Re: [Electric Boats] parallel - series

On Oct 19, 2014, at 10:13, acsarfkram@yahoo.com [electricboats] <electricboats@yahoogroups.com> wrote:

> If anyone has any "living with lithium on a boat" experience I would like to hear your thoughts and suggestions. I've got lithium batteries in a small electric van and really like the performance of the lithium.
>

Mark, not quite answering your "living with lithium" query…

I've been paralleling AGMs, GELs, LiFePO4, and Li(NMC) in a 48v system to be used for driving a Torqeedo 4.0R, all charging using typically GEL settings, limiting the upper voltage to 56.0v on all the chargers and 12vdc-48vdc converters and ensuring that any charger FLA-equalizing algorithm is disabled. Going onto an old Telstar trimaran which I have yet to re-launch after a 16-year haitus.

So far I've used this setup in driving transportable 48v—>120vac and 48v—>240vac power inverters (used for charging EVs) and not the Torqeedo. It's all modular and a great backup power source at home if the grid goes down. Also have a 48vdc—>12vdc converter to feed the boat's house 12v bank if needbe, and solar can feed either the 12v bank or 48v bank. Of course, have ac-powered chargers for each when attached to grid.

Use Headway 12Ah LiFePO4 in a 4P16S configuration and Enerdel 16Ah Li(NMC) in a 2P14S configuration.

Keep upper limit at 56.0V (below Lithium limits yet adequate for GEL and AGM), and have never pushed the lower limit which I've established as a compromise at 48.0vdc but have never yet gone below 50.0vdc.

Have had these Headways for a few years, separately charged using PowerLab8 with integral BMS for cell-group-level management.

Have used the Enerdels in my Sparrow EVs (daily drivers) running at 2P36S for over a year and they have kept excellent balance with no BMS, but I religiously keep them between 80% and 20%SoC. Still need to hookup the Orion BMS, but presently use both timers and upper voltage limit charger (lab power supply) for upper voltage cutoff.

Although I understand the rationale for bottom-balancing, I mid-balanced all the cells (LiFePO4 separately from the LiNMC) in parallel for about a week before building the packs, figuring it's where they'll sit most of the time and I DO intend to install my top-balancing Orion BMS.

I use 120A circuit breakers in the positive leg of each paralleled bank. Because of the very low series impedance of the Lithiums, it is important that the voltage be identical (within a few millivolts) when actually physically joining the banks together.

All the paralleled banks share current differently, a function of the exact voltage at any given point (so far I've simply used a clamp-on ammeter for quick checks). Reminds me of how well everything performed when I heretically paralleled AGM with FLA during my cruising days <http://www.katiekat.net/Cruise/KatieKat2007H.html#Battery>. For a permanent installation I'll have a shunt or Hall-effect coil in the negative leg of every paralleled bank just to see how well they're all playing together. For starters I'll just use the LiFePO4 bank alone and then add various banks in parallel depending on anticipated load needs.

Hope to report how this all works out after I've re-launched the boat, which at this moment does not look promising for this year.

JoeS. in Los Altos Hills.

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