BATTERY CYCLE ??????????????

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danie.e
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BATTERY CYCLE ??????????????

Unread post by danie.e » Thu Oct 04, 2012 3:15 pm

Will the electric and electronic boffins give us dom ouks a table with the correct voltages, amps etc. when batteries are cycled

For instance down to what voltage do we discharge a Lipo ? Life? NiMh? etc. etc.

A lot of peole have not the faintest idea what to do when cycling, storage, fast charge etc. batteries.

Thanks
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Re: BATTERY CYCLE ??????????????

Unread post by TimB » Fri Oct 05, 2012 9:58 am

I'll summerise what I know.


Nickel based batteries, 1.1V per cell mimimum. Below 1.0V permanent damaged will result.
If fast charging, use a temperature sensor for the charger to be able to monitor the change in voltage to the change in temperature.
This counts for Nickel Zinc as well with the following exceptions:
max voltage per cell = 1.9V
Min voltage per cell = 1.6V
Nominal voltage = 1.65V per cell
Charge current = 1C @1.9V
Max Charge current = 2C@ 1.9V with temperature monitor set to current current if temperature rise exceeds 15degrees C.

Lithium Polymer 3.7V per cell is min safe voltage.
Absolute minimum voltage is around 3.0V per cell but this can vary depending on the brand (slight chemistry and construction differences). Some are higher, none are lower.
For best life, charge at or below 1C and discharge at or below the continuous C rating (not the burst current C rating). High temperatures kill any battery.
Do not drain below the nominal voltage value of the pack for maximum life.

LiFePO4
3.3V per cell nominal
3.6V per cell maximum
3.0V per cell minimum
2.5V per cell absolute min voltage before permanent damage occurs.
Charger quaity is critical to get the best out of these packs as some chargers tend to simply monitor the max pack voltage without tracking the voltage per cell via the balance tap (Even thought it shows you its tracking the V/cell). This results in over charge of one cell and under charge in another. Repeated overcharging causes permanent damage.Chargers that actually cut the voltage to the cell taking more charge should be used.
A123 battery packs have similar specs but may not have balance taps, instead some brands fit a balance circuit.


Storge charge for Lithium battery packs should be in the range of the nominal voltage +2% (not lower than nominal)
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Re: BATTERY CYCLE ??????????????

Unread post by Gary Lees » Fri Oct 05, 2012 10:25 am

Hi All,

Here is an article from Battery University and the link to the web site. It give a great deal of information and the chemistry behind all sorts of batteries. (Danie I know that you will love this)

I hope that this will help.

http://batteryuniversity.com/learn/

Table 1 compares the characteristics of four commonly used rechargeable battery systems showing average performance ratings at time of publication.
Table 1: Characteristics of commonly used rechargeable batteries
The figures are based on average ratings of commercial batteries at time of publication; experimental batteries with above-average ratings are excluded.

1 Internal resistance of a battery pack varies with milliampere-hour (mAh) rating, wiring and number of cells. Protection circuit of lithium-ion adds about 100mW.
2 Based on 18650 cell size. Cell size and design determines internal resistance.
3 Cycle life is based on battery receiving regular maintenance.
4 Cycle life is based on the depth of discharge (DoD). Shallow DoD improves cycle life.
5 Self-discharge is highest immediately after charge. NiCd loses 10% in the first 24 hours, then declines to 10% every 30 days. High temperature increases self-discharge.
6 Internal protection circuits typically consume 3% of the stored energy per month.
7 The traditional voltage is 1.25V; 1.2V is more commonly used.
8 Low internal resistance reduces the voltage drop under load and Li-ion is often rated higher than 3.6V/cell. Cells marked 3.7V and 3.8V are fully compatible with 3.6V.
9 Capable of high current pulses; needs time to recuperate.
10 Do not charge regular Li-ion below freezing. See Charging at High and Low Temperatures.
11 Maintenance may be in the form of equalizing or topping charge to prevent sulfation.
12 Cut-off if less than 2.20V or more than 4.30V for most Li-ion; different voltage settings apply for lithium-iron-phosphate.
LIPO Chart.jpg
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Re: BATTERY CYCLE ??????????????

Unread post by thefrog » Fri Oct 05, 2012 9:11 pm

Here are some approximate charge percentages for LiPo. Don't discharge below 20% as it will shorten the life of the packs.

These figures all vary depending on the brand, C rating, age, etc. Also remember the resting voltage will be different to when it's just been used. These are resting voltages listed below.

100% 4.20 volts
90% 4.15
80% 4.10
70% 4.05
60% 4.00
50% 3.95
40% 3.90
30% 3.85
20% 3.80
10% 3.70
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Re: BATTERY CYCLE ??????????????

Unread post by doodapunisha » Mon Oct 29, 2012 6:55 pm

Hi guys.

The LOWEST lipo's can drop to is 3.0v per cell. After that they will get damaged. Thats why in flight voltage meters start warning at 3.3v per cell.

To work out safe charge current: eg 2200mah battery at 20c discharge: 2200 x 20c = 4.4amp safe max charge.
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Re: BATTERY CYCLE ??????????????

Unread post by Gary Lees » Tue Oct 30, 2012 8:28 am

HI All,

A LIPO starts to get damaged when it goes below 3,7V per cell. The cut off on the speed controllers stars at 3,3V per cell. Always use a timer and test flight times so that you always land when the batteries are at or near the 3,7V per cell mark. If you discharge further than the 3,7V per cell then you will get the puffing up and the expensive cycle will begin again.

Also never leave your batteries in a discharged state. Allow them to cool off after the flight and then recharge for the next flight. If you are not going to use the battery again, then charge to the STORAGE state, even if you are going to fly again next week.

Charge rates are measured as follwos:

2200mah @ 1C = 2,2 Amps
2200mah @ 2C = 4,4 Amps
2200mah @ 3C = 6,6 Amps

You really should not charge at above 1C and in most cases the chargers cannot charge much quicker.

A LIPO does not need to be cycled, but it must NEVER be left fully charged or Discharged for any length of time. Overnight is OK but not much more than that.

Hope this helps.
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Re: BATTERY CYCLE ??????????????

Unread post by clivem » Wed Oct 31, 2012 7:58 pm

Gary Lees wrote:
You really should not charge at above 1C and in most cases the chargers cannot charge much quicker.

Hope this helps.
my limited knowledge of lipos - 1C depends greatly on the lipo and the chargers..........
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Re: BATTERY CYCLE ??????????????

Unread post by Gary Lees » Thu Nov 01, 2012 8:34 am

clivem wrote:
Gary Lees wrote:
You really should not charge at above 1C and in most cases the chargers cannot charge much quicker.

Hope this helps.
my limited knowledge of lipos - 1C depends greatly on the lipo and the chargers..........
Quite right Clive.Whilst most modern LIPOs can be charged at higher rates (5C+) only the really powerfull (+300W) chargers can charge at these high rates especially with the larger batteries (4,5 & 6 cells).

A safe standard is to plan for charging at 1C, then you know that your battery will last and will not be damaged in the charging process. Another very importand check is to ensure that the charger is set on the correct chemistry. eg. LIPO, LiFe, NiCad. If you do try and charge on the incorrect type, the danger of fire is greatly increased.

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