Here goes nothing! After a lot of planning, and several revisions, it’s happening. I’ve started the process of replacing an aged house battery bank and inverter/charger with a new system based around lithium battery technology.
This isn’t going to be a simple remove-and-replace project though. While there are a number of commercial offerings already available using prismatic lithium iron phosphate cells (LiFePO4, sometimes abbreviated LFP), often packaged with a battery monitoring system of some sort, we’re going to look to a much cheaper source of batteries, and a system design that should yield far better performance in the long run.
Typical LFP batteries run in the neighborhood of $1 per usable Watt-hour. We’re going to be using a battery pack from a wrecked 2012 Chevrolet Volt as the starting point for this system–prices vary, but I’d estimate they’re out there for an average of $2100 or so. That gets a pack with 12kWh of usable energy, or about $0.18 per Watt-hour. That means that if we’re intending to use the full Volt battery pack that we’re saving about $10,000 just on cell cost.
This is a big project, and I’m going to be breaking down the design process into a bunch of separate posts. But we’ll end up with a power system with energy storage equivalent to 24 golf cart batteries with about 80% weight savings, and less total cost than even a conventional lead acid setup (at 50% depth-of-discharge, we’re looking at 0.5kWh each). We’re also going to be able to run some big loads (like air conditioners) without straining the system. Stay tuned!
–Dave
Wow, this is really exciting. Great work David! If you need Beta test rigs, I’m in.
Very interesting! Will you share plans? Can’t wait to see how it works out, Please add me to your email list!
V/r,
Dean Edler
I’m definitely going to share the overall project plans, and hopefully finish up with a how-to of sorts. If there’s interest, I may be able to put together a kit with the necessary components, including a couple of circuit boards to simplify things.
Would like to have that kit if you put it together. Want to put a big solar system on our next 5ER when we go full time. Thanks Ken
I’ll keep you posted Ken!
Howdy David,
Interesting! And I’d probably purchase the kit if/when you make it available. A few questions:
1) The Volt battery seems to be “conventional” lithium-ion, instead of the safer LiFePO4. Are you going to install any safeties or otherwise handle the additional fire risk?
2) Can you tell us how much did you pay for the junkyard Volt battery?
Cheers,
—
Vall.
Hi Vall,
I’m less convinced than most about the safety advantages of LiFePO4 batteries. They’re more readily a drop-in replacement for flooded lead acid batteries, and more easily assembled than a Volt battery in a small 12V package. But they’re still susceptible to thermal runaway (you can find videos on YouTube), and like “conventional” lithium ion and lead acid batteries, you can get fires and/or explosion under the right circumstances–most often due to overcharging or poor connections. One of the advantages of lithium ion as in the Volt pack is that voltage is easily used as a measure of state of charge, and we can make use of a little bit of software to detect a poorly performing cell–without having to monitor them individually.
I’m a nuclear engineer by schooling, and the final implementation of the battery control system will probably show it. While I won’t be monitoring individual cell voltages, I’ll have independent voltage measurements, and redundant disconnects with feedback to confirm that the charging and/or load relays have in fact disconnected.
As far as the Volt battery purchase, the price was $2000 before sales tax. Most seem to be in that range, with most of the cheaper packs having a larger core charge. Of course, at a usable 12V-equivalent of 1000 Amp-hours, one pack is enough to do more than one normal RV.
–Dave
Thanks Dave!
Hi Dave,
I am getting ready to purchase another pair of house batteries. Found your project while looking at battery alternatives. Looks like you have had a year to put your plan together. Could you drop me a note about what you discovered?
I would be very interested in your plans if they are available.
Thanks,
Jeff Bocott. 253- 219-4408
Hi Jeff,
I’m way overdue for an update. The system has been running for over a year–I’ve made a few tweaks along the way, but overall have been very happy. I’m actually getting ready to move one of the battery modules today, after redoing some of the cabinetry in the bedroom. Feel free to e-mail me at [email protected] if you want to discuss in more detail.
Dave