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Project blog

720 LiFePo4 cells for crosskart battery

1/21/2021

1 Comment

 
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​The cells for the buggy battery have arrived. I purchased these new 32650 LiFePo4 cells from batteryhookup.com for CHEAP. I don't think you're going to find a better price anywhere else. They're rated for 3.2V and 5Ah with a max continuous discharge of 15A (3C), and max pulse discharge (for 10 sec) of 50A. Max charging current is 5A (1C). They have another cell available rated for 6Ah capacity, 18A cont. discharge, 60A pulse discharge and 6A charge limit. Links for both can be found below.

As some of you already know, LiFePo4 isn't quite as energy dense as lithium ion but it is the safest type of lithium battery because it won't cause a runaway fiery explosion under your butt if a cell gets damaged somehow. This is the main reason why I use LiFePo4 in my projects when I can, aside from this type not containing cobalt.
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The battery that I'm building for the buggy with these 5Ah cells will be a 24P30S configuration to produce 96V and ~11.5 kWh capacity, with a continuous discharge limit of 360A, pulse discharge of 1200A, and a charge current limit of 120A. This is well over the ME1616 motor's capability of 250A continuous and 600A pulse, so I don't expect there to be any thermal issues at all and have chosen to incorporate a simple forced air TMS into the buggy design to help the cells shed what little heat they might produce while driving.

11.5 kWh should give me around 200 km's of range per charge in the trails with regenerative braking. A person can use the 6Ah cells to get around 14 kWh in the same space if they want. But, Batteryhookup's customers have been reporting 5.5Ah+ capacity with the 5Ah rated cells while the 6Ah cells are at or just slightly above 6Ah, so in terms of cost per watt hour you'll be getting a better deal with the 5Ah cells ($0.19/wh vs $0.17/wh). I normally don't put on more than 80-100 km per trip when I go off-roading, so I opted for the more affordable cells.
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The DOM tubing for the chassis will be here in a couple of weeks. I'll try to have the buggy CAD 'finished' and a few pics posted in a day or two so you can see exactly what I've got planned.

5 Ah cells:

https://batteryhookup.com/products/new-battery-hookup-lifep04-32650-3-2v-5000mah-cells

6 Ah cells:
​https://batteryhookup.com/products/100-brand-new-lifep04-32650-3-2v-6000mah-cellsbatteryhookup.com/products/100-brand-new-lifep04-32650-3-2v-6000mah-cells
1 Comment
Tim
3/24/2021 06:12:52 am

Hey James,

Love the battery choice. The life cycle are much higher and they have safer tendencies over Li-ion as you stated. Do you plan on spot welding your stacked nickel strip to each row of cells? If so depending on the thickness of the strips it’ll definitely take some trial runs prior to welding them to the battery terminals. Also, how do you plan on charging the cart? At 96V and 11.5kw you’d need a pretty beefy charger to charge in a decent amount of time. I was thinking perhaps from the reaper turbine or wind in general, but judging from the specs it’s only pushing out at most 48V. I guess you could always use a transformer and step that voltage up in order to achieve 96V. Full charge would be higher of course than the nominal 96V. That is of course assuming you are cycling the batteries to near empty in a given trip. (On a side note I see on the spec sheet of the reaper that it produces 12V,24V, or 48V... is this something that you physically set or limit the voltage at, or is it capable of producing up to 48V and you simply have to throttle that voltage to charge whatever your battery bank/load setup requires) As always thanks for your time, and I look forward to hearing from you.

Tim

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