If I build some LiFePO4 battery packs, would anyone buy them?

[rickst29]

1. They claim '400Ah', but they allow only 160 Amps of maximum output. Something is wrong with that. (A 400 Ah battery pack should support about 400A continuous output current).
2. They include protection from charging when too cold, but they do not add the fancy "battery warmer" for supporting charging in cold weather.
3. It seems to be locked inside a solid case, and unmaintainable.
4. It's "out of stock".
5. The battery pack appears uncompressed, and won't last 10 years.

[rickst29]

Photo of the new home-built LFP battery (the 120Ah "baby battery"). I built this in preparation for constructing a bigger one with about 270Ah. Both of them together can run the Air Conditioner without plugins, if I get a larger Inverter. (I've already connected my current "baby Inverter" with 2/0 wiring and a 300A fuse in preparation for eventually doing that).

The biggest and best-constructed LiFePO4 batteries compress the cells using spring-loaded rods and compression plates to spread the force onto the "face" of each cell evenly. In this battery, the pressure is about 380 lbs, and the plates are made of steel (eliminating some of the 'advantage' of lower battery weight, but helping them to last even longer). When the batteries expand, the pressure goes up - and when the batteries shrink back down, the pressure goes down.

In my final construction steps, I will be adding wooden plates (from the board underneath) to support the battery, make the sides "pretty", and cover the top from any accidents. But even then, all the internal components are individually maintainable, by simply removing the wood panels. They're held together with screws. The parts inside are a big ANL fuse, the red "Battery Management System" board, the individual cells, and the big "bus bars" which convert the 4 3.2 Volt cells into one big 12.8 Volt battery.

When installed, this battery will include an automatic "heater" for charging in cold weather. The heater pad will wrap around the bottom, and up the two "open" sides.

[Casey Freswick]

Looks like a great idea for last year :-)

[rickst29]

along with prices.

[Wavery]

Originally Posted by rickst29

[LIST=1][*]They claim '400Ah', but they allow only 160 Amps of maximum output. Something is wrong with that. (A 400 Ah battery pack should support about 400A continuous output current).

I'll be the 1st to admit that I don't know much about LFP batteries but Deep Cycle batteries typically have a lower max output than their cohorts "Starting Batteries". starting batteries will have as much as 800A rating but for a very short period of time.

Lead/acid deep cycle batteries have less available surface charge and a much larger charge stored in the larger plates and more lead. That results in a lower max output but over a longer period of time.

It only makes sence that a 400AH LFP battery might have a very high storage but if it were to have a load of 400A, it seems to me that it might overheat in a short time.

I just installed this 2000W inverter today. I can't believe the build quality of this thing. I brewed a pot of coffee this afternoon then boiled a qt of water in the microwave (18 minutes).
https://www.newpowa.com/products/200...hoC0acQAvD_BwE

[rickst29]

Originally Posted by Wavery

.... It only makes sense that a 400AH LFP battery might have a very high storage but if it were to have a load of 400A, it seems to me that it might overheat in a short time.

I just installed this 2000W inverter today. I can't believe the build quality of this thing. I brewed a pot of coffee this afternoon then boiled a qt of water in the microwave (18 minutes).
https://www.newpowa.com/products/200...hoC0acQAvD_BwE

(long reply, covering several topics)

That won't happen. I draw nearly 1C on my small-ish LFP battery pair when I run my own BIG microwave at full power, and they don't warm up at all (not even a tiny bit). LFP batteries use a different chemistry. The construction of larger "prismatic" cells (the big rectangular ones) is somewhat analogous to led-acid Gel cells, with anode and cathode descending into a liquid "bag" of LFP solution. But the speed of electron exchange in LFP batteries is much faster, allowing high current.

My own "prismatic cells" (smaller than the ones discussed in this Thread, although I might soon be building a "big" battery for myself) are 100Ah and 120Ah, built into "100Ah and 120Ah batteries in parallel. Both battery packs consist of 4 cells at 3.2V nominal, rated for 1C continuous discharge from 100% State-of-Charge all the way down to around 10% SOC. They do not warm up at all, when I run them quite hard (running my own microwave).

This rating is typical for such "prismatic" cells, although recent designs offer even higher continuous current ratings (such as 1.5C). My cells are rated at 2C maximum discharge current for up to 40 seconds, although my two "Battery Management System" Boards will shut off discharge current in the case of such high output loads occurring for more than about 10 seconds.
- - -
That's an amazing price, for "2000 watt" sine-wave inverter. But there is a tiny bit of weirdness in their documentation, mainly this: 2. Use only deep cycle, sealed lead-acid, flooded, or gel batteries.. An LFP battery will provide more stable voltage while it is becoming more discharged (staying at 12.8 Volts until the last 15%), and that 12.8V value is smack-dab in the middle of their desired input voltage range. There is only ONE possible issues with using an LFP "12v" battery supply with this Inverter:

The Inverter offers 4000w peak power. That implies some decently-sized input "filter capacitors" on the 12V side, and those capacitors can create a big inrush of current when the Inverter is first turned on (or maybe when it is first plugged in). Lead-Acid batteries have high internal resistance, limiting the maximum current which can be delivered into those capacitors. But the internal resistance of LFP batteries is amazingly low, and that initial "peak" in current demand is very likely to exceed the instantaneous current limit of the BMS. BMS will shut down discharge from the battery pack in that case.
- - -
In anticipation of that issue, I added a "pre-charge" 12v circuit from the battery bus to the Inverter. The Inverter 12v is fed by both the 12v "mains" (2x 2/0 AWG) and the "pre-charge" circuit (one 8 AWG). The pre-charge circuit contains a large-ish 25-ohm resistor (1 watt maximum power), and it has a switch.

Before activating the Circuit Breakers on the "mains" (the use of circuit breakers is redundant, they could be mere switches) I activate the "pre-charge", wait a few seconds, and then turn on the Inverter with no load. I then turn on the circuit breakers for the "mains". No inrush occurs, because the capacitors of the Inverter have already been charged by the "pre-charge" 12v supply. (That happened slowly, due to the presence of the 25-ohm resistor).

(I'm in the habit of turning off the 'pre-charge' switch before adding any loads, even though the resistance of the "mains" 12v Path is than 1/200 of the resistance of the mains. This is for the extreme case of a "mains" circuit breaker disconnecting along one of the 2/0 "main" 12v connections.)
- - -
Except for the case of Inverter in-rush to fill the capacitors pulling too-high current and invoking BMS shutdown, this Inverter will have no way to know that the attached batteries are LFP, rather than Lead-Acid. It's too bad that it will not be big enough to run my air Conditioner, it otherwise looks great.

[rickst29]

Originally Posted by Wavery

I'll be the 1st to admit that I don't know much about LFP batteries

I'll be the first to admit that I know the characteristics of available cells very well, and I could probably DESIGN a really good LFP battery pack for use in an EV.

[Tymanthius]

If you do make a production run, please advertise it. I'm not in the market for them for probably at least a year (no panels yet), but this sounds like a pretty solid deal.

[Hdlaut]

I am very interested in purchasing one of your batteries. Can you use Winston cells?

[rickst29]

Originally Posted by Hdlaut

I am very interested in purchasing one of your batteries. Can you use Winston cells?

Hi. My pricing cannot possibly be as I previously described, because prices have gone up quite a bit. I now prefer to "coach" build-your-own battery packs, involving 4x cells of 280, 230, or 304ah cell shipped from USA locations (in which the vendors have already taken care of the shipping risk).

Winston cells claim very high cycle life (at discharge of 70% or 80%, and LFP batteries should not generally be used below 15%-20% state of charge). But the newest EVE prismatic cells claim a similar lifespan, and the lifespan of prismatic cells can be further enhanced by utilizing a compressive battery box (at about 600 lbs of compression on the larger cell faces) I've done that on all of my battery packs. That's a tested lifespan, and not merely unwarranted "projections". I frankly doubt that uncompressed Winston cells can genuinely match EVE tested results for compressed cells, and the newest EVE cells are claiming lifespan of 6000 cycles uncompressed. They've documented their tests, and I hold their claims in higher regard.

Winston battery cells are also super costly. As far is I can tell, they're not easy to buy in quantities < 10. Their purchase involves risky shipping by sea freight, prepaid, with really awkward "return" requirements for damaged cells. Don't underestimate that factor, I know of a man who went bankrupt upon following his USA reception of a destroyed pallet of LFP battery cells (for distribution to other persons, including me). Many persons (including me) were left holding the bag, to various degrees.

Winston is finally a very small company, with only about 350 employees. (Eve, in contrast, has almost 10,000 employees). I'm about to build another battery for my own use, 230Ah (because that smaller size is currently the lowest cost per amp-hour). My cells arrive from a USA shipper tomorrow. Do you have other reasons (besides n large cells size and claimed lifespan), to want Winston? Nobody on the leading "build your own" LFP forum, https://diysolarforum.com/ seems to be using them.