Nano-Tech LiPo, low voltage Warning.

[1001 Copters]

Hi guys,
I have tested a 4S 4500mah nanotech this week end and I have had a little "surprise".
I'm using it on a multicopter (quadricopter) it's hoovering with 24A, 350Watts.
On my quadricopter I have a visual and sound alarm that allow me, generally, enought time to land safely but here...
it's 10/15 second to land and the LiPo is really out of energy !

On the first LiPo, I cut of the atlitude control so I goes down sudenly but there was no response at all in the gaz: I pushed the stick to counter the effect of cutting the alti control, but nothing happen...
On the second LiPo I didn't have time to exit the landing gear: same thing: no more gaz :/

It seems that I have to place the low voltage warning at ... 14,5V to ensure a safe landing (cf curve)

here is the video:

and here is the graph for tension/intensity:

I have measured the tension on each individual cell at the end of the LiPo.
first LiPo; alarm has been placed at 13.2V
I had this result:
C1: 3.62V
C2: 3.20V
C3: 3.12V
C4: 3.10V
total 13.04V

second LiPo, this time alarm has been placed at 13.6V
I had this result:
C1: 3.47V
C2: 3.01V
C3: 2.88V
C4: 2.91V
total: 12,77V

Thats sound strange because the low battery warning has been lifted up from 13.2 to 13.6V and the LiPo was more empty.
Any advice about this very low voltage and the brutal end of the battery ?

 

[Crash]

I have heard that the nanotech batteries have a rather sudden voltage drop off. Maybe someone else can confirm or deny that.

Your cells appear to be discharging abnormally. C is highest, C4 is lowest. Any idea why?

How many Mah did you put back into the battery

 

[Droider]

Get yourself one of these

http://www.brchobbies.co.uk/?page=shop&action=additem&item=183

I set mine at 3.6v. the alarm sounds when the first cell hits 3.6 volts leaving enough to get down. Not sure about the Nanotech batteries I use Overlander and have not had an issue.

Dave

 

[Bartman]

Dave,
Nano-tech is another type of lithium based battery. Originally designed at MIT in the US they are known by a lot of different names but technically they are Lithium Nano-phosphate cells. The authentic ones go by the name A123 cells. They have much higher amperage capacity than regular lithium-ion or lithium-polymer packs, they don't catch fire, they can be charged and discharged repeatedly with no waiting and at high amps, plus they deliver rated voltage almost to the last second, which is the problem here. It's tough to know the exact capacity remaining as you get near the end. Time is a good way to gauge pack life but it will depend on flight conditions. I've got two A123 packs in a big RC plane and a single pack in a smaller plane. Cedric's experience with them is a lot of the reason why they haven't popped up in multi-copters. They also weigh a tad more than Li-po's for equivalent capacity.
Their biggest strength is high amperage but so far we're all well within the capabilities of Li-po's.
Sorry Cedric, I'm not sure what the best answer is for your problem.
Bart

 

[1001 Copters]

Thanks a lot for the answers guys
I will try to cycle these pack as suggested on another board

I didn't check how many mah I placed in yesterday after the flight. I will check on the second pack.
This evening I have a meeting with a very famous french motor/propeller tester (he has nearly 300 motors at home...) I will ask him some questions about bench testing to have the best measure in terms of precision.

 

[Droider]

My advice then after reading that lot is stick to the lipos we all know and love/hate. Them new fangled things may be ok for planes and cars but for a flying brick forget um.

 

[Bartman]

if one has the capability to keep a running total of mah used on their OSD then that is also a good indicator of when it's time to land.
an issue with these is that you can't use a voltage readout after a flight to gauge remaining battery life since they recover a bit and show high voltage even though they're nearly dead. guys will keep a field charger handy and just top them off every few flights. with the high amp chargers they can be topped off in ten minutes or so.
bart

 

[FlyEYE]

Dave,
Nano-tech is another type of lithium based battery. Originally designed at MIT in the US they are known by a lot of different names but technically they are Lithium Nano-phosphate cells. The authentic ones go by the name A123 cells.
Bart

A123 cells are LiFePO4 not LiPo.
Until I just did a search now I didn't realize there are Nano Tech LiFePo4 and Nano Tech LiPo, is there another battery out there that is confusing this?

Nano-Tech lipos are lighter and have the same voltage per cell as typical LiPOs (based on what hobby king calls them)., LiFEPO4 cells are heavier and have a lower voltage (these are the ones that can take the most amount of abuse).

4 Cells LiFEPO4 is 13.2V vs 4 Cell LiPO 14.8V

1001 Copters, which battery exactly do you have?

 

[Bartman]

A123 cells are LiFePO4 not LiPo.
Until I just did a search now I didn't realize there are Nano Tech LiFePo4 and Nano Tech LiPo, is there another battery out there that is confusing this?

Nano-Tech lipos are lighter and have the same voltage per cell as typical LiPOs (based on what hobby king calls them)., LiFEPO4 cells are heavier and have a lower voltage (these are the ones that can take the most amount of abuse).

4 Cells LiFEPO4 is 13.2V vs 4 Cell LiPO 14.8V

1001 Copters, which battery exactly do you have?

you're absolutely right, A123 cells are different from LiPo's. There are cells that are similar to A123 cells but they don't have the nanotube technology in them that gives the A123 packs the high current capability. An example of similar but not quite the same would be the Life packs from Tower Hobbies.

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXZTJ6&P=ML

Same 3.3 volts per cell as A123 but not quite the same max current capability.

Here's a Lipo supposedly with the nanotube technology built in rated at 3.7 volts per cell.

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=11920

When they say nanotubes they mean that the positive electrode in the battery isn't a solid core of material but a dense cylinder of tiny tubes all packed together to look like a solid. This makes the electrode have many many times more surface area available, compared to a solid material, for electrons to transfer and make current. The nanophosphate material is proprietary to A123 Systems so the other batteries are all sort of trying to sound like they have what the A123 cells have when they really don't. Reading through the hobbyking link above it sounds as if they stretch things a bit as well to make it sound like they have nanotube technology when they don't.

It's all very cool stuff and I was kinda blown away when I started reading about it.

 

[brendonvz]

I accidentally over discharged a brand new LiPo pack (I managed to recover it though) but for future ref , what should I set my voltage alarm to on the Tx via telemetry so as no to do it again ?

I use 11.1v 3S 3200mah batteries

 

[jes1111]

Bartman - I want to use A123 cells (ANR26650) in my forthcoming heavy lifter. The only retail sources I can find for them are in China (with the risk that I'm buying recycled cells). Did you find any USA/Europe sources? A123 themselves only seem interested in selling to car manufacturers. Enerland (which apparently belonged to them) has just announced it's closure.

 

[Emowillcox]

Hi Jes.. wonder why you wanna use a123... I actually have one of my trex 450 using a123 batteries and they work great.. they are heavier then the lipo.. but do hold up well.. we got some old dewalt battery packs and broke them down and made new packs from them.. sometimes you can find them on ebay or at hardware stores

 

[Bartman]

this is where i've bought mine in the past. use the "make us an offer" button and you can save a few bucks off the price listed.

http://www.bphobbies.com/view.asp?id=C2116942

just be sure you understand what you're getting yourself into. you may also need a new charger if your doesn't do a123 cells.
with the a123 cells there has to be a reliable way to know when to end the flight as low voltage alarms don't really work

 

[jes1111]

I'm a full-time photographer. My Y6 heavy lifter is going to be a photographic accessory, not a business in its own right. As such it will live in the back of my car along with all the other tripods, lights, reflectors and other paraphernalia. LiPo packs are not suited to such treatment - self-discharge, danger of leakage, etc. ;-)

Thanks for that link, Bart - bit pricey, though!

 

[goraplx]

About that nanotech 4s 4500 .. i had this lipo 1 month, used maybe 10x on my Hexa and today I had suprise . That was happened before fitting onto hexacopter.
Battery was fully charged as normal with turnigy balancer.. In the last 2 years used many different lipos and never had this problem, but now im scared to use lipo. Planning to buy some A123 from http://www.battery-matrix.com/A123-...le-Cell-3-3V2300mAh-120A-Rate-8-0Wh-0-75.html


https://lh5.googleusercontent.com/-PFUae2En7rU/UEMzsw9KRbI/AAAAAAAAe2s/y5s9Anoxd8s/s800/IMG_1869.JPG
https://lh3.googleusercontent.com/-ENAUo4yiZjI/UEM0FVsiVRI/AAAAAAAAe3M/6jz-DwhiniU/s800/IMG_1871.JPG

 

[arit88]

I would like to see nano-based batteries to soon surpass the competition. Right now they are up to par even when it is still kinda experimental technology. Once they polish it, it should be really good. With whole companies dedicated to tailoring these materials there is a good supply for manufacturers to experiment.