Quote:
Originally Posted by Aurel
Very cool project. I have 15 years of R&D in Li-ion cells if you need any advice on other chemistries. And own a 78SC too. LiFePO4 is a good choice for power, safety and cycle-life. But not the highest energy density cathode. Maybe when time comes to replace them, there will be cheap batteries with NCM cathode, or high voltage spinel. Could your controller handle other chemistries? I cannot wait to see the results of your conversion. I am also curious about your old 3.0L engine. What shape was it in? How many miles on it? Are you selling it? (Mine needs a rebuild).
Cheers.
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Thanks. I fully agree that LiFePO4 is a compromise compared to other lithium chemistries, but it is worlds better than lead acid. The safety factor and long cycle life were my main factors for selection. It is true that the price will need to come down (or gas prices go up) before electric will gain significant automotive market share.
The controller will accept up to 340 V, and that is the only controller limit as far as batteries go. The charger is the component that is most sensitive to battery chemistry. The charger uses a constant current, constant voltage profile (CC/CV). With these cells, a resting voltage of 3.38 is considered 100% charged, but it takes a few days rest before you can measure an accurate resting voltage. So it is accepted practice to charge these cells at a constant current until you reach 3.6 V per cell, and then hold the voltage constant until the current drops to a level of C/20 (cell capacity divided by 20). I have 180 Ah cells, so 180/20=9 amps for my cut off). The voltage will settle to 3.38 V using this recipe. Because the main failure mode of these cells (in automotive applications) is due to either overcharging or over discharging, it is a good idea to avoid taking the cells up to 100% charge. I plan to slightly undercharge to maybe a resting voltge of 3.33 V/cell. So any new chemistry may have charging profile implications. I suspect I'm not telling you anything new here and I'd be interested in hearing your take on battery charging.
I still have the motor. I'll be looking to sell it in a few months, after I figure out all of the electrical connections I need trace out through the engine harness (brake and reverse switches to connect to my controller). The motor has 97,000 miles, and ran great. The previous owner gave me service records for the last 10 years. Two known issues - the oil tubes dripped oil onto the muffler and you get some smoke during warm up after sitting overnight (no smoke from the tail pipe itself), and there is a loose muffler bracket that rattled sometimes at idle. The seal at the crank hub may leak. I found a coating of oil in the transmission bellhousing and I'm not sure if it was motor oil or transmission oil.