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-   -   Charging LiFe battery (http://www.Wattflyer.com/forums/showthread.php?t=72962)

Royall 01-11-2014 12:55 AM

Charging LiFe battery
 
I did a search for this and I didn't find what I was looking for.

I just got a Zippy, 1800mAh, 3s, 20c, LiFe transmitter battery from HK.

I used a Turnigy Acucel-6 charger and set it up to put the first charge into the battery on the balance setting. I set it for a modest .5A charge @ 9.9v All appears to be good but was concerned that when I pushed the start button, the charger started out at 10.8v.... Is this normal? The battery charge fine and didn't over heat. I put it in my Turnigy 9x Tx and it shows 10v. If this IS normal, what is the cut of voltage I should be looking for so I don't ruin the battery?

kyleservicetech 01-11-2014 02:43 AM

Quote:

Originally Posted by Royall (Post 936743)
I did a search for this and I didn't find what I was looking for.

I just got a Zippy, 1800mAh, 3s, 20c, LiFe transmitter battery from HK.

I used a Turnigy Acucel-6 charger and set it up to put the first charge into the battery on the balance setting. I set it for a modest .5A charge @ 9.9v All appears to be good but was concerned that when I pushed the start button, the charger started out at 10.8v.... Is this normal? The battery charge fine and didn't over heat. I put it in my Turnigy 9x Tx and it shows 10v. If this IS normal, what is the cut of voltage I should be looking for so I don't ruin the battery?

Hi
This LiFe (Or the similar A123 cell) chemistry is designed to be charged by the Constant Current/Constant Voltage (CCCV) charge system. Be sure to use the balancing system provided by your charger. IMHO, balance charging is mandatory for these Lithium Chemistry batteries. Nice thing about LiFe, they have zero fire hazard, even if severely abused. We had one LiFe battery bent some 45 degrees at our club after a straight in crash of a giant scale gasser. That battery was smoking hot for several minutes after the crash. (Elevator came off the airplane!) But, after an hour, that two cell LiFe battery stabilized, and was still putting out 6.6 Volts DC.

This CCCV charge routine is nothing new. That is exactly how your automobile's lead acid battery is charged by its alternator, or decades before that, the DC generator.

That said, the battery is charged at a Constant Current (0.5 Amps in your case) to the battery. As the battery voltage increases to a MAXIMUM of 3.6 Volts per cell, your charger is supposed to maintain the 3.6 Volts DC on each cell, and drop the charging rate down as the charge cycle completes.

Under no condition is the voltage on any cell to ever exceed 3.6 Volts DC. Some chargers do charge to 3.7 VDC per cell, but the battery is pretty much fully charged at 3.5 VDC or so.

These batteries have a very flat voltage discharge curve, dropping about 1% in voltage from 80% charge to 20% charge. And, they hold their charge for a very long time. I've got over 100 2300 Mah A123's in my various models. They typically loose about 5% of their charge after sitting on the shelf for a year.

As is common with all Lithium batteries, don't ever leave your transmitter on, and run your LiFe flat. Doing this just once can and will cause permanent damage to the LiFe battery.

One other thing, these batteries are very efficient in their discharge/recharge process. If you discharge 1000 Mah OUT of the battery, it will take about 1050 Mah to recharge the battery. These LiFe batteries can be safely recharged in an hour. I've been recharging my A123's in 15 minutes. And they last for hundreds of cycles, while pulling 40 Amps out of each cell.

Royall 01-11-2014 03:46 AM

Way cool! Thanks for the great explanation!! Curious tho.... I was told, and it is the voltage on the charger) that LiFe's were 3.3v per sell... and LiPo's were 3.7v...... Just gets a bit confusing when learning a new hobby with an unfamiliar source of power.

Mahalo nui loa!!

Royall

Turner 01-11-2014 05:27 AM

3.3 and 3.7 are the nominal voltage. Fully charged is 3.6 and 4.2.

Brick 01-11-2014 05:48 AM

I have a Turnigy 2200 LifE batt i just put in my DX7. it maxed out @ 10.7. It has been @ 10.7 for over a month. just flying my little mcpx heli's... I have not had to recharge in over 2 months

kyleservicetech 01-11-2014 06:09 AM

Quote:

Originally Posted by Royall (Post 936757)
Way cool! Thanks for the great explanation!! Curious tho.... I was told, and it is the voltage on the charger) that LiFe's were 3.3v per sell... and LiPo's were 3.7v...... Just gets a bit confusing when learning a new hobby with an unfamiliar source of power.

Mahalo nui loa!!

Royall

Yup
And as for receiver power, these two cell LiFe's are a DIRECT drop in replacement for those 5 cell Nickel Hydride cells. Their voltage discharge curve is virtually identical, within a percent or three.

The big difference, these LiFe batteries will easily put out 10 amps or more under giant scale servo loads. And, still hold 3.3 Volts per cell. (I've measured a 14 Amp peak on my giant Big Stick with its Hacker A60-16M motor, and 19X12 prop)

Doing the same 10 Amp load with a Nih "AA" five cell pack, and you'll find your receiver voltage dropping below safe levels of 3.5 volts or less within a second or two.

Most of the guys in my RC club have gone to those LiFe or A123 cells for receiver/servo power on their $$$$ kerosene jets, giant scale gassers, and a lot of the smaller models as well.

cyclops2 01-27-2014 12:57 AM

No extra switching regulators to poop out. Or cause interference. Or reduce the BEC rating as everything heats up in the summer.

Less parts. More reliable.

LIFEPO4 cells ARE the Timexes of the battery world.


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