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Thinking about moving to 18650 based power, opinions?

evranch

Well-known member
#1
I have a small collection of good 18650s for equipment around here on the farm, flashlights etc. Was looking in to building a bank of salvage cells for off-grid power. Then I recently was swapping out some cells and thinking - hey, these are pretty light. Sure enough other people are already flying them!

There appear to be plenty of benefits:
- half the weight per mAh
- much more crashable
- more available in Canada, cheaper, almost free as salvage
- build your pack to suit the plane instead of the other way around
- if put in holders, weight can be distributed easily and swapping cells is quick
- use the same cells in different configurations for goggles, transmitters, planes, quads etc.

Only one disadvantage? Low continuous currents?
It looks like there are lots of cells putting out 20-30A continuous now, and most of my planes have 30A ESCs on them. For the 60A planes that's just another parallel string.

Don't see very many good holders out there that look like they could handle 30A, though. Looks like I would be soldering them into packs.

They really appeal to me for my "sheepdog" quad as I can could cut the weight, gain performance and keep the flight time or gain even more.
 

LitterBug

Troll Spammer
#3
You probably won't be finding many cells capable of sustained output of 20-30 amps in the scrap heap. New.... maybe, But they probably come with a hefty price tag. You will probably have to run parallel and series to get the desired results. Soldering/welding and/or HD connectors are going to be required for higher loads too. Keep us posted with your finds. I would love to have a couple packs with higher current capability.

I have been flying them in a Strix Nano Goblin. Stock setup is <250grams with a 2 cell 18650 3200mah pack. It will easily fly 45 minutes, but that is with <=5 amp average load. Max discharge rate is about 3C (10A) Also use them with my FPV headset. That has a very low current draw by comparison.

The other thought is to go higher series, and lower current. Ie 6S instead of 3S. Half the amps required for the same watts. You just need to make sure your ESCs and ubec can handle the higher voltage.


Cheers!
LitterBug
 
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Hondo76251

Well-known member
#4
I dont know how well using scrap cells for a quad would work, much more feasible for fixed wing. It generally takes cells running in series and parallel to get the voltages and amps high enough to be useful.

Largest one I built was for my Beaver. It was 6s so I used 18 batteries! 6 cells in series x 3 to get enough amps.

Another thing to consider is, series or parallel, the cells should be identical. That can be a bit hard to with repurposed cells. And of course, it has to be mentioned that working with cells can be dangerous, enter at your own risk...

All that being said, if you are comfortable with soldering cells and like tinkering, go for it! They're pretty easy to make, dont cost much so (long as you dont scorch a finger) you're not out much if it doesn't perform well...
 

evranch

Well-known member
#5
Thanks for replies guys, that's really cool that the Goblin will fly 45 minutes and stay under 250 grams.

I definitely wasn't planning on running scrap cells on the quad. That would be an application for good quality new cells.
However, its amp draw is low due to a fairly gentle flight envelope. I'm currently running 3s 7700mAh which gets me 30 solid minutes of herding. Mostly just maneuvering around quietly with no big punchouts or freestyle.

That's only 15A average draw, and a lot of that goes to hauling that huge battery! It's literally over half the weight of the quad. I feel like going to 3s 3000mAh 18650s would cut down the weight so much I could get similar flight times. Even going 3s2p would still cut the weight way down.

Yes, scrap cells would be a fixed wing thing. I have been interested in going to 6s in the future for fixed wing, though many of my ESCs are 4s max. I know you can get away with not perfectly identical cells a lot better if they are in series. I was considering buying some EV or UPS battery modules and gutting them for the cells, which should be matched and evenly used.

What happens if you exceed the C rating on lithium ion cells for a peak load? Are they damaged or do they just heat up and sag in voltage?

@LitterBug what do you mean by HD connectors here? Could you point me in the direction of heavy duty cell holders? I know vapes draw a lot of current, but their battery box tends to be integrated into the unit. Cell holders would be a lot nicer to experiment with than soldering and desoldering the cells.
 

LitterBug

Troll Spammer
#6
I was looking around at various sites for info. Looks like there is a trade off with the higher current cells having a lower mah capacity. The 10A cells are 3200+, and the 20-30A cells are in the 2000-2500 range. So it may not be as easy as just going 3S1P if you want to be at 3000mah.

HD = heavy duty. I haven't done any research on HD holders for individual cells. Personally, I would not trust a spring holder for high current applications. The 10A packs I'm using in the Nano Goblin are soldered with XT-30 and balance connectors. I have both a 2S and a 3S from RMRC. I'm using individual cells with the Fatshark 18650 holder. (low current)

I also have a plethora of unidentified cells that have been pulled from Laptop Packs and an old pack from my Dad's oxygen generator. One of these days I should load test these scavenged cells and build(solder) a couple of packs up for flight use. Maybe try to identify some of them from their markings too. I'm thinking the FT Trainer might make a good experimental 18650 build. Possibly the FT Dart too. (2x 1106 5000 kv motors)

Cheers!
LitterBug
 

Hondo76251

Well-known member
#7
Thanks for replies guys, that's really cool that the Goblin will fly 45 minutes and stay under 250 grams.
I've got a sub 250 FPV converted chuck glider that I've put up for over an hour with room to spare, could probably get 1.5 hrs by the results of my last test flights. I'm using running 2s using 4 18350's (just slightly over half the length of 18650) which brings to mind another option I hadn't mentioned yet, there are other sizes of batteries available so its possible to build 2, 3, or even 4s setups that can be much smaller than 18650 cells would be.
Here's a list of battery sizes (LiIon about half way down the page)
https://en.wikipedia.org/wiki/List_of_battery_sizes
 

evranch

Well-known member
#8
I would not trust a spring holder for high current applications.
Agreed, my flashlights all have screw together battery holders. Integral to the device again, though. I couldn't find any discrete holder I'd trust with even 10A while looking around online. Looks like I'll be soldering, which isn't really a big deal.

Part of the appeal of holders was that I could do something like put them on each leg of the quad, cutting down the bulky mass of the pack hanging in the middle. Without holders, that's a lot of work to secure the cells on every change.

I didn't notice that the large capacity cells were limited in C rate. Hmm. Something to think about. Maybe I'd be looking at that 3s2p pack @6000mAh after all - it would still be under half the weight of the 7700.

I definitely want to get some 18650s onto my goggles, the lead to a bulky LiPo pack is certainly inconvenient. That little Fatshark holder is pretty nice. I didn't realise that RMRC was already making premade 18650 packs. That 3s 3200 is already a lot cheaper than a 3s 2200 LiPo here in Canada... I paid $50 for one last week. Only 10A though, as you mentioned.


So many different lithium sizes, I was looking at 18650 because they are kind of the standard. Yes, a compact 4s from a small cell would be pretty neat - also interesting is the 21700 from the Tesla packs. 3000-5000mAh would solve the C rate/capacity issue with the quad just mentioned.
 

Hondo76251

Well-known member
#9
What happens if you exceed the C rating on lithium ion cells for a peak load? Are they damaged or do they just heat up and sag in voltage?
I've run quite a few times with batteries that didn't have quite enough C but thats not as big of a deal with fixed wing. I'm sure in the long run its not great for the cells and they can get warm but mostly, at least in short bursts, they just sag a bit more than a typical LiPo in my experience.

I also use my stuff around the ranch out here, I assume by your pic you've got some sheep... ;)
 

evranch

Well-known member
#11
Yup, lambing right now actually which is why I'll post here and there but not build or fly much. Got a couple videos planned but no time for that sort of thing!

Here's a DVR recording of chasing a couple loose ewes back to the corral with my quad:

That was in the early days of this quad build when I still was having some stability issues on descent. Tuned a lot tighter now. You can see how heavy she flies with that 7700 underneath, though. Also notice consistent throttle settings in the 70% range.

That 26650 is quite the cell! Where do you order your lithiums from? There is sure a world of fakes out there, I have a couple "3000" aka 500mAh 18650s sitting on my desk that came with a charger off Amazon.
 

Hondo76251

Well-known member
#12
Yeah, hard nope for me on that one, I calve when the Antelope do! I don't like to work that hard! lol

I've got a phantom I've used quite a bit, even done a fair bit of "herding" with it too... ;)
herding cows.png

I'm more of a fixed wing guy normally but I've messed around with quads some...

Thats how I got started with tinkering with LiIon, trying to get longer flight times for checking larger pastures. I can't remember for sure where I got those 26650 cells but I do have my doubts on the 8800mah claim. I usually don't hold any battery to what it claims as very few seem to measure up to their claims, even the better ones. I've had Amazon ones, Banggood ones, cheap ones, expensive ones... I don't have any one company or brand that I've found reason to stick too. Some are certainly better than others but I have yet to purchase one I thought was garbage.
 

LitterBug

Troll Spammer
#14
I just heard soybens and pumpkins at our local AMA field. This autotune gone wrong flight was also my first 3S flight on of the Nano Goblin. Max throttle @ launch you can see the voltage drop a bit when pushing close to 10A. iNav locked the controls up when I switched in to autotune. All I could do was chop throttle and wait for the imminent "landing". For some reason, either I couldn't find manual mode to recover, or iNav wouldn't switch. Found most of the pieces and have rebuilt it with FoamTac. Also picked up a second Kit to build another using ArduPilot instead of iNav. it will be nice to compare them when done.

I pulled out a few of the Thinkpad 18650 cells, and one got extremely hot when charging. Thinking there may not be too many decent cells in that pack. Looks like they are 10A 2900mah cells.

I have two sets of 4 loose batteries that I've bought in the past from https://liionwholesale.com. 1 set is panasonic 18650B 3400mah 4.9A, and the other set is Sanyo 18650GA 3500mah 10A. All of them have worked flawlessly and up to advertised specs.

This site seems to have accurate information. https://www.18650batterystore.com/Best-18650-Battery-Guide-s/142.htm

Cheers!
LitterBug
 

evranch

Well-known member
#15
Nice herd Hondo, it seems you are on the same path as me looking for more cruise time for our wide open spaces. I'd like to try to herd with a fixed wing, but the quad is nice because it can apply pressure to the herd compared to just swooping and circling. I've had great success using it to push through gates, I use Viper goggles without the shrouds so I can see what I'm doing. I put the quad in position hold, then move myself, then move the quad, and can funnel the sheep through a mid-fence gate in a couple minutes.

Have you had any cows get aggressive with your annoying bird? I was practicing circling and pushing around my rams last summer when they were alone in the ram pasture, and one decided he'd had enough and took a run at my quad! Broke the two front props on his hard head and dropped to the ground, but luckily no damage to the rest of the frame. Again, this is where non-puncturable cells would be nice as I'm constantly in fear of putting a hole in a $100+ pouch cell.

Here in Canada Amazon.ca is a lot more like Ebay with a lot of third party sellers selling absolute junk fakes. Also for some reason, batteries are quite rare. Unfortunately, it seems Amazon is the only company capable of slipping packages through our border without incurring punishing customs fees, though I have received stuff from banggood labelled as "cell phone charger" that slips through.

@leaded50 thanks for the link, this guy really cares about vaping and battery testing! Tons of data on different cells, some of the larger ones will even put out over 40A continuous. Impressive! Interesting that some are actually a LiPo hidden inside a can... sneaky.
It looks like a "mechanical mod" is a high current lithium cell holder, but wow, crazy prices.

This looks like a good cell, tested to 30A/40A peak, 4200mAh https://www.18650batterystore.com/21700-p/molicel-p42a.htm
Wonder if either of the sellers linked will ship to Canada at a reasonable rate.

@LitterBug Bummer on the crash, I run ArduPilot on fixed wing and have never had it do anything like that. Not much time to come up with a solution and sometimes it's hard to remember to flip the manual switch. I like ArduPilot better for full auto flight, it has more flight modes, more features for waypoints etc. It did try to crash my plane once in full auto when it decided the altitude was completely different from reality, but I recovered before it hit the ground. Amazingly low currents from 3s to fly at those speeds, I have always stayed away from minis in my high winds but maybe I should give one a try!
 

LitterBug

Troll Spammer
#16
@evranch ,
The minis get VERY bumpy in wind. The flight above was on a pretty calm night. The 3S battery added some weight which probably helped some too. Using an FC with stabilization also helps. I can see a noticeable difference between manual and stabilized modes. I'm working on turning an FT Dart into a tailsitting VTOL running ArduPilot. Something like that might be a good hybrid solution. May scale up to the FT Kraken if it goes good.

Cheers!
LitterBug
 

evranch

Well-known member
#17
Sounds like a fun project! Yeah a stabilized mini using a cheap F4 controller might be the ticket to try to smooth out the bumps. ArduPlane will run on F4/F7 now but I haven't tried it yet.

I used to use ArduPilot's TAKEOFF mode for hand launches of heavy planes, but ultimately settled for the simplest VTOL system - hold the plane by the nose and toss it straight up :) Planning to make a video focusing on this style of launch as it's intimidating the first time but hard to mess up. Easier and far more powerful than the leading edge wing toss, I'm tossing my 80" wing into the air this way.
 

Hondo76251

Well-known member
#18
@evranch more often I get them just ignoring the drone! Lol especially if I've been flying a lot like during calving, that's where I like fixed wing. Of course, cows in big rough country handle a lot differently than sheep...
 

evranch

Well-known member
#19
OK so I got my first pack up and running here, it's balancing on the charger right now. I bought a set of 3 Aspire 3000mAh "35A" 18650 cells at the vape shop when I was in the city. Mooch's charts show these to be capable of delivering a continuous 20A for 2900mAh, and Aspire's own literature states they are good for 20A continuous and can take "vaping-type" peak loads up to 35A as long as you don't overheat them.

They also had some Samsung 40T 21700s and some bad-ass 26650s like yours Hondo but at $20 a pop I took a pass. There's got to be somewhere cheaper to get these in this country. Though those cells can both put out some serious currents.

Not hard to solder up at all. As the cells came with about 4V in them I put them in a plane on the bench that draws ~20A and ran the motor at full throttle with a wattmeter to see what would happen, then put them on the charger to balance out.

These definitely have higher internal resistance than a LiPo pouch cell. Voltage sags an extra volt under full load, but the difference was fairly marginal - the difference between 210W on LiPo and 190W on LiIo. However, the cells did heat significantly compared to the LiPo cell after I had burned off 500mAh. Definitely not hot but warm to the touch. I suppose this is because they are actually running at their C rating, something rare for a LiPo pack.

They weigh the same amount as a 2200 LiPo but should deliver 2900 mAh. The big difference is that you are supposed to be able to hammer the LiIo down to full discharge for 500 cycles instead of having to leave 30% in it. So that's a significant capacity boost, or lifespan boost if treated nicely. And no worries about puffing or punctured cells which is my big thing.

The pack is a totally different form factor as I built it 3 cells wide to sling under my quad and be flat as a landing surface. Not great in a fuselage, looks really nice under the quad. Planning to get out for some hover tests tomorrow.
 

Hondo76251

Well-known member
#20
@evranch I'm not sure where I got those big ones, but they sure weren't $20 a pop!

I'm interested to see how they do on flight times, I've never pushed them that hard and I've usually run them way under the c ratings...