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Old 17-03-2015, 11:18   #4396
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by SV THIRD DAY View Post
<SNIP> Why not have one smart device that takes the charging inputs from Solar, Wind, alternators, battery charger, and hamster wheel and then charges what ever type of battery bank you have? That idea/concept isn't LiFePO4 battery related....but really a boat power management issue.

The answer....I wouldn't want such a device because WHEN it dies (not if) you would then be left with no ability to charge you battery. System integration like you are describing works great until...well until it doesn't. <SNIP>
Though not restricted to LiFePo4 technology, might point out that there are architectural approaches which can bring the benefit of better system wide coordination of charging w/o introducing catastrophic, or even cascading, failure modes. It all comes down to original design goals - plus a massive amount of ‘isolated business model' approaches which would have to be overcome.
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Old 18-03-2015, 18:02   #4397
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Thank you all who replied to my questions.
I have learned much, found links to more info and now have enough knowledge to make the right decision.
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Old 18-03-2015, 18:23   #4398
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by thomasow View Post
Though not restricted to LiFePo4 technology, might point out that there are architectural approaches which can bring the benefit of better system wide coordination of charging w/o introducing catastrophic, or even cascading, failure modes. It all comes down to original design goals - plus a massive amount of ‘isolated business model' approaches which would have to be overcome.
Good post thomasow. Why don't we all draw up a wish list of what would be the best kind of interface and control technology for a simpler almost plug and play system for a choice or mix of input power sources. Draw up the specs and lets see if it can be built.
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Old 18-03-2015, 19:17   #4399
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Good post thomasow. Why don't we all draw up a wish list of what would be the best kind of interface and control technology for a simpler almost plug and play system for a choice or mix of input power sources. Draw up the specs and lets see if it can be built.
Dear all, I just registered since I was looking at the Lifepo market in the US.

Apprently, few manufacturers offer an integrated solution with BMS + Cells + Controller.

I found a few company who seem to offer battery packs but never really sell a device that does not require additional connections and addons.

I found several European companies, such as EZA, or LAVI, which offer something interesting. It seems to be more focused on the RV market but I guess I would do the trick.

I do not know if I can post the link, but since it's not available in the US:

EZA ® - Integrated Lithium system Powered System for motorhomes, caravans, boats, houses,...

You can clearly see the different features and would be promising.

Edit: actually the boat indsutry is mentionned on the website.
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Old 19-03-2015, 10:42   #4400
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Ganryu
I see nothing here that isn't already being offered by solid companies like Genasun and Victron. What did catch my attention was their ad for the 520 Amp/h product that says “15 MINUTES charging, 25 AMPS* (*25 amps charged in 15 minutes on an empty EZA system with a 130 Amp alternator)”. Then the following paragraph says; “In our tests on a "standard" valéo alternator 130 Amp, we obtained currents of 130 Amp at the beginning of the loading process (EZA completely empty), and an average of 70 Amps ... This means that the smallest distance can be utilized to recover a significant charge level. In all cases, you are sure to properly use your power source (engine, solar, wind).”

If they are touting that a 130 Amp alternator can charge at 100 Amps into LiFePO4 cells that’s hardly news. I’m always leery of a slick websites designed by marketing folks that use sweeps to catch your attention rather than simple facts!

If I were going to purchase a drop-in (I built my own), I would go with Genasun or Victron!
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Old 20-03-2015, 06:23   #4401
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[QUOTE=goboatingnow;1776927]I wonder why you feel it's necessary to do in circuit top balancing in these boat environments

Dave


Sent from my iPad using Cruisers Sailing Forum[/QUOTE


Note the words very occasional. I live aboard my 37ft sailboat I do not have the space for a lab power supply and if I did have one I estimate it would last about 6 months in the vibration and damp atmosphere aboard. I need an alternative. This is going to be used for the initial top balance of my cells when I get them and is a method of moving the SOC of individual cells in a safe controlled manner when I need to 500 cycles down the line.

I recognize that cycle by cycle balancing is not required in fact that was the most important point I learned from this forum. A BMS that can switch balance resistors across my cells is not required, in my opinion this is an unnecessary and unacceptable reliability hazard. What is needed is a battery protection system.

This brings me to my next point. I have been looking at the alternatives for the bits for deploying LiFePO4 in my boat. As a retired EE system design engineer I am appalled. The current solution is at best a kludge. This is nobody here's fault, the boxes needed to do this properly are just not available and we are doing the best with what is. The boxes and boards that are being used are in my opinion totally unfit for purpose, there are times when I am at least 3 weeks from the nearest port, reliability for me has to be top of the list in design criteria and the bits should be low enough in cost for me to be able to afford spares. As has been suggested in the last few pages the whole system concept is wrong and still mired in the lead acid mindset.
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Old 20-03-2015, 06:30   #4402
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[QUOTE=matureee;1779356]
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Originally Posted by goboatingnow View Post
I wonder why you feel it's necessary to do in circuit top balancing in these boat environments

Dave


Sent from my iPad using Cruisers Sailing Forum[/QUOTE


Note the words very occasional. I live aboard my 37ft sailboat I do not have the space for a lab power supply and if I did have one I estimate it would last about 6 months in the vibration and damp atmosphere aboard. I need an alternative. This is going to be used for the initial top balance of my cells when I get them and is a method of moving the SOC of individual cells in a safe controlled manner when I need to 500 cycles down the line.

I recognize that cycle by cycle balancing is not required in fact that was the most important point I learned from this forum. A BMS that can switch balance resistors across my cells is not required, in my opinion this is a unnecessary and unacceptable reliability hazard. What is needed is a battery protection system.

This brings me to my next point. I have been looking at the alternatives for the bits for deploying LiFePO4 in my boat. As a retired EE system design engineer I am appalled. The current solution is at best a kludge. This is nobody here's fault, the boxes needed to do this properly are just not available and we are doing the best with what is. The boxes and boards that are being used are in my opinion totally unfit for purpose, there are times when I am at least 3 weeks from the nearest port, reliability for me has to be top of the list in design criteria and the bits should be low enough in cost for me to be able to afford spares. As has been suggested in the last few pages the whole system concept is wrong and still mired in the lead acid mindset.
One of the nice things about LFE is that if the cells do become out of balnce by a bit, simply drop your max charge voltage and or stop charging earlier and don't go to 20% SOC instead go to 30% SOC as the bottom. Even if you chop 10% off either end, cycling from 30% SOC to 85% SOC, to stay out of harms way on an unbalanced cell, you still have more usable capacity then you do with LA... Unless there is something drastically wrong with the cells you can easily work around a top balance issue by adjusting your DOD and recharge points until you get to a place where you can do a top balance......
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Old 20-03-2015, 13:24   #4403
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Note the words very occasional. I live aboard my 37ft sailboat I do not have the space for a lab power supply and if I did have one I estimate it would last about 6 months in the vibration and damp atmosphere aboard. I need an alternative. This is going to be used for the initial top balance of my cells when I get them and is a method of moving the SOC of individual cells in a safe controlled manner when I need to 500 cycles down the line.

I recognize that cycle by cycle balancing is not required in fact that was the most important point I learned from this forum. A BMS that can switch balance resistors across my cells is not required, in my opinion this is an unnecessary and unacceptable reliability hazard. What is needed is a battery protection system.

This brings me to my next point. I have been looking at the alternatives for the bits for deploying LiFePO4 in my boat. As a retired EE system design engineer I am appalled. The current solution is at best a kludge. This is nobody here's fault, the boxes needed to do this properly are just not available and we are doing the best with what is. The boxes and boards that are being used are in my opinion totally unfit for purpose, there are times when I am at least 3 weeks from the nearest port, reliability for me has to be top of the list in design criteria and the bits should be low enough in cost for me to be able to afford spares. As has been suggested in the last few pages the whole system concept is wrong and still mired in the lead acid mindset.
I agree with you, available "solutions" are a heap of garbage from an engineering and reliability point of view. I simply wasn't going to have any on board, so I developed a protection module capable of driving standard or latching contactors with some redundant hardware on the board to control failure modes and an ultra-stable voltage reference.
It takes cell voltage and temperature inputs - with LFP things always get warm first when something is going very wrong.
It also integrates some other features to solve problems that are specific to house banks.

I made a small run of them and I have a few left, but I am not marketing them actively at the moment. We can talk about it more aside if you want. This could be interesting because of your background.

Unless you source garbage LFP cells, it is highly unlikely that you will get top balance issues before a very long time, and only very gradually. On a decent system with good protection, you will just get the odd HV warning at the end of charge at first. If you keep doing nothing about it, it will become more frequent over time and you might get a charge trip eventually.
On a good system, it should be impossible to take the cells outside their operating envelope no matter what happens externally, it is the most basic rule for long life and safety.

On your boat, without a regulated PSU, you can still parallel-charge them and balance them hooking them up to solar panels. Later, if you ever needed to take a high cell down a bit, you can do it online manually by discharging that cell a little with a resistor or a light bulb of course.

Eric
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Old 20-03-2015, 19:19   #4404
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[QUOTE=Maine Sail;1779359]
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One of the nice things about LFE is that if the cells do become out of balnce by a bit, simply drop your max charge voltage and or stop charging earlier and don't go to 20% SOC instead go to 30% SOC as the bottom. Even if you chop 10% off either end, cycling from 30% SOC to 85% SOC, to stay out of harms way on an unbalanced cell, you still have more usable capacity then you do with LA... Unless there is something drastically wrong with the cells you can easily work around a top balance issue by adjusting your DOD and recharge points until you get to a place where you can do a top balance......
Thanks for that. However I have no intention of controlling charging based on pack voltage. That decision is being forced on you by the available hardware. I will build something that will cut off alternator charging when the highest cell hits 3.5V. This will do automatically what you are suggesting and imbalance will appear as loss of capacity while still keeping the cells in their safe zone. I will eliminate the current taper area, you suggest yourself that the cells are 95%+ full by the time you get to this sort of voltage with a .4C charge. The current taper is wasteful of fuel and engine hours and the money I would spend on a programmable alternator regulator is better spent on more capacity. All of your comments on protecting the alternator have been noted.
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Old 21-03-2015, 01:02   #4405
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[QUOTE=matureee;1779908]
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Thanks for that. However I have no intention of controlling charging based on pack voltage. That decision is being forced on you by the available hardware. I will build something that will cut off alternator charging when the highest cell hits 3.5V. This will do automatically what you are suggesting and imbalance will appear as loss of capacity while still keeping the cells in their safe zone. I will eliminate the current taper area, you suggest yourself that the cells are 95%+ full by the time you get to this sort of voltage with a .4C charge. The current taper is wasteful of fuel and engine hours and the money I would spend on a programmable alternator regulator is better spent on more capacity. All of your comments on protecting the alternator have been noted.
You are right. I do exactly that kind of things, very short to no current taper. It is far more efficient to charge all the way up to a higher voltage (without becoming unreasonable) and cut, rather than absorbing forever at lowish voltages. I do the same for solar charge regulation with no float or regulation at elevated voltages.
With cell-level data and protection, LFP systems can be managed much more efficiently.

In my experience third-party alternator regulators are less reliable, especially some blue ones that seem to have a habit of blowing up just a few months out of warranty. Eliminating them is money saved multiple times.
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Old 21-03-2015, 18:24   #4406
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Good post thomasow. Why don't we all draw up a wish list of what would be the best kind of interface and control technology for a simpler almost plug and play system for a choice or mix of input power sources. Draw up the specs and lets see if it can be built.
It does seem this thread has been rather sidetracked a bit - - -

I just now started a new thread at your suggestion:
'Desired systems approach to DC charging - discussion thread'



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Old 21-03-2015, 18:53   #4407
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[QUOTE=OceanSeaSpray;1780072]
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You are right. I do exactly that kind of things, very short to no current taper. It is far more efficient to charge all the way up to a higher voltage (without becoming unreasonable) and cut, rather than absorbing forever at lowish voltages. I do the same for solar charge regulation with no float or regulation at elevated voltages.
With cell-level data and protection, LFP systems can be managed much more efficiently.

In my experience third-party alternator regulators are less reliable, especially some blue ones that seem to have a habit of blowing up just a few months out of warranty. Eliminating them is money saved multiple times.
The voltage I will charge to is not elevated, highest cell at 3.5V corresponds to a pack voltage of around 13.8 to 14V. I did a lot of analysis when I first started looking at this to try to determine the pack voltage to charge to. The answer I got was fuzzy in the range above for a nominal 12V pack and very hairy for a 24V pack. Then came the revelation that the battery is full when the highest cell hits 3.5V, done.

As I have said before I want to avoid time in the upper knee and I am about to try to explain why. The battery works by moving Lithium ions from a graphite matrix to Iron Phosphate particles on the cathode. The normal flat part of the charge curve represents Lithium being stored in easy to get to sites as you move into the knee you are storing Li in more difficult sites until eventually there are no sites left and raw Li plates out and oxidizes. Think of this as storing your Li on a set of shelves most of them are low down and easy to get too, the knee sites get higher and eventually you get to shelves you cant reach any more. Moving Li on or off the higher shelves involves slow damage to the battery all of the time you are at a higher voltage you are doing this. In addition to this the Lithium on the higher shelves is just as difficult to get off the shelf as it is to get on. In an environment where we dont force its removal by only going to 80%DOD I think this may cause apparent loss of Li or in other words capacity.

I think Terry may have hit upon an ideal regime for his battery in that he capacity tests it (fully charges and discharges it) on an occasional basis. This cleans the Lithium out of the high shelves making it available at lower voltages maintaining the cell capacity.

This is just armchair theory on my part at the moment. I do however have a prediction from this theory. If you have cells which are exhibiting capacity loss try a conditioning discharge. Parallel the cells up and slowly discharge them to the lowest safe voltage you are comfortable with and then reconnect them and test.

I am open to this being wrong don´t do anything to your cells that takes them out of spec . If you do try it let us all know how it goes.
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Old 21-03-2015, 20:02   #4408
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Interesting theory.
A friend of mine recently put in a home grid tie.
72 240 watt panels, three inverters etc.
His backup is 16 700 ah Winstons with a dual BMS (two for 8 cells each)
When he purchased the backup bank, one of the cells had been discharged by a defective BMS which was replaced under warranty.
The cell was also replaced under warranty and the discharged one didn't need to be returned.
Just to see what would happen, he recharged it. It seems to be just fine.
The resting voltage of the cell when removed? 0.5 volts.
When questioned, the supplier (Balqon) said the cell was probably OK because it had been discharged at a low current rate, never being reversed in polarity.
We shall see, but it's an interesting data point nontheless.

BTW, MY home's grid tied 700 aH 24 volt bank from Balqon is doing nicely.
Unfortunately, the power grid doesn't go out like it used to.
Weird way of thinking, I know.
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Old 22-03-2015, 15:02   #4409
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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When he purchased the backup bank, one of the cells had been discharged by a defective BMS which was replaced under warranty.
The cell was also replaced under warranty and the discharged one didn't need to be returned.
Once they have been over-discharged, all bets are off. Note how the supplier didn't want the associated liability...

Quote:
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Just to see what would happen, he recharged it. It seems to be just fine.
The resting voltage of the cell when removed? 0.5 volts.
When questioned, the supplier (Balqon) said the cell was probably OK because it had been discharged at a low current rate, never being reversed in polarity.
We shall see, but it's an interesting data point nontheless.
At some point during over-discharge, even for a single isolated cell (it is not a pack problem dragging current through the flat cell - albeit this can be done), the polarity suddenly flips around, the phenomenon is internal to the cell.

I don't think it would be wise to start drawing "conclusions" from such "data points". It is too much like pushing the limit further and further because the technology seems so forgiving, and next thing an accident happens. People playing with EVs and LFPs did manage to ignite some packs "just recharging them" and those burned hot enough to melt aluminium and glass into puddles. Nice prospect on board on a cold winter day.
Recharge following over-discharge is a known pathway to get there, so I wouldn't get too cute trying to finely define "how much excessive discharge is not in fact excessive and quite acceptable in my own personal single data point speculative opinion" if you see what I mean! The stakes are just too big.

The main manufacturers seem to be aligned on 2.5V as bottom limit and the absolute voltage limit for the chemistry is 2.0V as far as I know.
A fairly recent study in cell destruction by over-discharge showed that the process caused internal micro short-circuits to appear and the cells ran warmer upon recharge afterwards, but they over-discharged them to set amounts like 110% capacity, not down to a voltage ("Failure Investigation of LiFePO4 Cells in Over-Discharge Conditions", Hao, 2013).
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Old 22-03-2015, 17:40   #4410
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

I'll keep the readers informed if I hear anything new about that cell.
He lives only a half mile away from me.
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