I've got a distributed BMS as well, with little modules attached to each cell. The current draw is supposedly "less than 4mA" per board. I leave my pack unattended for 6 months of the year (let's call it 200 days for ease of calculation).
My cells are 100Ah
So 0.004A x 24h gives 0.096Ah per day
x 200 days gives 19.2Ah consumption, in addition to the 3% per month leakage.
So if I store my cells starting at about 70% SOC in November, they should be down around ~30Ah by launch time in May.
I store them out of the boat, completely disconnected from any load other than the BMS cells, in series groups of 4 cells.
Perhaps you left the head end control board connected as well and this is what drew down the pack?
At any rate, I am very pleased with my distributed BMS installation and see j reason to change. At $15 per cell the cost was acceptable. I found the Orion BMS was a little expensive when I was putting everything together and just wanted to get on with it and go sailing.
/Jason
On Jan 24, 2017, at 13:13, George Ojdrovich go@springsips.com [electricboats] <electricboats@yahoogroups.com> wrote:
John-
here is my experience with lithium on my Tartan 34C sailboatOriginal battery pack was (16) cells, 260AH and a distributed BMS. I made the mistake of not disconnecting everything over the first winters storage and completely drained and wrecked my Thundersky cells. I think the little circuit boards for the BMS had a slow drain all winter.I had the system redesigned with (20) CALB 180AH cells and a centralized BMS (Orion). The first winter I disconnected the BMS, removed the jumper between my (2) ten cell battery boxes— totally isolating the batteries. I took voltage measurements in October. In May, absolutely nothing had changed. Connected things, dropped the boat in the water and motored to my slip.I have heard it is recommended to leave the cells at 50% SOC more or less, but I left them closer to 90 to 95% SOC.Second winter- sameThird winter (now)- same and I will expect the cells to be healthy in May when I get back to the boat.I have not been able to measure any self discharge over these 7 months of cold storage. The spec is less than 3% per month which would be like 21% discharge over 7 months. I really don't think I've seen more than a couple of percent- at least by the basically unvarying voltage measurements. And I can roughly confirm the battery capacity by the time required to recharge the pack- example- if the BMS says I have discharged 40% capacity, I find it takes about 4.5 to 5 hours at 15 amps to recharge.The boat is on Lake Superior- extremely cold and long winters (sub zero)Regarding the original 16 Thundersky cells- last summer I decided to try to revive them with a charging protocol recommended by the manufacturer. They were basically at zero voltage. To my surprise I believe all but three or four of the cells are now good. I will know better in the spring when I return to them and measure their voltage. If they prove good I'll be trying to find someone who wants some high capacity cells at essentially give away cost.George O.On Jan 24, 2017, at 10:31 AM, John Acord jcacord@gmail.com [electricboats] <electricboats@yahoogroups.com> wrote:John A.thanks,I'm making the move to lithium. I'm OK with charging & BMS, and it will be a 100 AH stack.What is the best practice when the batteries are idle for periods of time?
What I would like to know is how to manage the batteries when the boat is idle for periods of time. We tend to park the boat for three or four months in the winter.
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Posted by: "Jason (Electric Boats) Taylor" <jt.yahoo@jtaylor.ca>
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