Dual Battery Concept

[cr117]

I've been noodling on this idea for several months now, and with how well my portable power station build went, I'm kind of interested in building a proof of concept just for the heck of it. I decided to draw it out to at least verify what I had in my head could actually work.

I really liked AAL's cargo storage battery mount, which allowed up to 72Ah of power to be tucked away underneath the floor. If I ever wanted to add an integrated dual battery setup to my Bronco, I thought this would be the way to go. Unfortunately, now that the batteries this mount was designed around are no longer available from Dakota Lithium, using their closest replacement 20Ah battery would only allow 3 in the same pace, getting you only 60Ah total. Not quite ideal.

Back to the drawing board. How can I fit a decent sized battery in that under floor space? Then it hit me. Why don't I just build a battery that's custom fit to the dimensions of the box?

My solution is a self-contained 105Ah LiFePO4 battery using 4x 3.2V EVE cells. The enclosure would be constructed out of HDPE plastic boards.

On the underside, there's plenty of room for the wires to connect all the cells. I'd also install a 120A BMS to ensure the cells remained balanced and would cut power if temperatures get too hot, too cold, or if there's an over current load (like a short).

The whole assembly would fit nicely in the under floor storage box (for both 2 door and 4 door), sitting flush with the top, with some room to spare for other wiring/electronics. I'm thinking I'd just need a plate or two to hold it in place using the bolts with which the storage bin is attached to the floor.

Anyways, wanted to gather some feedback on this concept before moving forward. Cost of materials I'm estimating to be around $600, so it's not a terrible price point. Is this a garbage idea? Is it worth all the effort? Is there a better solution out there that I'm missing? Is there something better I should be doing with my life?

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[PWillette]

Interesting idea...I think you'll have some interest.

 

[Brian_B]

You have room for electronics noted - you have an inverter/charger/BMS model in mind? Get that all mounted in that thing and you'd have a hit I think.

The only thing I would be worried about in that cargo box - in the winter it gets awfully cold, and when running in the summer it's right near the exhaust line / muffler underneath and it's likely to get fairly warm without any way to easily ventilate it. BMS would manage that to some extent, but not sure what the temperature extremes hit there since it's not exactly climate controlled or even well insulated.

 

[NVCowboy]

Oof. Id be pissed if i laid out the cash fir the AAL setup, and the are unobtainium.

I'd look up building lithium batteries on YouTube. I've seen where the builders use metal strips and spot weld them the cells. You may already know that, but i keyed in on your comment about room for wires.

 

[UtahBrandon]

Love it. I assume I could plug my portable solar panels into it when overloading to keep it topped off? I'd be interested in it to keep my fridge powered as well as a CPAP at night, and recharging LED camp lights during the days.

Oh, and a switch that allows my vehicle battery to be jumped by the house battery which would mean I don't have to carry my NoCo jump starter anymore.

 

[Bruno]

You could build a box for this secret spot.
Its potentially much bigger - yes theres some things you would need to overcome but the capacity with stock battery units could be greater

 

[PEGB]

Depending on your resources, or you can even upload to a service, but 3D printing that box could be an excellent option.

 

[mvilla]

This is great. I was actually thinking about this as an option. I love the AAL setup, but it’s biggest downside is that you cannot remove it.

 

[Squatch]

I will second the concern about temperature regulation, but otherwise an interesting concept.

The construction using HDPE sheets in a box shape may not be as strong as it could be. I'm not sure if I would farm that out for 3D printing the whole thing, but maybe the bottom half or third of the cell box (with structural ribs or other features) to give it some rigidity and then add the risers underneath and top out of HDPE sheets. My luck, if I built it using just sheet material, would be that it folded up or collapsed, like a parallelogram, as soon as I went to move it for the install. Just something to consider.

 

[CriticalB]

I like this idea. I have an Ecoflow river portable battery that I keep in the back, but have been considering breaking it down such that the batteries and other hardware are hidden in the cargo hold and then cut the driver side rear trim panel so I can mount the interface panel and power input/outputs flush for a clean install. Could either charge it through the alternator or run solar from the roof through the back gate for camping/ over landing.

 

[cr117]

Thanks for the feedback everyone. Giving me some more things to think about.

You have room for electronics noted - you have an inverter/charger/BMS model in mind? Get that all mounted in that thing and you'd have a hit I think.

I'm thinking the BMS will be mounted on the underside of the main enclosure so it'll remain with the cells as one unit. I've never liked the idea of storing a charger or inverter in an inclosed space like the under floor storage area as those can produce quite a bit of heat when in use and air flow is definitely limited down there. Additionally, with this being under the floor, I wouldn't want to have to remove everything from my cargo area to check/monitor those devices, especially if I ever installed a drawer system. At least initially, I'm thinking I only want to keep the battery storage down there, maybe a wireless shunt to monitor loads & capacities, but everything else would be above where they can stay cool.

The only thing I would be worried about in that cargo box - in the winter it gets awfully cold, and when running in the summer it's right near the exhaust line / muffler underneath and it's likely to get fairly warm without any way to easily ventilate it. BMS would manage that to some extent, but not sure what the temperature extremes hit there since it's not exactly climate controlled or even well insulated.

This is true, but the AAL setup is mounted in the same location and I haven't heard of any challenges due to extreme temperatures. At least with the BMS down there, it'll know if things are too hot/cold and cut the power to avoid any damage, if that ever were the case.

Oof. Id be pissed if i laid out the cash fir the AAL setup, and the are unobtainium.

I'd look up building lithium batteries on YouTube. I've seen where the builders use metal strips and spot weld them the cells. You may already know that, but i keyed in on your comment about room for wires.

Yep, tons of resources out there. Most of the battery cells come with threaded studs or holes, so no welding is required. The space for wires is for connecting end of the battery to the other. With the cells I designed this around, I'd have to orient them facing away from each other, so I'd need to connect one end to the other to keep them in series.

Love it. I assume I could plug my portable solar panels into it when overloading to keep it topped off? I'd be interested in it to keep my fridge powered as well as a CPAP at night, and recharging LED camp lights during the days.

Oh, and a switch that allows my vehicle battery to be jumped by the house battery which would mean I don't have to carry my NoCo jump starter anymore.

Yes, in theory this should be able to handle all of that. Granted, this design is just for the battery portion, so any chargers, outlets, plugs, and switches would need to be added on top of this, depending on the use case.

You could build a box for this secret spot.
Its potentially much bigger - yes theres some things you would need to overcome but the capacity with stock battery units could be greater

That is an interesting idea, are we sure there's nothing occupying that space, like the gas tank?

My preference is to avoid needing to modify the Bronco itself in case I ever wanted to reverse the work done.

Depending on your resources, or you can even upload to a service, but 3D printing that box could be an excellent option.

I don't have any experience with 3D printing, but that could work. Most of the DIY stuff I've done has involved wood as the primary construction material, so I'm more comfortable with that approach.

The construction using HDPE sheets in a box shape may not be as strong as it could be. I'm not sure if I would farm that out for 3D printing the whole thing, but maybe the bottom half or third of the cell box (with structural ribs or other features) to give it some rigidity and then add the risers underneath and top out of HDPE sheets. My luck, if I built it using just sheet material, would be that it folded up or collapsed, like a parallelogram, as soon as I went to move it for the install. Just something to consider.

From a structural standpoint, the HDPE should hold up just fine. The enclosure would be built around the cells, so there shouldn't be any flexing. Additionally, since this would form fit inside of that storage box in the floor, there wouldn't really be anywhere for it to move around under there.

 

[Russ.Cere]

A great source for batteries is DIY Powerwalls & Lithium Battery Modules & Components by Jehu Garcia – JAG35

Associated Facebook Group is also packed with info.

IF you need any sheet metal or cut materials check out SendCutSend they are a great on demand service.

 

[WarthogJr]

The cost of materials is $600? What about labor? Any overhead? Marketing? Then after markup (guessing you want to make a profit)…selling price is: ? Will there be actual demand at that price, or just tire-kickers from the Bronco-overlanding niche group? Then there’s the whole “stability of the supply chain” thing. I’m thinking your appetite for risk is much higher than mine. Cool idea if you can get it to market and make some bucks!

 

[cr117]

A great source for batteries is DIY Powerwalls & Lithium Battery Modules & Components by Jehu Garcia – JAG35

Associated Facebook Group is also packed with info.

IF you need any sheet metal or cut materials check out SendCutSend they are a great on demand service.

Thanks for the resources! I've had my eye on SendCutSend for a while but haven't had a good excuse to try them out yet.

The cost of materials is $600? What about labor? Any overhead? Marketing? Then after markup (guessing you want to make a profit)…selling price is: ? Will there be actual demand at that price, or just tire-kickers from the Bronco-overlanding niche group? Then there’s the whole “stability of the supply chain” thing. I’m thinking your appetite for risk is much higher than mine. Cool idea if you can get it to market and make some bucks!

This is intended for a DIY project. I've already got a full time job, I'm not really interested in trying to sell this at the moment. Just looking for feedback on the design and application for now.

 

[Raskew]

Interested. Following!

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