I’ve added a battery housing to place six 18650 cells neatly inline to triple my runtime, but I don’t know if my plan to connect them is sound. Currently the idea is to wire the two sets of three into the existing battery board after desoldering the existing battery holder off the board. What I’m unsure about is whether the unit will continue functioning in the same way. I know my batteries will continue providing the same voltage since they’re in parallel, but I’m concerned about the two electronic components on the battery board and the role they play in protecting the batteries+device. They’re labelled D1, D2, F1, and F2 below, no idea what they are. I wasn’t able to locate a pcb schematic for the uConsole’s battery board, it’s conspicuously absent from the pdf located in the github repo for uConsole. I went spelunking in the forums and found a DevTerm battery board schematic that looks like it matches, at least in terms of component count. I can’t clearly see the traces on the uConsole battery board because of the way the pcb is made. Anyway, assuming all my info is correct, I think I can just wire the new batteries directly in, replacing two parallel sets of one with two parallel sets of three. But I think I need some kind of battery bus bar to link the three of each set together before running a small jumper wire to the respective pad on the battery board. Diagrams of the plan below:
D1 and D2 are diodes, components that help keep the output voltage consistent. F1 and F2 are fuses, which will cut power if there is too much current so your board doesn’t blow up. Both should work fine with more batteries in parallel like you showed - the voltage and total current will be unchanged, and the fuses should still protect the main board as well as before (they might have a maximum failure voltage beyond which they aren’t reliably safe because the circuit will start arcing, but the batteries in parallel can only provide extra current). Since your cells will be wired in parallel, they won’t need any additional cell balancing besides what I assume the main board already provides for the original 2 cells.
I would probably charge all your cells in the original 2-cell circuit just to be sure they’re starting from the same baseline, and I would recommend using only matching cells (at least for each set of 3) to get the most life out of them. Otherwise, I think your plan looks good and safe.
(source: I have multiple degrees in electrical and computer engineering (caveat: my specialty is really computer engineering))
keep in mind, that if you add so much cells you also need to make sure to have a BMS. even if you wire them in parallel and hope they simply balance themselves, these cells will age differently to each other and in the future it could result in a lot of magic smoke (or worse)
A user above you with a degree in electrical engineering did not believe I need a bms, so long as I use the same model of battery and always charge/discharge them together. Could you elaborate on why you think I need a bms?
wiring them in parallel normally results in auto balancing (mostly on discharge), but the cells age differently as they are never 100% identical, even when you order them from the same batch. on your picture i can clearly see, that you’re mixing cells from different vendors.
if you apply voltage to these you will likely overcharge the weaker batteries if there is a too big power gap between them. If you additionally use non protected cells, this can result in an explosive surprise. so you should always buy the protected ones in such a setup.
it is considered less critical than in serial (where a missing BMS will most likely lead to fatal failure), but as you want to hold this device in your hand while charging and you are only protected by a thin layer of burnable plastic because of the printed backplate, i would highly recommend not to try your luck.
if you decide not to use a BMS, you could also use a balancing charger. The one in the uConsole is designed for two, not six batteries. i dont know if the integrated charger would even work, as most chargers have a charge cut-off, which will most likely will not be designed for a cell capacity higher than 5000mah.
source: common sense and basic knowledge of safety with batteries
Thank you, I understand better now. I’ll be purchasing 6 of the same cell and charging them on a separate 18650 charger with capacity readout. This should ensure the same baseline before I do my run flat testing.
as long as you always remove them for charging, thats perfectly fine. just dont use the integrated charger. but you can try to look for a balanced battery pack instead of 6 individual batteries, the cells in them are usually selected by comparing hundreds of batteries and picking ones which are extremly close to each other and most of the time contain a protection circuit in case one cell will get bad to prevent a thermal runaway
i took a peek at the specifications of the charger and the schematics of the uconsole - the uconsole does not balance the two individual cells either, both are simply connected to a single AXP228 single cell charger. so you indeed need 6 absolutely identical batteries, not 2x3 like upsidedowner suggested.
Also the diode in there is not for output voltage consistency but for polarity protection (in case you insert the cell in reverse). if i recall correctly, this will also prevent the cells to parallel discharge into each other. This safety feature will be missing if you simply connect the cells behind it in a bundle.
→ http://www.x-powers.com/en.php/Info/down/id/60
the charge cutoff is time based (480min), based on your power source, efficiency, charge mode and the charging curve it is possible that it would not charge your cells completly. If i calculated correctly it would be okay for 8-10ah. (but i did a very conservative calculation)
