LiFePo4 batteries, at last

What do you call the stage between bleeding edge and early adopter? I don’t know, but we spent the day there… after buying 16 lithium battery cells two years ago, their installation got started today. There’s been a lot of learning, planning and fretting for months. Anton has built electric vehicles and complex land battery systems, so we listened carefully to his practical advice and I thank him greatly for the encouragement to tackle building a lithium system from scratch. This morning he told me to wrap the lug wrench handle in electrical tape to avoid any mistaken arcing. Let’s not make any short circuits with a 400 amp hour system!

A few months back we made these straps from a sheet of copper. That took longer than expected but at least saved some $ for quality (lowest resistance) balanced power across the cells.

The battery tray was built back in Santa Rosa. Today we built out component mounting spaces around it.

After mapping out parts locations it was time to make all the custom length cables. No fancy hydraulic crimpers here; just old school compression.

Here’s a progress view as the parts go in.

You’re looking at the 16 three-volt cells that have been made in to 4 twelve volt batteries (via parallel strapping). They are resting as separate groups overnight so that the individual cells within each of the four batteries balance among each other. Tomorrow hopefully we’ll find that the four groups have very close voltages to each other (ideally about 13.2volts based on how they were stored). If not we’ll balance them manually with a charger.

Ravenswing is coming out of the water this weekend so we can trim the daggerboard exit slot at the bottom of the hull to match the new daggerboard shape. I thought we could get away with not having to adjust down there, but when the v.2 dagger was slid home last month, it didn’t make it out the bottom. Oh well. Silver lining is the opportunity to finally get some artwork on the float hulls.  Hope you like it next week.

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4 thoughts on “LiFePo4 batteries, at last

  1. Good for you, getting the lead out! Even though LiFePO4 fully-charged is 3.65v per cell, I usually charge mine to no more than 3.45vpc max (13.8v total) just before use, and store at 3.333vpc. What type of series/parallel arrangement are you going with, do you have a cell-level battery management system, what charge controllers/regulators are you using for both your solar and alternator, what’s your backup overvoltage and undervoltage protection, and what’s your technique for coulomb counting (Ah in/out)? Enquiring minds are interested… :-)

  2. Heh, not to be too pedantic, but I think you will fine that you have made you 16 individual cells into 4×3.3v batteries that then gat hooked up in series to make the 13.2v battery. Hopefully each 3.3v group will be the same voltage as all the others. One good thing about using multiple cells is that you can actually measure the capacity of each cell and swap them around to make 4 groups that have the same capacity. The lazy way is to just put them all together and assume that the law of averages will make the groups of 4 more consistent than larger individual cells might have been…

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