We haven't heard too much from Trent@MyGeekShow since he restructured his time late last year. He has however just uploaded a video outlining some exciting news.
These new professionally-built 4S packs are based on Panasonic's NCR18650GA Lithium-Ion cells which offer comparable energy density but with upwards of twice the power density as Panasonic's well known NCR18650B.
With the primary factor prohibiting use of Panasonic's NCR18650Bs in a broader range of unmanned aerial craft having been the relatively conservative power density (compatible only with the most efficient craft) as well as the limited availability of suitably sized and terminated packs, this new offering is a fantastic option for many smaller fixed-wing (AXN/Bixler/Wicked Wing XL) and mini-multirotor (<350 ships, not fpv racing) flyers who are chasing a bit of extra endurance.
The only problem I can see at this point is that they appear to be available exclusively via Amazon and shipping is not available to me here in the land down under. It is a shame too because I would love to grab half a dozen or so for my park flyer!
Comments
The charge efficiency is not accurate in my post its an approximation to illustrate the losses needed to take care of the charge acceptance rate of the battery, it covers losses through heat and resistance.
This is nothing to do with the charge efficiency of the charger taking 100watts from the wall socket and giving 50watts to the battery. we dont really care about that.
if you charge at 4amps for 1hr then you put into the battery 4ah. The internal resistance of the battery will produce heat and that energy will not be absorbed by the battery as stored electrical energy but as stored heat energy, this heat will be given to the surroundings and so effectively `lost`to the charging process. so now your 4ahr put in less the losses leaves you with approx 3.6ah useful energy some of this is also lost due to the chemical changes within the battery. .
If you check most battery chemistry`s then you get various figures of efficiency ranging from 60% to 90%. I used 67% just to show the relationship.
Dwgsparky - You raise some good points, though I am not sure that your stated figure for charge efficiency is accurate (does that perhaps include losses in a very inefficient charger too?). It will be interesting to see just how much the discharge efficiency drops at these higher claimed rates in Trent's subsequent videos.
Guy McCaldin - I just watched the video again and noticed that Trent does actually claim a 20-Amp continuous rating, which is very optimistic and certainly more than seems sensible. With that said Trent does seem confident based on his heat soak tests comparing performance to the NCR18650Bs, so perhaps the follow up videos shead more light on this and justify the claim.
Hi Guys
Just some notes
1) The ratings on battery's for the capacity is always the capacity based on a 20hr discharge rate. so a 5000mah battery should be able to provide 5000/20 or 250ma for 20hrs before reaching the low voltage cut off point.
2) The 25C rating is the maximum discharge rating that can be tolerated without damage. so a 25C 5000mah battery can provide 125amps without damage for a limited time only.
3) it will not produce 5000mah. it does not mean that you get the same capacity from the battery as the battery is now producing heat and the internal resistance is higher.
4) Its no different to the fuel tank in my car. at 30mph I can drive for 600miles. at 90mph i can drive for 300miles. the tank is the same size.
5) What matters more is the internal resistance of the battery , the lower it is then the lower the internal volt drop will be and the cut off point will be reached after a longer time. Also consider that the efficiency of the battery is lower as the battery temperature increases due to the higher current.
6) The relationship of current put into a battery to the current that can be taken from the battery is not 100% it is closer to 67% so you charge a battery with 1000mah you will only get 670mah of useful energy out of it (approx)
Guy McCaldin - You do have a point and I agree that it is not good practice to over state the performance of a given battery, however Trent has qualified the 6C rate as a "burst" rating. I also do not place much faith in the ratings given to the lipo packs we use now and expect that they are unlikely to line up with the relevant manufacturer's datasheets either. I do have access to a carbon-pile battery load tester, but have never bothered to see happens when you load a super high rate (65C) lipo up to it's burst rating (even if just for a few short seconds). It would be interesting to see just how capable they are of meeting their stated numbers though.
Rob_Lefebvre - Sounds like your project was incompatible with the selected cell type, if perhaps not necessarily the chemistry itself. I seem to remember reading somewhere that the NCR18650B chemistry was available in smaller prismatic variants but I have never seen them available for sale.
It's not a quad, and I don't think your batteries would fit. Currently is uses just 2 cells. It's a micro air vehicle. I can't say a lot more. I would be interested to try your batteries, but the project is ending.
Rob - Thanks for the info.
I should have asked what you're currently using for batterie(s) on your quad, could you tell me that also? If your quad peaks at 24A, assuming it hovers at ~10A then it should be able to fly with a single Titan. 10A would be easy. 20A for the whole flight would be it's upper limit for sure. Two Titans would easily be able to fly your quad, no problem.
Good stuff! Thanks for the questions and feedback, it really helps.
Hi Trent, no, the LVC is turned completely off. It just doesn't have enough power to fly as the battery drains. It starts out with 70% hover throttle, and then after a few minutes is 90% at which point it can't fly anymore.
I'm not sure what the actual power requirements are, I didn't design the thing. I know it uses only 2 12A ESC's. So 24A max.
Rob - Great stuff. I've done similar testing (although not with a quad, and as you've stated, they have different energy needs). Some thoughts / questions for you:
Have you adjusted your ESC's for a lower voltage cutoff? Since NCRs can safely be brought down 10v (on a 4S) your ESC's may see that its a 4S, and then when the voltage drops, it reduces throttle? I've had a much better experience with a low voltage cutoff.
Also, what would you estimate for your quad's hover and peak need wattage requirements?
Thanks Rob!
Great question Guy!
As you may know, there isn't really a standard on determining / stating C rating. As I'm the one that had to determine what would be the C rating on the label I conducted pretty extensive testing and research to make it accurate based on our RC uses.
I wanted the C rating (in this case 6C) to perform the same as if you bought a LiPo with that same C rating and mah. To determine what burst and constant C ratings meant on other packs I tested them at their stated burst for 5 seconds and then held them at their stated constant until they were 80% discharged, the whole time measuring the pack temperature (was just sitting on a bench, no airflow over it). I then pushed the NCRGA Titan Li-Ion until it met that same temperature curve. This resulting in 6C to 10C. Yes, if you push it to 6C the entire flight time you will end up with a very warm battery. The same is true for any other LiPo (push it for it's entire flight time at it's constant C rating). I found that all the LiPo packs I tested went from 70F to about 140F + or - a few degrees when held at their constant stated rate until 80% discharged (again, keeping in mind they were sitting bare on a test stand with no air cooling).
Does that make sense?
-
1
-
2
-
3
-
4
of 4 Next