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Old 16-01-2013, 06:52   #1
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Basic Designs for LiFePO4 Battery Systems

All,

Is there someone out there than can reference plans for basic system architectures for LiFePO4 battery based electrical systems? I looked for a thread but could not find one. Maybe a e-book?

I would be looking for a system that included wind, solar, alternator, wire sizes, whatever...

While the technical discussions on the pros and cons of LiFePO4 batteries are useful, and I am sure are especially useful for people that are debugging a system, these discussions obscure the basics of implementation and how it differs from a standard wet cell battery implementation.

Thanks!
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Old 16-01-2013, 07:07   #2
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Re: Basic Designs for LiFePO4 Battery Systems

Wire sizes don't change between lead acid and LiFePO4 batteries. The big differences are in charging.
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Old 18-01-2013, 06:03   #3
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There is some of what you are looking for here:

http://marazuladventures.files.wordp...batteries8.pdf
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Old 18-01-2013, 08:08   #4
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Re: Basic Designs for LiFePO4 Battery Systems

If Boeing and GM can't get it right (not to mention Dell, HP and Lenova), what makes you think that the average boater can?

David
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Old 18-01-2013, 08:26   #5
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Re: Basic Designs for LiFePO4 Battery Systems

It is true that the Boeing 787 batteries are comprised of cells using lithium chemistry, one of many lithium chemistries available. It appears that these cells are lithium cobalt based which provides higher energy density but are less stable than the lithium iron phosphate (LFP) cells that we are using in the marine and DIY EV market.

LFP cells have are stable and are arguably safer than LA batteries of any composition. The incidents that I am aware of with LFP batteries were caused by human error or a failed BMS or battery safety circuit or component.
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Old 18-01-2013, 08:50   #6
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Re: Basic Designs for LiFePO4 Battery Systems

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Originally Posted by djmarchand View Post
If Boeing and GM can't get it right (not to mention Dell, HP and Lenova), what makes you think that the average boater can?
The average boater is not mired in mindless bureaucracy or fettered by an idiotic regulatory burden.
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Old 18-01-2013, 09:01   #7
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Re: Basic Designs for LiFePO4 Battery Systems

So Charlie, you're saying the Boeing was too dumb to pick the right lithium technology, as well as too dumb to engineer their batteries and battery boxes safely? Or, let me generous and concede that since the box contained most of the damage, maybe it was built well enough.

Not that it couldn't be, but if those guys couldn't figure out how to use batteries, we'd all better stop flying on their products.

Of course there might be nothing wrong with Boeing's choices (although they made the choice around 2006-7, so that technology may actually be obsoleted by now) the last mass recall of computer batteries was apparently from a problem at Sony, who the computer makers trusted to make a safe (or cheap?) battery.

It will be interesting to hear how the Boeing problem resolves, although everyone involved seems to think that may take a couple of months to find out.
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Old 18-01-2013, 09:08   #8
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Re: Basic Designs for LiFePO4 Battery Systems

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Originally Posted by mcarling View Post
Wire sizes don't change between lead acid and LiFePO4 batteries.
Because LFPs can dish out more current than lead acid batteries, the terminals are generally larger. I had to replace my 5/16" cable lugs with 1/2" ones.
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Old 18-01-2013, 09:11   #9
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Re: Basic Designs for LiFePO4 Battery Systems

Quote:
So Charlie, you're saying the Boeing was too dumb to pick the right lithium technology, as well as too dumb to engineer their batteries and battery boxes safely?
I am not saying that at all.
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Old 18-01-2013, 09:30   #10
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Re: Basic Designs for LiFePO4 Battery Systems

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Originally Posted by CharlieJ View Post
It is true that the Boeing 787 batteries are comprised of cells using lithium chemistry, one of many lithium chemistries available. It appears that these cells are lithium cobalt based which provides higher energy density but are less stable than the lithium iron phosphate (LFP) cells that we are using in the marine and DIY EV market.

LFP cells have are stable and are arguably safer than LA batteries of any composition. The incidents that I am aware of with LFP batteries were caused by human error or a failed BMS or battery safety circuit or component.
It seems a similar argument could have been made about gasoline if it and the Pinto had been invented at a similar time. "Hmm the Pinto blows up all "gasoline" cars will blow up..."


Please can someone lead me to some proof of LiFePO4 fires. I would like to read how they happened or even if they exist. I've been reading for many, many months and all I seem to find is that LiFePO4 is very, very safe except to your wallet when you over charge or go beyond the discharge knee..

Boeing and LiFePO4 are two entirely different technologies both with different levels of safety. It's like saying I got burned and blinded by a flooded battery so AGM batteries are unsafe because you will get blinded and burned by acid because they both have lead and electrolyte......
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Old 18-01-2013, 09:35   #11
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Quote:
Originally Posted by djmarchand View Post
If Boeing and GM can't get it right (not to mention Dell, HP and Lenova), what makes you think that the average boater can?

David
I believe the biggest risk by far is the stored energy potential and related wiring not the chemistry. I'm not saying the average boater can, but have said if you are competent to install a traditional large house bank and inverter charger, then the differences are not that great.

But I admit this is based on information available today about lithium ferrous cells. As more data becomes available, I might need to change my opinion.
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Old 18-01-2013, 09:50   #12
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BTW an hour in to capacity testing, at 100A, and the battery is holding steady at 12.85V....

A 400Ah bank of FLA with a 1.27 Peukert would be seeing an equivalent load of 154A +/- and be significantly more deeply discharged than 100Ah....
That's a very nicely done test setup. Please post the final results. If you get into more Li work take a look at the RC Aircraft battery chargers...some of them work both ways, charging from an external battery, then during discharge recharge the external battery, all while logging the results. When I get back to the US, and easy shipping again, Im planning on picking one up.
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Old 18-01-2013, 10:02   #13
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Re: Basic Designs for LiFePO4 Battery Systems

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That's a very nicely done test setup. Please post the final results. If you get into more Li work take a look at the RC Aircraft battery chargers...some of them work both ways, charging from an external battery, then during discharge recharge the external battery, all while logging the results. When I get back to the US, and easy shipping again, Im planning on picking one up.

That is my home built Ah capacity tester for LA batteries..


Anything I am doing for customers at this point is going to be pre-built factory batteries with factory BMS systems. Working on a Genasun installation next week and really like their execution of the system. Alex is a very, very smart guy....

This pack is for my own boat and mostly for my own knowledge. I like to take things apart, break them down, build them up, load them, charge them, design and test things until I know exactly how they perform and have seen it with my own eyes. Not that I don't trust what I read on the net, but I just need to see it, measure it and experience it for myself....

I did not do enough of this when AGM's came on the scene so I am understandably cautious when it comes to customers boats. I will let the manufacturer take the hit on warranty etc...... I am also waiting on guidance from the ABYC before building my own custom packs...
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Old 18-01-2013, 16:23   #14
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Re: Basic Designs for LiFePO4 Battery Systems

Re the Dreamliner's battery problem, we don't have enough information to know if it was even the fault of the batteries.
It could just as easily been wire chafe or overheated wiring bundle causing a short.
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Old 18-01-2013, 16:38   #15
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Re: Basic Designs for LiFePO4 Battery Systems

At this point in time I personally would not want my safety and boat dependent on the proper functioning of a battery monitoring system. Stuff just goes wrong all the time on a boat. Yes, there are potential problems with LA batteries, but their problems and pitfalls are well understood and you can use them without sophisticated electronics and monitoring if you need or want to. Yes, Boeing was using different chemistry that is inherently more dangerous, but even they couldn't get the BMS correct, apparently. I strongly suspect we will all be using different battery technology onboard eventually, but I won't be using it until it is considered safe enough to be selling to any Joe at WalMart, like LA batteries. Also, despite all the pooh pooing by lithium fanboys, I strongly suspect your insurance carrier would find any battery out of the ordinary a serious problem if there was any sort of claim. Think of it this way, if your boat's insurance survey indicated you had a kerosene stove and afterwards you changed it to propane and blew up the boat, do you think your insurance company would say "no problem!"
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