Lithium iron phosphate battery (LiFePO 4) battery for Solar applications ?

Re: Lithium iron phosphate battery (LiFePO 4) battery for Solar applications ?

Oops, sorry about that - it is Jonr's link to the article at artechhouse that shouldn't be followed for LiFepo4.

That article deals with a different chemistry (LiCo02), and while general precepts are good, details are quite different for LiFePo4 in operation. I know it is well-intentioned, but here the article is intended for another chemistry on a worst-case basis using laptop and small consumer gadgets. Many of the percentages and emphasis are just wrong for lifepo4. If one is running an ebike with a duct-taped pack and trash LiCo02 components, then yes, follow that to the letter.

One of the reasons for lifepo4's existence starting about 15 years ago was to get away from this unstable chemistry, needing pin-point accuracy. I'm sure Prof J. Dahn at Dalhousie U would agree.

To be sure, there may be many EXCELLENT bms / balancing systems out there, but a red-flag goes up when they state it is mandatory in a Sub-C / low current application like ours where if reasonable care is taken, you don't need it. Then again, there is a lot of money to be made by using FUD to drive sales for low-quality componentry on the unwary.

Re: Lithium iron phosphate battery (LiFePO 4) battery for Solar applications ?

PNjunction seems to think that balancing isn't needed in his particular case. While not true in most cases, it could be true for his. But who knows - he also seems to think that an occasional balance check proves that balance is always being maintained.

I never said balancing isn't needed. In fact, it is the one thing I do before I put one into service. Or at least verify that the manufacturer did indeed balance before shipping. I can do that by discharging each cell individually from the top of SOC to about 3.45 - 3.5v with a small load and letting them rest awhile to make sure it holds. Yes, they will be ragged at the bottom of the discharge curve. Don't go there. Plan / monitor / lvc accordingly.

You will NEVER get batteries to stay in perfect balance, regardless of chemistry. What I'm trying to get across here is that for LiFePo4, while perfect balance is admirable, you DO have a little bit of real-world operational leeway when you don't run them at the extremes.

If you do that, you don't have to treat them with kid gloves as long as you are the type of person who frequents forums like these.

Perhaps you are missing the point about our "Sub-C" application. This means 1C or less. And in real-world terms, MUCH less. Nobody building a 400ah lifepo4 bank is going to discharge them at even a leisurely 0.5C on a regular basis! There is PLENTY of time to catch things when run under our conditions. That's the point often missed earlier. We are not EV'ers, RC-modelers, E-bikers etc. Our application is different and affords us the option of not going bananas over balance.

What are we accomplishing here? Thread lock, and that would be a shame. I honestly invite you to obtain a bank of your own, and we can continue to provide meaningful first hand experience, instead of theoretical debate.

I really think you would find it a fun hands-on learning experience. Here is what I think would happen: You would prefer to monitor / balance / calculate and predict things down to the last .0001 percent. And that's FINE. I on the other hand, would be more pragmatic combining theoretical perfection, with real-world usage accepting a small amount of skew.

Just two different ways of looking at it, that's all.