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Old 14-02-2010, 12:03   #16
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Interesting comparisons. And, on paper, they seem valid. But, in the real world, not so much.

Look around you at the boats in your marina...the sailboats. What percentage of them go out at all and how often? How long do they stay out? Overnighters on weekends? One two-week cruise a year, and a bunch of weekenders?
Thanks for pointing that out! Under light-load conditions like you describe, of course you're right, and pragmatism would dictate that the extra money could be (and probably should be) spent on other things. Beer, for instance.

I'm just not one of those people, though. (I do like beer, however.)

It all comes down to trade-offs and choices, and I'm interested in the wisdom of the group before I make this one for myself. After looking over my own situation and doing the math, I can't come up with a compelling reason not to buy these batteries for a liveaboard, less-shorepower type situation -- and I was hoping that if I was missing something huge it'd be pointed out.

So far, it still sounds like a big win.
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Old 14-02-2010, 12:22   #17
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Jallum;

One thing you may have overlooked, the need for a battery Management system. LIFEPO4 cells are very sensitive to over or under voltage and charging. They need to be monitored at the cell level. The cells need to be balance, which means individual charging at the end. They need to kept above a low voltage or you will destroy the cells. Often this is 2.0 volts per cell. They need to be kept from too high a voltage, and shutoff charging at the cell level when they reach that cutoff.

All of this is the role of the BMS system. I have not yet seen a reasonably price BMS that can take the multitude of charging sources on a cruising sailboat - alternator, shore power, wind and solar, and have them all work together.

Anyone know of such a system?
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Old 16-02-2010, 02:38   #18
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One thing you may have overlooked, the need for a battery Management system.
Previously, you mentioned that you sourced yours from Hong Kong. Would you mind sharing the link to their site?

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Anyone know of such a system?
Anyone? It seems like the closest thing is the BMS from GenaSun, which monitors, and has contactors (solenoids) to cut off the charge/draw when voltages reach critical values.
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Old 16-02-2010, 03:12   #19
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Not sure if I'm missing something here, but surely it's not necessary to construct such a large bank if the LIFEPO cells can discharge down to 20% (and more)?
If my daily requirement is 240ah, my AGM bank is probably going to be 720ah because I won't want to discharge below 65% or so.
An equivalent LIFEPO cell bank would only need to be 300ah.
Or not??

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Old 16-02-2010, 03:22   #20
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Not sure if I'm missing something here, but surely it's not necessary to construct such a large bank if the LIFEPO cells can discharge down to 20% (and more)?
If my daily requirement is 240ah, my AGM bank is probably going to be 720ah because I won't want to discharge below 65% or so.
An equivalent LIFEPO cell bank would only need to be 300ah.
Or not??
The larger bank would dramatically increase the time between generator runs (lessening the maintenance requirements / extend the service life) and would also provide extra run-time for bilge pumps. If the extra capacity only costs dollars and isn't costing more in terms of space and weight... then, why not?
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Old 16-02-2010, 06:00   #21
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I'm interested in the wisdom of the group before I make this one for myself.
I have three concerns:

(1) Will the batteries really delivery those sorts of life cycles in a live-aboard cruising situation? We (cruisers) have been burned by previous battery marketing claims on life cycles, made based on experience in different battery environments that just did not translate to the cruising situation. One of the key problems with the cruising battery environment is that we can't (usually) leave the batteries on charge overnight (as with most other battery environments), so they rarely get a complete soaking charge and that has proven a killer of many previous battery claims.
(2) How sensitive are the batteries to f&^k-ups, which happen more often in cruising situations than in most other battery environments. You will be a bit pissed if you screw your $15,000 battery pack by accidentally over charging or shorting the batteries.
(3) These BMS, how expensive is one that will last in the marine environment - looks like quite outrageously expensive to me.

There was a well known superyacht launched a bit over a year ago that was designed to have these batteries and to be a battery run boat (not a full time genset boat as most other superyachts are). Well, it did not work out as the battery claims suggested and they installed two gensets.

I would be delighted if these things turn out to be as good as the claims, but I am sceptical. I would be happy if you try them first, and as a multi-huller they do add more value to you than to use
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Old 16-02-2010, 08:26   #22
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One of the reasons that the Genasun batteries are so expensive is that the BMS circuitry is integrated into the battery. Bruce Schwab is selling these (http://www.rigworld.com/battery.htm) but last time I talked with him he agreed that these aren't really the way to go for the typical cruising boat. Their real application seems to be in a cost-no-object race boat program where saving weight is critical...
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Old 16-02-2010, 08:35   #23
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One of the reasons that the Genasun batteries are so expensive is that the BMS circuitry is integrated into the battery.
On their site, Genasun is selling the BMS as a standalone part for $500, and each monitor (which can manage a single battery, or a short string of batteries) for $50/ea. I'm sure that they provide a ton of handholding and support, but that's what you're paying for when you buy everything from them -- not batteries.

If you want just the batteries and monitoring equipment, it seems that it can be had for much less than what they're charging.
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Old 16-02-2010, 08:42   #24
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I setting up to go with LiFePO4 (Thundersky)for the house bank- See the "Running two Alternators" thread. To make best use of the available charge acceptance rate you really need BIG alternators.
The cost amortization works out even at the presently higher pricing. We're setting our BMS for 75% discharge and can expect a 20+year pack life.
What I've found is that alternator charging large banks of LiFe cells takes more finesse if you want reliability, and I still have to build an alternator controller that talks with the BMS. For lower field coil currents than what I'm using one of the Balmar or Ample regulators may work.

Evans, they're not magic but they do provide a higher energy density than lead acid. Working within their constraints I'd expect a good system.
To get the value out, you really have to DIY. Genasun or Elithion seem to be the best BMS's around for marine use.

Nice to see your interest, jallum.
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Old 16-02-2010, 08:44   #25
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Let us know in 20 years how it works out for ya, OK?

:-)
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Old 16-02-2010, 08:46   #26
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Let us know in 20 years how it works out for ya, OK?

:-)
The question is: will YOU still be around?

Bank life per depth of discharge /cycles is pretty well categorized- thanks to the electric car people. I'm confident enough to put my money where my mouth is.
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Old 16-02-2010, 09:36   #27
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How does the LiFePO4 hold up to heat? Batteries in tropical climates succumb to heat before death from cycles, at least in my experience.
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Old 16-02-2010, 09:40   #28
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What did you end up choosing for your BMS?

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I setting up to go with LiFePO4 (Thundersky)for the house bank- See the "Running two Alternators" thread. To make best use of the available charge acceptance rate you really need BIG alternators.
The cost amortization works out even at the presently higher pricing. We're setting our BMS for 75% discharge and can expect a 20+year pack life.
What I've found is that alternator charging large banks of LiFe cells takes more finesse if you want reliability, and I still have to build an alternator controller that talks with the BMS. For lower field coil currents than what I'm using one of the Balmar or Ample regulators may work.

Evans, they're not magic but they do provide a higher energy density than lead acid. Working within their constraints I'd expect a good system.
To get the value out, you really have to DIY. Genasun or Elithion seem to be the best BMS's around for marine use.

Nice to see your interest, jallum.
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Old 16-02-2010, 11:34   #29
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What did you end up choosing for your BMS?

Chris
Went with Genasun. I wan't convinced that Elithion's circuitry would hold up on a 700Ah cell. Even so they're doubled up on both the cell and master.
Turns out tying it into the alt. is requiring some one-off engineering. Field and temp control are critical.
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Old 16-02-2010, 11:36   #30
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The burning question...

I seem to remember something about Lithium batteries sometimes catching fire.

Web reference here.

I do accept that there are lots and lots of sources stating that the new batteries don't burn, but we are talking about new technology, very high currents and almost continual charging.

Charging lead acid batteries still isn't perfect after how many years?

There is an interesting Wikipedia entry here.
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