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10

LiFePO4 vs LiIon vs LiPo Some peolpe have commented on LiIon batteries, but the question and this answer are about Lithium Ferro Phosphate batteries / LiFePO4 which I'll abbreviate in places as LFP4. . These are related to LiIon and LiPo batteries but have major differences. Notable, compared to LiIon and LiPo (which are chemically similar) LFP4 has an ...


8

Lipos have higher voltage per cell (3.7 vs 3.2). All else being equal this equates to more power. Lipos may also have lower internal resistance and higher maximum discharge rates, which equates to even more power. If you want to make a fair comparison then weight and size must also be taken into account. Lipos are generally lighter and more compact than ...


7

So far, my answer is, I don't know but TI are usually very solid people who tend not to go around making ICs that walk on the dark side - as this is of significant applicability to me and I have an application where it is of immediate potential relevance this needs further investigation. The following is my starting on the journey - more a problem ...


6

EDIT: TL;DR: Use an LDO with a much L'er D.O. Use an MPPT controller, or do some research (if not done already) on what your buck regulator will do when Solar Power stops. Add a thermal Sensor You shouldn't, but if you want, you can use an NPN transistor to manipulate the output voltage. END OF EDIT / END OF TL;DR The 3V regulator Let me ...


6

Let's start with a very important point: With Lithium based batteries a thermistor is a nice last line of defence, but you seem to be making it the centre point of your thoughts. If your thermistor triggers on a Lithium based battery, purely from charging, you might want to hook that up to an airhorn so you know to start running. Do not get me wrong: I ...


5

Although we have already spent some time chatting about some details of your implementation, I'll try to take you through the steps I take in designing a long-life LiFePO/Solar project and leave you to fill in the specifics. First thing to do, with regards to all your power conversions and intermediary steps, is find the losses. If you have a ...


4

"Blind" charging of batteries in series, regardless of chemistry, is a bad idea. By "blind" charging I refer to the treating of multiple series cells as one single battery. However, blind charging is cheap and simple. If you don't care too much about the longevity of the cells, but you do care about the cost and space, then blind charging of multiple ...


4

That's not how it works. What happens is that under low temperatures you cannot extract more than 2 Ah out of a fully charged cell because internal resistance rises under low temperature. The voltage of the charged cell will not change.


3

I would stick with the standard lead acid style of battery. They are safer, cheaper, more rugged and drop in replacement. Another real good reason is that the Lithium style batteries require very specific and stringent charging circuitry. You would not be able to simply connect the Li style batteries up to the existing charging system that was designed for a ...


3

You should try charge testing with one cell so as to understand its characteristics. LiFePO4 behaves somewhat differently than conventional LiIon. Once you understand how one cell behaves when supplied by a power supply set to <= 10A and <= 3.8V then you can better understand what your series string is doing. BMS 'interference': If you are using a ...


3

LiFePO4 cells have a very flat charging voltage curve that doesn't peak until just before full charge. When charging a 400mA pack at 10mA it may stay below 3.5V for 30 hours or more. As a result of the sharp voltage peak at end of charge, a small imbalance can cause large voltage variations between cells in series. An aggressive balancing circuit will fix ...


3

Batteries are commonly sealed as air contact would increase the speed at which they dry out and die. An exception to this rule are Air-batteries which need the air to function properly. The epoxy-dipping might interfere with the internal pressure relief valve in case something goes wrong inside the battery. So the cell might rupture with a higher pressure - ...


3

EDIT1: New answer to modified question (original see below) First of all I need to tell you that this set-up is very risky. Very very very risky. This way of connecting the batteries means there's a much higher risk of damage over multiple charge/discharge cycles. To your specific problem, if one battery in one chain becomes short circuited, the other ...


3

The two requirements (reverse protection & reverse polarity) are not easily met in the same single device. By itself a MOSFET's Vgs is too poorly defined between parts and not sharp enough yto make a good low battery cutout. By adding the world's lowest cost IC and two or three resistors you can meet both needs. A P Channel MOSFET in the +ve lead, ...


3

What you propose is OK as long as the battery is not charged beyond its maximum voltage rating. For really critical applications, that maximum voltage rating must be adjusted as a function of temperature. Otherwise, use the lowest allowed voltage over the temperature range the battery will encounter. The charge current must also be limited, especially ...


3

When working on the fringes of specifications, it is always best to speak with an applications engineer at the manufacturer. They often have access to data that is not part of their published specifications. With that being said, you should give careful consideration to thermal management within your design. For example, a large insulated thermal mass in ...


3

If you want to drop a small voltage like that, you can simply use a diode. That will have a (almost) consistent 0.7V(ish) drop. If you want a little less of a drop, use a schottky diode. Checking the datasheets for the Vf vs current graphs should enable you to find one suitable for what you want.


2

117VAC is a sinewave that rises up to a peak of \$\sqrt2\times 117 = 165.5V\$ then back through zero to a negative peak of -165.5V then back through zero and repeats. How does this allow you to charge a battery of 117V even if you rectified it - you'd still get peaks of about 164V falling to zero then back up to 164V.


2

I've discovered a number of related "data points". No one shows with certainty that this is a universally acceptable charge method with LiFePO4, but the indications are that it probably is, with certain "caveats". The degree of acceptability will depend on many factors such as degree of overvoltage, charge state, charge rate, time held at over-voltge, ...


2

It sounds like C+/C- is for putting current into the battery pack (connect to charger), and B+/B- is for getting current out of the battery pack (connect to load). Presumably there is some circuitry inside the pack which handles limiting the charging current, cell balancing, over/undervoltage protection, safety, and so on. But, it's possible that some or ...


2

First let's adjust the battery pack voltage to 165.6V or 46 cells, because the peak voltage of the AC signal is \$\sqrt { 2 } * 117 = 165.46V\$. Then rectify the voltage, so we aren't reverse biasing the battery pack: Now apply that AC voltage to the battery pack when it is fully discharged to 92V (2V per cell) and the only time a charge current will flow ...


2

Short answer: Yes, you can use up to 15 LiFePo4 cells in series (aka 15S) at the input of the ESC without any problems. Long answer: LiFePo4 cells definitely work all Lipo ESCs... as long as you don't exceed the max input voltage of the ESC. Your specific ESC lists that it can handle 12S Lipo batteries. This means, it can take an input voltage is greater ...


2

This will work only if you are able to maintain the junction temperature at 25C. Normally, this is not the case and the forward voltage of the LED will drop as it warms up. This will lead to a increase in the current, the current increase will accelerate the rise of the temperature and this "snow ball effect" may destroy your LEDs. Check page 7 of the ...


2

You will need: A few million dollars for an engineering team to develop a good enclosure with all the spacing/creepage clearances/insulators. A very sophisticated central BMS that can work across the full kV range. This will likely require fiber optic insulation. Good testing facility with very expensive battery testing equipment that works at 1 kV. Full ...


2

From the linked instructions: Charge the cell at the maximum continuous charge current until the maximum recommended charge voltage is reached. Apply a constant voltage hold at the maximum recommended cell voltage until the total charge time reaches the fast charge time. And Maximum recommended charge voltage: 3.8 So Charge at 10A until the ...


2

1) pretty standard. Get a 4S LiFePO balancing-protection board with over/under charge protection. About $8 on eBay. This will prevent the 4S to exceed the limit voltage, and will cut off the current if undervoltage is detected. This board simply goes in parallel with the CV power supply and the laptop. The supply CV voltage must be between 14.2 and 14.4 V....


2

Generally charging cells slowly means they stay at high charge levels for very, very long, because they have internal leakage that increases with their voltage. Or they may even never reach completely full. A completely full cell degrades much quicker. However, LiFePO4 is a bit special, it deteriorates much less differentiated over state of charge. (It ...


2

BQ24650 is a MPPT controller/charger for solar panel. While the BQ24620 is designed for adapter charger. I would try the MPPT, because it is suited for panel, I guess when you will connect the DC voltage on the input, the MPPT point is trivial and it shouldn't make troubles. Anyway you can experiment with different DC voltages - higher or lower than 18V if ...


2

I don't know array size or serviceability of cells, but I would remove all swollen cells first. "Good" Batteries are balanced for mAh <1% when new. This imbalance obviously increases with aging such that the weakest cell dies 1st due to more rapid aging from rising ESR during charge and discharge and more from undercharge condition and cold temps. ...


1

6.4 -> 5V, then 5V -> 3.3V would be fine. You may also consider dropping 6.4 -> 5V with one regulator, and 6.4 -> 3.3V with a second one. The spec for the radio says 13mA, so Power dissipated = 0.013A * (6.4-3.3) = 0.027 Watts, which isn't much to worry about. I can't think of anything to choose between the two approaches. At these low-currents, you ...


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