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Batteries & Chargers Discuss Li-P, Li-Ion, NiMh, Nicad battery technology and the chargers that juice 'em up!

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Old 03-12-2011, 02:43 AM   #1
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Default Knew it would happen sooner or ..........

11.1v 3s 3200mah eflite lipo got excited on second flight of a 182 and forgot to start watch timer, so.....approx. 13mins later no.1=3.17, no.2=3.13, no.3=3.02, battery never got much more than warm, is it ok to try to charge it? Kinda snuck up on me had good power till the last 30secs.

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Old 03-12-2011, 03:21 AM   #2
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Fail to see the problem. Yeah, it's a bit lower than say 3.5-3.7v/cell for 'best lipo practice' but it IS ABOVE 3.0v. Charge it and have a good time.
People hammer their lipos way worse that that all the time. They may only get a few dozen flights out of them though.

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Old 03-12-2011, 03:25 AM   #3
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ez enough thanks
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Old 03-12-2011, 01:24 PM   #4
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If its down that far, it would probably be a good idea to charge it at a very low rate at first and watch for signs of puffing.

If the resting voltage is right at 3 volts, that means you ran them a good bit lower under load.

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Old 03-12-2011, 03:43 PM   #5
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Yeah within a min of post-flight all three cells were approx 2.85-2.88 then 40 mins later they were all mid 3.10's that make sense voltage under load mite have been even lower during the flight but batterys apparently can recover a tiny bit after resting voltage this morning was 3.24, 3.22, 3.13
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Old 03-12-2011, 04:03 PM   #6
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If possible you might want to program your ESC for a higher LVC (some can, some can't). Sounds like you generally fly by time-a sensible policy. I consider LVC a "I got distracted"
failsafe.

Rechargeable batteries of all types do rebound immediately after the load is removed. They continue to recover voltage head for awhile but that does not recover capacity. The only thing that is really good for is allowing chargers that reject lower than 3v to charge a lipo.

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Old 03-12-2011, 04:08 PM   #7
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Originally Posted by CrimzonRider View Post
11.1v 3s 3200mah eflite lipo got excited on second flight of a 182 and forgot to start watch timer, so.....approx. 13mins later no.1=3.17, no.2=3.13, no.3=3.02, battery never got much more than warm, is it ok to try to charge it? Kinda snuck up on me had good power till the last 30secs.

p.s.
Please remember the people tonite east of oklahoma city who lost their houses to huge wildfire this afternoon.
Bad day around the world in japan and at home.......
I had one cell on a 1300 mAh battery drop to 2.7 once. Never knew why. It has taken about 25 full, troublefree recharges since.

...The Bum
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Old 03-12-2011, 04:30 PM   #8
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The 'knee' where the voltage suddenly drops off fast and hard is ~ 3v. On more modern lipos that spot is a bit higher (they sustain loads better/longer) but they fall faster and harder once you cross that line. They also don't take to it as well.
I find low voltage damage is a function of battery age, HOW low it went, HOW LONG it was low, and 'luck'. Some lipos are just better than others. The tough game in town is figuring out which ones those are. We have LOTS of opinions but very little hard, reliable data. By the time good data is gathered by a conscientious few (takes awhile to do long term study) the entire field has moved on an that particular lipo is no longer available even if it has the same skin/brand on it.

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Old 03-12-2011, 04:47 PM   #9
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Thanks for all the info, this board has and continues to be very helpful as i become more competent rc pilot.

Starting out with the dx5e has been very easy, but i think in tha next months of investing in higher grade tx that will fill my upcoming needs. Does the computer tx like the dx8 have some sort of LVC warning? I have read about that it can transmit voltage and other readings

also My esc is a grayson hobby 50a w 3aBEC
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Old 03-12-2011, 05:08 PM   #10
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Some of the newer high end TX have telemetry capability. You have to have it both in the TX and have suitable transmitting modules on board (can you say $$$). Do your homework. Just because the TX can do it, doesn't mean it happens automatically.

No idea what that Grayson ESC really is. This is right out of the manual:

[Cutoff Voltage:
− Cutoff voltages are auto-set
− Lipo 75% of initial startup voltage
− 0.8V per unit for NiMh selection

If the proper cell type and cell number is
selected, the ESC will cut off at 75% of the
initial voltage. For example, when using a 2s
lipo when fully charged, the initial voltage is
4.2V [4.2V x 2 (2S pack) = 8.4V.] ESC cut off at
8.4 * 0.75 = 6.3per pack or 3.15V each cell.
If the cells are not fully charged or if there is
any other reason causing the voltage to be
lower than 4.2V a cell in some circumstance
the LVC will be lower than 3.0V a cell.
PACKS MUST BE FULLY CHARGED
BEFORE USE
]


IMO, all ESC that use a fixed % of initial starting voltage should be avoided. Some brands (GWS, electrifly) are set so low (not adjustable) they can be damaging.
Doesn't look like you can do much about yours except be careful.

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Old 03-16-2011, 06:04 PM   #11
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Originally Posted by CrimzonRider View Post
Thanks for all the info, this board has and continues to be very helpful as i become more competent rc pilot.

Starting out with the dx5e has been very easy, but i think in tha next months of investing in higher grade tx that will fill my upcoming needs. Does the computer tx like the dx8 have some sort of LVC warning? I have read about that it can transmit voltage and other readings

also My esc is a grayson hobby 50a w 3aBEC
Look at the Hitec Aurora 9 transmitter. All its receivers have built-in voltage monitoring, and you can set the low voltage warning on the transmitter to anything you want. I've learned a lot by watching how the voltage drops at full throttle, then recovers. The Aurora 9 RXs are more expensive than Spektrum but the telemetry is built-in and easy to program. Cost is currently about $320 with 2 RXs if you shop around (one of the RXs is a promo from Hitec).
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Old 03-16-2011, 09:37 PM   #12
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Thanks just looked at it on their website 349.00 was the cheapest I could find not too bad of a deal, the dx8 that im looking at is around 429.00.

Maybe i missed it, but I couldnt find the info on the telemetry on the aurora.

I am looking to upgrade and I like it, huge screen and back lit too. This tx is a whole lot more than I need right now, just looking for a tx that is expandable along with my needs
thanks
cr
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Old 03-17-2011, 12:34 AM   #13
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Originally Posted by CrimzonRider View Post
Thanks just looked at it on their website 349.00 was the cheapest I could find not too bad of a deal, the dx8 that im looking at is around 429.00.

Maybe i missed it, but I couldnt find the info on the telemetry on the aurora.

I am looking to upgrade and I like it, huge screen and back lit too. This tx is a whole lot more than I need right now, just looking for a tx that is expandable along with my needs
thanks
cr
Astonishing but true - the reviews barely mention telemetry! The reason is that it only became available with a firmware upgrade in late 2010, so the early reviewers did not have it. The Aurora IS a lot more than you need now, but if you are considering the $ for a DX8, I'd certainly recommend it.

Exhaustive information about the A9 is compiled in a FAQ and guide to web sites:
http://www.rcgroups.com/forums/showthread.php?t=1141715
For me, the other big improvement is touch-screen programming. Very intuitive, well-thought out. For example you can select which switch goes with what channel; to make the selection, you get a diagram of the front with all switches labeled, and you press on the one you want!
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Old 03-17-2011, 12:47 AM   #14
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Exhaustive info ....you aint kiddin!!!! thanxs for the info...touch screen is attractive as long you dont touch it midflight!!!!
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Old 03-20-2011, 04:18 AM   #15
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Funny thing happened tonite and Im not sure what I did "right" My first post showed apprx 13 min flight and had dropped the 3s 11.1 3200 battery down to or below 3.0v underload, resting : the cells were 3.10's

that being said, this evening's flight was almost the same actually shorter (12:06) and approx. the same style zooming around at 1/2 to 2/3 throttle and a little work on approaches, even worked on getting more used to flaps, probably turned flap servos on and off 10x's(figured using the servos = using more juice)..... etc..,

tonite my batt is 3.83's across the board ....WHAT THE DEAL? Honestly both flights were very similar, maybe just a bit more wind, maybe 10 or so last week, bout 6mph tonite

Not complaining but this was kinda nice does 5mph more wind really make your battery, motor work that MUCH HARDER? lol kinda gotta laugh at myself, just kinda giddy right now at what I guess I would call "correct throttle management"(not on purpose or because im "good") lol can do for a beginner.

motor is neodym 10 and 50amp esc, 3s 11.1 3200 mah
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Old 03-20-2011, 07:06 AM   #16
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If you look at lipo voltage discharge curves voltage alone is a relatively poor approximation of capacity remaining, even more without a load on it.
LVC - Low LVC Damages High C LiPolys !!!

Wind can make a big difference in power use. You are almost talking about 2x the wind speed. That is 4x the force.

Servos take very little power all by themselves. In a glider you may eat 100-200mA/hour off an RX battery.

When I started I could barely tell the difference between a full battery and one that was seconds from LVC. You get better at it.

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Old 03-20-2011, 09:29 AM   #17
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Default Lipo tips

Originally Posted by CrimzonRider View Post
Funny thing happened tonite and Im not sure what I did "right" My first post showed apprx 13 min flight and had dropped the 3s 11.1 3200 battery down to or below 3.0v underload, resting : the cells were 3.10's

that being said, this evening's flight was almost the same actually shorter (12:06) and approx. the same style zooming around at 1/2 to 2/3 throttle and a little work on approaches, even worked on getting more used to flaps, probably turned flap servos on and off 10x's(figured using the servos = using more juice)..... etc..,

tonite my batt is 3.83's across the board ....WHAT THE DEAL? Honestly both flights were very similar, maybe just a bit more wind, maybe 10 or so last week, bout 6mph tonite

Not complaining but this was kinda nice does 5mph more wind really make your battery, motor work that MUCH HARDER? lol kinda gotta laugh at myself, just kinda giddy right now at what I guess I would call "correct throttle management"(not on purpose or because im "good") lol can do for a beginner.

motor is neodym 10 and 50amp esc, 3s 11.1 3200 mah
A few things i have learned about lipo batteries that is NOT common knowledge.

1) Any lipo battery that hasn't swollen up to an unsafe size (or frozen) can be saved, regardless of voltage (although people will argue it can't be done). I recently saved a battery that had a cell drop to 1.2v, when i put it on the charger, the pack only registered as a 2S rather than the 3S that it was. The trick is isolating the cell from the others and charging it at the lowest rate possible (0.1 mAh). I isolated the cell by using the "Astro Blinky" device then charged it till the dead cell reached above 3.0v, then up the charge rate to 0.5mAh till battery was fully charged. I've gotten a dozen or more uses out of the battery since and all cells charge as though nothing ever happened.

2) You get the best performance out of Lipo's during their midlife... meaning a brand new battery will not be at it's peak performance until you have used it a few times or as other may put it "Breaking it in". It's important to never push a brand new battery too hard the first few flights, meaning don't discharge it more than 2 or 3 "C" ratings even though it may be a 30C battery. And charge them at about 1/2 of what a normal charge rate would be for the first few times (ex: 1000mAh = 0.5mAh charge rate).

3) Lipo batteries do not like cold weather. I have the advantage of living in Hawaii where it's always warm year round. But if it's 30 degrees outside where you live, you are almost guaranteed to have a 30-50% decrease in performance out of your battery. (This one should be common knowledge but you'd be surprised how many people don't know this). P.S. Don't EVER freeze a lipo... you can't rez it.
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Old 03-20-2011, 04:30 PM   #18
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Per the recommendations above:
1. Partial agreement - Any lipo that takes a low voltage hit will be damaged. HOW damaged depends on the battery, age, quality, HOW LOW it got, and HOW LONG it was low. To say it just doesn't matter is to ignore chemistry.
The safety is hotly debated, a completely different argument.

2. Lot of controversy about that one, but many of the major battery manufacturers suggest a 'break-in'. I do it.

3. They do NOT like cold weather. Keep them warm before flying.
There is no evidence I can find that freezing will damage a lipo. On the contrary storing them at or above freezing at storage voltage will increase their longevity. How to prolong lithium-based batteries
I store mine in zip locks in the fridge, which sometimes is a pain as it can interfere with a spontaneous opportunity to fly.

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Old 03-20-2011, 06:25 PM   #19
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I never knew that twice the wind, 4x's the force, but it makes sense. I didnt really think servos really took alot of mah from the battery.

I think i have taken care of this battery, maybe 3 or 4 LVC in about 45 charges and it does seem better than when I first bought it for whatever reason.

The only time that I charged it at 1/2 rate was before this last flight, took forever to charge it. That was probably the only major difference in the two flights.(kinda forgot about that til now) So charging at 1/2 rate once in a while might be a good idea IMO. Always in a hurry ya know

I have left it deck overnite and it got down to like the low 20's and then charged it after it warmed up to room temp( bout 3 wks ago with less than 10 flights on it). The temp was a little lower on the 2nd, maybe 75 on the 1st and 68 or so on the 2nd.

Recently, like during the last 5 flights, right before I go fly, I kinda "Top-off" the battery for like 5 mins. I have read that after discharging a battery you should wait a while til it cools down a bit before your start to charge it.

Thanks for the all the info....I will use it.
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Old 03-20-2011, 06:37 PM   #20
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There is a persistent myth that slow charging (less than 1C) is better than even 1C. There is no evidence to support that for a decent BALANCING charger. If you are not balancing it 'may' help to equalize unbalanced cells. There are so many ways a lipo can be screwed up (from factory mis-matched cells to the highly variable field use/abuse) there is no good way to properly test that IMO.

If you charge in the cold (below 50*F) beware of warming those cells up significantly if they are not discharged. As the temp rises the voltage rises and you can effectively over-volt the cells. There is more than 1 story of a pilot finding charged cells he left in a HOT car all puffed up from a single exposure to that heat at that charge. Heat kills lipos.

Topping off a recently charged lipo shouldn't get you much-a percent or 2...maybe. If it's been sitting fully charged for a long time > well, you have other problems.

fly
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