I checked other posts for answers but couldn’t find any, so here goes… (I’m a total battery nerd so I can’t help myself; forgive me ePPG gods that have engineered the amazing SP140!
As for the new SP140 batteries:
can a 4kWh pack be paralleled with a 2kWh pack, assuming both are fully charged, same voltage, etc.? I want to fly longer on my trike but I don’t want 80 lbs of batteries (rather go with 6kWh than 8kWh)
Is the 2kWh pack the same physical size, i.e, have the same dimensions as the 4kWh pack? I’m assuming yes because it has to fit in the slot behind the motor.
Do the 2kWh pack cells have a greater power delivery capability, i.e, are they different cells than the 4kWh pack? I ask because if you can fly with just one 2kWh pack it seems the C-rate on the cells in that pack must be greater. Unless you over-designed the pack in the first place to handle both scenarios.
What is the nominal voltage of the pack? Or put another way, how many cells in series are used?
What are the physical dimensions of the pack(s)?
I’m guessing since no one has their hands on an SP140 yet that these answers may only come from the top. I just want to start getting my trike ready.
Technically you can parallel the packs, but probably not recommended. as it drains, the 4kw pack will charge the 2kw pack. If it was low amperage draw, id say ok go for it.
as far as we know 2kw pack is same size as 4kw pack. just less batteries inside.
Thank you for the answers and insight. Questions always lead to more questions. The webpage says the SP140 can put out 25kW. I assume that is its peak rating, not its continuous rating (so you could push it at 25kW for a minute or so before the thermal mass gets overloaded). So how long can it put out the 25kW before overheating, and are there two numbers for that, one for the motor/controller and one for the battery pack (I guess technically that’s 3)? So what is the continuous rating of the motor and battery? So many questions…
To clarify where this is coming from…if I’m putting this on a trike the first question that comes up is can the unit handle the extra weight. Then if you dig deeper, the “unit” is actually 3 main parts, each with its own thermal properties. So if I tried to fly a trike with a single battery pack, and I had to push it past the continuous rating, which am I going to risk damaging first, the battery, the motor, or the controller? If the answer is the battery, then paralleling 2 packs (of equal capacity) would help with that. If the answer is the motor or controller then I’m not sure what I could do, especially since adding extra battery weight only makes the problem worse. Anyway, that’s where the questions are coming from.
Regardless of the brand, which system. Flying a trike makes sense from a battery of around 6 kilowatts / h. or more. then good climbs are also possible, e.g. to be able to safely fly over obstacles or not to lose altitude in falling air masses. Whether the batteries consist of several packs is not relevant as long as the c rates are not exceeded. briefly about thrust performance. (pilot is assumed to be 85 kilograms) for a light trike (only 3 wheels under one eppg.) you need around 55-60 kilograms of thrust (12-13 kw) for a safe start. for a real trike with its own frame, brake, cage, comfort seat etc. you need around 70-80 kilograms of thrust (15-18 kw). in level flight the light around 35 kilograms (5.5 -6.5 kw), the heavy around (6.5 -8 kw). variable depending on the wing and propeller setup.
Since I have seen a lot of fatal accidents with light trikes only screwed to ppg, I myself only fly trikes with a safety roll cage. It is also important if you want to fly a light 3 wheel trike with large batteries. the batteries must be secured separately. the mass acceleration of the batteries in the event of a false start at 40 km / h can easily break the neck or cause serious injuries to pilots.
With two packs in parallel, the voltage on both must remain the same, which means that current draw on both should also be the same (unless the fewer cells of the 2k pack present lower internal resistance in series with the load, in which case it would drain just a bit faster due to higher current than the 4k pack). The 4kw pack could only charge the 2kw pack if its voltage could drop to a lower level than the 4kw pack. When the 2kw pack is “empty”, only the 4kw pack could continue to supply the current demand, which would generate more heating of the pack. Ordinarily, I would recommend a diode on the output of each pack to prevent any feedback from one to the other.
I noticed that the battery pack weights (4kWh = 40 lbs, 2.2kWh = 28 lbs) shows that the 2kWh pack has about 8 lbs of extra weight that is not going toward energy storage. That seems like a lot of packaging weight. Are these weight numbers accurate?
The 2.2kwh pack uses the same size case as the 4kwh pack and same bms. So that doesn’t help it be the most lightweight per kwh. Then the other majority of the weight comes from the extra 24cells it has and that adds about another 2kg. Thats why its 2.2kwh and not just 2kwh.
