

 

[HRTKD]

The warming system for the cells held up the battery build for way too long. The warming pads I had custom made by Ultra Heat (aka Annod Industries) were sized just right to fit on both sides of an 8-stack set of cells. However, the battery box the cells are going into was just a tad bit too narrow to fit the cells and warming pads. I checked to see if a single warming pad would fit on the bottom of the cells, but the pad was wider than the cells and would have also been too wide for the battery box. My final solution was to strip off the foam backing material (insulation) from the warming pads. That allowed the cells with warming pads on both sides to fit in the battery box.

Warming pad with the foam backing material during a test fit. It fits with just one pad, but not with two.


Assembled cell stack with the adhesive warming pad applied. The foam backing material has been removed.


1.5" wide electrician's tape was used to cover up the edges of the pads as well as the electrical part of the pad. Holes were drilled in the center divider of the battery box, as well as the cell compression plate, to allow the wires to come through. The yellow plastic divider runs along the entire length and height of the cell stack, providing further insulation keeping the warming pad from making contact with the sides of the battery box.



All cell fasteners were tightened to 6 nm. Before using the torque wrench, all fasteners were installed and hand tightened. By doing this, it may have reduced the strain on the terminal. The busbars that cover both holes in the terminal are very helpful in this I think.


How the balance leads came from the vendor.


I stripped off a bit more of the insulation.


Slipped on heat shrink tubing.


Doubled over the exposed wire.


Crimped on the ring terminals that were provided.


Shrunk the tubing and added labels to keep them straight.


Checked to make sure the balance leads were making contact.


Installed the cell compression plate, attached the BMS and installed a Class T fuse holder. Battery cables are 2/0 welding cable from TEMCo Industrial. The battery cable run is very short for this install, maybe 5' from cell terminal to the Lynx Shunt. If it was any longer I would have run a pair of the 2/0 cables. As it sits now, my calculated (theoretical) voltage drop along that length is under 0.5% at 120 amps.






Looking at the battery from this perspective, I wondered if connecting the battery to the BMS using the outside terminals, instead of the inside terminals, would have made it easier to wire up. The fuse holder would have gone on the right side instead of the left. The connection from the fuse holder to the front plate bus bar was a very tight turn. It would have been a lot easier if the fuse holder was on the right.


The finished front panel. I put two "Powerwerx Chassis Mount Kit for Two Anderson Powerpole Connectors" on the front panel instead of the circuit breaker. The hole had to be widened slightly for them to fit - that was a lot of work with a hand file. It's not perfect, but it works. Power for the warming pads will connect through the Powerpole panel on the left.

The temperature sensor leads (upper left corner of the picture) come out an existing hole between the front panel and the battery box. I could have run them through the other Powerpole panel, but I reserved that for future upgrades.

 

[HRTKD]

A few months back I was at my favorite aluminum scrapyard, which sells mostly brand new aluminum. I cruise through the cutoffs sections to find the hidden gems that are dirt cheap. I came across what I thought was ~40' of low profile aluminum strut. Turns out it's low profile aluminum but not standard strut. The strut pattern that the fastener goes into isn't anything that I could find a fastener for. Since it was what I had, I bought some square washers that fit in the channel. The square washers in the picture below are 1" square, .066" thick, with a 1/4" hole. As you can see from the picture, I have two washers in the channel. I have another set of washers on order that are twice as thick.



The plan is to cut the strut into short sections of about 12" to 18" and that will be the base of the mounting system. The RV has a fairly rounded roof (cathedral ceiling on the inside) so using one long piece of strut across the roof (perpendicular to the trailer) won't work. The solar panels will be oriented parallel to the trailer. I could put the strut on in the same orientation as the solar panels but that would seem to limit what size panels I can use should the originals need to be replaced. This isn't set in stone. I could go either way.

 

[HRTKD]

 

[HRTKD]

The Victron Quattro is used instead of the Multiplus II because the Quattro is over 7" shorter. 14.3" versus 22.8". The two compartments that the inverter will go in probably aren't tall enough for the Multiplus II. The extra room for air movement is good too.

The Multiplus (not the Multiplus II) is similar in size to the Quattro, but does not come in a 48 volt model.

Since the trailer needs 12 volt power, the Orion-Tr 48/12 is used to step down from 48 volts to 12 volts. The 30 amp rating is good enough to run everything in the trailer, but not enough to start the generator. I'll retain one 12 volt battery on the tongue for starting the generator. It may also be used to run the tongue jack and the trailer breakaway system. From my experience with my current trailer, not all loads go through the trailer's main distribution panel. The Orion-Tr will power anything going trough the trailer's main distribution panel.

I would like to have the ability to turn off the Orion-Tr if the LiFePO4 house battery gets too low. The default (non-adjustable) low voltage cutoff is 28 volts, which is way too low. I'm looking into using the Orion's remote on/off switch and a relay on the Cerbo GX or one of the relays on the Lynx Shunt or Quattro to do that. If that doesn't pan out then I'll put the Smart Battery Protect between the Lynx Distributor and the Orion Tr.

Having a Smart version of the Orion Tr would have eliminated the need for interfacing it with a relay or the Smart Battery Protect.

The Orion XS is intended to keep the tongue battery charged when the generator is running. I'll throttle it back to 5 to 10 amps. There should be enough solar to keep the tongue battery charged otherwise.

I don't have any power coming from the tow vehicle to the LiFePO4 house battery at this time, mainly because there is no Victron component that supports that. The Orion-Tr 12/48-8 is not intended for battery charging.

I may have to add a Victron "Fuse holder 6-way for MEGA fuse" to handle 12 volt distribution that occurs near the battery/inverter. However, the MEGA fuses typically start at 40 amps and for the 12 volt loads I'm thinking of that's overkill. A non-Victron fuse holder may be needed.

 

[HRTKD]

Breakers and Fuses. Breakers are from Midnite Solar, purchased through InverterSupply.com. All fuses were sourced through Mouser.com because they have the absolute best selection, inventory and very good prices. Shipping wasn't free but it was fast, however that wasn't a consideration. Mouser is my preferred vendor for fuses because they have more specifications (datasheets) available than anyone else.

There are lots of spares here. I don't want to be in the middle of nowhere with a system down because I blew a fuse.

All fuses are rated to work in a 48 volt system.
CNN (E) 175 amp fuse will go in the Lynx Shunt. Max of 80 volts
MEGA fuses will go in the Lynx Distributor. The Lynx Distributor is nice until you realize that MEGA fuses for 48 volt systems don't exist that are rated below 60 amp. Max of 70 volts.
The Class T will go in the battery box. Max of 300 volts.
The 30 amp dual pole breaker will be my solar disconnect. Max of 600 volts.
The 40 amp breakers are noted on the diagram in post #6. I order 150 volt breakers but that model has been deprecated. I got an actual phone call from InverterSupply telling me that and the breakers they were sending were rated to 300 volts. No change in price.
The 5 amp breaker will be used for the warming pads and do double duty as a switch. Rated to 150 volts.

 

[HarryN]

Looks like a great start on your project. Thanks for all of the details.

 

[tsawind]

Very Nice! Have you considered running the 48/12-30 directly into the 12/12-50, then back to the distro panel from the 12v lead acid battery? Might actually work out cleaner, and you have some more upgrade paths that way?

 

[HRTKD]

Very Nice! Have you considered running the 48/12-30 directly into the 12/12-50, then back to the distro panel from the 12v lead acid battery? Might actually work out cleaner, and you have some more upgrade paths that way?

That would require more wiring, but I see what you meant.

 

[HRTKD]

A bit off topic but since I had 90% of the stuff pulled out of my old camper and sitting in my garage I decided to weigh everything. And I do mean everything, I even weighed the mop, broom and first aid kit. It came to 418 lbs! I'm guessing that the last 10% will weigh 70 lbs. That's a lot of stuff. I'm going to try to cut that down as much as I can.

 

[HRTKD]

My new trailer might get built next week. In the meantime, I wanted to see how the components could be laid out on a board that could then be mounted in the trailer. The board I'll be using was recovered from the pallet that my solar panels came on. I would have done the layout on the wood board itself but it's still wet from painting and I don't have a lot of open space anyhow.

I was hoping the components would use less space. Maybe I left too much space for the wires? My experience has been that no layout plan survives contact with the wires. A wire will bend only so much to make a turn.

 

[dcg9381]

Questions:

• You're running 18 cells of 3.2v 280 Ah (LF280K) = 57.6V. Their "preconfigured" "48V" battery is 16 cell. Why +2 cells?
• You have an existing 120V power distribution panel in that RV, these come with 12V converters. Why not use that? (I get it if you want to use the automated gen-start feature)
• Manual cell balance, correct? No BMS.

 

[HRTKD]

Questions:

• You're running 18 cells of 3.2v 280 Ah (LF280K) = 57.6V. Their "preconfigured" "48V" battery is 16 cell. Why +2 cells?
• You have an existing 120V power distribution panel in that RV, these come with 12V converters. Why not use that? (I get it if you want to use the automated gen-start feature)
• Manual cell balance, correct? No BMS.

No, I'll be running 16 cells. The count of 18 cells includes two spare cells, just in case. I top balanced all 18 cells and picked the best 16 cells based on IR (internal resistance).

Leaving the existing converter in place creates a charging loop. Plus, RV converters - even with a LiFePO4 charge profile - are about as dumb as a box of rocks. They just don't work that well. The programmable nature of the inverter/charger that I'll be using makes for a much better system.

The BMS provides up to 2 amps of active balancing. Never run without a BMS.

 

[dcg9381]

The BMS provides up to 2 amps of active balancing. Never run without a BMS.

Thanks for that info. I'm missing it in the diagram. Running the manufacturers BMS in "your box"?
Appreciate the info, looking at doing something similar based on 48V.

 

[HRTKD]

Thanks for that info. I'm missing it in the diagram. Running the manufacturers BMS in "your box"?
Appreciate the info, looking at doing something similar based on 48V.

Yes, the BMS will be in the battery box with the cells.

 

[HarryN]

I will usually make a prototype layout on a scrap plywood board and play with that for a while.

For me it is just easier to see where it will go "in person" vs a computer screen.

I always start with this simple diagram and work from there.

If you do it this way, then your wiring can be done almost entirely with good quality 6 awg if I am reading it correctly, maybe 2 awg in a few spots.

6 awg can handle a 70 amp fuse.

____________

For fun, try putting the lynx at the top and the other chargers along the bottom = terminals facing the lynx like you are doing.

Just feed all of the wires directly from the chargers to the lynx with nothing in between. It might take 2 of them.

Feed the 12 volt power in and out through a 12 position fuse block or safety hub directly.

SafetyHub 150 Fuse Block - Blue Sea Systems

Ignition-protected fuse blocks capable of consolidating and protecting multiple 1A to 200A circuits.

www.bluesea.com

ST Blade Fuse Block - 12 Circuits with Negative Bus and Cover - Blue Sea Systems

Compact ATO® / ATC® fuse block consolidates branch circuits and eliminates the tangle of in-line fuses for electronics and other appliances.

www.bluesea.com

 

[MarioP]

Please keep this updated as you progress.
I'm in the design stages of a 48v system and this build looks similar to what I'll be doing, except my RV is a 50amp shore power.

 

[HRTKD]

I took ownership of my new camper about 10 days ago and headed straight for an out-of-state camping trip. A lot of rain with cloud cover for a few days coupled with a shady camp site and factory lead batteries led to a less that ideal first trip. It did give me a better appreciation of what I had in my old trailer. The upgrades to the new trailer will get installed in a couple of days.

 

[HRTKD]

The under bed storage area is where the inverter, battery and component board will be installed. The walls of the storage area aren't strong enough to mount the Quattro to, so it will be mounted/attached to the floor. To provide enough room for the cables to come out the bottom of the inverter I added some legs.

 

[HRTKD]

One of my concerns with this project is limiting how much weight is added to the RV. Just the battery and inverter alone are close to 300 lbs.

By using the low profile aluminum strut instead of standard height steel strut I'm going to save around 133lbs for four PV panels Unistrut is 1.85 lbs/ft and the aluminum strut is about .456 lbs/ft. 96' of strut are ready to be put on the roof.

 

[RV247soon]

Great build out. Your project is giving me the final details for my RV update.

I'm taking a 1998 Class-A with FLA and migrating to LFP and replacing the solar panels. I need more capacity for a quieter boondocking experience.

 

[HRTKD]

Today I installed the inverter - for the second time. The first time it wouldn't turn on. The capacitors seemed to get charged, but nothing happened. No lights, no action. That was two days before I left for hunting camp. I ended up rewiring at hunting camp so I could run the generator to get 120v AC power. The problem turned out to be a ribbon cable connector that had come loose. The connector was hidden under another connector, so I didn't see it to try and push it in.

Everything is working, but I'm a bit leery of the inverter. It didn't want to turn on with just the battery connected. When I turned on the generator, the inverter came alive and seemed to work normally. I ran a 1500 watt space heater for about 20 minutes using the inverter (no generator). The PV kicked in about 750 watts and the remainder came from the battery. I'm going to stress test the inverter by running two 1500 watt space heaters, one on high, the other on low. I'll use my Flir One Edge Pro infrared camera to check for hot spots.

They're hidden a bit but there is a second MPPT150/35 to the left of the one you can see and the Orion XS is hiding below the Cerbo GX on the right. There are a LOT of wires running behind the board. These go to the two PV roof glands, tongue battery, trailer main distribution panel and the chassis ground.


In retrospect, I would have put the circuit breaker box at the top of the board, not the bottom. Putting it at the bottom worked well for wire runs. But it's hard to get to the breakers. I had to remove the transparent cover so that I have access to the breakers. I also would not have put so much stuff in such a small compartment. It's nice to have it all together to reduce the cable runs, but it was very difficult to install the inverter which used 8/2 cable.

Still to do:

• Add vent fans in the compartment. I have 48v fans on order from CoolerGuys.com. The fans will be triggered off of the inverter. There are three relays in the inverter that are programmable. I'll set two of the relays to come on 30 seconds after the internal fan comes on and 30 seconds after the internal fans turns off. If the fans are too loud (the compartment is right under the bed) then I'll see about running 12 volt power through the relays instead of 48 volt power, or perhaps run the fans in series off of 48 volt. That will reduce the RPM and the noise.
• Two more PV panels to install on the roof. This will take me from 2s / 2s to 3s / 3s. It is not 2s2p since each string has its own solar charge controller.
• Replace the heavy OEM 12 volt lead acid deep cycle battery on the tongue with a NOCO NLP20 LiFePO4 battery. The NLP20 is a very small battery, only 7 Ah and 3.73 lbs, but it has 600 amps of starting current for the generator. The Victron Orion XS DC-DC charger will keep the NLP20 charged. The Orion XS has been keeping the OEM tongue battery nicely charged for a couple of months.
• Find some place to mount the Victron Touch 50 screen. In one of the pictures above, it's sitting on top of the battery.
• Tidy up. Add strain relief were needed. Add labels for documentation. You can't tell from the picture but all the circuit breakers are already labeled as well as many of the wires.
• Add an outlet for the inverter's AC-out-2 circuit. This will allow me to use excess PV power to run a space heater in the winter or an air conditioner in the summer without running down the battery state of charge much.

 

[HRTKD]

The battery is ready for winter. The warming system is turned on and today I put 2" rigid foam around the sides and top. The bottom is not insulated, other than what is under the camper from the factory.