Slightly Off Topic LiFePO4 Use in Mobile Robot

[terrahawk]

I am participating in a NASA robot contest and I want to ask if large LiFePO4 batteries are a viable alternative to cu$tom packs?
Basic details are this:
- Robot has to run for 15 days/nights as continuously as possible.
- Location is Southern CA desert. Temps expect to range from ~95F to ~50F
- peak vehicle draw is ~300 amps @ 48 volts for a few seconds
- need 200 amp draw for 5 minutes at 50% duty cycle for 60 minutes once per day
- need 50 amp draw for 5 minutes at 50% duty cycle for 60 minutes once per day
- most of the time, the current draw is about 25 amps
- Two sets of batteries, one being charged (off vehicle) and one being discharged, they will be swapped as necessary.

Simpler is better. Fewer batteries, integrated BMS.
I have seen some batteries with 200 amp BMSs and short term testing up to 450 amps.
Is there a moderately priced solution that works?
Thank you!

 

[agt]

Ignoring the infrequent bursts, it sounds like you’re looking for (200A x .5 x 1h + 50A x .5 x 1h + 25A x 22h) = 675Ah/day or about 33Kwh/day. So maybe 36Kwh with a bit of reserve?

That’s EV territory- at 140-150Wh/kg you’d get from lightest off the shelf LFP you’re talking 275kg or more for the batteries. For server rack setups like EG4, add another 25% or more. 6-8 100ah batteries in parallel ought to handle the peak loads.

What size chassis are you building? Could you repurpose a full EV battery system? Or maybe even a full EV?

 

[terrahawk]

Ignoring the infrequent bursts, it sounds like you’re looking for (200A x .5 x 1h + 50A x .5 x 1h + 25A x 22h) = 675Ah/day or about 33Kwh/day. So maybe 36Kwh with a bit of reserve?

That’s EV territory- at 140-150Wh/kg you’d get from lightest off the shelf LFP you’re talking 275kg or more for the batteries. For server rack setups like EG4, add another 25% or more. 6-8 100ah batteries in parallel ought to handle the peak loads.

What size chassis are you building? Could you repurpose a full EV battery system? Or maybe even a full EV?

Thanks for the reply.
I expect to swap out batteries 5 times per day. The vehicle only weighs ~250kg without batteries so I would like to keep the total battery weight to about 100 kg. My first back of envelope calcs was 4x 200 ah batteries while 4x more are charging. Batteries would be swapped about every 4 hours and charged to 80%.

 

[terrahawk]

I came across a product that might do the trick. Vestwoods has a 220Ah Battery at 25.6V with a 200A BMS. As a bonus, it has bluetooth connectivity. Vestwoods look like they make whole house systems so maybe quality is OK? Anybody have issues?

Thanks!