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Nick
From: harryproa@yahoogroups.com.au [mailto:harryproa@yahoogroups.com.au] On Behalf Of sigurd grung
Sent: March-16-13 8:02 AM
To: harryproa@yahoogroups.com.au
Subject: Re: [harryproa] Lithium batteries?
Hi Gardner,
LiFePo has usually longer life than lead acid. Some have 3000 cycles. If you put that number into the cost calculation, it changes, obviously. It's been a while since I checked but at that time the smaller round cells were the best deal. Look for A123 brand for instance (ebay?), used by DeWalt and Milwaukee power tools I think, and radio controlled toys. At 2v there is almost no juice left, and if you draw them below this, they might be damaged. An 80% charge will probably increase life of the cells a lot, so I heard. They don't need a constant current charge, just keep it below 1C for better lifetime. You should probably have a charging cirquit if your solar cell bank is big. Either way a max Volt cutoff cirquit with hysteresis (since resting voltage is lower than max charging voltage) is needed for charging.
I would see if it is possible to use 24v with all of the equipment, then there is less current and copper, and less copper losses. 24v is pro standard, trucks and such. Even if most of your equipment is low current, perhaps you want a 100w searchlight, coffee maker, autohelm or other "high" current things.
From everything I've read, LiFePo is not flammable. But put good fuse/cirquit breaker.
From: Gardner Pomper <gardner@networknow.org>
To: harryproa@yahoogroups.com.au
Sent: Sunday, March 10, 2013 3:39 AM
Subject: Re: [harryproa] Lithium batteries?
Very informative reply. Thanks!
I have a few more questions... My reading on Li batteries speak of 1C and 5C charging and also of constant current charging. Is there a requirement to charge these batteries as a constant current? I am planning on using solar (perhaps 400w or so) panels as my primary charge, with shore power as a backup and possibly a small gasoline generator for emergencies.
Another question is about the minimum 2V requirement on the cells. I had thought that Li batteries could be drawn all the way down without harm, as opposed to lead/acid where you should not discharge them more than 50% or so. Is 2v 100% discharged?
I went internet shopping, just to see pricing and availability. I found a 100Ah LiFePO4 battery (28lbs, $620) listed as a replacement for 12v LA batteries. Here is the link http://www.batteryspace.com/LiFePO4-Prismatic-Battery-12.8V-100Ah-1.28-KWh-10C-Rate-Without-Balance.aspx I was thinking of it as a replacement for something like this http://www.wholesalebatteriesdirect.com/marine-batteries/52236-12-v-200-ah-4d-deep-cycle-agm-marine-battery-ub-4d.html (200Ah 4D deep cycle AGM battery 125lbs $385). As a 12v battery replacement, it claims to have internal protection for the cells, so does that mean I would not need a BMS?
Finally, on a more general note, if you were building a cruising boat, without electric motors, would you consider LiFePO4 batteries a safe, reliable solution for a house battery bank?
Thanks,
- Gardner