A 4S2P is same thing as a 4S1P with larger cells. You can't put a different charge on 1 half of a "cell" than the other. So no, you can't use 2 balancing circuits. Well, I suppose you could take 2 separate 4S1P batteries and only connect them in parallel at the + and -, but the typical way to do it (which is probably more efficient) is to put each pair of cells in continuity into one larger cell.
If you allow the battery to draw too high of a current, it will increase in temperature. And this will reduce cell life and/or cause spectacular failure.
OTOH, if the cell charge rate is higher than your circuit can provide, you also have a problem. If cell can take 3A, either your boost circuit will fail via oversaturation of the inductor, and output will plummet to next to nothing. Or the 12V PSU will fail. If switchmode, it will just cut out. If transformer, same situation as with boost circuit. So if your battery is "bigger" than the PSU, which may well be the case, you need to limit current to protect the PSU, not the battery. Either way you cut it, you need to limit the max current draw to make it work. But when the cell nears full charge, you need to reduce/remove this limit, or it will take a super long time to charge the last 20% of the battery.
Rule of thumb is that max charge of an average li ion battery is probably at least 1C. Li ion batteries are made with much much higher charge/discharge to C ratios than this, maybe 20:1. They sacrifice some max capacity in order to achieve this higher charge/discharge rate. But there's decreasing gains going the other way of trying to maximize capacity at the cost of charge/discharge rate. So some batteries can be charged at 10 or 20C, but it would be rare to find a 1Ah battery which could not be charged with at least 1A. Hence the rule of thumb of 1C. But this is a max rate; if you want to extend life of the battery, you only want to charge at a small fraction of this max. I tend to use 1/5C to 1/3C as the mark for reg'lar li ion cells, unless in a hurry.
For 4S cells, I tend to charge to 16.6V in lieu of balancing. That can work ok, too. You have to examine how balanced your cells are, though.
Cell is one single li ion cell. Battery is more than one cell in series. Just to be super clear. Now:
When I say "put each pair of cells in continuity" I mean connect both +'s together and both -'s. Then take the four pairs of "double cells" and put them in series to make the battery. This is more efficient. It's easier to balance, and if using balancing circuit it can increase efficiency.
As opposed to making two isolated stacks of 4S1P and connecting only the output in parallel. Either way you only need one charger. But if want an active cell balancing circuit, in this latter configuration you'd need two of them.
But upon reading some posts I came to know that the charging should be done with constant current and voltage mode. but my boost module only have constant voltage mode. So is it really necessary to maintain a constant current mode for charging??
OTOH, if the cell charge rate is higher than your circuit can provide, you also have a problem. If cell can take 3A, either your boost circuit will fail via oversaturation of the inductor, and output will plummet to next to nothing. Or the 12V PSU will fail. If switchmode, it will just cut out. If transformer, same situation as with boost circuit. So if your battery is "bigger" than the PSU, which may well be the case, you need to limit current to protect the PSU, not the battery. Either way you cut it, you need to limit the max current draw to make it work. But when the cell nears full charge, you need to reduce/remove this limit, or it will take a super long time to charge the last 20% of the battery.
A 4S2P is same thing as a 4S1P with larger cells. You can't put a different charge on 1 half of a "cell" than the other. So no, you can't use 2 balancing circuits. Well, I suppose you could take 2 separate 4S1P batteries and only connect them in parallel at the + and -, but the typical way to do it (which is probably more efficient) is to put each pair of cells in continuity into one larger cell.
If you allow the battery to draw too high of a current, it will increase in temperature. And this will reduce cell life and/or cause spectacular failure.
OTOH, if the cell charge rate is higher than your circuit can provide, you also have a problem. If cell can take 3A, either your boost circuit will fail via oversaturation of the inductor, and output will plummet to next to nothing. Or the 12V PSU will fail. If switchmode, it will just cut out. If transformer, same situation as with boost circuit. So if your battery is "bigger" than the PSU, which may well be the case, you need to limit current to protect the PSU, not the battery. Either way you cut it, you need to limit the max current draw to make it work. But when the cell nears full charge, you need to reduce/remove this limit, or it will take a super long time to charge the last 20% of the battery.
Rule of thumb is that max charge of an average li ion battery is probably at least 1C. Li ion batteries are made with much much higher charge/discharge to C ratios than this, maybe 20:1. They sacrifice some max capacity in order to achieve this higher charge/discharge rate. But there's decreasing gains going the other way of trying to maximize capacity at the cost of charge/discharge rate. So some batteries can be charged at 10 or 20C, but it would be rare to find a 1Ah battery which could not be charged with at least 1A. Hence the rule of thumb of 1C. But this is a max rate; if you want to extend life of the battery, you only want to charge at a small fraction of this max. I tend to use 1/5C to 1/3C as the mark for reg'lar li ion cells, unless in a hurry.
For 4S cells, I tend to charge to 16.6V in lieu of balancing. That can work ok, too. You have to examine how balanced your cells are, though.
1 cell with 5800mAh? Those are big ones. For a cell with 5800mAh, 1C means that you charge at 5800mA which means 5.8 Amps. 2C would be twice as much so 11.6Amps, or 0.5C means 2.9Amps . These numbers are for cells connected in serial. If they are parallel you can multiply that by the number of cells.
Another example, having 4S2P, so 4 in serial, and these 4 another time in parallel. So 2 blocks, where each block consists of 4 cells in serial. These two blocks are connected parallel. Resulting in 8 cells total would result in Capacity * number of cells, which is 5800mA * 2 => 11.600mA => 11.600 Amperes
Please check the datasheet of your cells regarding the C rating, that's usually specified there. 1C may be a good rule of thumb but I saw cells which take more or even less.
Charging the cells with too much current can result in a steam/fire/explosion.
I sometimes use twice the specified current, but I also check the temperature every 5-10 minutes since it's really dangerous. I think fast charging also reduces the livetime so better stick to the recommended values.
Edit: Also very important: If you connect cells parallel you need to ensure they are evenly charged. If one cell is full and the other one is empty, the full one will charge the empty one uncontrolled. It might be possible that the current is way too high and the empty cell starts steam/fire/explosion.
And as katzohki said, use balance charging. That means if you have cells connected in serial you have an additional wire between each cell.
So for a Block of 3 cells it looks like this: -C x1 C x2 C x3 +
C is a cell, - is minus, + is plus, x are balancing connectors. Where minus and plus give you the total voltage of the block. x1 is the first balancing connector providing 4.2 volts between - and x1, x2 is the second balancing connector at 8.4 colts between - and x2, and x3 is the same as + giving you the total of 12.6 Volts. A balancing charger can use these different voltages to determine the voltage of each cell, and these points are also used to charge cells independently. The balance charger first charges the empty batteries until all batteries have equal charge, then they are charged together.
In whatever way cells are connected, serial or parallel it's getting dangerous if they are not charged equally.
Edit2 You should also think about buying a battery charger from the car/airplane/quadrocopter area like the Imax B6. I'm really happy with mine, I can charge EVERYTHING with it. https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2380057.m570.l1313.TR12.TRC2.A0.H0.Ximax+b6.TRS0&_nkw=imax+b6&_sacat=0
But for your case you might want to look for a stronger one which can provide more Amps.
Assuming you're talking about 18650 cells, 5800mAh is clearly in the total fiction marketing hype range, especially since you combined it with the words "low cost" and "ordinary". The only thing you can do with those is actually measure their capacity with a charge-discharge cycle, see what you ended up with, and go from there. Don't be shocked if it's in the 600-1000mAh range.
Name-brand batteries from trusted vendors will typically be in the 2200-2500 area for those that look for a good price/performance ratio. If performance trumps price, then you can find real capacities up to around 3500. Plus you can find valid datasheets for genuine batteries that tell you what C is, and the recommended charge cycles!
- You can go for 5.0A or 5.5A. That should be enough safe margin. But you're going to use 1/3C already to improve safety and lifetime, so I say you can use the full capacity as base for your calculation. 5.8A / 3 = 1.7A
- You should do "4 groups of 2 cells in parallel first". This will balance the batteries a little bit. Just watch them while you're building the first groups. Check temperature with your hands. Getting warmer is ok, getting too hot to touch is not. And before you make the final connection in series wait half an hour.
- Current increases in parallel, because at the same voltage, double capacity you need to deliver twice the energy. In case of serial you have the higher voltage, but the same capacity, so the current stays the same. This means 1.9A * 2 because you've got the double capacity. The charging voltage increases as well, one time for the obvious reason in the next sentence, and the other time because a higher current needs to flow, and therefore U=R*I where R is the batteries internal resistance. But the voltage is managed by the BMS. Obviously you can't charge 3*4.6V batteries, connected in series with 5V.
One final thing, as Nusa mentioned. Which types of batteries are you using? I know there are packs at 5800mAh, but if you've got 18600 batteries you got ripped off and those batteries will be dangerous!