I am building an ebike and plan to use some C020 high capacity lipo cells at 14s 2p to give me <200A continuous discharge and 40Ah! (I only plan to use 150A max so should be a breeze for these!) Due to the size of the frame opening, I cannot create 1 large pack with two rows of 14 cells. I am going to split the pack in two but I'm not sure whether to have two 7s2p packs or two 14s1p packs. Are there any advantages of one over the other?
2 14s lipo packs in parallel or series?
- Thread starter cg_ebiker
- Start date
There is a one big advantage to 7S, it is very easy to find excellent but inexpensive balancing chargers from the RC market. Higher than 10S, not so much.
You could still use it as a 14S "split pack", keep connected in series except for when you need to balance charge.
Also, you avoid the potential imbalanced power flow issues of paralleled sub packs.
All the paralleling done at the lowest 1S voltage level is the better way to go.
You could still use it as a 14S "split pack", keep connected in series except for when you need to balance charge.
Also, you avoid the potential imbalanced power flow issues of paralleled sub packs.
All the paralleling done at the lowest 1S voltage level is the better way to go.
I also vote for a pair of 7S packs. They can be at wildly different voltages, but when you series them, they will work fine. There are several issues with using two 14S packs in parallel. If I had to run two 14S packs to extend range, then I would run on one pack, then swap the pack connectors when the first pack was low.
Of course better to get them to similar voltage before connecting.
Not for safety, no current will flow between them, but unless your balancing charger has high current transfer capacity, such disparate SoC's will grossly extend charging time.
Most balancing circuits both on BMS and hobby chargers are well under an amp, and slow down **a lot** as the delta narrows.
There are dedicated balancers with a rate of even 2-5A but they can be expensive.
Best approach is fully charge both your 7S sub packs with an RC charger to the same termination profile (a Duo unit will do both at once)
or discharge them both to the same storage setting,
and then join them together at that identical SoC.
Not for safety, no current will flow between them, but unless your balancing charger has high current transfer capacity, such disparate SoC's will grossly extend charging time.
Most balancing circuits both on BMS and hobby chargers are well under an amp, and slow down **a lot** as the delta narrows.
There are dedicated balancers with a rate of even 2-5A but they can be expensive.
Best approach is fully charge both your 7S sub packs with an RC charger to the same termination profile (a Duo unit will do both at once)
or discharge them both to the same storage setting,
and then join them together at that identical SoC.
As it's going to be in the bike, I'd ideally have a single charge port and do it through the BMS rather than having to connect wires to the individual packs. This (https://www.cloudsto.com/ebikes/bms-1/smart-bms-8-24s-for-vbms-detail.html) is the bms I want to use and it has 200mA balance current and the batteries can handle 20A continuous charging. No matter whether I connect the two blocks in series or parallel, I think each cell will still be monitored by the BMS. Making a 7s2p pack would just mean I don't have to run two balancing leads to each 14s pack per cell. Sounds like two 7s packs is the way to go though? Just for context this is a high power enduro ebike not a 250w pedal bike!
cg_ebiker said:
A 14s1p pack will use different busbars than a 7s2p pack, but both will be the same physical size/shape, etc.
The 2p pack will already have parallel connections made for balancing, etc, and will only need a heavyduty series single wire connection between the most negative half's positive busbar, and the most positive half's negative busbar.
The 1p pack will require adding parallel connections between the two packs for balancing *and* will need a heavyduty connection between the main + and - busbars.
