Lipos

[Geoff Daunt]

Many thanks. Yes l have the Multiplex Charger so l can discharge the Lipo's. I do not normally do so, l recall being told that unlike nicads and NIMH, lipo's do not retain a memory so usually not necessary. Do you know if that is good advice or should l disharge all the batteries from time to time.
Could you also tell me a suitable discharge rate, since l will need to input that figure into the charger. Lastly do l also couple up to the balencer when l disharge.
Thanks Timbo. What a great site to be able to get help from other modellers.!!

[Tim Mackey]

They do not have a memory issue, ( incidentally there is now doubt that the memory issue with nicads is a myth...but thats another story)and they dont require discharging or cycling under normal circumstances, however i suggested it on this occasion as possible means of establishing your issue with capacity.
Suitable discharge rate, - most chargers are ususally limited to around .5A on discharge, but if yours goes higher...use the highest setting you can in order to most closely resemble the inflight useage.
Do not use the balancer for this particular test. HTH

[Geoff Daunt]

Having investigated, my charger only has set values for discharge rates 11.1, 7.4, or 3.7 so l left it on 11.1. It will also only allow me to discharge at a max of 1.00.so off l set. It started it's discharge at 12.1v and stopped at 10.072v.
It also showed a discharge in Amps of 1078.
I then recharged at 1c and it ended at 12.49v and input 1152 Ma. I am assuming if all was well it should have put in 1500.
It looks therefor that it will not take a full charge for whatever reason.
I do not know if there is anything else to try but once again many thanks for your advice. A new battery might be the answer. By the way yes they are all the same make and are the batteries supplied specifically for the Twister 3D heli.

As a matter of further interest the other two batteries when recharging always take exactly 1100 Mah Never 1050 or 1000 but always 1100. When l recharge Nicads or NIMH they always give different input readings depending l suppose on state of charge......Just wondering if Lipo's behave differently since it cannot be a coincidence that every time l use the other batteries l discharge them when flying to exactly the same point? A matter of curiosity thats all.!!

[Geoff Daunt]

I tried the problem battery tonight and it lasted about 1 min before it lost all charge. The Voltage was wellup but nothing in the battery so a safe disposal looks to be the answer and a new one ordered in due course. Thanks again for the advice and assistance. If you are ever coming to Spain In the region of Javea (about 100 Km north of Alicante)let me jknow and we can have a beer or 2.
Best Regards
Geoff.

[Tim Mackey]

Cool :)

[Mike Wyatt]

Timbo

Just as a matter of interest, do you know what the chemistry of LiPo cells is (cathode, anode, electrolyte etc.) ?? I have looked in various places, but can't find.

Also, what is the difference between LiPo's and Li Ion cells ?? I gather they are similar, but there must be some signicant difference(s).

[Tim Mackey]

I am not a chemist I am afraid...and do not really take too much interest in that side of things :(
From a purely practical point of view, the LiIon cells are heavier than polymer, but can be charged faster. As one of the MAIN advantages of LiPo batteries is their lightness....I personally have not bothered looking at LiIon. Although they are also alledgedly far safer than LiPo ( they do not "combust furiously" as the polymer ones do )I believe that almost all the horror stories of LiPo fires etc are user induced, and if care is taken with their handling they are no ore dangerous than any other fuel...including the liquid variety !!
Quick call me a cab before I get a torrent of criticism for daring to suggest this :)

[Alistair Taylor]

This is some help

http://batterieswholesale.com/lithium_polymer_lipo/lithium_polymer_myth.htm

This is waaaaaaaaaay out of date...but a bit helpful.

http://www.wppltd.demon.co.uk/WPP/Batteries/Chemistry/chemistry.html

http://www.batteryuniversity.com/partone-5.htm

I think this borrows from the source the first link is for.

HTH

AlistairT

[Mike Wyatt]

Thanks Timbo
I agree entirely with your feelings as regards the safety of LiPos - my own Perspective is that I am not particularly scared of them, but I do treat them with the care that they warrant.

[Mike Wyatt]

Thanks Alistair
Those sources are very informative - I shall continue my day a wiser man !!!!!!

[Tony Jones]

Having destroyed a 5S/3200 Lipo by accidentally charging it as if it were a 6S, I thought you might like to know what happened.

Firstly, my attention was attracted by a 'pop' noise. The battery had swelled up and one of the cell covers had ruptured.

Shortly after that it began to emit smoke. The smoke increased gradually for about 2min, and then the battery burst into flame rather like one of those 'Volcano' type fireworks. The flame was about a foot high. It did NOT explode. In fact, I get the impression that LiPo cell casings will rupture at a very low pressure, so explosion is not a real risk.

The intense flame lasted for about 90 secs. After that it smouldered away for about half an hour while cooling down.

[Tony Jones]

My 2p's worth on C ratings.

Any LiPo manufacturer can claim any C rating he likes as there is no 'industry standard' for what it means. However, the general consensus seems to be that when discharged at the max C rating, pack voltage should not fall below 80% of the 'fresh off charge' voltage.

E.g: Let's take a 20C rated 11.1V/3300 pack. This will come off charge at around 12.5V. When discharged at 20C(66A) the voltage should not fall below 10V. If it does, the manufacturer is being, shall we say, optimistic about battery quality.

If you continue to discharge at that rate it obviously won't be long before the voltage falls to the safe minimum of 9V.

Personally I try not to draw more than 18C max from 20C packs - and then only for a very short time on take-off and perhaps for a few seconds at a time during aerobatics.
Hope this is useful.
Best wishes
Tony Jones.

[the unmagnificent man]

Hi all, I havent read all this thread as its very long so maybe this has already been answered?.. I am new to electric flying and wondered....If I have a 11.1v lipo fully charged and start to fly, how will I be able to tell if I go below the safe voltage level of the battery without landing and checking with a meter. Or is there something I should know and dont? Any help or advice appreciated. Al

[Tony Jones]

Dear UMAHM

Ideally you should fit an ESC that will not allow the voltage to drop below 9V - i.e 3V per cell. The very best brushless ESCs IMHO are the Castle Creations ones which can be programmed very simply with a free piece of software and a USB link cable. See the CC or Overlander websites for full details.

One alternative is the LiPo Saver from J Perkins. This is a little PCB gizmo that you connect to the battery leads and fix to the outside of the plane. While the cells are above 3V it flashes (very brightly) once every 8 sec. At 3V per cell it starts to flash very quickly, warning you to throttle back and land.

The conventional wisdom is that you should never draw LiPos down below 3V per cell, but in my experience the better quality ones can be safely pulled down to 2.8V ON LOAD. The really important thing is that the voltage recovers to 3V+ per cell within a few seconds of the load being removed. You can check this after landing with a cheap multimeter.

Hope this helps
Best wishes
Tony Jones.

[the unmagnificent man]

Tony and jetsome Thank you for both your information, I like the idea of the little flashy light, less room for error.
JETSOME Once again a forum member comes up with a simple but yet effective formula to work out something that otherwise would be difficult for me to comprehend. I'll let you both know how I get on. Al