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Old 16-01-2013, 07:20   #1111
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

It took a few days but my 1600Ah 3.2V paralleld pack finally charged to 3.785V.. I am going to do a discharge to about 50-60% then recharge to 3.6V and I can begin wiring up the BMS and bench testing and playing with everything before installation on the boat..
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Old 16-01-2013, 07:35   #1112
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Not really , its the primary reason Ferrous cells were developed. There are some side effects like longer shelf life. Do you know of others.

The data I have for cylindric cells all state that a pre-qualification charge is neccessary below a point. You also agree, but my concern is that typical LA chargers have no such ability. All the Integrated circuits for LifePo4 charging implement all the things Ive mentioned.

Sure but its an issue

Yes they store well at various SOCs but for how long.Its Li achilles heel.

The technical data I have, is very clear, Li should not be floated, Floating in effect feeds small currents into the cell on a continous basis, The data says the charge should terminate and remain terminated until some threshold is reached, Some data indicates quite significant loss of capacity if floated. Again all the ICs etc implement this feature.

yes the great thing about Li is it doesnt care.

correct , I was drawing attention to the fact that many chargers do not have temp sensing for Li as a safety feature, Ie you cant really use LA chargers for Li.

i think for sub 1C chargers I would pick a common cutoff voltage
I tried to ignore material specific to non ferrous cells for the most part in order to keep from getting confused...so I can't really expand on the differences.

Other than unattended boats stored on a mooring, I don't see issues with "shelf" life or gradual discharge. We just don't see that on live aboards or marina stored boats much. But I would wager they hold a charge better than lead acid does for sure and might even be better than AGM. I've read LiFePO4 self discharge rates are low, so I'm not sure why this is an issue?

I would like to see the data, even for other chemistries on floating. But assuming self discharge is low, I can't see where a few milliamperes trickle charge on a house bank sized capacity bank would cause problems. If the voltage is kept low enough. What you don't want to do is float then top, float then top. We saw this issue at a marina with poor power where every time the power blinked, the charger went back to bulk charge. So perhaps I'm helping make your argument for a custom charger, but this was an unusual occurrence.

If temp sensing is required for Li, and Im not sure it is for marine, then it needs to be in the BMS/battery monitor not the charger.
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Old 16-01-2013, 07:58   #1113
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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To the best of my recollection, every C- and D-sized flashlight I've ever had was "wired" in series. I just checked one of my Maglite flashlights and the D-cells are definitely arranged in series.
Sorry, I should have been clearer: C- and D-cells are never wired in the same series string together.
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Old 16-01-2013, 08:14   #1114
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Sorry, I should have been clearer: C- and D-cells are never wired in the same series string together.
That makes more sense. However, I've never seen a flashlight with both C- and D-cells.
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Old 16-01-2013, 08:20   #1115
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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That makes more sense. However, I've never seen a flashlight with both C- and D-cells.
That's my point. When cells are wired in series, you want all of them to be the same capacity. That's why LiFePO4 matching is important. If the cells aren't well matched, it's like mixing C- and D-cells in the same series string.
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Old 16-01-2013, 08:34   #1116
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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That's my point. When cells are wired in series, you want all of them to be the same capacity. That's why LiFePO4 matching is important. If the cells aren't well matched, it's like mixing C- and D-cells in the same series string.
I hope no one here was planning to wire up a series of cells mixing, for example, 100AH and 160AH within the series string. Personally, I would not worry about a 1% difference in capacity among the cells in a string. I would simply accept that the string would have the capacity of the weakest cell. Life is too short to stress over trifles.
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Old 16-01-2013, 08:49   #1117
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Personally, I would not worry about a 1% difference in capacity among the cells in a string. I would simply accept that the string would have the capacity of the weakest cell. Life is too short to stress over trifles.
Unfortunately, there's more to it than that. With even minor capacity differences, the string will end up having well less than the capacity of the weakest cell. This is because it has a magnifying, ongoing negative effect on cell balance.

With well-matched cells, an initial top or bottom manual balance may be all that's needed. But with any mismatch, you will eventually need to invest in some kind of active balancing circuit.
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Old 16-01-2013, 08:53   #1118
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Unfortunately, there's more to it than that. With even minor capacity differences, the string will end up having well less than the capacity of the weakest cell. This is because it has a magnifying, ongoing negative effect on cell balance.

With well-matched cells, an initial top or bottom manual balance may be all that's needed. But with any mismatch, you will eventually need to invest in some kind of active balancing circuit.
That's a theory. I haven't seen any evidence. I neither believe nor disbelieve it.
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Old 16-01-2013, 09:25   #1119
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

A typical 12 volt battery is just a bunch of 2 volt cells in series and I've never heard anyone worry about cell balancing or matching.
In the big picture, I don't see any problem slapping a minimal BMS on a set of lithiums.
It's working fine for me.
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Old 16-01-2013, 09:28   #1120
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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A typical 12 volt battery is just a bunch of 2 volt cells in series and I've never heard anyone worry about cell balancing or matching.
That is only because lead acid cells are not irreversibly damaged by undervoltage or overvoltage like LiFePO4s are.
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Old 16-01-2013, 09:37   #1121
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by senormechanico View Post
A typical 12 volt battery is just a bunch of 2 volt cells in series and I've never heard anyone worry about cell balancing or matching.
In the big picture, I don't see any problem slapping a minimal BMS on a set of lithiums.
It's working fine for me.
Checking specific gravity, and then equalizing, often brings the SG readings back close to even..

With LiFePO4 you can actually reverse the battery polarity if drawn too low. They can also be rather quickly destroyed if a cell goes too high. LA batteries also don't have the sharp knees that LiFePo4 does..
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Old 16-01-2013, 10:36   #1122
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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That is only because lead acid cells are not irreversibly damaged by undervoltage or overvoltage like LiFePO4s are.
I should have been clearer.
I knew that, but meant to address the probably imperceptible differences in capacity of cells in series making the least of them being the first to take the deepest discharge/charge limits.
I am also aware of the voltage vs charge curve. It has a very flat middle with near 90 degree curves on both ends.
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Old 16-01-2013, 17:56   #1123
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Everyone is making a case for a minimal BMS or cell voltage monitor I think? Even if cells are matched at installation, there is no reason to believe they will age exactly the same. And it doesn't matter...so long as none are driven to extremes?
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Old 16-01-2013, 18:07   #1124
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Finished top balancing today with the power supply in parallel. The House Power BMS and cell modules from Clean Power Auto LLC. arrived today as well.

The cells were taken to exactly 3.800V for the top charge (Balquon said 3.8V - 3.9V was preferred):


These cells drop voltage quite slowly. This was about 10 minutes after turning off the power supply..


I wired them in series for a 12V bank and installed the Mini-BMS Cell Boards. I ordered an extra cell module just in case I broke one. I will wire them up to the House Power BMS Module tomorrow. This 14.67V was the resting voltage about two hours after taking it off the power supply at 3.800V/parallel.....
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Old 16-01-2013, 18:50   #1125
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

I mentioned in an earlier post I was going to run one pack with a bms and one without to see if you start balanced, don't subject to high C, is a bms worth it.

I'll keep you all posted.






$27 plus $13 for a upgrade from 4 cell 30 amp to 4 cell 50 amp.

Do it yourself EV goodies, good selection of lithium battery chargers at good prices. http://www.evassemble.com/index.php?...=index&cPath=6
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