And they say smoking is bad - Part 2
Last time I looked at a set of 18650 batteries that had some nice specs, but in the end proved to give me less flying time than my half capacity LI-PO.
I got a lot of comments - thank you so much - and several people whispered NCR18650B as an almost mythical 18650 sized battery.
I went ahead and order two with solder tips - this caused by the uncertainty of the effects of using a cheap battery holder of dubious quality.
The NCR Panasonics state a 3400 mAh capacity at nominal discharge. The cell has a fuse that melts at 10A discharge for a longer period but is otherwise unprotected.
I quickly soldered the two batteries in series, and taped everything together in order to protect the solder tips and wires. End result was not the prettiest, but it worked and the pack is easy to charge.
The other day was a nice calm flying day, and I took my trusty delta wing to the skies with the stopwatch ticking. First up was my good old 1300 mAh turnigy lipo, which clocked just below 18 minutes at cruise speed (approx 45-50 % throttle).
Next up was the NCR18650B pack, which is approx. 15-20 grams heavier thus needing a bit more throttle to get airborne and cruise along.
I flew both packs until the ESC would automatically cut out to prevent battery damage.
The NCR18650B gave me 28 minutes and 10 seconds. So around 10 minutes extra time!
The flight itself wasn't particular interesting, flying slow in big circles - but the extra time was very noticeable.
This all sounds good, but there are some things to consider
Flying faster means a higher discharge rate, which also decrease the real capacity of the batteries - an effect that is much less seen in LiPO batteries. Flying both packs at full throttle would probably get more similar flight times.
The extra weight means that my delta wing is almost maxed out payload wize.
If you can carry several packs in parallel, it’s probably better because the load on the individual battery is less.
So I will probably fly the NCR18650B if I want to fly slow, for a longer period with little payload, and LiPO if I want fast and/or more payload.
That said, the NCR’s were definitely good batteries that seem to keep up to their specs unlike so many 18650 type batteries these days.... you get what you pay for :-)
Comments
I maybe late to the party with these but is anyone using them? They're not the high capacity of the 18650B's but it's claimed they can do 10A (3.4C) as opposed to 3.4A (1C).
Panasonic 18650 2900mAh High Drain NCR18650PD
"(ignoring the volt differences for the moment)"
there are too many problems with just connecting them in parallel.
1. with lipo connected in parallel, lion will rarely provide power because as voltage drops fast as load increases. plus the lower mark 0% on the two battries is very different 3.2 for lipo 2.7 for lion.
2. lipo may charge lion at a very rapid rate or may discharge it at a very rapid rate as soon as voltage differential builds among them due to loading.
I don't think it will be worth trying.
Regards,
Pritam
Would it need electronics? Could one put the two packs in parallel (ignoring the volt differences for the moment) so that when the current demand is high then the LiPo pack resists the volt drop more by supplying more current?
Yes - been thinking along the same lines - but the battery controller is a bit too much for me to build.
It should definitely be current based (meaning that when amps go above some threshold, the LIPO kicks in and saves the day).
It should also feature seperate voltage sensing so as not to harm the lipo or the 18650 pack when either one starts to wear down.
Anybody up for some electronics?
How about mixing 18650 pack with small high-discharge standard LiPo for burst power?
Of course, adding some ATTINY-based PWM controller to balance the current based on Throttle would be even better. I.e. at low Throttle 80%(vs 20%) of current would be routed via 18650 pack, then, proportionally increasing the throttle would swithch vice-versa (20% via 18650 vs 80% via std. LiPo). Such controller could be build by hand under less than $5.
Welcome to the Lion world :)
Great real application test, with useful quantitative results.
Good to know about considerably reduced capacity at discharge rates above .5 C that is certainly something they don't make much mention of.
I am afraid the "Vaping" thing has resulted in an unusually large number of bogus manufacturers / distributors dumping large quantities of considerably under-performing 18650 batteries on the market.
There are even counterfeit Panasonic's.
It also points out that the challenges to make these useful in multicopters to get anything like their rated capacity are not insignificant.
On the plus side they can have a considerably greater number of recharge cycles if treated well.
Likewise a very similar experience and it all comes down to the C rate of discharge, if used at 0.5C or less they give close to their rated capacity. At 1C (3.4A) they give just over 3000mAh (http://lygte-info.dk/review/batteries2012/Panasonic%20NCR18650B%203...).
Max rated discharge is 2C (6.8A) but I suspect their delivered capacity then is way down although I haven't yet found any official graphs or data to show exactly how much.