Dual battery sp140 FOOTLAUNCH!

Maybe I’m a masochist, but I really want to try to fly this setup. Dual batteries, 1 4kw battery strapped sideways, with the 2kw feather battery in the original location. Ive already tried handling it on the ground, it is very difficult especially for a smaller guy like me at 155 lb. If the machine is on a raised platform I can put it on stand up and walk around with it. If I put it on from the ground I am just barely able to squat it up to a standing position. I think this is set up would only be feasible to launch with 5 to 10 mph wind. I’m going to figure out how to parallel both batteries into the ESC and I’m going to use the dally BMS bluetooth app and the amperage readout from the controller to determine what percentage of power is being supplied by which battery and do a bit of a study to see that both batteries are being discharged appropriately to their capacity.

Thoughts you guys?

Try the heavier battery in the stock location to lift the weight more onto your shoulders. Might be easier to manage on the ground.

Try it on a trike.

I have no trike.

Update, I’ve ran into two issues that prevented me from trying the dual battery foot launch setup. The first one is hangpoint. This was an issue for me even with the original 4kw battery, I relocated the 4kw battery under the seat to help compensate the weight and attain a reasonable hang point angle. Once I added the 2kw battery to the stock location my hang angle was once again 15 to 20°. In order to try this setup I’m going to have to find extra solutions to get the hang point angle reasonable, right now I’m thinking of doing the longer / extended shackles plus the foam behind the seat. The second issue was battery voltage balancing. For whatever reason the feather battery only charged to 99.8 volts, then the BMS cut it off. The 4kw battery with the old style non Bluetooth BMS charged to 100.8 volts like it typically does. I used the same charger for both batteries. I was concerned about connecting both batteries together with a voltage mismatch so I need to figure out what’s going on with the BMS on the feather battery so that it can also charge to 100.8volts, or I need to babysit the 4kw battery and unplug it when it is at 99.8 volts so they can be matched.

If you connect the small and the large battery in parallel and discharge them together you have an over all lower load per battery (cell) than on a single battery flight. Discharging at a lower C rate usually gives you more usable Ah (check the Chart for the Molicell cells at lygte-info.dk).
On the other hand you have to carry more load, which will cost you some flight time.

While the overall load for the combination is smaller, you will still stress you 2kW Battery more than then the 4kW battery, as every cell in the 4kW needs to deliver only half the load of the cells in the 2kW battery.

My advice would be to use the same batteries (cell type, count and age) if possible, and maybe also do more squads :wink:

511 / 5.000

if the output voltage of the different packs (cells) is approximately the same at the start, you can operate any number of them in parallel. the age or the cycles should ideally be similar to what daniel has already written. the volts drops evenly with all packs. you can compare it with connected water tanks that always keep their level the same when water is removed. as long as you don’t drop the volts below 3 V per cell (better 3.2 volts) you can’t go wrong.