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Old 24-09-2013, 03:41   #421
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I agree charging isn't the source of heat. But a smart regulator could reduce to say 80% SOC if bank is hot. And it could alert user that battery life is being reduced.
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Old 24-09-2013, 04:33   #422
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Re: Lithium Batteries (for the rest of us)

Quote:
Originally Posted by ebaugh View Post
Floating was perhaps a poor choice of words here, but I was thinking ahead, because I want to leave a cell at 3.35 for 48 hours and see if it continues to accept charge. Any point beyond the chart posted is floating. It just wasn't charged to a higher voltage first.

The problem is the PowerLab firmware won't allow charging for more than 8 hours before it shuts off due to a "safety" limitation. It will log voltages, but not current if an external power source is used. But that log would be pretty boring.

Probably use a lab power supply set to 3.35 for the 48 hour period, and then measure the current required to attain full charge.
This would be a very interesting experiment, don't worry about graphing the current throughout. If you could just leave the cell connected to a 3.35V supply for 48 hours, measure any residual charge current at the end, disconnect, wait for an hour and measure the open-circuit voltage (same curiosity as always!), it should tell us quite a bit already.
Then you could do a metered full charge from there to see how much capacity was left indeed.
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Old 24-09-2013, 05:31   #423
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Re: Lithium Batteries (for the rest of us)

LiFePo4's are more subject to cold then heat I was to understand. In most cases they are more tolerant to heat than even Lead bats. The fact that they are going into an engine room that gets to 140d only asks why the room is that hot. Ventilation of that much heat should be considered just for the engine let alone the batteries. The Leaf had issues with high temps and battery degradation do to no active or passive heat removal in high temp climates (AZ) and there is a need for heat removal with cylindrical cells such as in the Tesla which is liquid cooled (also different chem I think) but no active cooling mentioned for prismatic. I also would think that if this was an issue it would have shown up in EV's as a red flag. Since most of you are only talking about 12 cells I'd move them out if there was a concern.

Steve in Solomons MD
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Old 24-09-2013, 07:35   #424
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Ok I admit to knowing very little, so usually I sit back and keep my mouth shut.

Transmitterdan-yes that device is what the masses are begging for. I would suggest it also be able to divert any surplus energy from solar or wind to the hot water heater (is there such thing as too much hot water on a boat?)

Ebaugh- I often look at these cells and all those vertically oriented grooves and ponder the feasibility of using them to contain a liquid cooling system. From something as simple as copper tubing to more complex like channeled aluminum plate. Yes, I admit complexity breeds failure, and I also have concerns about the consequences of a "dropped wrench short" scenario. However, I wonder if something like this might solve your problems without creating to many of its own.

I will now go back to reading only mode....my fount of wisdom having dried up.
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Old 24-09-2013, 08:01   #425
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Hmmm.... The problem seems to be, who do you believe:
The guy with the most runs on the board but not actually in a boat,
The guy with a lot of runs on the board in a boat but using a slightly different chemistry so the results and figures may be a little different
The guy who has based a lot of his knowledge on a different style of cell so some of his knowledge is in dispute
The other users who have results of their own
The guy who had a professorship award because of his knowledge in these batteries and is the person who sets up the stuff for NASA and the longest running house battery to date
The ones who don't actually have any of these batteries but seem to think they are a fount of knowledge

Or a combination of all this knowledge, weigh one finding against another, look for repeat results or patterns of results so the grain can be sorted from the chaff and build a system that suits your needs. Only you can decide the answer to these questions.

T1 Terry
Terry you have begun to personalise this debate. All that can be done is to let each person reLate their experiences and listen to their professional opinion where they are professionals

In you case , undoutably you have a big bank with lots of cycles. Yet we've yet to see actually capacity graphs. ebaugh and others have provided data and Maine sail has related his boat specific experiences.

As another poster said

" I don't see the value in personalizing what should be a purely technical issue illuminated by real data."

I think we can summarise

That the charge and discharge limits and advice are at a consensus

Cell monitoring to warn against out of balance series cells

Lvc and optional HVC cutoff

If possible don't float charge the batteries ie disconnect on completion

Strap the bank to prevent " panting "


The other issues like mini cycles and load sharing issues , temperatures issues and degradation in cycle life due to usage storage , discharge depth etc await further information and all we have is adhoc data. That is not to say they should be ignored but we have to collect more scientific data.

Dave
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Old 24-09-2013, 08:08   #426
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Re: Lithium Batteries (for the rest of us)

Simply moving cold air across the cells would solve the battery degradation due to heat, a small air to sea water heat exchanger unit run by the motor pumping cool air into the bottom of the battery box and baffles to direct the air up between the cells and then venting this air outside the battery box.
The whole max available energy to temp thing balances on a knife blade 60DegC, the drag race boys heat their cells to this temp so they can get the most out of them for that short but huge current demand, short cycle life is the cost of such an exercise, but a price they are willing to pay.
Prismatic cells can shed heat much better than cylindrical cell purely by their design, but they must have a method of getting that heat away from the cell cases.

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Old 24-09-2013, 08:20   #427
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Re: Lithium Batteries (for the rest of us)

Hi Dave,
I'm trying to personalise it to suit the question asked
Quote:
Originally Posted by Hyprdrv View Post
Understood Terry and believe me I have read every post here and a lot else where on the subject. I've also read the DIY pages as well. Other than the Genset and Solar Cell issues for recharging the Car guys are where I get my Propulsion info from.
Don't get me wrong, I love the info and have learned a lot from you guys and we ALL are appreciative of the discussions, it's just at some point there has to be conclusions even if it's by vote. Some are simple to get to others are more complicated but there has to be conclusions and that was what this post was suppose to be about. The more people going to LiFePo4's the more suppliers and then the lower the cost for the cells will be. As I said the "other" string can be for the Tech side of an answer and if there is a disagreement on something we can be sent there for a more in depth discussion. Just because your a Techy doesn't mean you should ignore this thread but there has to be SOME points you all agree on!

Steve in Solomons MD
So my reply stands,
[QUOTE =T1 Terry] Or a combination of all this knowledge, weigh one finding against another, look for repeat results or patterns of results so the grain can be sorted from the chaff and build a system that suits your needs. Only you can decide the answer to these questions.

T1 Terry
[/QUOTE]

I'm sorry if the information doesn't come in the scientific methodology you require, possible this could be a result of the price you are paying for it.
To quote someone well known around the forums in our part of the world.
" It's bad enough they demand free information, now they demand it be presented in a formate of their choosing"
As I often said else where, if you want to data, spend the money, buy the batteries, do your own tests, itís for your interests not mine.

T1 Terry
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Old 24-09-2013, 08:21   #428
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Re: Lithium Batteries (for the rest of us)

Thank You Dave, That's all I was asking for. What would be great is if we could have a new posting that had limited access to a few of you "Brains" to add to the list as conclusions or important data is established.

Terry I remember reading a number of boats with Diesel engine compartments don't have mechanical ventilation. I don't know if this is true but if so this should be added with a thermatic switch.

Steve in Solomons MD
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Old 24-09-2013, 08:32   #429
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Quote:
Originally Posted by I.Grind View Post
Ok I admit to knowing very little, so usually I sit back and keep my mouth shut. Transmitterdan-yes that device is what the masses are begging for. I would suggest it also be able to divert any surplus energy from solar or wind to the hot water heater (is there such thing as too much hot water on a boat?) Ebaugh- I often look at these cells and all those vertically oriented grooves and ponder the feasibility of using them to contain a liquid cooling system. From something as simple as copper tubing to more complex like channeled aluminum plate. Yes, I admit complexity breeds failure, and I also have concerns about the consequences of a "dropped wrench short" scenario. However, I wonder if something like this might solve your problems without creating to many of its own. I will now go back to reading only mode....my fount of wisdom having dried up.
You could water cool them or use forced ventilation. I know another DeFever that implemented forced fresh air cooling to their Pb battery box in the ER to manage temperature. Worthy of consideration...
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Old 24-09-2013, 09:11   #430
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Re: Lithium Batteries (for the rest of us)

Quote:
I'm sorry if the information doesn't come in the scientific methodology you require, possible this could be a result of the price you are paying for it.
To quote someone well known around the forums in our part of the world.
" It's bad enough they demand free information, now they demand it be presented in a formate of their choosing"
As I often said else where, if you want to data, spend the money, buy the batteries, do your own tests, it’s for your interests not mine.

your missing the point T1 Terry, The point is to build up documented experiences from different usages. Collaboration helps advance everyones knowledge, You wouldn't have Linux , for example without it , not to mention a whole host of free excellent software

what I meant by documentation was capacity versus lifecycle. Because thats one of the things we really know little about, How do these cells respond to a particular usage pattern. We know they are robust, but Li tends to exhibit all issues as capacity reduction , so its helps to determine from a range of sources how capacity diminishes with time.

In my case I have some small capacity large format cells, and a whole host of cylindric cells. Im trying to draw conclusion from the raw data and independently draw conclusions, any of which Im quite happy to share.

Furthermore there is research on mini cycles, pulse response , temperature , storage life etc going in on Li and hence the debate.

not to mention the EV and RC boys that are really stressing this technology to its limits and finding a few things along the way

Dave
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Old 24-09-2013, 10:10   #431
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Re: Lithium Batteries (for the rest of us)

Regarding recent comments that we should look to the EV community for advice/information when considering LFPs for electric propulsion, I disagree.

An off the shelf 12kW electric propulsion system I am familiar with is limited to 250A peak at 72VDC. Thus a nominal 400Ahr bank of LFPs, probably the minimum reasonably sized bank, is still operating at fractional C. Normal operation of this 12kW system is typically < 100A, very much fractional C for the minimal 400Ahr bank.
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Old 24-09-2013, 12:53   #432
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Re: Lithium Batteries (for the rest of us)

Charlie,
I'll be running a 144V system at a 80A peak and probably 100Ahr, hoping to get 200Ahr batteries if the price works out. That should give me around 2 hours of run time on bats alone at 6/7 knots. Please tell me why you think the fractional C is a problem. I agree that the EV system end use is different than the EBoating as far as the batteries loads. How do you think this effects the batteries?

Steve in Solomons MD
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Old 24-09-2013, 15:06   #433
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Re: Lithium Batteries (for the rest of us)

Steve-You and I are in violent agreement ;-)

A point was made about ten posts ago that implied that e-propulsion put more of an electrical demand on a battery bank. My point was that even when used for e-propulsion, LFPs are going to be operated at fractional C so we will not experience the same issues that our fellow early adapters in the DIY EV world do.
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Old 24-09-2013, 17:31   #434
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Re: Lithium Batteries (for the rest of us)

Terry-
Does the NASA guy mention that most of their projects are probably designed to run at -270C with a battery pack heater to bring them back UP to an optimized temperature?
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Old 25-09-2013, 03:30   #435
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Re: Lithium Batteries (for the rest of us)

The problems you need to address with propulsion batteries is monitoring and tapering charging of a very large number of cells in series, not 4 cells like a house battery. The differences in monitoring requirements are quite large, but monitoring is still the key. On the EV DIY forum there is a member called RW Audio who has made up boards to use the Junsi cell logger for large series pack monitoring, all the alarms are linked so any cell going over 3.6v or under 2.8v would set off what every warning system or protection system you connected to it.
I agree the C rating demands may not be as high driving a prop as driving wheels from a stationary take off, but there will still be high demands at times. If you plan to use a 200Ah pack that is very different story, most EV guys are down around 40Ah so there are very high demands on the cells.

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