48v lifepo4 batteries serries and parallel output?

[Braaaptain]

Hello everyone,
I am trying to design a solar RV EV with modular 48v lifepo4 batteries. I plan on having 10x 100ah 48v batteries in parallel to use with a growwatt 12kw inverter+charge controller. The batteries need to be in parallel in order to use the inverter for appliances and charging. I am trying to figure out how to run a 2nd circuit to combine the batteries in serries to achieve 480v to run an EV motor to propel the rv.

Does anyone have a theoretical wiring diagram on how to achieve a parallel 48v array of batteries that also has a series output? I assume it will require rectifiers to keep the circuits separate.

 

[MisterSandals]

how to achieve a parallel 48v array of batteries that also has a series output?

It is not possible to wire batteries this way as it results in direct shorts.

I think your only best bet is to build your 480V battery and find/build a step down converter for 48V, or have a separate 48V battery bank for the house. Have you located a 480V DC charger for LiFePO4? I'd be wildly surprised if the Growatt charges 480VDC.

 

[Dzl]

Not to throw water on the plan, but my intuition is that this while this sounds like a cool idea it sounds infeasible (or at least impractical and pretty unformed. Have you done any back of the envelope math to determine feasibility? If not, this site is a good place to do so. I should note I'm an absolute novice when it comes to EV's and not an expert when it comes ot pretty much anything, but here are some considerations to think through:

10 x 100Ah @ 48V = 51 kWh.
This presents two problems.
1. Range. 51 kWh is roughly half the size of the new F150 battery pack, which has a base range of 230mi. I'm assuming your RV would not be nearly as light or as aerodynamic or as optimized as the F150.
2. Recharging from solar. How much solar can you fit on your RV roof? 1000W you are looking at needing 51+ hours of full sun in perfect conditions, 2000W halves that to 26. 3000W brings it down to about 17.

The combo of the limited range (how limited I don't know, but I would speculate double digits) and long recharge time from solar seems like it would make this design impractical economically and in terms of usability for how most people use their RV's. However I can maybe imagine some use cases where an approach like this might possibly be workable for a specific use-case with short distances and long periods of charging between uses, or where solar is just a secondary/novelty charging method to supplement grid charging. But even then, lots of challenges, tradeoffs, and $$$ I would think.

Then there is the matter of the Growatt 12kw. Growatt is one of the only inverter manufacturers that is not upfront/clear about idle consumption, but based on user reports here and elsewhere, I recall reports ranging from about ~100W to about ~200W, a forum search will probably turn up a lot of results and be better than my foggy recollection. That is a lot of power to burn for a mobile system. 100W-200W x 24hrs, is roughly 2.5 to 5kWh burned just powering the inverter while it sits there idle. That is 5-10% of your battery capacity and probably more of your solar generation capacity which will be your largest bottleneck.

 

[Cajunwolf]

... No.

 

[Bluedog225]

Soon. I expect to see electric 18-wheelers on the road in the next decade. Maybe with hydroden.

 

[rmaddy]

One other issue I haven't seen addressed is that you are very unlikely to find a LiFePO₄ BMS for a DIY battery that supports more than 48V. I'd be really surprised if you find a 48V LiFePO₄ battery that supports being put in series at all, let alone 10 in series.

 

[Cajunwolf]

@Bluedog225 I suspect we'll see commercial electric trucks before long; let the price of diesel keep going up. The only drawback is the lack of charging stations and recharge times right now. Back many moons, when we hunted dinosaurs for food, I drove trucks for a couple of years; big cross country rigs. An average fuel stop could take anywhere from 30 minutes to an hour, depending on how many pumps and how many are waiting. If there was a line at some truck stops, you parked and left her idling, get a ticket from one of the attendants, and go have a meal, shower, or whatever. When done, pay your bill, and your trucks parked nearby fueled up, windows washed, oil and tires checked. Those days are long gone, I know, now, you sit in line and wait, but electric trucks could bring this back if they could get charge times down to an hour.