Li-ion and Li-po in parallel?

[Osarus]

Hello!

I have a dream.... to fly my drone longer then 10min than my Li-po provides but still have the option to occasionally let it rip with high current which Li-ion will not support.

What would I need to overcome to put a 6s pack of Molicel P45B - 50A 4500mAh 21700 Li-Ion's in parallel with a small 6s Li-po. I don't understand how they will discharge together and what voltage sag might do even if they had the same internal resistance, I'm sure there are other things I'm not even aware of...

I could create a cutoff on the Li-po easily enough to take advantage of the lower min cell voltage of the Li-ion.
What else would I need?

Much thanks.

 

[amberwolf]

Unless I'm forgetting the stuff I once knew about RC LiPo (I don't think I still have any around nowadays) the LiPo is almost certainly lighter for the capacity / power you can get out of it, especially for the volume of the pack, than any of the cylindrical cells are likely to be.

I think you would be better off just adding more LiPo packs in parallel.

FWIW, the usable capacity of the cylindrical cells is usually less than the rating, unless you are draining them down totally empty, which is hard on them (just as it is on the RC stuff). So running them down to the lowest voltage limit in the spec sheet ages them faster, so they'll last less cycles than if you used them a little less, stopping at a higher voltage. (say, 3.0-3.3v, vs 2.8v or less).


As for how different types of cells will discharge together, it depends on the cell resistances, mostly--the higher resistance cells will supply less of the current. If you had one pack that's say, 100milliohm total resistance, and another than is 50milliohm, the latter would supply twice as much current as the former, under the same load conditions. So if you have them both connected to that load at the same time, the former supplies 1/3 of the current, and the latter 2/3.

It's not always as straightforward as that, but that's the gist of it.

For more detailed info, there are a number of threads over the years discussing dissimilar chemistries or cells in parallel, if you poke around a bit--most in the battery technology subforum.

 

[scianiac]

Connecting such dissimilar batteries and pushing their power draws hard can cause issues, they will somewhat balance their current draws due to the difference in IR and voltage sag but it's probably not safe to rely on this at high power levels. You have to remember that these are complex chemical devices that do not respond linearly and you may end up with weird behavior like them charging each other after hard punch outs. For an Ebike where you're talking about discharging a battery over hours I think you can design a combo pack that can operate safely (although it's often pointless to actually do so) but for a drone that will always be running the batteries pretty hard it may not go well.

While I understand the interest in the idea I don't see the real application. I have drones I fly hard and ones I cruise around at lower power levels and I don't really see the point in trying to make one do both and be worse at both. Why not just have two battery packs and switch them over for different flights? Or better yet two drones that are optimized for it. You can get just as much more flight time and more performance by optimizing the quads for such builds as you can from the batteries. Yes there are some applications for a quad that can do both but those are probably a very small fraction of how you actually fly.

 

[eMark]

I have a dream.... to fly my drone longer then 10min than my Li-po provides but still have the option to occasionally let it rip with high current which Li-ion will not support.

What would I need to overcome to put a 6s pack of Molicel P45B - 50A 4500mAh 21700 Li-Ion's in parallel with a small 6s Li-po.

With the existing weight of the smaller 6s Lipo ... in addition to the additional weight of a larger 6s P45B Lion (4500mAh) ... will it extend the flight time that much longer than 10 minutes (e.g. 15-20 minutes?).

First parallel two smaller 6s Lipos (if you haven't already) and measure the flight time? You probably already have an extra backup 6s Lipo so you could easily parallel the two 6s Lipos (assuming both in good condition) and factor the additional flight time based on available increase in mAh (taking into account the additional weight).

Is weight of a 6s P45B Lion pack that much lighter than your current 6s Lipo as your reason to justify paralleling a 6s P45B Lion (4500mAh) instead of another 6s Lipo (3300mAh?)?

What about paralleliing two 6000mAh Lipos (60C peak burst) if the flight time of just one isn't long enuf for your enjoyment instead of paralleling your current 6s1p Lipo (3300mAh?) with a 6s1p P45B (4500mAh) Lion ...

 

[eMark]

Is your smaller 6s1p Lipo also 4500mAh ... the same capacity as a 6s1p P45B Lion? How much lighter is a 6s1p P45B Lion than a 6s1p 4500mAh Lipo ? If there's no decrease in weight advantage than try one 6000mAh Lipo and see with the extra Lipo weight how much of an increase (if any) beyond 10 minutes. Ten minutes of maximum flight time was the same conundrum that faced RD pilots 30 years ago when i was into RC hobby flight.

The age-old RC problem with any plane is matching the power lift/flight to the ideal battery weight for maximum performance. Even with one heavier 6000mAh Lipo in place of a 4500mAh Lipo you may only be able to fly 9 minutes. With two of them paralleled you may have some difficulty in getting airborne. Same scenario with a 6s1p 4500mAh Lipo and a 6s1p 4500mAh P45B Lion.

If you have a good-sized drone with plenty of lift/flight thrust power you may be better-off with a 6s2p 9000mAh Lipo. However, again the extra weight of a bigger drone with a heavier 6s2p 9000mAh Lipo may still not allow the gain of - "I Have A Dream" - flight time . It's the same conundrum that has always frustrated RC pilots wanting to fly for more than 10-12 minutes.

With the advances in lighter composites and lighter batteries over the past 30 years it would seem where there's the will there should be a way to make your "I Have A Dream" a Reality - :thumb:

 

[Hillhater]

What sort of drone are we talking about that can only get 10 mins fly time from a single pack ?
Most half decent “domestic” drones can fly 25-30 mins on a 2.5ah battery , or 45-50 mins on a 4ah battery (Dji mini 3)
Is this some race/custom drone ?

 

[Osarus]

Much thanks for all the great points, sounds like it's going to be beyond my ability.

I've been looking at this 4" Flywoo Explorer LR 4 drone setup for long range.

There recommended options are a 4s 900mah Li-po or a 4s 3ah Li-ion, they don't list battery weights.

I've seen it flown with 3ah Li-ion packs but it's sluggish and slow, thinking more on this it's also due to weight, not just power.
I was thinking of adding a small say 0.4ah Li-Po with a very high C rating which would only come into play during high current draw to give it more play. Like mentioned just hooking it up and hoping for the best isn't going to work so I'm guessing this would need to be built into the flight controller.

Regarding flight time, most DJI drones have a very low power to weight ratio, big batteries and large motors. They are built for very slow stable cinematography. It's much much higher for freestyle/racing drones, even cruisers like I'm looking at I'm guessing are higher.

 

[eMark]

I've been looking at this 4" Flywoo Explorer LR 4 drone setup for long range. There recommended options are a 4s 900mah Li-po or a 4s 3ah Li-ion, they don't list battery weights.

Specs claim flight times as long as 30 minutes ...

• Sub250 (even with battery)
  Support 4K\60fps recording
  Up to 10KM away
  Super long flight time 30 minutes (Explorer 18650 battery)
  GPS search of up to 30 satellites

You've probably already watched these Flywoo Explorer LR 4 drone 30min flight youtubes. So what's different about your Flywoo Explorer LR 4 drone flying routine that may limit your flight time to only 10 minutes ? That seemed to be your concern (just 10 minutes of flight).

Fly For 30 Minutes? Flywoo Explorer LR - Setup, Review & Flight
https://www.youtube.com/watch?v=VJ8juI56DOs
37minute FPV Flight - Flywoo Explorer LR ... 3s Lion VTC6 Sony 3000mAh[/b]
https://www.youtube.com/watch?v=mZ7sogO778Q
Supposedly easy-going cruising for 30 minutes as is ... so if your enjoyment is doing some racing and aerobatic power bursts ... then only 10 minutes of flying time?

Regarding flight time, most DJI drones have a very low power to weight ratio, big batteries and large motors. They are built for very slow stable cinematography. It's much much higher for freestyle/racing drones, even cruisers like I'm looking at I'm guessing are higher.

There is no advantage to ever adding another battery increasing the overall weight and defeating your objective.

Even spending a few more bucks for a 6" Quadcopter for better cruising speed and power bursts in wind ... https://www.getfpv.com/ready-to-fly-quadcopters/6-rtf-quadcopters/iflight-bob57-ellis-van-jason-lr-6-drone-hd-w-dji-o3-air-unit-6s.html ... you're again limited to a 9-10 minute flight time with a 3000mAh 6s Lipo ...

• 9-minute flight time with 3000mAh 6S Lipo

With a racing stunt 6" Quadcopter ... https://www.dronerush.com/best-stunt-drones-flip-barrel-roll-3d-9510/ ... only 9-10 minutes of flying time, but with conservative cruising the majority of the time you may achieve at least 15 minutes of flight time with proper propellors.

You may want to consider a more powerful beast to satisfy your Quadcopter flying passion ... https://www.rc-wing.com/arris-m900-frame-with-motor-esc-propeller.html ... then flying it 90% of the time at an easy-going conservative pace to extend flight time 45-60 minutes.

Another possibility ... https://www.rc-wing.com/iflight-mach-r5-hd-6s-fpv-racing-drone-w-caddx-polar-vista-digital-hd-system-bnf.html ... with easy-going cruising speed 90% of time for extended flying time.

Keep doing your due diligence. With all the available choices today you should find one to satisfy your flying passion ... Best Of Success Flying Your WAY :thumb:

 

[Osarus]

An Image to explain better what I was thinking, excuse my paint skills haha. Trying to take advantage of the benefits of both Li-Ion and Li-Po.


The red would be the larger more efficient Li-Ion, the Blue the small high current li-Po.

This way would could have long flight time and high current. Now we have long flight time AND the ability to get out of steep dives or do an odd loop, really hard turn ect. Instead of just choosing one or the other.

Like mentioned trying to keep the voltages the same without them charging one another, managing voltage sag and even just controlling current like that. Looks like it's more effort then anyone with the know how would bother with!

Until technology catches up I'll have to settle for 2 drones or maybe a plane... I guess that can do both!

I like that iFlight Mach R5, thanks for linking it.

 

[eMark]

Yesterday sent them the following message concerning their iFlight Mach R5 HD 6S FPV Racing Drone w/Caddx Polar Vista Digital HD System BNF ...

Intend fly it at easy-going speed 85% of time to hopefully extend flying time to at least 15 minutes. What propellors would you recommend?

Received the followiing answer (impressed with quick reply) ...

We recommend 6S 1300mah battery. Reagrding propellers, you can use Nazgul R5 Propellers that is okay.

Regards,
Cherish

Would have thought perhaps a 5S 2500mAh battery to slow propellor spin with less thrust/speed for more flying time (range). And still just enuf thrust for simple aerobatics with the right props for both thrust/speed and flying range, but what do i know.

Should you decide to buy get as good estimate from them as to optimum flying time with only 25% thrust/speed, while 75% easy-going for maximum flight time (12-15 minutes). See what they think about using a 5s 2500mAh for extended easy-going flying time (15min).

Will have fun experimenting with different props and batteries to decide which to use depending on your days' flying pattern and passion for achieving optimum performance (easy-going or speed/thrust) ...

Looks more like 65% easy-going to 35% thrust/speed ... 12-15 minutes may be max airborne. Will need to experiment with both battery and prop options to satisfy your flying need (12-15 minutes??).

iFlight Mach R5 HD 6S FPV Racing Drone w/Caddx Polar Vista Digital HD System BNF ...