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Author Topic: Lipo Usage Best Practice. Avoid Both the Hazards and the Fear.  (Read 15775 times)

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Offline Alexmacro

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Lipo Usage Best Practice. Avoid Both the Hazards and the Fear.

This post's purpose is to provide a best practice guide for
lipo usage. I hope it will help people to make their lipos last
longer, be safer and encourage people who find them intimidating
to overcome this and be able to use them without being overly
fearful.

Now before we go any further, it is prudent to mention that
improperly used lipos can explode and cause fire. But if you use
them properly this is very unlikely to happen.

People, please feel free to chip in with your comments and I will
edit the first post to incorporate all new best practices as and
when they are added.

There are two main issues here as I see it. Safety and longevity.
We'll deal with safety first.

Lipo Safety

Charging

Use only a charger suitable for Lithium Polymer batteries. Make
sure that you set it to the correct number of cells. Ensure
charging current does not exceed the battery's capacity C (e.g.
1000 mAh max charge current 1 Amp).

Unless specified in the manufacturer's instructions, lipos should
never be charged at more than 1C. (For 2000 mAh battery 1C is 2
Amps. For 1000 mAh battery 1C is 1 Amp.)
Many people adopt a practice of field charging at 1C and charging
at home at about 0.5C. Charging at <1C is said to give the lipos
a better chance of a longer useful life, although manufacturers
do not endorse this. It cannot do any harm though.

Lipos under charge should either be closely supervised, or they
should be placed somewhere where the "worst possible outcome"
(explosion and fire) will not have a devastating effect.

Many people use a fire safe, ammo box or Lipo Sack to keep
batteries in whilst charging. Many others prefer to be able to
monitor their lipos. Both are legitimate choices.

Be methodical! It is a very good idea to have a fixed procedure
you follow each time you set up a battery on charge. Do not allow
yourself to be distracted while putting a battery on charge.
Better to charge it later than give it insufficient attention.
Charging errors are responsible for the majority of lipo fires.

Do not charge lipos in your car.
If you wish to use your car battery as a 12v source it is better
to make up a long set of leads so that the lipo can be positioned
well away from the car.

Do not charge lipos placed on flammable materials.

Use a fireproof container and have sand or a dry powder fire
extinguisher to hand.

Do not charge lipos in your model.


General Care
Do not allow your lipos to be short circuited.
Particular care with battery and charger leads may be required,
depending on what connectors you use.

Do not pierce or puncture lipos.

If you short-circuit, drop, damage or crash a lipo, put it in a
safe place and observe it for a couple of hours.

Connectors
It's a very good idea to use a type of connector that cannot be
connected the wrong way round. e.g. Deans or powerpoles (JST for
low current applications) or gold bullet type connectors. If
using gold bullet connectors, it's best to use one male and one
female on each battery.

A common convention is male to battery positive, female to
battery negative. Whichever way you do it, it's a very good idea
to protect the male connector all the time when it's unplugged. I
managed to short a lipo under "impossible" circumstances on a
spanner in my toolbox. After that I used a small piece of
heatshrink on the male connectors. Other people use fuel tube.
There's even a name for these things "doobers". Another thing you
can do with gold bullet connectors is rig up the leads such that
it is impossible to connect positive to negative accidentally.

I've recently changed to Deans type connectors for almost all
my lipos. With Deans, you have to be very careful when
soldering them, but once soldered they are almost bulletproof Wink


A few links to manufacturer's safety guidelines
http://www.enerland.com/support/s1.php
« Last Edit: March 03, 2009, 08:43:24 AM by alexeames »
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Offline Alexmacro

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Lipo Usage Best Practice. Avoid Both the Hazards and the Fear.
« Reply #1 on: March 03, 2009, 08:22:29 AM »
Lipo Longevity

Breaking in


Some manufacturers (e.g. Thunder Power, Hextronic & HiModel)
recommend a couple of easy cycles (4-6C)  when your lipos are
new. I know some people don't bother but it's not much
effort and if it helps them last longer, I'm all for it

Propping for WOT Current

Enerland make the best lipo cells in the world. According to
their own data, lipos used at their maximum C rating (ie 20C or
25C) will only retain up to 70% of their capacity for 50 cycles.
What? Yep. If you use them to the limit they will not last long.
Cry
At the other end of the scale, used at 1C they will last 500
cycles. So hopefully, when used somewhere in between we'll get a
number of cycles somewhere in between 50 and 500.

Assuming you have 20C lipos, for greatest lipo longevity and
decent flight times, if you choose a motor/ESC/prop/battery
combination that will give you 10C discharge current you will...

* not be stressing the poor little darlings too much so they
should live longer
* get at least 6 minutes flight time (much more with throttle
management)

Example. 2000 mAh lipo, 20C = 40 Amps. Prop for WOT
current of 10C ~20 Amps. This is not set in stone. Your lipos
will likely be fine at 12C too  ;)


Time Your Flights, Rather Than Flying to LVC


Lipos will last a lot longer if you never run them down to LVC.
If you always aim to land with 20% left "in the tank" your lipos
will live a long and healthy life and you will also have plenty
of reserve left in case you overshoot or someone else calls
'landing' just before you.

The only lipo I have killed so far is one that was flown to Low
Voltage Cutoff. Not only that, but it was on a cheap Tower Pro
ESC which cut the voltage off at 2.75 volts/cell. EEEK. That was
before I knew how to treat lipos properly. Even so, this lipo
continued to work as normal over the next year for 30 or so more
cycles until one flight, when I noticed after about a minute that
it had "no juice". So I landed. It turned out that the middle
cell had died, so I made it into a 2s pack.

Set your LVC to no lower than 3.0 volts per cell, but try to time
your flights so that you do not reach it. So how do you know how
long to fly for? By measurement and experience.

At rest, a fully charged lipo should have a voltage around 4.2
V/cell.
At rest (15 minutes after use) a fully discharged lipo should
have a voltage around 3.7 V/cell.

It is important to measure these at rest, since lipo voltages
under load will be a lot lower. The nice thing about lipos is
that their voltage is a good indication of "how much is left in
the tank".

3.7 V/cell = empty
3.8 V/cell = 20%
3.9 V/cell = 40%
4.0 V/cell = 60%
4.1 V/cell = 80%
4.2 V/cell = FULL

So if you've got a new setup, fly around for a few minutes, land,
let the battery settle for 15 minutes and measure the voltage.
If, say, you flew for 5 minutes and your battery reads 3.9 V/cell,
you landed with about 40% 'juice' left. So, having used 60% in 5
minutes you could have flown for 5 x 80 / 60 = 6.7 minutes and
landed with 20% left.

You will develop a feel for this but beware that flying in windy
conditions you will use more throttle, so shorten your flight
times accordingly.


Get the Balance Right. Balance Ports and Balancing

Until a couple of years ago most lipos were not routinely fitted
with balance ports. But these days, most are. The rationale
behind them is something like this...

No lipo cell is supposed to go above 4.30V or there is a risk of
pack damage or autoignition. So imagine the situation where the
voltage of one of the cells in a 3 cell (3s) lipo gets a bit
below the other two. If there is no balancing, over a number of
cycles, one cell might get substantially lower than the others.

We could have a situation where the fully charged 12.6 volts is
not made up of 4.2 + 4.2 + 4.2 as it should be. If the middle
cell was only 4.00V and no balancer was used, the other two cells
have to reach 4.30 V/cell before the charger will terminate the
charge. Getting into dangerous territory.

Using a balancer can not only improve pack life but can also
improve charging safety. Most people agree that balancing a pack
is not necessary every cycle. It does no harm, but it can take a
bit longer.


Temperature Sensitivity


Lipos are damaged by getting too hot or too cold.   :'( If they
reach 70° C they are irreversibly damaged. If they reach 80° C
they may autoignite. If the ambient temperature is less than 20°
C you shouldn't have any temperature problems unless you are
pushing your cells very hard. Hence it's essential to know how
hard your application pushes your cells. So always use a
meter to measure the current draw of any given setup, and
realise that if you change anything in the powertrain (motor,
prop, ESC, battery) the current draw will also change. If you
ensure that your lipos are not pushed much past one half of their
maximum C rating they should not get too hot.

Cooling in flight
Additionally, particularly in summer, it is often a good idea to
ensure cooling airflow is able to flow over the lipos while in
flight. Generally speaking the air outlet holes need to be 3
times bigger than the inlets.

What about when you land and the cooling airflow stops? Perhaps
your lipo could get too hot after use? If the ambient temperature
is 40° C and you've been pushing your cells quite hard,
additional cooling may help once you have landed. Some people use
cooling tubes...

Cooling tubes
Basically a tube with a fan (old hairdryer fan, PC fan or even an
EDF unit) in which you can place your lipos after use in hot
weather.

Winter
Lipos don't like getting too cold either. And there is a problem
here because if a lipo is charged at a significantly different
temperature from the temperature at which it is used, the cells
can be damaged.

If you charge a lipo in your house and then store it in an
unheated shed or garage, it can be damaged. I know of at least
two people who have done this and the lipos were ruined.

You should not let a fully charged at room temperature lipo
battery get cold. So if you charge at home and then leave your
box of lipos out in the cold, your lipos may deteriorate.

There are people who only charge their lipos to 4.1 Volts per
cell when going out to fly in the cold to mitigate against this
possibility, but most simple lipo chargers will not do this. I
have heard of people using the Lithium Ion settings on their
chargers to achieve this, but I cannot recommend it myself as
I've never tried it.

Conversely, do not charge a lipo in the cold and bring it into the
house or it may go overvoltage with disastrous consequences.  :o


Field Charging
Try to avoid leaving lipos in direct sunlight (a lipo sack may
help). Allow lipos to reach ambient temperature before charging.
A cooling tube may help here - particularly in summer.

Long-term Storage if Not in Use

For long-term storage (weeks or months) lipos are best left at
about half charge. That is 3.85-3.90 volts per cell (resting
voltage). Every lipo I have ever bought has been at this level on
purchase. Surely the manufacturers know something? Wink This
minimises the reduction in capacity. If stored unused for long
periods, lipos will suffer reduction in capacity and performance.
This is minimised by storing them half charged.


« Last Edit: March 03, 2009, 08:36:55 AM by alexeames »
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Offline Alexmacro

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Safe Lipo Disposal

Should you be unlucky enough to kill one of your lipos, here are
ThunderPower's recommended steps for disposal...
 

    "Unlike NiCd batteries, lithium-polymer batteries are
    environmentally friendly. For safety reasons, it’s best that LiPo
    cells be fully discharged before disposal (however, if physically
    damaged it is NOT recommended to discharge LiPo cells before
    disposal - see below for details). The batteries must also be
    cool before proceeding with disposal instructions. To dispose of
    LiPo cells and packs:

    1. If any LiPo cell in the pack has been physically damaged,
    resulting in a swollen cell or a split or tear in a cell’s foil
    covering, do NOT discharge the battery. Jump to step 5.

    2. Place the LiPo battery in a fireproof container or bucket of sand.

    3. Connect the battery to a LiPo discharger. Set the discharge
    cutoff voltage to the lowest possible value. Set the discharge
    current to a C/10 value, with C being the capacity rating of
    the pack. For example, the 1C rating for a 1200mAh battery is
    1.2A, and that battery’s C/10 current value is (1.2A / 10) can be
    used, such as a power resistor or set of light bulbs as long as
    the discharge current doesn’t exceed the C/10 value and cause an
    overheating condition. For LiPo packs rated at 7.4V and 11.1V ,
    connect a 150 ohm resistor with a power rating of 2 watts
    (commonly found at Radio Shack)to the pack’s positive and
    negative terminals to safely discharge connecting it to an ESC/
    motor system and allowing the motor to run indefinitely until no
    power remains to further cause the system to function.

    4. Discharge the battery until its voltage reaches 1.0V per cell
    or lower. For resistive load type discharges, discharge the
    battery for up to 24 hours.

    5. Submerse the battery into bucket or tub of salt water. This
    container should have a lid, but it should not need to be air-
    tight. Prepare a plastic container (do not use metal) of cold
    water. And mix in 1/2 cup of salt per gallon of water. Drop the
    battery into the salt water. Allow the battery to remain in the
    tub of salt water for at least 2 weeks.

    6. Remove the LiPo battery from the salt water, wrap it in
    newspaper or paper towels and place it in the normal trash. They
    are landfill safe."

Quoted from...
http://www.thunderpowerrc.com/PDF/DISPOSAL-OF-LIPO-BATTERIES.pdf
 
« Last Edit: March 03, 2009, 08:37:17 AM by alexeames »
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Offline Alexmacro

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Additional info to be posted
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Offline JJ

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Re: Lipo Usage Best Practice. Avoid Both the Hazards and the Fear.
« Reply #4 on: August 26, 2009, 20:53:52 PM »
Am I doing the wrong thing?
To explain, I have always realised the importance of correct lipo usage, and have always used the following procedure:-

1 time the flight, aiming for about 70% usage, based on mah used as a percentage of the lipo rating.
2 charge using a Pro Peak Prodigy charger and RC System balancer.

Example.
7 min. flight
lipo voltage (never taken too much notice if this) 11.32
58 min. charge time
2197 mah replaced
3300 mah lipo hence 66% used
12.6 V charged
I use a spreadsheet to record each usage of each lipo.

The above figures are typical for all my lipos (5), all of which have about 20 - 30 cycles, with no apperent loss of performance.

In the above example the charger display informed me that the pack was fully discharged and refused to charge. I removed the balancer and the charger worked as usual. This has never happened previously but raised doubts in my mind.

I do not understand how using mah to calculate usage can differ so much from using voltage to calculate the same thing.

I have followed this procedure on all my packs, always aiming for 60 or 70%, based on mah used, I do not always record the discharged voltage but it seems to be always between 11.3 and 11.5

Sorry to have rambled on a bit

Any advice gratefully received

JJ


JJ


Offline Alexmacro

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Re: Lipo Usage Best Practice. Avoid Both the Hazards and the Fear.
« Reply #5 on: August 26, 2009, 21:16:10 PM »
I don't think you're doing anything wrong JJ. But assuming that your 3300s can deliver 3300 is perhaps optimistic. From the point of view of capacity I would normally treat them (in your percentage calculations) as, say, 85% of nominal. ~2800

Also, it is important if you are going to use voltage as fuel gauge that you allow the battery to recover for a few minutes before measuring.

I would be more comfortable leaving about 20% in the cells. 11.3 is OK (3.76v/cell ~12%), but I certainly wouldn't aim to deliberately go any lower.
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Offline JJ

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Re: Lipo Usage Best Practice. Avoid Both the Hazards and the Fear.
« Reply #6 on: August 27, 2009, 19:35:26 PM »
Thanks for the reassurance, the 85% "safety factor" makes a great deal of sense,l I will adjust the formula in my spreadsheet accordingly.

John
JJ

Offline GlideHer

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Re: Lipo Usage Best Practice. Avoid Both the Hazards and the Fear.
« Reply #7 on: January 09, 2010, 20:02:52 PM »
here is a post about lipo batteries everyone should read
All about Lipo Batteries lithium polymer batteries  | Remote Control RC Planes

Offline Alexmacro

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Re: Lipo Usage Best Practice. Avoid Both the Hazards and the Fear.
« Reply #8 on: July 20, 2010, 21:59:12 PM »
Addendum:

Travelling with lipos.

IATA Document here The relevant bit for air passengers starts on page 8.


This link to the passenger leaflet is also useful

Quote
Passenger Provisions
Transport within Passenger Baggage
Certain restrictions apply to the carriage of lithium metal and lithium ion batteries even when carried by passengers as baggage. Once again, only batteries that have successfully passed the Tests outlined in Part III, Sub-Section 38.3 of the UN Manual of tests and criteria may be carried.
As said before batteries manufactured, distributed or sold by major companies do meet this requirement, however, certain replacement batteries which are not OEM or aftermarket batteries but simply low-cost copies of those – also called “fakes” – may not have undergone the required tests. Untested batteries are consequently excluded from air transport.
Users of equipment powered by lithium metal and lithium ion batteries should therefore be vigilant when buying replacement batteries from unknown sources, such as on markets or Internet auction platforms. The differences between genuine and copied battery types may not be visible but could be very dangerous; such untested batteries may have a risk of overheating or causing fires.
Because of the risks associated with the carriage of spare batteries these may not be transported within passenger checked baggage. Spare batteries must be in carry-on baggage.

These requirements are stipulated by subparagraph 2.3.5.9 of the IATA Dangerous Goods Regulations:

2.3.5.9 Consumer electronic devices (watches, calculating machines, cameras, cellular phones, lap-top computers, camcorders, etc.) containing lithium metal or lithium ion cells or batteries when carried by passengers or crew for personal use, which should be carried in carry-on baggage. Spare batteries must be individually protected to prevent short circuits by placement in the original retail packaging or by otherwise insulating terminals, e.g. by taping over exposed terminals or placing each battery in a separate plastic bag or protective pouch, and carried in carry-on baggage only. In addition, each installed or spare battery must not exceed the following quantities:
(a) for lithium metal or lithium alloy batteries, a lithium content of not more than 2 g; or
(b) for lithium ion batteries, a watt-hour rating of not more than 100 Wh.
There is also provision, with the approval of the airline, for larger lithium ion batteries with a watt-hour rating in excess of 100 Wh, but not more than 160 Wh in equipment and no more than two spare lithium ion batteries as set out in subparagraph 2.3.3.2 as follows:

2.3.3.2 Lithium ion batteries exceeding a watt-hour rating of 100 Wh but not exceeding 160 Wh may be carried as spare batteries in carry on baggage, or in equipment in either checked or carry on baggage. No more than two individually protected spare batteries per person may be carried. Although the text provided above does not impose a limit on the number of lithium metal and lithium ion batteries that fall under the 2 g or 100 Wh limitation (See 2.3.5.9) being carried as spares within a passenger’s carry-on baggage it must be emphasized that the number of spares must be “reasonable” in the context of the equipment used by the passenger and his or her itinerary. Furthermore, these must be intended to power consumer electronic devices (including, but not limited to, cameras and professional film equipment, laptop computers, MP3 players, cell phones, Personal Digital Assistants (PDA’s), pocket calculators etc.
Batteries which are carried for the purpose of resale or beyond personal needs are clearly not covered.


This rather begs the question "are model planes consumer electronic devices?" Is there a strong case for arguing Yes? I hope so.

page 10
Quote
Packaged batteries or cells must be separated in a way to prevent short circuits and damage to terminals. They must be packed in a strong outer packaging or be contained in equipment.


This link to the passenger leaflet is also useful
« Last Edit: July 20, 2010, 22:28:38 PM by alexeames »
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Offline vinnie

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Re: Lipo Usage Best Practice. Avoid Both the Hazards and the Fear.
« Reply #9 on: September 12, 2011, 11:22:45 AM »

Perhaps the end is in sight for LiPo fires...

http://www.bbc.co.uk/news/science-environment-14852073
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