Quote:
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.
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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.
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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.)
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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.