Ramblings of a Techno-Viking

Lithium Ferric Phosphate Batteries -- Part 2

If you missed it, please see Part 1. This is a continuation, (stuff I forgot to mention) with some minor updates.

There are some integrated systems of LiFePO4 batteries (including battery monitor and charger), mainly marketed for yachts, but they are much more expensive than buying the parts and assembling them yourself. The boating market has been using LiFePO4 longer than the RV market, but the earliest adopters are racing teams that don't disclose information to avoid loosing their edge on competitors. There are threads on LiFePO4 batteries on Cruisers Forum, including one of more than 3500 posts.

Part of the reason cells are cheaper and more available than assembled batteries is shipping safety certification, where the certification would need to be re-obtained for each configuration.

Since my LiFePO4 batteries are reaching full charge early in the day, for the last week I've been running my refrigerator on an inverter (rather than propane) for several hours a day. My solar controler reports that doing this I'm using about 80 amp-hours more on sunny days, more than doubling my normal usage.

While my alternator is hooked up to charge my house battery when driving, I have not been driving my motorhome a lot since I installed the LiFePO4 batteries. (About 200 miles in about two months, moving about every two weeks.)

The Winston 260 Ah cells use M12 bolts, just a bit smaller than 1/2 inch. Balqon does sell the hardware, but it is not listed on their web site so I did not learn that until after my order was placed. I flattened (in a vice) and drilled holes in 5/8" soft copper tubing to create the bars between cells and to the ANL fuse holder I hung off the positive terminal. The same tubing with one end flattened and drilled is used for lugs on the 1/0 and 2/0 wire used in rewiring. The tubing needed to be deformed a bit to get it in my hydraulic crimp tool.

I am not using pressure plates to keep the cells from bulging when they self-heat, this seems to be mainly needed on high current applications. There is a ratchet-strap around the cells to keep them together and another to hold them down.

We went with LFP last year on our current 5th wheel. Older son is in the solar/wind business and designed and fabricated our current system (former system/trailer/pickup are in a wrecking yard near Mexico City. We were in a 70 care pileup between Vera Cruz and Puebla, Mexico). This is 1420 W of solar (6 x 235 watt panels). These are ganged 3 in series to they go to controller at around 90 V. The battery suite is 4 batteries of 4 cells each for a battery suite of 180 Amps at 54 V or approximately 9600 W-hours. We generally run refrigerator during day with AC and at night if it will be sunny the next day (are down -3000 W-hours in morning if we do this). Run the micro-wave in preference to propane stove since there is no added cost. Wife uses a 55 W heating pad on her back every night and we have used A/C for up to 3.5 hours on battery suite/solar. It is definitely the way things will go as the prices go down
Comment by Reed Cundiff Tuesday 29 July 2014 23:53 UTC