August 11, 2016                Team Meeting “Technical Discussion Topic”                          Jeff Jones

Battery Terminology:                                     wordfile:  TEAM Technical Topics – Batteries, charging, use.doc

                V = volts,  potential energy.  (think of velocity of the current.)

                S = series,   how many cells are wired in series to achieve the stated voltage.

                A = amps,   How much energy the battery has stored when fully charged. (think of amount)

                                A 1000mah (milliamp) battery can store 1 amp hour of energy.)

                C  ratings = discharge rate.  How rapidly can the chemistry release the amperage.

                                A 1000mah battery with a 20C rating can be discharged at 1amp x 20 or 20amps.

                                A 1000mah battery with a 40C rating can be discharged at 1amp x 40 or 40amps.

Higher  C ratings indicate a more pure chemistry that has less internal resistance. This allows more amperage to flow under load with less voltage drop.  Better burst power and longer flight times since the surges in the later flight stages do not hit the LVC. Also, smaller lighter batteries can be used which reduces the work load and extends flight times.

Charge Rate=    The manufacturer will also state the max charge rate in terms of C.  Not the same as the discharge rate.  A 1C charge rate is 1x the battery amp size.   (a  500mah battery at 1c = 0.5amps)

Battery Chemistry:                                                          Full        Storage                Discharged

Ni-MH Nickel-Metal Hydride                    1.50v     1.25v                     1.00v                     per cell

                                2 cells                                    3.00v     2.50v                     2.00v                     overall

                                3 cells                                    4.50v     3.75v                     3.00v                     overall

4 cells                                    6.00v     5.0v                        4.00v                     overall

5 cells                                    7.50v     6.25v                     5.00v                     overall

6 cells                                    9.00v     7.5v                        6.00v                     overall

7 cells                                    10.5v     8.75v                     7.00v                     overall

8 cells                                    12.0v     10.0v                     8.00v                     overall

                Lower energy density, slower charging, slow steady discharging,   long storage life.

                                < 20C capability

 

August 11, 2016                Team Meeting “Technical Discussion Topic”                          Jeff Jones

 

                                                                                                Full        Storage                Discharged

LiPo       Lithium Polymer                              4.20v     3.70v                     3.00v                     per cell

                2S           2 cells                                    8.40v     7.40v                     6.0v                        overall

3S           3 cells                                    12.60v   11.1v                     9.00v                     overall

4S           4 cells                                    16.80v   14.80v                   12.0v                     overall

5S           5 cells                                    21.0v     18.5v                     15.0v                     overall

6S           6 cells                                    25.2v     22.2v                     18.0v                     overall

                High energy density, fast charging, fast discharging, sinking storage voltage,

                Fire hazard from physical damage or over charge or over discharge. Best motor power.

Currently, the high end Lipo batteries are advertizing over 100C discharge rates!!!

NOTE:   LIPO type batteries will spontaneously combust  from a direct short, like a puncture, wires crossed, charging at too high a rate or discharging at too high a rate.  I recommend a ceramic pot to place the charging batteries in while charging.

 

                                                                                                Full        Storage                Discharged

                LiFe        Lithium Iron Phosphate                 3.60v     3.30v                     2.50v                     per cell

                                2S           2 cells                                    7.2v        6.60v                     5.00v                     overall

                                3S           3 cells                                    10.8v     9.90v                     7.50v                     overall

                High energy density, fast charging, medium discharge rate (about 20C discharge ),  long shelf life, more stable If  physically damaged. Note: the voltage drops suddenly at the low end.   Lower cell voltage best for steady draw like ignition modules and transmitters.

 

 

http://s17.postimg.org/rw7j1uykf/discharge.jpg

 

August 11, 2016                Team Meeting “Technical Discussion Topic”                          Jeff Jones

Charging NiMH:

NiMH batteries use a voltage spike and temperature sensing technology for charging. They need a temperature sensor for this.  If it is a simple charger, it will have a very slow <10% C charge rate. Follow the instructions on the charger and the battery manufacturer.

Charging Lipo’s: 

Charge Rate=    The battery manufacturer will state the max charge rate in terms of C.  This is Not the same as the discharge rate.  A 2C charge rate is 2x the battery amp size.                                                         (a 2200mah battery at 2C is   2 x 2.2amps = 4.4amps)

Chargers included with a RTF plane are usually low power to protect from overcharging.

Programmable chargers can be set for the higher charge rates , greater than 1C. Care must be taken to keep the heat down or the battery will puff or even combust!!  

Programmable chargers often have several charging modes, direct or balancing. Balance charging will give a more full charge and extend battery life.   They also indicate the total milliamps put into the battery for recharging. This tells you how far you depleted the battery.  Fully discharging the battery will shorten the battery life. I recommend ending with  a nominal voltage with the battery at rest after flight.

Multiple Battery Charging Boards:

Batteries that are of the same cell count and discharged to the same voltage can be charged together with a charging board.  I only recommend this technique for those who are very knowledgeable about battery and charging techniques.

Some advanced chargers like the icharger, can measure the IR, Internal Resistance, of a lipo battery.  This is the only way to get an honest measure of the Crating of a battery.  It is done by applying a known load to a battery, measuring the voltage drop and calculating the resistance with OHMs Law. R=V/I

Over time a lipo will show a little puffing as gases are created from the charge/discharging process.  However, Sudden puffing indicates a chemistry problem or abuse and the battery is not trustworthy anymore. Measuring the internal  resistance will probably show a weak cell. Usually the center cell due to heat.   Very often these batteries will show a full voltage, but they don’t accept or give up a full charge and will hit LVC unexpectedly.

Lipos are very temperature sensitive. They work best at about 90*f and performance drops off rapidly if they get cold.  In winter, reduce cold air flow during flights, monitor temps.

 

Battery Meters:

The basic meters read voltage of the overall battery voltage (without a load)  and if a balance connector is present, voltage by cell too.  This is valuable information to have before each flight to assure you that the battery is fully charged for the flight and that all cells are in good working order.  They  cost from $4 to $25.

The Wattmeters give much more information in addition to battery charge.  A wattmeter is inserted between the battery and the plane’s ESC.   The meter will then indicate the voltage overall, the watts being drawn and the amps being drawn.   By increasing the throttle, you will see the amp draw, voltage drop and watts loading.  This will tell you how your system is loaded with the motor, propeller, ESC and  battery system under load. 

 

 

Chargers:

The chargers that come with most RTF planes are usually dedicated to that plane.  The voltage, amps and connectors will be selected for a safe conservative charging cycle.

Aftermarket Programmable chargers have a wide range of capacities and capabilities.  They usually have a lot of information about what they can do and how to use their options.  Read all the info carefully.  They will do what you program them to do even if it is wrong for the battery condition.   Options to look for are:

How many batteries will it charge at one time?      One, two, four

What chemistries will it charge?       NiMH, LIPO,  LiFE,

What voltages will it charge:    1S, 2S,3S,4S,5S,6S,  1 to 12 cell (NiMH).

How many Amps per channel?     Overall Amps?

Internal vs external power transformers.  120v to 12v

Auto cell count?    Caution:  miss cell count of under or over charged!!

Temperature probe for NiMH?

Polarity alarm and/or fuse?

 

Battery Disposal and discharging for Disposal:

How to discharge a battery for disposal:

1-      Use the discharge option in your programmable charger.

2-      Connect a 12v automotive bulb (taillight/) and let it draw down, takes days.

3-      Take it to a store that sells that type of battery for disposal. Cost?

4-       

How NOT to dishcharge a battery for disposal:

1-      Do not place a battery in salt water.  The terminals dissolve first and it stops the discharge.

2-      Do not slice open the battery.  Especially puffed batteries, will squirt, gas, fluid or flames!!!

3-      Do not drive a nail or other conductive item through the cells. The sudden discharge is volatile.

4-      Do not run the battery down in your aircraft. It could cause damage or programming failures.

5-       

 

 

Where to dispose of spent batteries:

Not all stores that sell batteries will accept them for recycle.   Each store makes it’s own rules on what kind, condition, weight or count of batteries.  Each store also prescribes the condition of the batteries, ie: discharged, leads cut, damaged or not, etx.   Some charge a fee, some don’t. 

Municipal Recycling Companies also recycle batteries.      Most charge fees by weight or count.

Batteries + Bulbs              Yes         (no charge for rechargeable types, others $ per pound, tape leads)

Coyote Hobby- Oregon City         Yes         no charge for recyclable types

Radio Shack                                        Yes?       No charge for recyclable types

Pride Disposal- Sherwood            Yes,   cost?

Horizon Hobby- Wilsonville          No

Tammies- Beaverton                      No

Home Depot –                                   ???         rechargeables for hand tools only?

Lowes-                                                 ???         rechargeables,  drop off at front entrance

 

 

 

Connectors by Amp ratings:

Connector

Continuous Amperage Rating

Servo/Battery Lead

< 800mA

JST

1-5 A

Mini T Plug

5-18 A

3.5mm Bullet Connector

10-35 A

4mm Bullet / Banana Connector

15-50 A / 0-10 A

Deans T Connector

20-60 A

5.5mm Bullet Connector

55-110 A

6.5mm Bullet Connector

65-150 A

Connector Placement

On the motor to ESC connection it is common and recommended to use the best bullet connector that fits your specific use. On the ESC side, this is where the female plugs go. On the motor side this is where the male plugs should go.

When using bullet connectors on the battery, it is best to follow and remember the phrase “Red Hot Female.” This refers to the battery as being the “hot” source having a “female” plug on the “red” or positive terminal. The negative side of the battery would then get the male connector for polarizing the connection.

The ESC of course would get the opposite connectors to properly mate up to the battery connectors. In order to prevent any shorts a piece of PVC tubing is recommeded to be placed over the male battery connector when the pack is not in use. This is very important to prevent any electrical shorts.

Wire Gauge Chart by Amperage Rating

This chart assumes less than 6-8 inch run of wire.

Wire Gauge

Continuous Amperage Rating

18 AWG

10-18

16 AWG

18-25 A

14 AWG

25-40 A

12 AWG

40-75 A

10 AWG

75-120 A

Dual 12 AWG

80-150 A

Dual 10 AWG

150-240 A

Source:     www.Radiocontrolinfo.com

 

http://www.electronics-micros.com/img/figure/ohms-law2.jpg

 

http://www.sengpielaudio.com/ohms-law-illustrated.gif

 

 

References:

Terminology                       instructables.com

Overview of lipo chemistry          icharger.co.nz

Parrallel charging             icharger.co.nz

Salt water discharging    http://forum.flitetest.com/

LIPO chemistry                  en.wikipedia.org

NiMH chemistry               en.wikipedia.org

Connectors and Amp ratings        Radio Controlinfo.com

Wire Gage Chart by Amperage Rating     Radio Controlinfo.com

 

 

 

 

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