The Skinny on the Chafon lithium battery charging: Advanced battery management system

 So inside the 500 watt Chafon (youtube review I have not seen yet) - there should be 9 of the below packs for 36 cells total: Oh  now this is real interesting!  Wow glad I'm researching this.

 Must wait min of 30 minutes after battery is fully charged to allow the PCM to perform balance function on all the cells within the pack

So it's a Li-NiCoMn battery aka

Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO₂ or NMC)

One of the most successful Li-ion systems is a cathode combination of nickel-manganese-cobalt (NMC). Similar to Li-manganese, these systems can be tailored to serve as Energy Cells or Power Cells. For example, NMC in an 18650 cell for moderate load condition has a capacity of about 2,800mAh and can deliver 4A to 5A; NMC in the same cell optimized for specific power has a capacity of only about 2,000mAh but delivers a continuous discharge current of 20A. A silicon-based anode will go to 4,000mAh and higher but at reduced loading capability and shorter cycle life. Silicon added to graphite has the drawback that the anode grows and shrinks with charge and discharge, making the cell mechanically unstable.

The secret of NMC lies in combining nickel and manganese. An analogy of this is table salt in which the main ingredients, sodium and chloride, are toxic on their own but mixing them serves as seasoning salt and food preserver. Nickel is known for its high specific energy but poor stability; manganese has the benefit of forming a spinel structure to achieve low internal resistance but offers a low specific energy. Combining the metals enhances each other strengths.

NMC is the battery of choice for power tools, e-bikes and other electric powertrains. The cathode combination is typically one-third nickel, one-third manganese and one-third cobalt, also known as 1-1-1. This offers a unique blend that also lowers the raw material cost due to reduced cobalt content. Another successful combination is NCM with 5 parts nickel, 3 parts cobalt and 2 parts manganese (5-3-2). Other combinations using various amounts of cathode materials are possible.

Battery manufacturers move away from cobalt systems toward nickel cathodes because of the high cost of cobalt. Nickel-based systems have higher energy density, lower cost, and longer cycle life than the cobalt-based cells but they have a slightly lower voltage.

New electrolytes and additives enable charging to 4.4V/cell and higher to boost capacity. Figure 7 demonstrates the characteristics of the NMC.

So this - due to 36 cells:

  For high voltage Li-Ion pack ( > 20 cell),  you shall consider advanced BMS ( battery manage system) to monitor each cell's performance to ensure battery safer operation.

So pretty impressive Protection Circuit Module.

Over-charge protection voltage	4.350 ± 0.025V
Over-discharge protection voltage	2.40 ± 0.080V
Over-current protection	7.5±1.5A
Maximal continuous Charge & Discharge current	4A
Maximal Current consumption	50uA
Protection  circuitry  resistance	≤50mΩ
Dimension	50mm(1.96") x 16mm(0.6") x 3.5mm(0.2")

To repeat from last night - the "cell balancing" function:

 36 pieces, 3.7 V, 26000 mAh 18650 lithium battery

2.18 V is the maximum.

PER CELL FOR CELL BALANCING 
so 
36/2.18 volt= 16.5 volts for cell balancing -  (36/16.5 volts = cell balancing of 2.18) the internal volt regulator in the Chafon.
14.8 volts is the 4 cell max at 3.7 per cell.

So a lower TOTAL volt = a higher voltage per cell. 

So 2.18 volt is the "differential charging current" when one cell has higher capacity than another cell.  So more current is drawn from that cell to balance it with the others. So a power transistor and current limiting resistor exists for each cell - to enable current to bypass the cell if necessary. So then a differential amplifier is necessary to boost the voltage internally for the 16.5 voltage with an input range of 2 to 4.5 volt.

 Charging rate: 6.0A (maximum)

OK that's good to know.  The car inverter is 80 watts from 12 volts which equals 6.6 amps. But there should be voltage regulation - since it's inverted to AC.  The AC fuse is 8 amps.

So it says the "maximum continuous charging current is 4 amps. So that is what the bicycle generator is kicking out!!

So the AC charger on the Chafon is 5 amps. Which means it is losing 1 amp in the conversion to DC.

So then the Solar port DC charging states that with a solar panel at 18 volts (to maximize amps) you lose 20% of the amps to convert to the DC battery charging.

Also the car DC charging through the Solar port states if the input charge voltage is over 12.4 volts - then the battery voltage regulator flashes on the green light.

This is what happened to me BEFORE I got the DC/DC buck converter. I always saw that green light flash on the solar charger before it turned to Red. I had no idea that meant the voltage regulator was having to then lower the voltage.

So when I set the DC/DC buck converter to 12.2 volts that was the IDEAL most optimum voltage - even though each "pack" of cells is actually at over 13 volts to charge it. But the advanced battery management is not based on the pack (wired in a series) nor is it based on the 9 packs (wired in parallel) but it's based on EACH cell at 3.7 volts.

So that is what I needed to find out - and now I know I do not need to increase the my voltage on the DC/DC buck converter.

Also the battery cell management goes into "trickle charge" (higher voltage, lower current) at 90% of the battery charge. So to extend the battery capacity - it's best to not use the trickle charge, as this relies on a lot of heat to regulate the voltage and can have overcharge accidents (besides it takes a long time to finish the trickle charge).

But to use the "car charge" pass through you need at least an 80% charge since you are changing from an energy cell to a power cell mode (meaning high current). This can damage the battery also.

That's why Chafon removed the car jumper option - and went for lower watts - to extend the battery capacity lifespan.

But personally - living in a cold climate - I like having that car jump charge option along with the longer battery capacity or is it capability? 

Anyway....looking at academic analysis on advanced battery management of this type of lithium battery:

So I'm guessing it's better to fully recharge this so it goes through the "cell balancing" function. As I typed that sentence - I looked over - and the cell balancing function just finished on the Chafon. It is when the charge is at 100% but the red light is still on - (so it is in charge balancing mode). This takes a half hour - just as the above directions specify. Then the green light switches on to show that the charge is complete (the cells are now balanced again).

 

So there is cell balancing during discharge as well.

this is a higher cost due to the nickel and cobalt