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« on: March 23, 2009, 09:32:34 PM »
anwar
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For the sake of beginners, here are some rules/tips to ensure safety and longevity of lithium polymer (LIPO) batteries.

1) Respect them. If not properly taken care of, they are extremely dangerous.  I know of a car that burnt down from lipo fire.

2) Always use a balance charger, that can ensure each cell is individually balanced to 4.2 volts. A fully balance charged 3 cell lipo should show a voltage of 3 x 4.2 = 12.6volts.

3) Always charge at a rate of 1C, where C is the capacity of pack.  If you have a 2200mah pack, you can charge at 2.2A or less.  The correct detection of the number of cells in the pack and setting the appropriate  charging rate are the most important aspects of charging lipos (of course, using a balance charger is assumed).

4) Do not over discharge your lipos, by using them for too long between charges. It is best to limit the usage to 80% of the capacity of the pack.  If you have a 2000mah lipo, use it in such a way that when you charge it after use, you are putting in around 1600mah. Most modern chargers show you how much are you putting back in.  Use of the timers in your tx radios help prevent discharging the packs too much. If you discharge them too much, they tend to puff up, reducing their effectiveness.

5) If you are storing lipos without using for long periods of time (months), better to put them at half charge, which is around 3.9v per cell.  So for a 3 cell lipo, keep it charged upto 11.7 volts or so.

6) While disposing lipos, soak them in salt water first.

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« Reply #1 on: April 24, 2009, 05:25:02 PM »
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Anwar, CAN I ADD;
If you ever drop a lipo, keep it on the floor or on a non inflammable surface and observe it for 15 minutes. 40% of them explode and catch fire. This article is very important for all the guys.... I cannot get the images on here so if you can advise your email, I will email it to you to display this complete article.
Thanks
Baggu

Lithium Polymer (LiPo) cells are the newest and most revolutionary cells to come to market. LiPo cells typically maintain a more consistent average voltage over the discharge curve when compared to NiCd or NiMH cells. Add to that the higher nominal voltage of a single LiPo cell (3.7V versus 1.2V for a typically NiCd or NiMH cell), making it possible to have an equivelant or even higher total nominal voltage in a much smaller package. LiPo cells also typically offer very high capacity for their weight, delivering upwards of twice the capacity for sometime ˝ the weight of comparable performance NiMH cells and packs. That’s right, with LiPos you can often achieve higher voltage and power output, with more capacity, in a lighter weight package.
With all of these benefits, why aren’t LiPo packs more widely used? With so much energy packed into such a small space, there are some important safety measures to take when dealing with LiPo cells. A LiPo cell needs to be carefully monitored during charging as overcharging a LiPo cell (to beyond 4.2v), or the charging of a physically damaged or overdischarged cell (discharged to below 3.0v under load) can be a potential fire hazard.
 

Many LiPo batteries come with safe charging circuitry integrated into it. This circuitry prevents over charging, over discharging, and in some instances helps to balance the pack out. If your pack has a “Charge” lead on it, always charge through that connector.
 
 

While some battery chargers can charge either NiCd/NiMH or LiPo cells, chargers that do all three major chemical types are starting to surface. The Dynamite Vision Peak Ultra can charge your LiPo packs along with NiMH and NiCd batteries as well.
If you are going to go the LiPo route, use a charger that can correctly charge them (using a constant current, constant voltage method of charging as LiPo cells can not be “Peak Charged”), such as the Vision Peak Ultra (DYN4053) or the E-flite Celectra 1-3 Cell charger (EFLC3005). Not only must care be taken when charging LiPo cells, but when discharging them as well. You should never over-discharge a LiPo pack to below 3.0v per cell under load, and you must use an ESC programmed to provide the proper low voltage cutoff for your pack (for example, a 9v cut off for a 3 series LiPo pack). Also, you should never dead short a LiPo pack, even if only for an instant, as the large amount of energy stored in the small package can catch fire quite quickly as a result. While these seem like major deterrents to using a LiPo battery, these usage guidelines are quickly becoming well known as they are typically well outlined in the instruction manuals included with most LiPo packs, ESCs and LiPo chargers. However with all of their performance benefits, there is little doubt that lithium polymer battery packs are currently the future of battery technology for electric powered models.

To Build or Not To Build:


Some people prefer to assemble their own battery packs rather than buy preassembled packs. Before you solder on the cells, scuff up the terminals to provide a better connection and more secure solder joint.
 


Many people damage their battery packs before they use them for the first time with poor soldering techniques. Remember to use an iron with a large enough tip to transfer heat, apply solder to the items being joined and not the iron itself, and don’t hold the iron onto the battery for too long.
There are two different ways to purchase your batteries, either as loose cells or as pre-assembled packs. With individual batteries (cells), you’ll need to solder the cells together yourself to create your own battery pack. The second option is to purchase a pre-assembled battery pack that comes with the pack pre-assembled and shrink-wrapped, often times with the connectors pre-wired. If you do not have much soldering experience and/or do not have a high-quality soldering iron, it will generally be best to purchase a pre-assembled pack.
As a safety note, you should NEVER attempt to solder LiPo cells together into a pack configuration yourself. LiPo cells are very susceptible to heat damage, and excessive heat can cause them to possibly leak or even explode. For this and other reasons, most LiPo manufacturers willl offer pre-assembled packs only.
Discharging and Storage:
Discharging and storage really go hand in hand. For NiCd packs, you should completely discharge them, to 0.9v per cell, before you store them NiMH packs should be stored with roughly a 50% charge in them for best performance. And before you charge a NiMH pack for the first time in the day, simply drain the pack completely on a discharger or in the model and you are then ready to charge the pack for use throughout the day.
LiPo batteries are completely different when it comes to discharging and storage. Depending on the output voltage of your pack, you should only discharge your pack so far. For example, during use, a 7.4V LiPo battery (also known as a “2 series” or “2S” pack) should never be discharged below 6.0 volts under load (3.0v per cell). For storage of 2 weeks or more, LiPo packs should be stored at approximately 3.8v per cell to prevent overdischarge or imbalance from developing among series cells in the packs due to differing levels of each cell’s self-discharge rate. In the case of a 2S 7.4v pack, the pack should always be stored at 7.6v. You should also store your LiPo batteries in a fireproof container or cabinet and never store your LiPo, or any other battery for that matter, in the model itself.
Pehaps no other item has quite as much effect and influence on our hobby as rechargeable batteries do. There are almost as many different theories and misconceptions out there about rechargeable batteries as there are individual battery sizes and types. Just remember that knowledge is key when it comes to batteries, as is consistent charging, discharging, and storage. Whether you are in the hobby shop or at the flying field, feel free to ask questions of those around you who may be more experienced. That is one of the best ways to learn and grow in the hobby.
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« Reply #2 on: September 15, 2009, 09:08:51 PM »
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Questions from a newbie....

1) do not over discharge lipos
    How does one know? What guidelines to use when setting times for first time flight?

2) do not drop lipos
 OK, what happens if I crash? Just let the plane lie where it is?

3) If the lipos are so inflamable, do I store them out of my house?

Pankaj

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« Reply #3 on: September 16, 2009, 12:46:30 PM »
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To safely use lipos it is a good idea to own a lipo voltage checcker that tells you the voltage of each cell. DO NOT DISCHARGE EACH INDIVIDUAL CELL BELOW 3.3 Volts. That is what over discharging is about.

If it is a bad crash, wait 15-20 minutes before picking up the battery. It may be a very good &(safe) idea not to reuse the battery. I saw a lipo explode after a crash as a person was throwing it away, before it even hit the ground..
Lipos are probably dangerous when they are charged and discharged at a very rapid rate.
Glow fuel is highly inflamable, nitromethane is borderline explosive. LPG cylinders can explode and so can petrol.
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« Reply #4 on: September 16, 2009, 01:15:59 PM »
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What are the reasons of getting Li-Po pack puffed?Huh?Huh???
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« Reply #5 on: September 16, 2009, 03:04:08 PM »
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Main reason is poor maintainance...
also for motors... when they discharge the battery if the discharge it too fast it gets puffed..
the also get puffed if you over charge or over discharge them
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« Reply #6 on: September 16, 2009, 03:50:11 PM »
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Guys,
I still don't get it.

I am aware that the prop dia and pitch determine the amp being drawn from the battery, but I still don;t get the relation or equation to calculate the amp drawn

In such a situation, how am I to estimate the flying time of a lipo? Mind you this is for staters. Probably more experienced flyers have developed some sort of thumb rule for themselves, but for the first (first few) time that the a newbie takes off, how is he/she to determine when he/she should land the plane so that the battery does not over discharge?

Speaking for myself, chances are that I shall try and land every 5 mins, but then as far as I have understood lipo, the volt drop is only drastic at near total discharge, till then it maintains the voltage. Then in this case how do I determine the amount of charge left in the battery?

Pankaj
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« Reply #7 on: September 17, 2009, 01:34:14 PM »
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Dear Pankaj,
In a Glow( i presume you have mainly used glows till now) the engine output is sort of fixed. So if you put a smaller prop then you get high RPM and the RPM drops as you go for larger props.
In electrics, the RPM is sort of fixed- depending on the voltage (2 or 3 or 4 cell pac). So if you run the motor with no prop, it spins at the same rpm, but does very little work and draws very little current.
As you increase the prop size, the rpm remains same, but the workload on the motor increases and it draws more current ( higher amps). There are watt meters available that tell you what the load on the system is for that particular prop at that RPM.
Also after your 5 min flight check the voltage on your lipo. if it is above 3.7v per cell  fly again. also the esc will cut out the motor when the cell voltage drops below 3v while the reciever is still powered. like a dead stick landing.
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« Reply #8 on: September 17, 2009, 01:42:47 PM »
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Many ESCs allow you to select the cut off voltage.  Keeping it on the high side (say 3.3v instead of 3.0v) helps prolong your lipo battery life, at the expense of slightly shorter flight times.  It does give you a safety margin in terms of being able to land properly with enough power to drive the receiver and servos.

Yet another method of determining how long you can fly on a battery is to fly for some time, and then try to charge the battery, noting how many "mah" you are putting back into the battery.  It is recommended that you deplete lipos only up to about 80% of their rated capacity.  So if your battery is, say, 2000mah, use it for 1600mah worth of flying time. 

Say if you test flew for 6 minutes, waited the lipo to cool down a bit, and then charged it noting how many mah you put in (most good charges show you that, even though the numbers may not be perfect), and assume that you put in 1200mah.  This means that you have about 20% more flying time left, which equates to 2 more minutes (20% of total 10 minutes, not 20% of 6 minutes). Again, these are guidelines, not perfect numbers/calculations.
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« Reply #9 on: September 18, 2009, 10:21:37 PM »
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Anwar,

So as I understand, one needs to first imagine that the motor is drawing max rated current and plan for battery drain accordingly and then slowly adjust the time based on the actual drain (calculated by the charge being fed in).

Is this correct?

Pankaj
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« Reply #10 on: September 19, 2009, 12:05:09 AM »
anwar
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One good thing about the method I was mentioning is that it takes your flying style and conditions into account.  So if you got 6 minutes of flight at the expense of 1200mah drain from your lipo, that is *for your flying style and conditions*.  If I did torque rolls the whole time, or flew at full throttle, I may only get 4 minutes for 1200mah.

If you have a new lipo, you would be doing a break-in for them anyways, flying conservatively.  Use that as an opportunity to do the above calculation also.
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« Reply #11 on: January 08, 2010, 11:11:56 PM »
anwar
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More lipo safety information from AMA posted here :

http://www.rcindia.org/rc-general-topics/satefy-tips-for-rc-flying-and-racing/msg11451/#msg11451
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« Reply #12 on: January 09, 2010, 12:20:04 AM »
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For calculating the amp draw by a motor/prop combo...a very good starting point will be as follows :

The power required to rotate a particular prop at a particular rpm is :

Power = Kp *  D^4 * P * Rpm^3

where
Kp is the propeller const. and almost every prop manufacture mentions this. If you dont know the Kp for your prop ageneral assumption will be 1.25.
D is prop dia
P is pitch
and dia and pitch are in feet not inches and rpm is specified in thousands. eg. if your rpm is 8000 then put 8 in the formula.

then amps can be calculated as :

Amps = Power/Volts(of your lipo)

But of course this is theoretical and does not include real world factors.For a detailed understanding of electric power systems please read

http://www.rcindia.org/electric-power/understanding-electric-power-systems/

Hope this helps Pankaj
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« Reply #13 on: February 25, 2010, 10:25:35 PM »
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I was charging my brand new lipos for the first time thought of running a " SEARCH " on our forum & came up with this informative thread...

Great stuff anwar..

Am charging a 2200mah battery at 1.8amps and not 2.2, someone told me its better to charge it at lesser amps... Is it mandatory to balance all the cells for the first charge ? Am not balancing them right now..As they came perfectly balanced from HC..

any comments ?



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« Reply #14 on: February 25, 2010, 10:40:20 PM »
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If you use a balance charger every time you charge, then the above issue becomes irrelevant, right ?

And regarding the 1C charging, that is the max (unless you are using the Hyperion G3 etc).  I only know about charging at 0.5C for the first few cycles for lipo "break-in" but even that is disputed.  But them my knowledge about cell chemistry issues is rather limited.
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« Reply #15 on: February 25, 2010, 10:53:54 PM »
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As per some guys on the field..Balance charging your lipos after every 10 or 12 cycles is recommended..

Hmmm..as you rightly mentioned Hyperion batteries are awesome..some guys charge them at 5c on the field and these batteries have a huge life..

Love Lipo's...
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« Reply #16 on: February 25, 2010, 11:05:07 PM »
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As per some guys on the field..Balance charging your lipos after every 10 or 12 cycles is recommended..

Actually it is always safer and highly recommended that every charge is a balance charge.  The chances of an imbalance growing and becoming a problem is pretty significant if you wait for 10 cycles.
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« Reply #17 on: February 25, 2010, 11:11:43 PM »
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That's true..

Thats why I ordered the lipo monitor but I will be doing some experiments personally regarding the charging and balancing..

What's the oldest lipo you have or anyone has ? I know a guy who has a lipo since 5 years and still using it..
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« Reply #18 on: April 12, 2010, 11:43:27 PM »
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Hi Guys,
RE; Never discharge a Lipo to nill... AN EXPENSIVE  LESSON..
Two weeks ago I felt like flying my Multiplex Pico Jet, an eight year old brushed motor Delta model that I used to fly on 8cell nimh pack.
It had been tucked away in the attic and I thought I will change the motor to a brushless one if it flies reasonably.

 The nimh were lost in the clutter somewhere so I took my 3 cell pack from Park Zone T-28 Trojan and set it up on that. Later, I switched the switch to off and left the 3 cell 1800mah lipo battery pack connected.
On Saturday night, a week later, I tried to charge the Lipo and realised somehow the electric switch even though on off position had somehow let all the current pass and the Lipo was dead.
Tried with 3 different chargers but in vain.
Some batteries have known to come back to life after being totally discharged when connected with olden non balancing type of charges
Today Sai has suggested I should try discharging it... lets see what happens, I would hate to throw away an expensive Park Zone battery that has only had about 6 flights out of it.....
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« Reply #19 on: April 12, 2010, 11:51:20 PM »
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Hope you tried this : http://www.rcindia.org/batteries-and-chargers/how-to-restore-a-low-cell-voltage-on-a-3s-11-1-v-1350-mah-lipo/
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« Reply #20 on: April 13, 2010, 12:47:38 AM »
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pls get a lipo safe bag... one of the lipos almost bursted on me and beleive me its not fun to see this... a guy on helifreak lost his house and managed to save only his family due to a 3 cell lipos... DO NOT charge or discharge without supervision... i had also posted a link on lipo's sometime back, hope it might help...
http://www.rcindia.org/helis/some-good-links-and-info-for-heli-flyers/

i usually chage in storage mode for my lipos ( around 3.85 v per cell)... if the lipos are puffed pls throw them away, they are many guys meddling and puncturing the lipos (HIGHLY NOT RECOMMENDED) and sealing the punctures hole again and using the lipos, pls DO NOT do this...
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« Reply #21 on: April 13, 2010, 12:53:43 AM »
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I did tinker with it all Sunday evening but did not leave it long enough. Will try it again without connecting balance connecter...
As I do not leave them unattended, did not really have any time...

No Sujju, I never try to tinker with PUFFED or PUNTURED ones. Best to throw them away... as Sai says leave them in salty water and they will disintegrate themselves..
Thanks Anwar
Deepak
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« Reply #22 on: April 13, 2010, 01:11:52 AM »
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am not too sure about the salt water thing.. there are some mixed reaction with the guys around... if you google around there are some more info on some pros and cons for salt water, etc...

http://www.rcgroups.com/forums/showthread.php?t=209187

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« Reply #23 on: April 13, 2010, 01:14:08 AM »
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opps... forgot to send this link in my earlier reply regarding salt water disposal..

http://www.wattflyer.com/forums/showthread.php?t=12173

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« Reply #24 on: April 13, 2010, 01:22:41 AM »
sujju
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City: mysore
State: Karnataka
RC Skills: Beginner
Posts: 334
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Some batteries have known to come back to life after being totally discharged when connected with olden non balancing type of charges

B4ggu... i had a similar problem and was lucky to get this sorted out.. used my intellegent charger to charge the lipos using nimh or nicd mode... got the voltage to around 3.1 and charged them as lipos again (but again with supervision around and on a concrete floor).. i now have had around 15 cycles with this lipo and doing good... on the other hand 2 of my 6 cell turnigy lipos went bust when on cell got to 0V ( dont know how)... so rahter than throwing them away i removed the bad cell from one lipos and replaced a good cell from another lipos (again you need to know what you are doing here)... and now again i have had 5 cycles on this 6 cell lipos and its fine and strong...
« Last Edit: April 13, 2010, 08:26:32 AM by anwar » Logged

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