Sorry for the delayed response. First off, a 5300mah 7.4v two cell pack is not possible. I assume you're trying to use 2x2650mah cells in series to get the 7.4v but the capacity isn't additive. You either get 3.7v at double the capacity or 7.4v at the same capacity. Anything else would not conserve energy. 5300 x 7.4 = ~39Wh but if you have a 2650 cell at 3.7v, 2650 x 3.7 = ~10Wh. Two cells cannot produce more than 20Wh combined in any parallel/series configuration. If this isn't clear, look up the difference between series and parallel. You're also probably at a very very basic level and I would not advise you to be messing with custom lipo cells.
As for the charger and pack you want to produce, what you're trying to do is again, not advised. You cannot charge two lipo cells off a charger designed to charge a single cell. You want 7.4v but the charger you've chosen is only designed to charge up to 4.2v on a single cell.
Some really basic info about lipo charging:
- The charger generates 4.2v constant
- current is applied to the cell and the cells voltage is constantly monitored
- as the cell approaches the maximum charged voltage of 4.2v, the current is slowly reduced
- at 4.2v charging is turned OFF. No trickle charging
(I may not be 100% right about the 4.2v constant voltage but I'm pretty sure)
What you need is a charger designed for TWO cells. This means that EACH cell has a +/- lead attached to the charging board. This is absolutely required for balancing of cells. You cannot have one cell that has more capacity than another. If that were the case, one cell would drain while the other is still chugging away...the drained cell will fall below the critical ~3.0v and will be damaged or potentially burst into flames/heat up a lot.
The other issue is cell protection. The protection circuit is designed to avoid the cell being overcharged or over discharged (bursting into flames, or, thermal runaway). You can buy cells that have built in protection circuits (advised), or you can use a power management board which both charges/balances the cells while also protecting EACH cell from over/under voltage. In the latter scenario your +/- terminal to whatever application you're using it with would come off the POWER MANAGEMENT BOARD and NOT from the cells themselves. The board must be specifically designed to take 2, 3, 4, 5, 6 whatever number cells and provide you with 3.7, 7.4, 11.1, 22.2v whatever voltage...basically must be designed to operate with parallel/series designed circuitry.
Due to this very custom design necessity, there aren't very many readily available power management boards that are cheap. Even fewer offer a simple charging solution in addition to power management. They'll often need some specific voltage and minimum current to be applied to the charging leads. Not to mention it would be very inefficient trying to charge more than a single cell off a very convenient cell phone charger. Instead, the typical model is to have a separate cell charger that charges single protected cells then drop those cells into a flashlight, plane, robot, laser, whatever you're using them for. Take them out when they're drained and recharge. Or the modern R/C model of having cells linked in simple 1S, 3S, 4S...with a balance wire which just has + leads from each cell and a common ground so the charger can balance the cells.
There is one semi trick you could do however. You could hook up two protected cells to a single TP4056 in parallel but operate them in series. I'm not 100% sure how this would work, but I imagine during charging, the charger would just keep going for a longer period since the charge current is being split (you'll want a higher charge current but mind the charging chip heat). One charging issue however would be if the cells eventually become unbalanced, one would charge to max first and the charger would just cut out and not charge the other cell. During discharge they should operate normally until again over time they become unbalanced; one cell will drop to the 3.0v minimum and cut out. So this method is not really advised (at least not for several charge/discharge cycles).
If you really want embedded cells, your best bet is probably just using two TP4056 boards and two cell phone chargers. Wire your cells in series to get your 7.4v but have separate circuits for charging also hooked up to the cells. Don't ever use soldering solution on electronic boards, but it's highly advised to use some sort of soldering agent when soldering lipo cells to avoid overheating them with the solder/iron.
Hope that helps, good luck.
Last edited:
