DIY LiFePO4 battery install under ARB drawer wing (1 Viewer)

sdnative

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I have been considering a second battery for aux loads since I bought the truck about a year ago. I went through a few iterations before ending up where I am now.

Goals were to power aux loads like the fridge, lighting, radio gear, charge devices, etc for several days while camping, jump start the truck if needed (I also carry a lithium jump pack), light weight, low maintenance and safe.

First I was trying to shoehorn a group 24 or 27 AGM battery in the engine bay and using a Redarc BCDC to charge. I wasn't able to find a way to fit anything larger than a group 35 cleanly without more effort than I was interested in. Another downside of the lead acid battery is the low capacity even with the largest group 27.

Second I considered installing an AGM battery in the cargo area, but quickly abandoned that as I did not want a lead acid battery in the passenger area due to potential gas release. And again, low capacity.

Third I looked at off the shelf LiFePO4 batteries like the Battle Born Lion Energy, ReLion, etc. I was attracted to the high energy density, deep discharge capability, low weight, high cycle count and safe operation (compared to other lithium chemistries). Problem with these "drop-in replacement" lithium batteries was the size. They were a bit too large for the space I wanted to use. I wanted to install in under the driver side ARB drawer wing. I have seen a few installs in this area, but it was a tight fit scratching up the plastic panels and blocking the AC vent.

I also considered the lithium power stations like Goal Zero, but felt the price point was too high.

At this point I was committed to LiFePO4 so I started looking at building a battery from raw cells. I looked at various manufacturers, shapes and sizes. I found some 105Ah prismatic cells, took some measurements and determined I could stack 8 of them and still barely fit the space.

I ended up with 8x of the EVE 105Ah cells in a 2P4S configuration. I added a Overkill Solar BMS (rated 120A), BlueSea manual disconnect switch, BlueSea class T fuse (150A) and Victron SmartShunt to complete the "battery". Charging will be done with a Victron Orion Smart DC-DC charger and Victron MPPT Smart solar charge controller. The Victron "smart" devices are bluetooth enabled and can all be configured and monitored by app.


This battery has 210Ah of capacity (>200Ah usable). It is capable of 3C discharge rate or >600A in the current configuration. The BMS is rated for 120A but being a Chinese made and FET based I wouldn't feel comfortable pushing much more than half that. If I needed to use the battery to jump start the truck I would remove the cover and attach jumper cables directly to the bus bar.


Here are some pics:

Initial assembly with all cells in parallel using 3/4 birch ply in a compression fixture and performing the initial top balance to 3.65V.
The prismatic cells need to be compressed to maximize longevity. I am using all-thread top and bottom.
IMAG4436.jpg


IMAG4438.jpg


IMAG4437.jpg
 
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sdnative

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Here are some pictures of the completed "battery". I cut up and drilled some 3/4" x 1/8" copper bar for the busing. I ended up using 6 pieces of all-thread to make the compression more evenly distributed.

Note the pairs of cells wired in parallel and then the cell-pairs wired in series. This makes a 12.8V nominal battery.

I also added probe holes in the cover to be able to measure cell voltage without taking the cover off.

IMAG4807.jpg


IMAG4808.jpg
 
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sdnative

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Here are some pictures of the battery installed. The wiring and DC are still in progress as I find the time.

It barely clears the plastic panel on the ends, but it does clear. There is just over 1.5" between the side and the AC vent. There is about 1" of clearance between the top and the drawer wing cover.

The red switch will go on the outside of the ARB end cover with the wires routed under.

I used plumbing strap to secure the battery to the side of the drawer. I drilled two holes to attach the front, and the rear uses the existing end cover bolts.

IMAG4811.jpg


IMAG4810.jpg


IMAG4814.jpg


IMAG4815.jpg


IMAG4819.jpg
 
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e9999

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Not familiar with prismatic cells, but the final capacity seems very high for the size. Nice.
 

sdnative

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These are the cells I used. There is a 280Ah version available but it is too large for the space. I also read that the larger cells are not suitable for use in off road vehicles due to the higher weight to support structure ratio.
 

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spressomon

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I used Prismatic cells for the 6500w/400Ah LFP system for our little Escape 15A. So far, so good. But at only 1-1/2 years old its still young ;).

I learned the hard way and relied upon threaded rods at each corner of top and bottom along with top to floor compression straps. But recently discovered two of the busbars that connect two cells were stress cracked. Today, I installed a good quality ratchet strap around the perimeter of the pack to contain flex. Always something to learn 🙄
 

GLTHFJ60

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Nice setup. Similar to the setup I put in my truck, and @J Mack put in his. LiFePO4 is the way to go!!

How do you like that smart shunt? I put a cheap one in with the display in my dash. I find it convenient to be able to check in on the lithium pack (that powers my whole truck) without noodling around in the back.
 

sdnative

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I used Prismatic cells for the 6500w/400Ah LFP system for our little Escape 15A. So far, so good. But at only 1-1/2 years old its still young ;).

I learned the hard way and relied upon threaded rods at each corner of top and bottom along with top to floor compression straps. But recently discovered two of the busbars that connect two cells were stress cracked. Today, I installed a good quality ratchet strap around the perimeter of the pack to contain flex. Always something to learn 🙄

What caused the stress cracks? I am using 6 pieces of threaded rod to achieve the compression. I am also using 1/16" thick rubber sheet between cells to provide additional support. When installed the pipe strap will also help keep things in place. It is very solid.

I can't imagine the busbar cracking, I would expect the cell terminals to be damaged first. If this is a potential failure method I would like to know however.
 

sdnative

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Nice setup. Similar to the setup I put in my truck, and @J Mack put in his. LiFePO4 is the way to go!!

How do you like that smart shunt? I put a cheap one in with the display in my dash. I find it convenient to be able to check in on the lithium pack (that powers my whole truck) without noodling around in the back.

I haven't actually used the battery with the shunt or charger yet so not sure yet. Online reviews seems to be good. I was planning on getting the BMV-712, but realized I really didn't need the display so this seemed like a good alternative. Will report back when I get some time on it.
 

spressomon

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What caused the stress cracks? I am using 6 pieces of threaded rod to achieve the compression. I am also using 1/16" thick rubber sheet between cells to provide additional support. When installed the pipe strap will also help keep things in place. It is very solid.

I can't imagine the busbar cracking, I would expect the cell terminals to be damaged first. If this is a potential failure method I would like to know however.

The battery pack needs to be compression supported on all planes. I had top & bottom in compression and the two vertical ends were tied together via all-thread rods at each corner running horizontally. And that left enough rotational flex to occur to stress a couple buss bars by not having the front and back vertical walls of the pack tied together. The ratchet straps should address the problem I experienced by eliminating the rotational flex.

IMG_6218.jpg
 
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e9999

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geez, you guys make it sound like these things are pretty difficult to work with...
 

sdnative

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The battery pack needs to be compression supported on all planes. I had top & bottom in compression and the two vertical ends were tied together via all-thread rods at each corner running horizontally. And that left enough rotational flex to occur to stress a couple buss bars by not having the front and back vertical walls of the pack tied together. The ratchet straps should address the problem I experienced by eliminating the rotational flex.

View attachment 2518126

Interesting. Are those the fortune cells? I can see using a ratchet strap on those as the plastic outer case would prevent too much compression on the cells directly. I could easily over-tighten mine so need to be careful.
 

spressomon

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geez, you guys make it sound like these things are pretty difficult to work with...

You can purchase plug-n-play 12v LFP batteries, as I'm sure you know, from Battleborn, etc., etc., with good results with a commensurate price too. Kinda like comparing dropping off your LC to one of the shops versus DIY approach.
 

sdnative

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Cost wise, for 8 cells, BMS, Class T fuse holder with fuse and shunt I am in about the same or maybe slightly less than one 100Ah Battleborn.
 
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That looks pretty sweet. Nice and tight 210ah! Diy seems like you can maximize battery capacity with the space allowed vs drop in formatted sizes. You mention the battery is capable of 3C but the BMS has a 120A cutoff? So is the 600A only for short bursts (jumpstarts)?

I went with a drop in 100ah from Relion in my 80 that is 1C but also specs 800A for 5 seconds. I figured if I need to jumpstart my truck with a dead start battery this spec would be able to do it. Would be a good test. The possible lack of having a backup starting battery was my only potential drawback with a cargo LiFePo4 vs dual engine lead batteries. Everything else about LiFePo4 is a major upgrade in a power platform.
 

sdnative

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That looks pretty sweet. Nice and tight 210ah! Diy seems like you can maximize battery capacity with the space allowed vs drop in formatted sizes. You mention the battery is capable of 3C but the BMS has a 120A cutoff? So is the 600A only for short bursts (jumpstarts)?

I went with a drop in 100ah from Relion in my 80 that is 1C but also specs 800A for 5 seconds. I figured if I need to jumpstart my truck with a dead start battery this spec would be able to do it. Would be a good test. The possible lack of having a backup starting battery was my only potential drawback with a cargo LiFePo4 vs dual engine lead batteries. Everything else about LiFePo4 is a major upgrade in a power platform.

Yes the cells are capable of 3C or ~600A in this case, but the BMS is limited to 120A max. If I wanted to jump start the vehicle I would take the lexan cover off and connect jumper cables directly to the bus bars on the battery.

I designed this for low C-rate charge/discharge due to the confined space and lack of ventilation. I wouldn't expect this setup to generate any significant heat at all under 60A. Jump starting would generate heat with prolonged cranking but under normal situations I would hope the truck starts quickly. If not, the covers will be off allowing air flow.
 
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Yeah no it looks like a good layout with the battery. i have a 1500 watt inverter that can pull some high amps but most of the time it’s pretty low amp use too. Lights, charging, fridge.
 

Bambusiero

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This is really cool. Nice work. These issues have been nagging at the back of my brain for a while. Mainly the conundrum of big rectangular shaped standard batteries just not fitting the available odd shaped spaces.
There is a startup company in the netherlands called Ultrabatt that is talking about a very nice sounding modular LiFePO4 battery, but - still seems to be just vaporware. Sigh...technology just isn't up to where I want it to be!
 
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