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Old 27-02-2015, 12:01   #4306

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

"The MPPT part doesn't know anything about the battery. That's a different system."
Semantics, Dan. You say "system" I say "controller".

Companies like BlueSky and Morningstar sell MPPT controllers, which connect to the panels and the battery, and marry the two of them. They sometimes call these systems, in the sense of complete working systems, but not in the way you're using the word.
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Old 27-02-2015, 12:26   #4307
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by NahanniV View Post
After two seasons of very light usage I just completed a capacity test on my 12v 400AH 4S Winston LiFePo4 2009vintage cells.

I did not charge the cells as aggressively as I did in the previous test 3.5VPC vs. 3.7VPC. I just brought the pack up to 14.0V and did some minor balancing (first adjustment since initial).

The results:
330AH over 17h
Lowest Cell: 2.98
Maximum cell difference:100mv
Lowest pack voltage:12.05V

The cells have clearly lost capacity since my first test.

Cheers,
JM
Wow that's pretty bad.. How are you using the batteries? Floating them? Storage or battery temps? Are they often sitting at or near full...?

It seems your lowest cell could go another 0.2V before hitting 2.8V. With a 100mV spread it seems you also have some healthy cells and some not so healthy??

What was the discharge rate?
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Old 27-02-2015, 12:58   #4308
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by hellosailor View Post
"The MPPT part doesn't know anything about the battery. That's a different system."
Semantics, Dan. You say "system" I say "controller".

Companies like BlueSky and Morningstar sell MPPT controllers, which connect to the panels and the battery, and marry the two of them. They sometimes call these systems, in the sense of complete working systems, but not in the way you're using the word.
All I'm saying is that MPPT can be used in lots of other applications besides battery charging. Whether a solar controller has MPPT or not has nothing whatsoever to do with the algorithm the battery charging regimen uses. MPPT can speed up the charging because it allows the charging subsystem to draw more power from the PV array than if it did not have an MPPT feature. Lots of people are confused about that it seems. For example, I read people using PWM and MPPT as if they are two completely different things. MPPT uses PWM to achieve its purpose.
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Old 27-02-2015, 13:13   #4309
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by Maine Sail View Post
Wow that's pretty bad.. How are you using the batteries? Floating them? Storage or battery temps? Are they often sitting at or near full...?

It seems your lowest cell could go another 0.2V before hitting 2.8V. With a 100mV spread it seems you also have some healthy cells and some not so healthy??

What was the discharge rate?
I am using them very lightly. Day sailing and overnights. I manually switch them on when sailing or at anchor. Charging with dedicated 20A charger to 13.8 no float. Leave them at 50% during storage. 15-20deg.C storage for 6Months/year. On the boat they are below the waterline and not in the engine compartment, might ocasionally reach hi 20s Deg.C. Never had any over/under voltage events.

The voltage on the lowest cell was dropping quite rapidly at the point I terminated the test, it was already well below the level of the initial test.
My monitor is set to alarm when a cell is below 3.0V; Never reach that level except in this test.

Yes, two of the cells always charge and discharge first, the one depicted by the red line being the worst.

The discharge rate for the test was around 20A; It varied slightly over the test as the voltage dropped (inverter load).

I almost never use more than 100AH before recharging. So did not know that they had lost so much capacity.

Cheers,
JM.
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Old 27-02-2015, 13:33   #4310

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

JM-
A 13.8 V charger would bring each cell up to only 3.45 volts. Assuming the charger is right on spec, maybe this undercharging has hurt them?
Were the batteries clearly date-stamped, new production, when you got them?
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Old 27-02-2015, 13:40   #4311

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

Dan-
I see how you're referring to things but I would disagree that most of the public sees them that way. You say that an MPPT controller uses PWM. Sure, but you might as well call that AC since it is going through a transformer and that's the only reason it is being used. Most folks care about what TYPE of controller they have, they don't play Chinese marketing "sorry, we confuse" semantics. They refer to the entire piece of equipment as PWM, meaning that's all it is, or MPPT, meaning it is an MPPT system combined with all the other necessary pieces, regardless of what they may be.
That MPPT or PWM does mean anything about what charging protocols are used is something else again. Why confuse the issue? MPPT or PWM will say nothing about the manufacturer's choice of often "trade secret" charging algorithms, except that an MPPT controller (complete black box system) is more likely to have the more complex charging algorithms rather than a one-stage cheapie.
I see your point, and I would call it a valid way to clarify the nonsense distortions of the cheapo ripoff sellers. But that's almost like a Monty Pythonesque argument about the details, when there's a "plain" meaning that most folks will understand, as long as the swindlers aren't in the conversation.
"I'm having a cup of coffee". No you're not, there's milk and sugar in that cup, I saw them. And a cup is eight ounces, you're having five.
Really?!
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Old 27-02-2015, 13:44   #4312
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by hellosailor View Post
JM-
A 13.8 V charger would bring each cell up to only 3.45 volts. Assuming the charger is right on spec, maybe this undercharging has hurt them?
Were the batteries clearly date-stamped, new production, when you got them?
Yes, the charger is actually set to 14.0V but the battery sees just over 13.8V at the end of charge.

I did manually bring the cells up to 3.5V for the test.

Yes, they were date stamped 2009. I got them on clearance from Balquon.

Cheers,
JM.
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Old 27-02-2015, 14:00   #4313
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by NahanniV View Post
Yes, the charger is actually set to 14.0V but the battery sees just over 13.8V at the end of charge.

I did manually bring the cells up to 3.5V for the test.

Yes, they were date stamped 2009. I got them on clearance from Balquon.

Cheers,
JM.
What current did you allow it to tail off to at 13.8V or 14.0V? The clearance cells from Balqon have clearly been very hit or miss. I suspect I got very lucky with mine and a few others have too but some have not.... Seems like two of your four cells may still have the oomph to do 400Ah, or close to it, but the other two don't..
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Old 27-02-2015, 14:05   #4314
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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All I'm saying is that MPPT can be used in lots of other applications besides battery charging. Whether a solar controller has MPPT or not has nothing whatsoever to do with the algorithm the battery charging regimen uses. MPPT can speed up the charging because it allows the charging subsystem to draw more power from the PV array than if it did not have an MPPT feature. Lots of people are confused about that it seems. For example, I read people using PWM and MPPT as if they are two completely different things. MPPT uses PWM to achieve its purpose.
Bingo...

It is hard to believe so many can't grasp the simple concepts of CC/CV charging or that an MPPT controller can only provide a "boost" during bulk/CC charging and then only if it has the array voltage to do so....

Once the batteries have come up to absorption or limiting voltage the MPPT controller essentially becomes a CV/PWM controller and no more MPPT boost is happening.....

Luckily on boats with the smallish arrays we use our controllers lots of time in bulk, thus we can extract some decent boost, if the panels are not too hot......
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Old 27-02-2015, 15:17   #4315
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Hello all,
First thanks to everyone who have shared their knowledge and experience here. I can safely say I am on my last set of LA batteries. I will be replacing my t105s with 200AH of LiFePo4 when they expire. I have read most of the forum please forgive me if I bring up some things that have already been discussed as this was not done in an organized manner. I will be raising some points over a few posts.
A question for those with some experience, if I charge a reasonably well balanced bank at 0.4c until the highest cell is at 3.5V and then stop charging what is my state of charge?. I have looked at the curves published particularly rough charge curve.jpg and it would seem that I am looking at the 90-95% region.
One of the attractive features for me and one area that is not well presented is the efficiency of these cells. I have seen statements that they are close to 100% efficient because they return as much current as you put in.
The bad news is that this is not true you are putting in the current at about 13.4V and extracting it at about 13.25V this means that the power efficiency is around only 98.9%.
The good news is that if you do the same calculation for lead acid putting in current at average 14V and extracting 90% of the current at average 12.3V you get an overall efficiency of 79%.
Lead is not only dead it would be buried if it was not environmentally unsound to do that.
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Old 28-02-2015, 03:54   #4316
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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How about real world head to head into an actual LiFePO4 battery.....

MPPT vs. PWM - LiFePO4
Any chance of a similar test with 3 panels in series for the MPPT and 3 panels in parallel for the PWM controllers? Same deal, cable rated to current with less than 2% voltage drop. The losses within the MPPT controller converting high voltage low current to low voltage high current will be the real difference.
The other thing about the test that swings it in favour of the MPPT controller was panel temp, full sun panel temp would lower the Vmp therefore reducing the difference between panel output voltage and battery charging required voltage.

T1 Terry
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Old 28-02-2015, 04:39   #4317
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by NahanniV View Post
Yes, the charger is actually set to 14.0V but the battery sees just over 13.8V at the end of charge.

I did manually bring the cells up to 3.5V for the test.

Yes, they were date stamped 2009. I got them on clearance from Balquon.

Cheers,
JM.
Try redoing the test, bust first bring the cells up till they hold 3.5v after 1 hrs rest, this will clear any memory charge they may have developed during the 3.45v end of charge regime. You may need to bring the cells up to 3.6v before allowing them to rest for the hr and repeat it few times till they hold 3.5v, this will point to memory charge being the culprit and the capacity has not really been lost, just locked away.
The 3.45v per cell is a good safe range and there is nothing wrong with using that as a general upper charge point but to do a capacity test, the cells must be truly full to get an honest result.
You may find a repeat of the same regime gives an even greater capacity the second time, these cells do like to work, they are hopeless for standby UPS work.

T1 Terry
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Old 01-03-2015, 13:04   #4318
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

OOOOPS I see I opened a can of worms and yes it was T1's post on MPPT / PWM charging that I read elsewhere.

BUT can someone tell me

ONE What is the 'best' voltage to top balance my WTS 200AH cells to?

TWO I have a Lab P/s with up to 30A available - what current value should I use?.

THREE Should I balance one cell at a time or parallel up 2/3/4 cells when i am going to top balance them?

thanks

kindest regards

David
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Old 01-03-2015, 14:30   #4319

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

I think anything with the Thunder Sky brand on it was an older chemistry, so you might want to confirm case color and model number, and that the voltages you get are correct for that, not for newer models. FWIW.
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Old 01-03-2015, 14:54   #4320
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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First, there are fake MPPT controllers coming out of China. They say MPPT, they apparently aren't, so folks who use them will see no improvement.
Right. A proper MPPT controller has a DC/DC step down converter that seeks max power during the bulk phase and a PWM controller that kicks in to keep the battery at float voltage when there's excess power.

There are fakes out there that don't do either of those things:


Tom.
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