Dual battery question

[acwhitney]

Im building an eeb frame up and realized the frame could actually hold 2 battery packs i own. More than increasing range i am theorize that it should also cut the max draw of each battery in half. The last purchase i need for next project, working title "2 Chainz" a cyclone eeb build, is a controller. I was about to buy a 40a controller tonite. But now i think i could easily step to 60a and be within the amp rating limit for each.

About the packs.

The first battery i was originally intending to use is a em3ev pack 14p9s 52v 30ah with smart bms. Used for about 1000mi and the pack is still balanced!

The second is a 52v 20ah chinese battery. Had some trouble with it until i got a cycle saitiator to nurse it back to health. Needs some more tests but i dont have a working bike at the moment.

I believe both are 18650 cells but unsure of brand.

Side note: 6 weeks ago i thought my bbshd build was perfection, cut to getting t-boned in a crosswalk, in a PARK! And now im one purchase away from building a monster 3000w eeb.

Ps is it possible to run a 60a controller at 40a and be confident it wont over demand amps from my pack?

 

[john61ct]

Paralleling two packs you want to be pretty sure their SoC - voltage correlation at least is pretty darn close.

Actual (measured with CC load) Ah capacity is less critical, but does also impact how evenly the load is shared between them over a discharge cycle.

As does ESIR.

The stronger pack will bear most of the high-amp loads, and backflow from sub-pack to sub-pack wastes a lot of energy.

So, adding a weak pack to a strong one may really impact range more than sustained power output, but neither as much as two equally healthy ones, and not as much as you hope.

Also to the extent you take advantage of faster acceleration, your Ah/mile efficiency drops.

 

[john61ct]

I was about to buy a 40a controller tonite. But now i think i could easily step to 60a and be within the amp rating limit for each.
...
is it possible to run a 60a controller at 40a and be confident it wont over demand amps from my pack?

If the controller does not let you set a hard Max Battery Amps limit, adding a CAv3 will do, and give much more too.

I personally really like the idea of a grossly over-capable controller, so long as that feature is enabled

so that the bottleneck moves to either

the pack power capacity, or

rising temp inside the motor, which CA can also further limit