Lipo Basics

[XF-15DCC]

A friend of mine passed this along. Being the safety officer at the club, I have been asked to try and come up with topics. This month (thanks to those who donate info here) is a reminder for the throttle cut switch. I thought I could post this and have Hobby Squawks best kick this around, add or delete things and see what comes out of it and be ahead for next months meeting.

Thanks in advance,

Kevin

Basic Lipo Batteries

AWARENESS

• Charging multiple-cell packs is the most dangerous time for fires/explosions

Common Fire/Explosion Causes:

• Charger settings (Battery type incorrect, Cell count to high, damaged/puffed packs, shorting, reversed polarity and over charging (4.2 volts per cell max)
• A LiPo cell base voltage is 3.7 volts. Never charge above 4.20 or discharge below 3.0 volts
• *NOTE* Moving a Lipo from a cold environment to a warm environment raises the voltage.

ALWAYS

• Have a plan for handling a burning pack for all locations where packs are stored, charged, used. (e.g house car field)
• Make sure all charging is done in a fire protected environment. A bucket of sand is a good fire suppressant.
• Be present while charging LiPos (sleeping is not present)
• Use care on a ”first time charge pack” and puffed/swollen packs
• Use a balancing charger for LiPos with multiple cells
• Know your packs cell specs- “xS” (x=Cell count and MaH (Capacity)
• Set charger to “LiPo”, match cell specs and use “balancing settings”
• Use 1C charge rate settings for best battery life (260MaH =.2 or .3 Amp, 2700 MaH-2.7 amps)
• Ensure correct polarity
• Use a volt meter that displays all cell voltages (plug into balance plug)
• Pay more attention while charging if cell voltage difference in a pack is greater than .1 volt
• Immediately remove your battery from crashed aircraft and place in a fire-safe bag.
• Store all batteries in a fire safe location.

[martmichals]

Great information, you hit on all of the main points with lipos. I think it'd be worthy to mention that it's not a great idea to leave the house when a lipo is charging. An explosion or rupture can escalate quickly, and it's always a good idea to be somewhat nearby.

[The Huff]

Great post ! I'm usually more of a threat to my LiPo's while flying my edf's ...

My FrankenStinger 64 is a beast !

[fhhuber]

1C charge rate is outdated. Modern packs handle 2C (some up to 5C) charge rates without issues.

Most of the micro models charge at 3C.

[spraypilot]

Hey martmichals, what is that airplane in your picture? stearman? looks really cool!

[TiredIronGRB]

1C charge rate is outdated. Modern packs handle 2C (some up to 5C) charge rates without issues.

Most of the micro models charge at 3C.

So if I have a 2200mAh I can safety charge at 4.4?

[F106DeltaDart]

So if I have a 2200mAh I can safety charge at 4.4?

All depends what your pack is rated at. But if it is a modern Higher C rate discharge battery, charging at 4.4 should be fine.

[KJD]

And there is no data to suggest that charging at higher rates deteriorated the life of the battery. You might not get as high an energy density for the charge. Life is too short to wait for your charger!

And the 4.2 Volt limit is no longer a hard point on the fire line. There is a modern chemistry of 4.35V http://www.store.revolectrix.com/Pro...LiPo-Batteries

Note; that some (most) 6 cell ESC can't handle the new chemistry 6 x 4.35V=26.1v. Most ESC manufacture are already pushing the mosfet rating they are using in their ESC at 25.2V. That extra volt is really pushing into any headroom left in the mosfets. I know from their own tech's that the E-flite Pro and Castle Creation Talon 90 can't.

[fhhuber]

The 4.2v/cell was imposed for a safety factor when a lot of chargers didn't have a balance function and many batteries didn't have balance connections.

4.2v/cell average allows for some imbalance to build up between uses of the very slow balancing devices (AstroFlite Blinky) that were commonly used.

You could get away with 4.30v/cell if the pack was balanced even on the old 6C rated packs (that we never see any more) and using less accurate chargers than we have now.

RC car racers have been charging to 4.35 v/cell for years with notably low number of cycles before packs degrade which may simply be due to the high temperatures the packs reach while being used in the races.

[KJD]

Yep, 4.2v allows a safety margin. My original lipo charger the Bantam BTC-304 charges to 4.258V. This was scary as there were no equalizers (balancers) back then. The Blinky could bring the cells back in balance but not during the charge cycle (lacked the power to keep ahead of the charger). Later TP and others would bring closed loop charging to the market which added a huge layer of safety to the whole Lipo thing as an energy source for our planes.

The new 4.35v lipo is a "new" chemistry, not just a marketing ploy cutting into the safety head room we have with the 4.2 limit.

Yep temperature is a great concern. Remember when Kokam would build their batteries with separators to aid cooling.

[gooniac33]

1C charge rate is outdated. Modern packs handle 2C (some up to 5C) charge rates without issues.

Most of the micro models charge at 3C.

There is no benefit to charging above 1C.... it saves a little time but you aren't really gaining much since you are hurting the cells even though they are said to be capable of charging at that high of a rate. Also... the last 20% of the charge is what takes the longest. not to mention that most packs aren't able to retain the voltage when it is shoved down their throat with high rates. Lower C charging is always best. No matter what is marketed out there.... Don't believe me? Choose a battery and do this test. Charge it at 1C, noting the time it took to charge and then let it rest for an hour. Check the voltage again and note the voltage. If you can use the pack in a plane or edf and then when done note the temp and voltage. Now do the exact same thing but charging at 5C. you will be surprised.....