LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[T1 Terry]

Originally Posted by witzgall

I need some help getting our 120a balmar alternator and 612 regulator to charge oue lifepo4 bank. Currently, it is set to charge at 14.4v, and I set the float voltage to 13.7. I am getting about 60a max when first charging, and it tapers off in a few minutes to 40, then 30, then 25 or so. This is when the link 10 shows 200a down to start.

Where is the regulator battery voltage sense wire connected to? It should be run all the way to the positive battery terminal. Often lazy sparkies connect this wire straight to the B+ cable so the regulator sees alternator voltage output instead of true battery voltage. If the B+ cable from the alternator is too small to carry the full alternator output the voltage will climb and the regulator will cut back.

The other possible problem is the alternator is getting hot and the regulator is cutting the output back to save the life of the alternator.

I would advise against charging LiFeP04 batteries to 14.4v till they accept no more current flow, this is equivalent to 3.6v per cell and the manufacturers advise to stop charging at this voltage when the current flow drops to 5% of the 1CA rate, 5 amps per 100Ah of battery capacity.
The other restriction to charging at 3.6v per cell is the charging rate must be below 0.5CA of the battery capacity, 20 amps per 100Ah of battery capacity.
If you have better things to do than stand and watch the charging current going into your batteries I would recommend dropping the charging voltage to 14v at the battery terminals and float to 13.8v if it's constant charging like a generator run for very long periods or solar charging but if it's just a top up charging system that will be turned off as soon as the batteries are charged then a 14v flat charging curve would be ok.

T1 Terry

[OceanPlanet]

T1 is right, 14.4V is too high. 14V-14.2V is what I've seen. Sorry for my previous quick response, wasn't thinking clearly after a 2hr hard mountain bike ride.

The Balmar 612 alt reg has an optional alt. temp sensor which (as T1 points out) could be resulting in the alt reg cutting back. The Balmar alts do have a bit of a rep for overheating. At some point you may consider a larger alt that can handle continuous full-duty (American Power, Electrodyne, etc.).

[downunder]

Originally Posted by roetter

This is a translation from the German Blog of the “Pacific High” Lagoon 500 – commissioned in April 2009.
14.12.2011 Neue Batterien für die Pacific High | Pacific High
He has posted an interesting set of pictures there.
Important: Make sure to set the language to German (Deutsch), otherwise the blog entry will be empty.

Here we go:
12/14/2011 New batteries for the Pacific High

The power budget on board is important for every sailor, especially on Pacific High with all our power-hungry amenities. We therefore have a (relatively) accurate system for monitoring energy consumption, energy generation and the current state of charge our battery bank on board. For about half a year I have noticed that our GEL battery bank has aged considerably and does not have full capacity anymore. Even worse for us is that the charge acceptance is reduced. Therefore, we are wasting a good portion of our energy already during charging. We had hoped that would keep our GEL battery bank longer than this. We have 9x EXIDE GEL Deep Cycle 4D batteries on board, which now have about 800 charge cycles under the belt. Normally, the batteries were discharge max. 30% to 40% (DOD 70-60%) only about a dozen did we discharge them (60%) down to 40% DOD.

We were faced with the decision to install the same "old" GEL batteries or convert to the "new" lithium ion batteries.

Reasons to stay with the GEL are: simple exchange old for new, affordable price, "proven" technology.
Reasons for lithium ion batteries are: much lighter, much better charge and discharge characteristics, significantly higher specific capacity but also about twice the price.
Since all of our chargers have user-programmable 4-stage charging characteristics we did not have to change anything here.

To come to the point: We decided to go for Li-ion batteries from Smart Batteries in Florida, which were delivered and installed today. Smart Batteries is a young, professinell and dynamical, local company on the Li-ion market in the U.S.. Its two owners, Victor and Conrad are competent, trustworthy and nice. The conversion from GEL batteries to Li ion took us about 4 hours: only 1 hour of true conversion, the rest of the time we spent to build a solid wood construction for the much smaller Li ion batteries and to search for a shop that had two 600A power bars. Thanks to Victor's help the entire conversion went quickly and without any problem. And when we fliiped the main battery switch back flips and turned on the inverter / charger the system worked perfectly right away.

Here is some data to compare the "old" GEL battery bank with the new LiFePo4 bank.


Total GEL battery bank capacity: 1260 Ah, max. usable about 750 Ah, usable in practice about 500 Ah. Charge currents: Bulk (= empty batteries) 200 Amps, absorption ab out 150 Ah, from 85% capacity only about 30-40 amperes are accepted by the batteries, ie for the last 200 amps hours we needed 5-6 hours charging time. Discharge currents: we draw up to 600 amps, during which the battery voltage drops significantly, would be better if we had a max of 300 Amp Total weight: about 430kg



Total capacity Li-Ion Battery Bank: 600 Ah, of which max. usable about 500 Ah, usable in practice also 500 Ah. Charge currents: whatever chargers can deliver, in our case, we load the fully discharged battery bank into two hours again. It is fascinating to watch how the full charging current to about 97% of capacity, then within a few minutes it drops to 20 Amp and after a further 10 minutes at 14.6 volts it stops completely. Discharge currents: almost anything we want, our max. 600 amps are no problem. Total weight: about 80 kg. Space: Just under one-third of the GEL battery bank.



Addendum of 04/01/2012: We have had the Li-ion batteries in use now for 20 days and can fully confirm the statements made above. All 24 cells have exactly the same final charge voltage of 3.65 volts. Under load (400 amps discharge) the voltage does not drop under 13.2 volts. We will set up a separate page under the menu item "Blue Water Info" for the lithium batteries and post regular updates there.

Hi Roetter,

thanks for your interesting post.

Do you know what the actual cost of the 600 AH Li vs the 1200 AH Gels was ??

Cheers

[roetter]

Hi Downunder

No, I don't know what the cost was. The web site of Smart Batteries 12 Volt Lithium Battery shows the cells now enclosed in a container combined to 12V. I am not sure if there is a BMS in there. The cost for 600Ah is listed $5900.

I am not sure this is a good solution though, as their set up means that you are paralleling in-series cells, which was said to be a bad idea in an earlier post on this thread by Electric1. Taking the individual cells and connecting them parallel to make the desired Ahs and then connecting those in series takes better care of weak and strong cells as well as different SOC of individual cells. Basically the cells on each level balance each other.
This is the way it is supposed to be done (from another thread in this forum):


Also, I got a quote for Thundersky 400 Ah cells at $500 each, a much better price than Smart Batteries offers. The price difference is $9.8/12V-Ah (Smart Batteries) vs $4/12V-Ah.

[Hyprdrv]

You have to put the individual cells (at 3.4v lets say 100AH) in series 4x 3.4=13.6v at 100AH. Then parallel to get lets say 4 batteries at 13.6v at 100x4= 400AH. Series to up the Voltage, Parallel to up the AH.

[mrm]

Originally Posted by Hyprdrv

You have to put the individual cells (at 3.4v lets say 100AH) in series 4x 3.4=13.6v at 100AH. Then parallel to get lets say 4 batteries at 13.6v at 100x4= 400AH. Series to up the Voltage, Parallel to up the AH.

You are correct in saying, that:
Serial - increases voltage (V).
Parallel - increases capacity (Ah),

but your advice to first connect serial and then connect parallel is not optimal imho, for reasons explained above by roetter.

Also, it is a good idea to ask for a factory matched set of cells and/or equalise them when delivered.

[witzgall]

Originally Posted by T1 Terry

Where is the regulator battery voltage sense wire connected to? It should be run all the way to the positive battery terminal. Often lazy sparkies connect this wire straight to the B+ cable so the regulator sees alternator voltage output instead of true battery voltage. If the B+ cable from the alternator is too small to carry the full alternator output the voltage will climb and the regulator will cut back.

The other possible problem is the alternator is getting hot and the regulator is cutting the output back to save the life of the alternator.

I would advise against charging LiFeP04 batteries to 14.4v till they accept no more current flow, this is equivalent to 3.6v per cell and the manufacturers advise to stop charging at this voltage when the current flow drops to 5% of the 1CA rate, 5 amps per 100Ah of battery capacity.
The other restriction to charging at 3.6v per cell is the charging rate must be below 0.5CA of the battery capacity, 20 amps per 100Ah of battery capacity.
If you have better things to do than stand and watch the charging current going into your batteries I would recommend dropping the charging voltage to 14v at the battery terminals and float to 13.8v if it's constant charging like a generator run for very long periods or solar charging but if it's just a top up charging system that will be turned off as soon as the batteries are charged then a 14v flat charging curve would be ok.

T1 Terry

The + sense lead from the regulator was wired to a bus bar a few feet away. I moved it to the + battert terminal, and am now getting 90a to start, and 70a hot!

I also lowered the bulk rate and raised the float settings. Actually, I set the abaorption to 14.2, same as bulk. Does that sound right?

Thank guys!

Chris

[downunder]

Originally Posted by roetter

Hi Downunder




Also, I got a quote for Thundersky 400 Ah cells at $500 each, a much better price than Smart Batteries offers. The price difference is $9.8/12V-Ah (Smart Batteries) vs $4/12V-Ah.

This price you have been quoted is very competetive with GEL/AGM. The Smart Battery price was better than say Mastervolt however still a premium price. thanks

[sytaniwha]

I totally agree with Roetter - connect parallel strings up in series to get better cell balancing characteristics. In fact, if you can create a physical entity where all the cells in one parallel string are series connected to all the cells in the adjacent parallel string (and so on), this would produce the best result, but it's generally impractical.

This is different to what we are generally used to with lead batteries, because they come in already connected packets of series cells (12V), which we then connect in parallel to make the needed capacity. This is one reason why the Smart Battery guys' drop-in replacements for lead batteries are connected that way.

The reason why lead batteries are mostly built like that (6 cells in series to make 12V) is convenient consumer packaging, not the best technical solution. As with all cell chemistries, if you are then stringing these battery packs in parallel, you will get some premature cell failures due to cells becoming imbalanced, as Roetter describes.

In my opinion, even better than stringing parallel strings in series would be to buy larger capacity cells and not paralleling any. Yes, if you do have a cell failure it will be more expensive to replace than if you parallel, but there is generally more quality control and thus consistency in the manufacture of an individual cell than between cells.

Also, just a caution about the photo Roetter posted of the correct way to parallel/series cells. If I'm not mistaken, it's a picture T1 Terry originally posted of his initial testing configuration, not his final configuration. If you go back through this thread you will see some discussion about this, which both T1 Terry and I agree on. In a permanent working setup the connections between parallel strings, and the +ve & -ve cable take-offs should NOT be at one end of the parallel strings, as shown in this photo. The reason for this is that there is extra resistance for the cells at the top of the photo due to the links in the parallel strings. Much better would be placing the series links on the middle cells in each parallel string, or placing a link on both the top and bottom cells. Best would be to put a link between each cell in a parallel string, and it's corresponding cell in the neighbouring string - over-kill maybe, but you'd lower the resistance of the links significantly and remove all link resistance imbalances.

Be careful not to introduce imbalances with the physical layout of your cells and links.

Cheers,
Paul.

[Journeyman]

Hi all,

Wouldn't you need 300A capable alternators to fully recharge 500AH in two hours? Doesn't this exceed recommended Li-Ion charging current? E.g. the recommended charging current is only .3C for MasterVolt Li-Ion 320AH/12V.

In the example of this yacht Pacific High that would be .3(600)=180A.

Does anyone know what the consequences are of exceeding the recommended charging current by (250-180)/180=39%?

Reduced charge acceptance rate over time?

Thanks,
Journeyman


"Total capacity Li-Ion Battery Bank: 600 Ah, of which max. usable about 500 Ah, usable in practice also 500 Ah. Charge currents: whatever chargers can deliver, in our case, we load the fully discharged battery bank into two hours again. It is fascinating to watch how the full charging current to about 97% of capacity, then within a few minutes it drops to 20 Amp and after a further 10 minutes at 14.6 volts it stops completely. Discharge currents: almost anything we want, our max. 600 amps are no problem. Total weight: about 80 kg. Space: Just under one-third of the GEL battery bank."

[Hyprdrv]

Paul is it possible you could draw a correct wiring diagram of a 4 12v (16 cells) battery pack? I'm not picturing this at all based on the explanation.

Thanks,
Steve

[sytaniwha]

Sorry if my description led to decreased clarity, rather than increased.

I've attached a pdf of some hand-drawn diagrams that hopefully help clarify what I meant. I've used blocks rathr than circuit diagram symbols to try to make the representation of the physical cells as clear as possible.

Comments on each configuration in the drawing are:

1) This is the "Pacific High" configuration, with 6 lead-acid equivalent "batteries" of 4 parallel cells, connected in series to provide the wanted capacity. As Roetter and others have commented, it isn't ideal from an electrical viewpoint because with 12V across each series group, there is a greater chance of individual cells becoming un-balanced. It was probably done this way because it allows drop-in lead acid replacement modules, which can be a less intimidating way to change technologies for some people.

2) This is a representation of the photo of the yellow cells which Roetter posted just after the "Pacific High" post. Because the cells are paralleled first, each group of 4 parallel cells is held to the same voltage on charge and discharge, which is why it's preferable to example 1). However, with the connections between the parallel sets being on the bottom cells, the other cells in each set have higher resistance due to the extra links they go through (e.g. the top cells have 3 extra links of resistance on both the +ve & -ve terminals). This means that the voltage each cell receives under charge is slightly different due to the higher resistance path. Although probbaly not important in any given cycle if you use good links, over time this can cause some change in cell balance. The ideal is to have identical resistive paths for each cell within a battery.

3) If you just have a single link between each parallel cell set, then this is a better set-up than 2 because it moves the links between sets closer to the physical centre of each set, thus reducing resistance path imbalances.

4) This is the ideal situation, where every cell in each parallel set has the same resistive path. It does take a lot more links, which may be significantly more expensive. You could, of course, have custom copper plates made which each have 8 holes in them and drop over the sets of connectors on adjacent parallel strings to do the same thing. Probably overkill.

5) I would say that this is probably the best compromise, which largely evens up the resistive path, but with fewer links than 4.

I hope this helps clarify what I am trying to say.

Fundamentally I believe that there are 2 points which are important:

1) If you have both parallel and series connections, connect parallel sets in series,
2) Construct your inter-cell links to try to get the same resistive paths between all the cells.

I hope this helps.

Cheers,
Paul.

[Hyprdrv]

Paul,
Thanks for making this quite clear now. This was exactly what I was looking for.

Steve

[T1 Terry]

I thought I posted a photo of the new battery set up but I can't find the post so it must still be floating around in the ether along with a few hundred other posts of mine.
This is the latest set up to see if the cells really would go out of balance in a parallel connection set up. All the load is from the end of one bank of cells.
Looking at the photo I now realise I missed one link, must have got side tracked or something. These cells have been connected like this for around 2 mths, they have 200Ah plus dragged out every night and in poor weather discharged to below the 20% threshold and the recharge rate can be as high as 100 amps at times, depends on the sun.
I check it again yesterday and with all the cells at 3.5v (fully charged) they were still in balance within 11mV. I would have expected the set remotely connected to be at a higher state of charge to the loaded set but it appears the charge acceptance and discharge release rates (buggered if I can remember the proper terms) are so low on these cells that self balance very quickly.
Not a practical method of connecting 32 X 90Ah cells to form 720Ah @ 12v but it was really to test a theory, I proved myself wrong.
The more cells connected in parallel to make up the capacity, the better the balance becomes apparently.
T1 Terry

[Marqus]

Originally Posted by sytaniwha

I've attached a pdf of some hand-drawn diagrams that hopefully help clarify what I meant. I've used blocks rathr than circuit diagram symbols to try to make the representation of the physical cells as clear as possible.

Paul.

Very useful diagram; thanks Paul.