Good points Myles, and well summarised in your succinct summary of the situation.
Great advice Chris…
In light of this being advice to a newbie, I do believe that downside risks deserve mention as regards to the cheaper lithium batteries. First, the longevity: While these cells are claimed to be good for 1000's of cycles, their guaranteed 'lifespan' is merely in the low order of years---i.e. even at a relatively high usage rate of 4 times per month, you might not see 500 charge/discharge cycles in 10yrs---not sure what the expected lifetime is for the latest of these batteries, but I'd guess 10yrs might be pushing it. With but 500 cycles within a 10yr span, you might do better with lead acid. Second, while repeated deep discharges of lead acid batteries reduce the life of the battery, a single deep discharge of a lithium battery can cause it to be a boat anchor (if it were heavy). Charge cycle life could instantly end at that point for any cell that experiences this. Third, and perhaps most important to mention is the risk of fire. There have been numerous EV car fires in recent years ---most all of these involved cars with lithium batteries as I understand. There has been hot debate with EV-ers as to whether or not these were due to failures in BMS modules, flaws in BMS module design, dense packing of cells and overcharging, defective lithium cells or poor workmanship/mistakes by the operator/converter, etc. Among the casualties was Neil Young's Lincoln Continental EV called the "LincVolt", which also ended up damaging a substantial part of Neil Young's personal memorabilia collection in the fire. There's a strong case to be made that the BMS units are a significant contributing factor, if not the cause, of these fires. As a result, a number of EV'ers have taken the stand that some of the BMS modules and systems out there are not robust enough to ensure that a cell can't get overcharged, overheat and cause a fire. Or more likely: That these BMS's are not robust enough and that they can internally fail shorted, causing a lithium cell to dump massive amounts of current into them, causing both to overheat and melt anything nearby, if not cause a fire. That shouldn't happen with a BMS module that truly has a fuse.
It's great to have automatic controls that allow safe charging and discharging to ensure longevity of our batteries and the rest of the system. I totally trust my Lester golf cart charger to charge my lead acid batteries when I walk away. Given recent stories regarding lithium EV battery pack fires though, I'd want to have significant extra safety items in place to detect when something goes wrong if I had a lithium pack… even an over-temp-triggered relay that shuts a charger down would help----however, that wouldn't help at all to prevent a poorly designed BMS module without a fuse from suddenly shorting and melting your pack even without the charger on.
-Myles Twete, Portland, Or.
From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com] On Behalf Of chris Baker
Sent: Tuesday, May 31, 2011 3:49 AM
To: electricboats@yahoogroups.com
Subject: Re: [Electric Boats] Newbie
Hi Rob,
I have a totally solar trimaran and you can see the details at http://currentsunshine.com
I've used a Torqeedo outboard (and since installing it have become a dealer for them) and lithium batteries with solar as the main energy source. I also have a wind generator and Honda for emergencies.
The charge controller I use is a Xantrex C40 (other vendors have similar devices) which is a load diversion style controller and is suited to multiple charging sources. And cute thing about it is that by using a water heating element as the diversion load I get hot water whenever the batteries are full and there's leftover power.
I'd encourage you to consider lithium batteries, such as those from either Winston (was Thundersky) battery or CALB (was Sky Energy) which are chinese makers of these cells, and which need some time for setup of a battery managements system, or purpose built marine lithium batteries such as from Torqeedo.
In my calculations, based on Australian prices, the chinese lithium batteries are about the same cost as good quality AGM batteries, and offer substantial advantages particularly for a load sensitive solar powered yacht.
The weight will be about a third of that of a comparable AGM pack. And on a trimaran this can be important.
The losses in charging and discharge are near enough to zero, compared with lead acid cells which have a loss of around 15 to 30%. This means you need 15 to 30 % less solar panels for the same energy harvest. So its useful to consider this cost saving when comparing battery prices.
Another advantage is that they are tolerant of low state of charge which can easily happen on a solar powered boat during extended rainy and overcast periods. Lithium cells can be discharged to low levels without harm. And even then their expected life cycles is way better than lead acid cells discharged to only 50%.
I hope this helps, and good luck with your project,
Cheers
Chris
On 31/05/2011, at 10:55 AM, roblanford wrote:
Hey all. I am just restarting a rebuild project on my 34' Sailing trimaran. Have been looking around at several vendors for a conversion kit and am pretty well sold on the electric yachts 180ibl. Will go with AGM batteries, wind generator, solar, Honda portable, and a folding prop. The boat will be used for full time cruising hence the added power source choices. I also intend to use a 48v/12v converter for all the house loads.
I would like to know if anybody has set up a battery bank charging system and charged from multiple sources at the same time? I envision being under sail taking advantage of the regen ability, and charging from the wind generators and solar panels.
I was also thinking about an electric outboard for the inflatable but I have not researched that much yet.
Thanks for any input and advice.
Rob
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