Honda Civic Conversion --- LiFePO4? Opinions please!

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andrew
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Honda Civic Conversion --- LiFePO4? Opinions please!

So me and my brother are planning to work on a Honda Civic this summer. The conversion is absolutely pristine. It's been worked on for years by an engineer that my dad knows. It's about 80% done. The difficult stuff has all been done very well. The specs are:

Costov motor
Auburn controller 192v 600a (yea we know its probably junk, but it does use IGBTs)
Spots to place 18 Optima YTs of 55ah size for a 192v system
Zivan NG3 battery charger
Zivan battery balancing system (really nice expensive system, but I'm not sure how it works)
Ect... we have almost all of the high quality components needed

At this point we are trying to decide on batteries. I've not done enough research on LiFePo4, but from what I can initially guesstimate:

● Cost will be from $8,000 to $10,000 total cost for good quality LiFePo4, with BMS, and good charger(s)
● Range may be about 50 miles for what that amount of money can buy, and supposed battery life would be 75,000 miles or more
● There's no telling how long the LiFePo4 pack will last because there's no real world data to go by for the batteries we will likely use
● Who knows about the safety, again no proven real-world safety record
● No reliable assessment of quality, again no real-world testing accounts
● It is unknown how they will survive under the conditions used
● Lots of other unknowns such as charger and BMS quality, reliability, and safety without any real-world history to go by.

On the other hand, we can pretty well asses lead-acid AGMs. We plan to maybe use Exide Orbital 34XCDs, or some other good quality AGMs:

● Cost will be about $3,500, already have charger, and BMS
● Range would be about 25 miles, life can be reliably projected to at least 7,500 miles
● These batteries are designed, used, and survive in the real-world conditions we will be using them in. They are designed to be high-power deep cycle SLI (starter lighting ignition) batteries.
● Everything about them is well known, e.g., safety, quality, shock tolerability, failure modes, high-power output tolerance, power output, heat tolerability.
● These have a history of use in performance EV conversions. They were used in the "Gone Postal Van." Also used in quite a few other EV and motorcycle conversions. Known to perform very well, and our Civic is a high-performance EV.

So we pretty much have to decide between a known and an unknown. For now, we've decided that it's probably best to go with AGMs, and wait for LiFePo4s to progress. Plus, we can't really afford the LiFePo4, and they'd be quite a risk to take if we could.

I'm still very interested in any opinions. Maybe there are some things we can do to bring the LiFePo4 cost down?

rgx
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Re: Honda Civic Conversion --- LiFePO4? Opinions please!

andrew,

that's a great project. We don't have many car projects on this forum though, so experience is limited. I will try to give my view, based on limited experience of Thundersky LCP cells (not LiFePO). To summarize: the relative advantage of litium is bigger, the bigger the pack. In my own vision of a litium-converted car (still to be realised), I think at least 30 kWh is needed. Ideally around 50 kWh. Especially if you want fair performance, or plan to use 192V/600A (over 100 kW?). The battery pack alone could cost 20-30k. Plus BMS, which is still rather expensive. You would need to adapt the charger to interface with the BMS (should be possible, but requires some knowledge). Buying a too small litium pack will disappoint you performance-wise. This same advice has been given by a finnish litium guru, who wrote "if the system voltage is below 300V, you need at least 150 Ah cells". This whole discussion assumes you want to buy large cells, and are not prepared to knit together a pack of a few thousand 2 Ah cells. Or pay USD 10+ /Ah for high-output cells from A123 or similar.

So, given how far the vehicle already has been prepared for lead-acid, and the limited budget, I'd say buy lead-acids to get the vehicle in operation quickly, start getting experience and get all other stuff dialed in. I imagine a lot of things need some tuning, such as motor/controller/transmission, DC converter, power steering (?), heating (?), meters and gauges, charger. You could always switch to litium later, when you have the money to buy a big enough pack. Or prices have gone down. In the meantime you gain some experience of how much performance you really need, which helps dimensioning the (inevitable) litium pack. Maybe you find that range is more important than 0-60 mph time.

It's a boring advice. I would have liked to say - go for litium, but it's only favorable financially if you calculate the cost per km instead of looking at the investment.

In any case, please keep us updated on how the project progresses. We are all ears.

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