LiFePO4 controller + inverter

[agenthex]

Hi, everyone! I'm a newbie, and this is my first post here:

I'm looking to fit a work truck with solar panels, batteries, a charge controller, and an AC inverter. I wouldn't mind buying parts separately, but I must make sure they will work together.

I intend to use LiFePO4 batteries for their energy density. From what I understand I need the following components:

Charge controller (MPPT)
Batteries (LiFePO4)
Inverter (with LVC)
Solar panels

My question is this: does a combination charge controller and inverter exist? If I use a standard inverter, how do I protect the batteries from low voltage? Does a charge controller have DC outputs to go to an inverter? Is there a better option? What is the cost of such a device? Are there any limitations I should keep in mind (max number/voltage of PV panels, max number of batteries, etc.)?

Ideally, such a device would also allow AC grid charging when mains is available.

Thanks in advance for your help and advice!

[Sunking]

You are SOL, there are no charge controllers for LiPo batteries.

There is a better option in a vehicle. You don't need solar. All you need is an Auxiliary AGM battery, and a battery isolator to keep it charged via the vehicle alternator. Your alternator can provide more power in 30 minutes than a week of solar panels.

Also no inverters that work well with LiPo batteries. A 3 cell voltage is a little too low, and 4 cell is way too high.

[inetdog]

Also no inverters that work well with LiPo batteries. A 3 cell voltage is a little too low, and 4 cell is way too high.

Similarly to the situation for NiFe, there is a very wide voltage spread between full charge and a reasonable low voltage cutoff. And uniquely, lithium chemistries can completely lose the ability to be recharged safely when discharged (including self-discharged) below a certain voltage.

[Sunking]

Similarly to the situation for NiFe, there is a very wide voltage spread between full charge and a reasonable low voltage cutoff. And uniquely, lithium chemistries can completely lose the ability to be recharged safely when discharged (including self-discharged) below a certain voltage.

Well I need to correct myself. a 3-cell lithium can operate a 12 volt inverter. A fully charged up LiPo is 12.6 volts, and fully discharged is 11.1 volts. Most decent 12 volt battery inverters work from 10.5 to 15 volts. However a LiPo is problematic when being used in placed of lead acid batteries. If you should ever take one down below 20%, they go into Sleep Mode and will not wake up without special charging techniques. So that limits the operating voltage range from 11.45 volts to 12.6 volts. Most all 12 volt inverters will no tshut down until the reach 10.5 to 11 volts which would destroy a LiPo.

[Sunny Solar]

3 cells work badly.. I have spent way to much time trying to get that to work and to many problems.
The only way to do it is with 4 cells with a charger ..that can be limited to 14.4v..And a charger that can have equalization disabled.I have used very successfully PWM charge controllers on small systems below 400w of panels
You need a dedicated device set to a cut off at 10.5v . Many chargers have a + or - .5v of the usual 10.5 cut off. Far to dangerous for the cells. The cells voltage drops like a rock below 2.6v. Be careful as next reading down of voltage will be from destroyed cells.

[Sunking]

John 4-cell LiPo is 16.8 volts at full charge and 12 fully discharged. 14.4 is only around 40 to 50% capacity.

[Sunny Solar]

Sunking charging them to 4.2v is a waste of effort and reduces the cells life a lot.
3.8v is effectively "full" as there is little extra power you get into them by going above that voltage.. 3.4 is about 3/4 "full" ..And its a compromise as You cant get 12v inverters to work above 15v as most cut off at that point...
I have put together 4 small systems that operate completely unattended and have done so now for about 4 yrs. And have set the charge controller to 14.5 but its never exact as varies between 14.3 and 14.7 . Have a cut off set to 10.5v. And never a problem..
Its a case of having to use a slightly bigger bank of cells than ideal.But thats the price of reliability and never needing attention..

We have been experimenting with Lipo cells for over 6 yrs at work and have tried more combinations and charging rates than I can remember.
We have come to fully understand them and have found they dont like being fully charged and have a death wish below about 2.4v. Go to 2.2 and death is just about guaranteed even if done one time only.

Im only giving my and work experience . Others may have discovered different things about them and happy to use them that way.

[inetdog]

Sunking charging them to 4.2v is a waste of effort and reduces the cells life a lot.

+1. And if any Li batteries are going to be stored for any length of time, they should be stored at 3/4 rather than at full charge to get longest life. This causes some problems when you are using Lithium secondaries for critical portable equipment (like flashlights) and want to have them at full charge when you grab them for use.

And in addition to adding the fireproof box, Boeing reprogrammed the battery controller for the LiCo unit on their 787s to lower the maximum charge voltage and raise the minimum voltage cutoff. It lowered the available energy some, but they felt it was worth it for the increased reliability. That is especially important since they still do not know the root cause of the failure.

[SunEagle]

+1. And if any Li batteries are going to be stored for any length of time, they should be stored at 3/4 rather than at full charge to get longest life. This causes some problems when you are using Lithium secondaries for critical portable equipment (like flashlights) and want to have them at full charge when you grab them for use.

And in addition to adding the fireproof box, Boeing reprogrammed the battery controller for the LiCo unit on their 787s to lower the maximum charge voltage and raise the maximum voltage before cutoff. It lowered the available energy some, but they felt it was worth it for the increased reliability. That is especially important since they still do not know the root cause of the failure.

You are correct about not storing your fully charged LiPo batteries for a long time. I use them for flying RC planes and have noted that it is better to charge them the day before I go flying instead of charging them and letting them sit for a while. The ones that I have fully charged and let sit seemed not to get fully charged again after use even using a really good balance charger.

[Sunking]

John leaving them stored at full charge will shorten their life cycle no doubt. But in an RE system they never stay at full charge. As soon as they get to full charge you immediately go into discharge. If you want to make an argument of long life then 20/80% is the range and a 4 cell 80% voltage is 15.3 volts. At 14.4 is only 50% roughly and IMO is wasting your money.

To actually get a LiPo to 100% you have to hold a constant of 16.8 volts until the charge current tapers down to 3% of the battery capacity. If you terminate when the voltage reaches 16.8% you are at the 90% mark.

[Sunny Solar]

Sunking just charging them to 4.5v and then same day discharge them they dont like it .. They will show their displeasure with an early death. 3.8v is tops for longevity. Testing hundreds of them all different capacities has proved this beyond all doubt.
Discharging below 2.5v is also a dislike of the cells. And as that can drop under load very quickly to 2.2v or less will destroy they them very quickly. Thats why you need for their safety a fairly accurate automatic disconnect set to 10.4v (2.6v ea).

You are free of course same as others to charge and discharge them to whatever voltage you like. BUT you will make them have a short unhappy life AND that will be expensive for the user.

[Sunking]

Sunking just charging them to 4.5v and then same day discharge them they dont like it .. They will show their displeasure with an early death. 3.8v is tops for longevity. Testing hundreds of them all different capacities has proved this beyond all doubt.
Discharging below 2.5v is also a dislike of the cells. And as that can drop under load very quickly to 2.2v or less will destroy they them very quickly. .

Are you drinking heavily again John, or making up stories again? Because you sure do not know WTF you are talking about.

LiPo is only charged up to 4.2 volts max at 100% capacity if you let the charge current taper to 3%. At 4.5 you have a big fire on your hands. Nominal is 3.7 volts , 0%is 3.4 volts, and sleep mode is 3 volts. Leaving LiPo in storage at 100 % is a problem, but not if used immediately like an RE or EV application.

3.8 volts is only 40 to 45% capacity for a LiPo for a 3 cell pack works out to 11.4 volts. None of your math works.

[Sunny Solar]

Sunking make your mind up... If you terminate when the voltage reaches 16.8% you are at the 90% mark.
LiPo is only charged up to 4.2 volts max at 100% capacity .


And you would have tested under just about every condition possible how many hundred Lithium ion phosphate batteries. done comparison tests between different charge terminal voltages ,discharged terminal voltages and compared all the data against longevity of the batteries??.
How many Thundersky cells have you tested and what were the main causes of failure besides crap quality control? What are your findings of A123 prismatic cells?

Cost considerations are not everyone's concern . Longevity and ease of use are of more importance to some. So saying a cell is only charged to x is wasteful as it be better to charge it to y .. But not so good if that is going to shorten its life. Its better for some to buy more cells..
No one is using Li Po cells to save money compared to a quality deep cycle wet cell. They are still to expensive..

[chris_solar]

I think you two are not talking about the same cells at all: LiPo is Lithium Polymer, and LiFePO4 is Lithium Iron Phosphate, and only this last one is used in car conversions to electric drive, and are now being used for PV Storage - BTW the initial question was about LiFePO4, not LiPo -

LiFePO4 cells are empty at 2.7V and full at 3.65V
Their resting voltage, after being charged fully is 3.32V

Their charge method is rather simple:
- Bottom balance each cell, drain them to 2.7V
- Connect the cells as a string, here 4 cells for a 12V pack, which is 4 x 3.32V = 13.28V really
- Under Charge them up to 3.50V x number of cells, here 4 x 3.5V = 14V, and Stop the charger, NO FLOATING at all (!)
- Set a Low Voltage Cut off to 3V x number of cells, here 4 x 3V = 12V

Following all the above, you will preserve your pack from over charge and over discharge, and keep your cells for a long time