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› Voltage Caps and Charge numbers
06-03-2009 09:09 PM  8 years agoPost 1
Maverick3n1

rrApprentice

San Diego, CA

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New to Lithiums, so here's what I've got.

New Zippy 3s LiPo 2200mah 20C packs. Just arrived in the mail as well as a balance charger. With experience of NiMh and NiCd's, I know that when charging batteries, the fully charged voltage is typically higher than the actual stock output of the battery, and while charging, that voltage again is yet even higher. I'm not sure how much of the same that is with LiPo's however.

First question: When a LiPo battery is shipped, is it typically shipped charged or discharged?

2nd question: When charging a LiPo, is it really important to track how many times you charge it, or can you simply track the performance and as you notice your 6 minute flights tend to start turning into 3 minute flights, you know the battery is done?

3rd question: I'm using a new Turnigy Accucel-6 charger/balancer. I have it charging these packs in balance mode at 1 amp. Currently the voltage that's being pushed into the battery by the balancer is 12.17v. What should I expect it to top out at, so I know if I see the charger going out of the spectrum, I can stop it due to potential failure on the charger, and save myself from a bad experience...

4th question: Does the Turnigy Accucel-6 auto-detect a peak charge and shut off? I found a section where I could set max charge, which I set at 2500mah, knowing that sometimes these packs can handle a little more than they are rated for, but if the pack was at half charge when it arrived, I want to know that it's not going to attempt to push 2500mah into a pack that came to me with 1000mah already in it...

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06-03-2009 09:57 PM  8 years agoPost 2
mmc205

rrElite Veteran

PA - USA

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Batteries are typically shippped about 1/2 charge or 3.81 volts per cell.

Its nice to know how many times you charge it if you would like to keep track but how quickly performance degrades depends on how hard you dishcarge the packs and how deep the discharge is. Always try to stay above 3.0 volts per cell no load minimum, and an even better number is 3.7 volts per cell no load. the second number equates to roughly 20% capacity left and thats where you generally want to stop for longest life. in 10C (6 min) average discharge rates people seem to get 50-100 cycles. in 20C (3 min) average discharge rates people seem to get 50 cycles or less

it will top out at roughly 12.6 volts. lipo charges use constant current/constat voltage charging (CC/CV) basically it will use whatever voltage necessesary to charge at the set rate of 2.2 amps. the voltage it uses is dependent on the internal resistance of the battery. once it reaches a certain point in the charge it will switch to constant voltage and just put out 4.2 volts per cell until all cells reach that point. the CC portion of the charge is rather fast and the CV portion is kind of slow as the amperage its pushing in is falling off almost exponentially.

A good place to charge packs at is at 1C or for your packs 2.2 Amps this will give you the best cycle life with approx 1 hr charges. most lipo chargers act as peak chargers so the only reason you would have to enter the capacity is to give it a specific C rate to charge at such as 1C. it will not stop the charge at the capacity though. so basically set the capacity of the battery in your charger and then tell it to charge at 1C or 2.2 amps whichever it will take.

***Logo 600 vbar***Henseleit TDR vbar***

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06-03-2009 11:34 PM  8 years agoPost 3
Micro-Maniac

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Pasco,Washington Formerly: Captain Chaos

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I believe CC/CV works like this - It will charge at a set CC rate say 2.2A until the voltage reaches 4.2V per cell then will switch to CV and adjust the current to whatever it takes to maintain 4.2V per cell until the current tapers to about 1/20 of the original set CC current (2.2A / 20 = .11A) and end the charge

Q#1: Packs are generally at 40%-50% when purchased (3.8V/cell)

Q#2: You should time your flights so that they end at no less than nominal no load voltage (3.7V/cell - Approx. 20% capacity left meaning it shouldn't be taking more than 1760mah when charged) - As your packs lose capacity over time you may have to reduce your flight times to maintain this end of flight voltage - Never keep flying until you notice a power drop as by that time you've pretty much depleated the batteries and causing damage to them - End of battery life is at about 20% diminished capacity or when they become useless to you because they trigger your ESC's LVC when you pull a hard maneuver during your reduced timed flights

Q#3: Pack peak voltage? - Can safely reach 4.22V per cell so 12.66V for 3S pack but I've never seen a charger take one higher than like 12.62V - Most maintain 12.6V even so if you see like 12.64V you might get concerned and not let it reach or exceed 12.66V

Q#4: I believe some chargers such as my own allow you to set certain safety measures such as time and mah limits as to not overcharge a pack far beyond it's capacity if something is not right - You can set this to just a little more than what you think the pack will absorb if you want

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06-04-2009 12:00 AM  8 years agoPost 4
Maverick3n1

rrApprentice

San Diego, CA

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SO charging slower than 1C is not a good thing? I charged my packs at about 1/2C. I've always known it better for packs to be slow charged than fast charged...

Also, once charged, how long before power loss happens? For example, I charged them today, but I probably won't be flying for about 1 week. Will they still be pretty close to fully charged and not need to be topped off then?

When flying, how do you initially figure out how long to set your timer on your remote? Do you just fly it hard for say 3 minutes, land it, throw it on a charger to see what the charger puts back into it, and then adjust your flight time accordingly?

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06-04-2009 12:10 AM  8 years agoPost 5
fergus

rrKey Veteran

Ireland

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Here is a way for you to establish how long to fly your packs. 80% of 2200mAh is 1760mAh. This is the max you want to use in flight. If your charger displays the mAh put in during charge then you can fly for 3mins charge the pack and note the mAh put in. Divide it by 3 to get an average of mAh consumed per minute then divide 1760 by this number to establish your safe flight time.

Keep an eye on what the charger is putting back in during charges and adjust your flight time to stay under 1760. As already stated DO NOT fly until you loose power or hit the LVC of the ESC. At that stage you are already doing damage.

Don't store your packs long term fully charged it will reduce performance and increase cell resistance. Store at 50% and top up before you fly. I just charge them the night before a flying session.

EDIT: 1C charging is fine. I charge at 3c but only as I have a descent balance charger

Regards

Fergus

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06-04-2009 12:14 AM  8 years agoPost 6
Micro-Maniac

rrElite Veteran

Pasco,Washington Formerly: Captain Chaos

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Charging less than 1C doesn't have much benefit and can be annoyingly slow
I myself charge at 2C so I can keep flying with fewer packs and chargers - People will disagree with this but more than one battery brand have claimed negligible degradation from 2C charging (less than 1% more over 100 cycles vs 1C?)

Lipos hold their voltage very well - No need to top off before flying even after weeks - But store long term at half charge like you got them

Just like you said - Start with a mid-range time (3min?) and see what the voltage is after flight and what gets charged back into the pack and adjust your flight time accordingly - Settle on a little shorter time than you calculate for times when you fly harder etc

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