Big battery (~4000Wh) for long off-grid touring

[eTouringOldie]

Much as I’m excited about the potential of SS batteries, I’m too old to put things off until (say) 2030.

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I’m planning a touring e-bike trailer w/ a big capacity battery — say 3-4 kWh+. It needs to power a 52V Bafang M620 motor (stock controller), so 40+ amp discharge.

Requirements:

Faster (relative of course) charging — 500W / 10 amp+ if possible
Better cold weather performance

My initial idea is something like 20 EVE LF50Fs (50Ah), which would have a nominal voltage of 64V, so a bit high, but 3.2 kWh. 18 would do 57.6V, so better? Only 2.88 kWh. Each module weighs ~1kg, so 18 or 20 kg + bus + bms + case. Around 50 lbs for the 18 cell config, or 55 for 20.

Also, there are 55Ah Liitokalas which are actually spec’d as slightly lighter, so 18 of those would get me the 3 kWh+.

The point is to be able to do some serious long-distance, off-road touring — trailer will also carry a canteen (10L?) and I’m considering a hub drive on the trailer for regen braking on downhills (for the braking power, not the regen, maybe also for help up steep inclines).

I know I’m paying a weight penalty for LiFePo4 vs Li-ion, but fast(er) charging and cold performance are pushing me that direction. Also, I’m hoping I won’t get shut out of places to ride because of Li-ion fire paranoia.

So, my questions are:

Does this even make sense?

Are the EVEs better than the Liitokalas? Stronger, heavier cases? More reliable? More cycles?

Am I better off w/ 64v nominal, or 57.6v for my 52V motor? Is it possible to have a 19 cell config (so 60.8V)?

Is there a better Li-ion story I’m not understanding?

Is there an NMC story that doesn’t end up being $2k+ just for the cells?

Should I forget the rear motor and just add brakes on the trailer — might be carrying a lot of unused weight most of the time? (OK, that’s not an e-question).

Bonus for bms recommendations or pointers to battery builders who mights do this job

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Thanks

 

[offGridDownUnder]

Not a comment, but just a question. Have you made a design choice to have one battery as opposed to several interchangeable batteries?
If so, hearing that constraint might be interesting.

 

[eTouringOldie]

Not a comment, but just a question. Have you made a design choice to have one battery as opposed to several interchangeable batteries?
If so, hearing that constraint might be interesting.

I’ve been around and around on this. Multiple batteries which a produce the same energy as one big one — given the same chemistry — will weigh more than the one big battery (multiple BMSs, ports & cases). Not a significant difference, but it’s there.

Mostly it is about charging times though. LiFePo4 tolerates higher charging power. A 52V (nominal) Li-Ion battery charges @ 58V and they mostly take 3 or 4 amps, so 175W to 230W. LiFePo4 can charge at 1 - 3C, so 10 times faster or more — assuming I’m not mis-reading or mis-understanding the specs.

I’ve got multiple Li-Ion batteries for my bikes, and they give plenty of range, but they take a long time to recharge, and I have to either carry multiple chargers or wait a long time to recharge more than one. A 1k Wh battery charging @ 180 watts takes about 6 hours, and it would take 4 to get to 4k Wh.

I have 300W of solar panels, and my Li-Ion battery can only use a bit over half of that. Charging at 300W between full charges will really extend my range.

 

[rafalg]

with such big capacity i think any li-ion battery will be able to charge at 10 amps. Or even at 50 amps.