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Old 22-11-2011, 23:33   #181
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

There's an excellent short paper written by Electric1 (I think) on the initial balancing of cells process. It's written from the perspective of using his mini-BMS, but the process works well regardless of whether you have a BMS or not.

His method of creating balance between the cells uses only your 12V charger and a discharge load capable of running off a single cell (so a resistive load, or a high power resistor). That's a lot simpler than the cell charger using a dc:dc converter that we used. We used 0.1 ohm 180W power resistors for the load, which would work well in his process also.

Product Support

It's the 3rd article down: "How to perform initial LiFePO4 battery pack balancing"

BTW, thanks to everyone who has selflessly put out free info like this. I know it helps people like me get into the technology, and will hopefully ultimately benefit people like Electric1 who are trying to make a business out of the sector, but it's still a great thing to do. Well done to you guys

Cheers,
Paul.
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Old 22-11-2011, 23:49   #182
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Hi Terry,

You must have slipped your comments in whilst I was typing my next post.

Yes, by C/10 I mean 0.1C, or 40A in my case, and C/4 is 100A. I worked in the battery industry for 10 years a while back, and that was the more common way of writing it then.

Our shore charger is a 40A charger, and our main alternator puts out a max of 110A (so 100A is a practical upper level). On discharge, if we're not using the inverters (which is most of the time), we very seldom get to 20A total draw, and even using the inverters (microwave, vacuum, etc) we seldom get above 100A (which is approx 1200W - a big microwave on full power).

On the cells, the spec.s are:

Dimensions: 449mm (L) * 71mm (W) * 283mm (H - incl connection posts)
Weight: 14.3 kg

That gives the battery dimensions as:

449mm (L) * 284mm (W , i.e. 4*71mm) * 283 (H) weighing 57.2 kg

Those dimensions don't include the clamping bars.

I thought about parallel/series strings like you did, but wanted the simplicity of fewer cells. Also, if I end up needing more capacity in future, we'll add 4 more cells and arrange in a 2p4s configuration.

So far I really like these cells. Of course the big unknown is cycle life, but thus far the cells have exceeded CALBs performance spec.s in every way.

Cheers,
Paul.
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Old 23-11-2011, 00:09   #183
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Here's another take on the question Nick on "Jedi" asked about comparison with lead-acid (LA) capacity.

I think Terry was quite conservative (which is good).

A less conservative approach could be:

For Lead-Acid (LA) cells:
On a typical sailboat one can rarely achieve more than 85% charge in LA batteries due to charging inefficiencies and time-lengths (they have a really long taper to their charge curve). Additionally, most manufacturers of LA batteries for house-banks recommend a maximum discharge to 50% SOC.

This gives a practical usable amount of 35% of the rated capacity (C/20 rating typically). For Nick's 1000 Ahr battery bank, that's 350Ahr of practical usable capacity per discharge.
For LiFePO4 (Li) cells:
It seems that it is very easy to achieve 90 - 95% charge on Li cells, so let's use 90% to be conservative (we seem to get somewhere around 94% with our cells with the cutoff voltage at 14.4V, or 3.6V per cell). Most Li cell manufacturers seem to recommend a practical discharge maximum of down to 20% SOC.

That gives a practical usable amount of 70% of the rated capacity.
So if we take the 350Ahr practical capacity of the 1000Ahr LA battery, divide by the 70% practical capacity available in Li chemistry, we get an equivalent Li battery of 500Ahr. So that's a factor of 2 in capacity between lead acid and LiFePO4.

Of course, that's a less conservative approach, and the big unknown with LiFePO4 is the cycle life, so it remains to be seen whether they give a factor of 2 over a total lifetime, but it's a great starting point.

In practical terms, our 400Ahr, 57kg LiFePO4 battery is equivalent to 6.7 * 120Ahr Trojans (800Ahr), weighing 200 kg and more than twice the volume.

Cheers,
Paul.
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Old 23-11-2011, 00:12   #184
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Quote:
Originally Posted by sytaniwha View Post
T1 Terry,

Your battery pack and holder look great - it'd be good to have a custom made holder like that.

I'd like to make one suggestion based on your photo (which you may have already done).

As you said in one of your posts, your 4p4s pack is a good way of assembling a battery for a number of reasons, and I totally agree with your comment that you should absolutely NOT connect 4 series strings in parallel, but SHOULD connect 4 parallel strings in series, as you have done (for anyone who doesn't see why this is, draw a diagram of each - that's what I did. It then becomes very evident that a series first pack will be likely to create imbalanced cells quickly).

It looks like you have connected the parallel strings together at the cells at the bottom of the picture, and that you have also taken the +ve & -ve connections off at those points also.

It may be worth you considering the following:
  1. add another set of connectors between the parallel strings at the top cells in the photo, and move your +ve & -ve take-off connections to one of the middle 2 cells, OR
  2. move your connections between parallel strings to one of the 2 middle cells in each string, and your +ve & -ve take-off wires to the same cell.
The reason for this is that the most balanced battery is created by making the electrical paths for each cell identical. By linking the parallel strings through one of the end cells, there is a small extra resistance for the other cells in each string through the connectors in the parallel arrangement. The cells at the far end (top in your photo) have the biggest resistance because they deliver their power through the most connector links.

It's not a very big resistance if you're using really good connectors, but could become significant if you have a high rate alternator or use inverters (which have high discharge rates @ 12V).

The ideal situation would be to have a connector at each of the 4 cell pairs between adjacent parallel strings, and then 4 identical take-off wires at each end wired to a +ve and -ve post or buss. But that may be over-kill.

I think in this situation I'd probably go for 2 links between each parallel string on the end cells, and then 2 idenitcal take-off wires each for +ve & -ve brought to a common post.

This isn't a LiFePO4 only concept. The same theory is appropriate for any electrical parallel/series arrangement (lead batteries, resistors, etc).

Anyway, just an idea that I thought you might find useful.

Cheers,
Paul.
Hi Paul,
That set up was only for the conditioning balance charge. The set up now is where the link plates are in the photo is cell 4, there are link plates at cell 2, the charge and discharge are at cell 1. There is a second parallel bank with 00 gauge cable linking the cell 2 points on each parallel string the another identical battery bank, total capacity 720Ah. The max solar charge rate is 100amps so balanced across the cells it's only 0.14C but even if 1 cell was to cop the lot it's onlt 1.1C, still well withing the cells accaptance rate. The do get deeply cycled, this morning they were down to 17% SOC (83%DoD) but the max discharge rate is only 30 amps powering 2 inverter that are powering 3 fridge freezers. The discharge gets that deep if the sun forgets to shine for a few days.
Just a note regarding using terminal voltage to judge SOC, even at 17% SOC and a 25 amp load the terminal voltage was still 12.9v and as soon as the fridges cycled off the load dropped to 4 amps the terminal voltage returned to 13.1v
A state of charge meter is the only way to really know where in the charge cycle the batteries are, the only voltage indicators are fully discharged and fully charged, anything inbetween is purely guess work without a state of charge meter.

T1 Terry
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Old 23-11-2011, 00:18   #185
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Another annoying question Paul,
[QUOTE][It seems that it is very easy to achieve 90 - 95% charge on Li cells, so let's use 90% to be conservative (we seem to get somewhere around 94% with our cells with the cutoff voltage at 14.4V, or 3.6V per cell)./QUOTE]
The 3.6v per cell or 14.4v at the terminals, it that to zero current flow or till the voltage is reached? If it's voltage shut off, what amps would you be charging at when the shut off voltage is reached?

T1 Terry
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Old 23-11-2011, 02:19   #186
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Hi Terry,

No questions are annoying - I think if we can share info, then it makes it all a lot easier. We all learn from each other - and for me, the dialogue helps clarify ideas I'm thinking about, and gives me new ideas that I haven't thought of. I'm not a great fan of many of the web developments (Twitter, etc), but this is one of the few really useful things about the web, in my view.

Sorry, I wasn't totally clear on the charging regime. For both charge controllers the format is very similar, but I've got more data using the 40A shore charger, so that's what I'll reference.

It's a 3-stage regime:
  • Constant Current (@40A), which of course is really just the charger maxing out it's current delivery capability trying to bring the battery to a set voltage level of 14.4V (3.6V/cell). Without wanting to muddy the waters, these type of CC chargers are really just CV chargers with a current limit.
  • Constant Voltage @ 14.4V (3.6V/cell), during which the charger current drops really dramatically. In fact the charger starts reducing the current at 14.0V, which I think is part of it's programmed smarts to ensure it reacts in time to the voltage set point.
  • The charger takes the voltage up to about 14.48V before tailing the current to zero, which I think is simply a function of the accuracy and reaction time of the charger.
  • the charger then shuts off the charge process, but maintains a 13.5V (3.375V/cell) float voltage as the 3rd stage. With LiFePO4 batteries, this float volatge will probably never deliver any current to the battery because their self-discharge is negligible.
I'm probably being a bit conservative saying I only achieve about 94% SOC. The curves CALB gave me show the cells hitting rated capacity at about 3.6V/cell, with the charge cycle going through to 4.2V/cell where they achieve 105% of rated capacity (they're careful to recommend only charging to 3.6V).

This suggests that they build cells that actually have a higher capacity than they rate at, if you want to charge to a higher voltage level. I'm guessing that they down-rate the capacity and charge voltage to achieve greater cycles, which is a positive sign for decent cycle life.

I've attached 2 images of a charge cycle - one you can see in jpeg format, but where the scale numbers didn't come through, and a pdf with all the scale info on. This was taken by hand before I added the cell voltage logger, so it's a bit rough, but gives an accurate account of the charge cycle using the shore charger.

Cheers,
Paul.
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Old 23-11-2011, 04:23   #187
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

I think you sould invest in a cell logger and acurately measure the cell voltages, 3.6v per cell till zero current flow will rapidly heat the electrolyte. The 3.6v and 4.2v are very old specs from the very early days of LiFeP04 development. They used these figures because it was close to the figues standard lead acid chargers put out and they wanted the batteries to be direct drop in.
They sometimes use these voltages for constant current charging at 1C or higher and stop charging as soon as that voltage is reached. Because of the rapid charge rate towards the end of the cycle the terminal voltage rises faster than the absorbed voltage, once the charge is stopped the cells drop back to around 3.4v, this is full, anything past that point is torture.
Up to you, they are your batteries but have a look through the DIY EV forum posts recently and a lot of them have come back to the 3.4v per cell max charge. There is a thread on there about someone who put all their cells in parallel and charged them a 3.6v, destroyed over $2,000 worth of cells before they realised they were cooking them.

T1 Terry
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Old 23-11-2011, 08:53   #188
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

I bought (4) 200 AH HiPower batteries form another member here. I haven't installed them yet but have charged them individually using a 6 amp LiFePO4 charger at 3.7 volts to equalize them.

The mfg specs I can find on these batteries shows max charging votlage at 3.85 volts or 15.4 volts for the pack. The 15 amp lead acid charger I currently have charges at 14.7 volts. Is there a problem charging at this voltage? The manufacturer doesn't show that to be a problem in the specs.

The reason I ask is that I have two banks, starting and house, both running off the same charger and same alternator depending on the A B Both switch. The starting bank is two group 27 LA at 90 amps/hour. I am reluctant to get rid of the LA batteries as I already own them and they extend the amount of time I can be off the grid.

By the way, I think the biggest acceptance problem using these batteries (besides the cost) is that there does not appear to be a single charging voltage that is accepted.

Dale
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Old 23-11-2011, 21:37   #189
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Hi Dale,
I can only speak from my experience working with these batteries and from what I have managed to unearth through other peoples theories that I have put to the test and proved to myself to be correct or incorrect, others may have different ideas so keep an open mind.
Jay Whitacre from the Robotics Institute at the Carnegie Mellon university would the most widely accepted authority on the LiFeP04 batteries, he's been working with them for over 10 yrs I believe, I temper a lot of what I read and hear with the information he puts forward in his LiFeP04 battery overview.
It is becoming widely accepted that 3.4v per cell is fully charged, anything after that creates heat in the electrolyte and once the electrolyte is heated above 60 deg C it starts to separate causing the plated material inside to become coated with a substance that effectively seals them over, wrecking the cell. There is nothing to be gained charging above 3.5v per cell, safest is 3.45v per cell. 3.85v is the point where damage starts to happen if held at that voltage for even a short time so this is the absolute max over voltage after the cells have been condition charged and that only happens once in their life, no need to repeat it as it will cause cell damage.
Unlike lead acid batteries, these cells never need an equalising charge as such, charge all the cells to 3.45v and they are all equally fully charged, that’s as equalised as they need, anything else will just cause them damage.

How to charge these lithium batteries alongside lead acid batteries? My suggestion would be to charge the lead acid batteries and the lithium batteries the way you suggest, using an A + B battery switch so both A and B are linked but have the lithium batteries on the B terminal. This is to protect the alternator when the charge is cut to the lithium batteries, the lead acid batteries are still there to accept the charge so the alternator diodes don’t suffer.
Fit a voltage sensing circuit linked to a solid state relay with the relay mounted to interrupt the charge between the B terminal and the lithium battery. Set the voltage sensing circuit cut off to 13.8v is using a pulse width modulation voltage control or 14v with a 0.3v hysteresis if using a slow switching control.
Maybe senormechanico (Steve B) or one of the other electronics cluey people are still reading this thread would be willing to draw up a schematic or even make one up if there is enough of a market for a unit to do this job. I use a Plasmatronic PL20 with a solid state relay adapted to it so I have a solar controller as well as an alternator charge control and a mains power charger control and a battery monitor, all rolled into one package. All up package is about AU$550 and includes a 200amp shunt and adaptor so the battery monitor section can accurately record the State Of Charge (SOC) which is the only way to accurately know just how charged the batteries are. Worth spending the money if you don’t already have all that gear but I don’t know if it would be good value if you already have the other bits.
The bits you need are:
a state of charge monitor and a volt meter ( 2 separate meters, you can’t tell state of charge with a volt meter on LiFeP04 batteries)
an amp meter
amp hour meter (optional really)
solar controller is you are using solar panels as well.

Hope that helped

T1 Terry
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Old 23-11-2011, 23:58   #190
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Being pedantic, I both agree and disagree with T1 Terry's comments.

Firstly, I agree with:
  • A cell logger for each cell is a good idea, and I do actually have one (always on, recording each cell's voltage every 30 sec - it generates a lot of data). I did refer to that in one of my earlier posts, but they're quite long so I'm not surprised if everyone missed it,
  • Lower charge voltages are always better for any battery chemistry, as long as they aren't below a level that gives a decent charge at the charger's amperage rating.

But here's where I disagree a little with Terry's position:
  • The charge voltage limit you need to use is a function of the charge rate (Amps) which you are charging at, and your definition of what an acceptable cell capacity is (as a % of the rated capacity). There is not a single voltage level which works for all the different combinations of those variables.
  • The chemistry defines the maximum voltage you can use without causing the electrolyte to break down. Although the different LiFePO4 manufacturers use slightly different chemistries, the general consensus seems to be that rapid electrolyte breakdown occurs above 4.2 - 4.3 V/cell. So this is the obvious "never go above" point.
  • Below that 4.2 - 4.3V level, you will get some degradation of the cells as the voltage gets higher (which will tend to reduce the cycles you can get from the cells), so if you can keep your voltage lower you will see a benefit, provided that you have a voltage high enough to get enough capacity into the cells for your application,

Going back to the charge voltage limit for my particular cells (CALB 400Ahr prismatics), I have gone back & forwards with CALB's engineers over the last 12 months with various data and comments, and my opinion is that they really do know what they're talking about (which is quite a relief).

They spec the capacity of their cells at a 0.3C charge / discharge rate with a 3.6V charge cutoff, and a 2.5V discharge cutoff. This doesn't mean that you have to use those cutoffs and charge rates, but if you do you will get the rated capacity out of the cells (actually +/- about 1%).

They also spec the maximum voltage of their cells as 4.2V, which gives you about 104% of the rated capacity, at 0.3C. Of course you'd be silly to go that high because of the cell degradation it would be likely to induce, and the chance of catastrophic electrolyte failure, and the fact that you only get 4% extra capacity benefit for a whole lot of risk.

Interestingly, at 0.3C charge rate (120A for my cells), if you limit the voltage to 1.4V/cell, then you will only achieve about 70% of the rated capacity. At my max charge rate (0.1C - 40A), the typical capacity achieved with a 3.4V limit is about 78% of rated capacity, or 312Ahr. Of course, these are approximate values taken from charge curves in one set of conditions (temp, humidity, stage in cycle life, etc). These figures will vary slightly as conditions vary.

Because this is near the end of the charge cycle (i.e. near the "knee" of the curve), the SOC changes rapidly as the voltage limit increases from around 3.4V. So at my 0.1C charge rate with my cells I can achieve the following %'s of the rated capacity at the given voltage limits:
3.40V 78%
3.45V 94%
3.50V 98%
3.55V 99.5%
3.60V 100.5%
As I said, I totally agree with Terry that lower limit voltages are generally better for my cells, so if I can live with getting 78% of the rated capacity from my cells, then setting the voltage limit to 3.40V is a great way of prolonging cycle life.

For my particular cells, given the data above, it seems pretty obvious that setting the voltage limit somewhere around 3.45 - 3.5V is probably a really good trade-off, giving 94% - 98% of the rated capacity at my charge current. (So here I again agree with Terry that my current 3.6V limit isn't necessary - that's the power of these forums for me, they make us think about things more )

If my max charging current was different, then I'd need to look at the curve for that current to determine an appropriate voltage limit.

This all dove-tails into why higher charge rates are less kind to all battery chemistries: a higher charge rate requires a higher voltage limit to achieve a given % of the rated capacity. And higher charge voltages are generally worse for batteries, and can be cataclysmic if they exceed the electrolyte breakdown voltage for significant periods.

Why do higher charge rates result in higher charge voltages? Because a battery has an internal resistance, and through Ohm's law we know that V=IR, thus a higher current driven into the cell will result in a higher terminal voltage. Hence higher charge rates are less kind to batteries (sorry if I'm repeating myself).

But I disagree with Terry about a 3.6V limit being bad for the cells. Worse than a 3.4V limit? Yes. But for my cells at my charge rate, given that I'd like to get somewhere in the 90%+ range of rated capacity, it's a requirement (or at least 3.5V is).

On the EV forums there's a ton of really good data based on real world experience, but sometimes I notice that the conclusions drawn aren't necessarily logical, particularly around the charging area. A lot of statements are made like "when I first start charging my charger increases the voltage gradually ....", or "at some point my charger starts reducing the current in the CV mode".

This leads to my final slight disagreement with Terry's comments: that you shouldn't let the charger reduce all the way to 0Amps. In fact, the charger isn't reducing the current, the battery is, and that's it's natural way of making sure it isn't overcharged. It's just like at the start of a CC stage, the charger doesn't increase the charge voltage gradually, the charger only pumps it's maximum charge rate into the battery. It's the battery voltage that's increasing as it becomes more charged. Those are actually relatively subtle distinctions, which I sometimes gloss over or put backwards also, but it's quite important.

The chargers don't regulate very much. Typically a smart 3-stage charger regulates only the maximum voltage in the first 2 stages (both the CC & CV stage), and then the charger also triggers a timer once the current drops from it's maximum amount, which is somewhere around the time that the battery voltage hits the charger maximum voltage set point. That timer is a practical limiter that just stops the battery from drawing ever smaller amounts of charge for-ever, because keeping the battery at that higher set voltage forever is not a great idea (again this is where I agree with Terry )

SO, to answer Terry's comment about me trailing the current off to 0amps, my charger doesn't actually do that because it has a timer, but the charge acceptance of the cells drops so quickly once they hit the set voltage that it makes no practical difference. That's one of the many good things about LiFePO4 cells.

Yikes, that's a long post - I hope it's clear enough.

Oh, and my take on situations like that EV guy who killed his cells charging to 3.6V: I don't know the specifics on that one, but I tend to think that those types of situations are probably either user error, or a manufacturing defect in the cells, rather than an inherent property of the chemistry. These cells are still relatively low volume, and some of the manufacturers are definitely variable in knowledge and quality, so I can imagine quite high failure rates, and a production consistency curve skewed towards lower consistency.

I'll be interested in everyone's comments on my comments

Cheers,
Paul.
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Old 24-11-2011, 00:51   #191
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

My thoughts on Dale's setup:

We have a similar setup: using the LiFePO4 for house bank, using an Optima sealed lead for the start battery, and charging both off the same charging sources.

If you read my long last post, I agree with Terry's comment that you probably don't want to be charging the LiFePO's at 3.7V / cell on an on-going basis. (However I doubt you've damaged them by doing a single initial charge at that level). I don't know the specifics of HiPower cells, but I imagine that if their maximum specified voltage is 3.85V (vs 4.2V for my CALB cells), then it's likely that their charge curves are at slightly lower voltages than my CALB cells also. Combine this with your charge rate being less than 0.1C and I'd tend to agree with Terry's recommendation of a voltage limit of no more than 3.5V, and probably better if lower.

I think that if you design your charge system for the LiFePO battery, then it'll also work with your Lead battery without any additional electronics.

The reason for this is that you're using the lead battery for starting purposes only. Although that requires a large instantaneous current, it's for a very short time, and so it doesn't actually take much capacity out of the battery (e.g. our engine requires about 400A for about 0.5sec to start - that's less than 0.05Ahr!). Your lead battery is probably self-discharging that much per hour, and typical float stages of chargers are designed to compensate for self-discharge in lead-acid batteries. A typical float charge voltage is in the 13.6 - 13.8V range, so if your LiFePO4 setting is 3.4V/cell or above, then you're in that range and you'll be able to recharge your lead battery just fine.

I wouldn't charge it on the "Both" setting though - in fact I'd suggest never using the "both" setting in charge or discharge. Mixing chemistries like that isn't a good idea.

Charging your LiFePO battery on "A" most of the time, and then occasionally charging your start lead battery on "B" should work well: just remember not to switch from A to B whilst the engine is running because you'll go through a "no-load" state which could kill your alternator regulator.

Even better would be if your charger and regulator both have a dual battery bank charge capability. Typically these now have a main charge output for your "house" bank, and a residual output for your "start" bank. In many units these are already isolated so you won't be mixing chemistries. Again, set your charge parameters for the LifePo bank, and your start bank will be taken care of. This is what we've been doing for the last 6 months, and it's worked very well.

If you have that (which many sailors do now), then you can ditch the "1,2,both" switch altogether (I hate those things ).

Cheers,
Paul.
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Old 24-11-2011, 00:59   #192
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Quote:
SO, to answer Terry's comment about me trailing the current off to 0amps, my charger doesn't actually do that because it has a timer, but the charge acceptance of the cells drops so quickly once they hit the set voltage that it makes no practical difference. That's one of the many good things about LiFePO4 cells.
Hi Paul,
That answers that bit then. My charging system is solar with a PWM control function so it will hold the preset voltage to with 0.5v and keep trickling in current till no more will go in. At a 3.45v per cell cut off the last bit of charge takes around 45 min, that's from 100 amps down to zero amps into a 720 Ah pack, at 3.5v per cell, around 15 mins, any higher than that and the rate of climb is faster than the controller can shut it down. I guess this is because the open circuit voltage of the solar is 20v, the Vmp is between 15v and 17v depending on panel temp.
The difference between the cell capacity at a 4.4v cut off and a 3.45v cut off is the result of inherent internal cell resistance, it takes 0.05v over voltage to cause a current flow, this is why cells simple coupled together in parallel but not charged will not capacity balance to any degree of accurancy, they could still be 30% or more out of balance as far as state of charge after quite an extended period.

With the cells in parallel charged at 3.6v and many cells being destroyed. What was happening was some cells where reaching fully charged well before the others but the 0.2v over charge into a fully charged cell resulted in the electrolyte heating up till the 60 deg C mark was reached, then the electrolyte seperated, gasses, blow the cells up like balloons and killed them. If the charging voltage had been held at 3.40v till the current dropped to zero the voltage could then have been lifted to 3.45v and again left like that till the current dropped to zero and no harm would have been done to any of the cells.
I was going to put up a link to the thread but It's so far back now it would be buried in armchair expert nonsense, it sure is hard work sorting the wheat from the chaff regarding these batteries.
Glad to hear you battery pack has worked well for you so far, I'm more than happy with my pack, it's exceeded everythings I'd hoped for. One of the set ups I helped a mate with is a 24v unit and he emailed me this morning that a cell low voltage alarm sounded and them the system shut down, it appear one pair of cells in parallel droped to 2.6v while the others were at 3.1v still and the SOC was still 40%. it had been over a mth since he had top balanced the pack so that is happening today, it will be intersting to see if it's a cell failing or simpy an out of balance issue.

T1 Terry
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Old 24-11-2011, 01:39   #193
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Interesting info on the failures. I still think it suggests weaknesses in the manufacturing rather than the chemistry profile.

I only have direct experience with CALB cells in LiFePO4, but all the comments and apparent disagreement in forums makes me wonder if there aren't some basic voltage differences in different manufacturers' products due to slightly different chemistries (in the doping agents used most probably).

The one thing that is absolutely true is that because it's chemicals (not electronics), there's a lot less "absolutely correct" and a lot more "conditional on the environment".

Can you please post what happened to your friend's cells when you find out?

BTW, your cells are Thundersky, right (I assume that since they're yellow)? When I look at the TS published charge & discharge curves I wonder if they're at all real - the voltages look too high. Have you got a charge curve you can post (at say 0.1C)?

Cheers,
Paul.
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Old 25-11-2011, 14:37   #194
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Hi Paul,
I tried to do a 0.1C charging log yesterday and the B**** logger decided not to record it for some reason but I will try again this evening (need to let the batteries discharge a bit). All the other charging logs are from solar so the charge rate isn't constant and the fridges were still connected so the load as they cycled affects the graph.
There was one 20 min charge at 50 amps into a near fully charged 360Ah pack, roughly a 0.14C charge rate, Iíll post that one as a starter.
My cells are the Winston Battery Company units with the Yttrium in the + electrode, I think it was probably to get around possible legal issues with patent infringement but they do charge right to the last little bit faster than the older Thundersky cells that I also have and claim to have a greater cycle life, that is yet to be seen.
Thundersky doesn't actually still exist as a company, I think CALB was Sky Energy originally, there was a heap of name changing to do with major company restructuring and locking in supply factories to exclusive manufacturing deals. Thundersky was managed by Winston Chung for the last few years of it's operation and saw a great deal of quality improvement during his time there. I remember seeing an episode of EVTV where Jack Rickard read out an email from Winston Chung that claimed CALB were making cells using Thundersky technology under licence, I'm guessing that would be the SE series because all the specs are the same, just the plastic case is a different colour. CALB now make a different physical size spec cell, the CA line, they are grey and donít have the ribs on the case, they look a bit like the new green cells from Sinopoly.

The Thundersky company split into Sinopoly who still use the old Thundersky technology and formulae and Winston Battery Company that use the newer yttrium technology.
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Old 01-12-2011, 22:11   #195
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Quick question for some wise men .

Sorry to bust in but I figure you gentleman are much farther along the learning curve

I need to replace the SLA bricks in my ebike/scooter- Motorino XPN

Please tell me where to buy them.

How about these guys?

60V 30AH V2.5 LiFePO4 Battery Pack




60V 20AH LiFePO4 Pack + BMS / 6A Charger For Motorcycle | eBay

Or any suggestions?

Thanks
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