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Old Feb 13, 2013, 10:14 AM
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LittleMo's Avatar
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Originally Posted by maca55 View Post
I ran some quick tests a while back and came to the rough conclusion that the LVC was around the 3.00V level. My guess is that the control board monitors voltage and will 'take note' as soon as it dips under 3.00V. It will then permit you to continue to fly for as long as the battery holds enough voltage to keep the props spinning, however once you cut the throttle the board will prevent you from throttling up again.
Yep. I did constant on/off throttle tests. It refused to power up once it hit exactly 3.15V when I did it this way but it could be slightly higher than that. I don't think it's 3V because I never got that low at any point. I tested under actual load with a continuous logging of the minimum voltage saved on my computer.

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The LVC sounds low but you need to know how much the voltage dips on these little packs under high load. Do not believe the ridiculous C-ratings, especially the nano-tech ones which are outrageous. These packs struggle to hold 5A (16C) constant let alone the claimed 13A (45C)!
Yes. I tested my 35C (50C burst or something ) nano-tech's and they can't even hit 3A on my brushless Genius CP. Voltage drops way low of course.

Even my big nano-tech packs on the full size quad can't deliver their rating. Sad

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As you noted, if you check the battery voltage after the first 'throttle cut' is normally around the 3.6-3.67V mark. This end value will vary depending on the IR of the battery and how hard you were flying it when the voltage dropped below 3.00V.
I have never seen it go below 3V. That's crazy dangerous low. My Genius will shut down the entire board (literally dropping it out of the air) if voltage drops below 3.3V for 5 seconds. The V939 will refuse to power up again once it drops around that 3.15V mark. Although the V939 will like you said allow you to keep going until it kills the battery (I guess) if you never cut the throttle.
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Old Feb 13, 2013, 04:24 PM
it WILL fly! someday....
Richard_s's Avatar
Slovakia
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I discovered that original 939 batteries (from banggood) have some circuit themselves. 3 tiny chips on a circuit board. Part of LVC, or overcharging protection? Or both?
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Old Feb 13, 2013, 05:22 PM
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Originally Posted by Richard_s View Post
I discovered that original 939 batteries (from banggood) have some circuit themselves. 3 tiny chips on a circuit board. Part of LVC, or overcharging protection? Or both?
Overcharge definitely, Lvc I'm not so sure about, almost all "toy grade" LiPo have OCP (Over Charge Protection), as the "charger" plug is rarely more than a resistor or two and a charge indicator light. It's the little PCB on the LiPo that actually takes care of the charging.
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Old Feb 13, 2013, 05:26 PM
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Originally Posted by djdavies83 View Post
Overcharge definitely, Lvc I'm not so sure about, almost all "toy grade" LiPo have OCP (Over Charge Protection), as the "charger" plug is rarely more than a resistor or two and a charge indicator light. It's the little PCB on the LiPo that actually takes care of the charging.
Dunno, but wltoys chargers seem to have "proper" li-pol chraging ICs inside. Both I own do, v911 and v939.
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Old Feb 13, 2013, 06:24 PM
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That's the dual charger things yeah?

I can imagine them having Chios because there are essentially two chargers in one casing, the singe chargers like S107, Sh6020-1 and single Hubsan X4 (above two dont, I doubt Hubsan does) will not have chips in the charger, my mains plug in S026 charger had no chip but I took one off a dead cell and put it on the end of the cable so I could charger unprotected miniaviation cells.
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Old Feb 14, 2013, 12:51 AM
it WILL fly! someday....
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Originally Posted by djdavies83 View Post
That's the dual charger things yeah?

I can imagine them having Chios because there are essentially two chargers in one casing, the singe chargers like S107, Sh6020-1 and single Hubsan X4 (above two dont, I doubt Hubsan does) will not have chips in the charger, my mains plug in S026 charger had no chip but I took one off a dead cell and put it on the end of the cable so I could charger unprotected miniaviation cells.
Yup, dual chargers. Probably a matter of outsourcing and mass production, it was cheaper to get protected batteries + proper charger + LVC in quad, than otherwise .

Those charger chips look interesting, I got some for my lipol powered projects, to charge from USB. At 0,5eur / piece, quite handy.
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Old Feb 14, 2013, 01:52 AM
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Originally Posted by LittleMo View Post
Yep. I did constant on/off throttle tests. It refused to power up once it hit exactly 3.15V when I did it this way but it could be slightly higher than that. I don't think it's 3V because I never got that low at any point. I tested under actual load with a continuous logging of the minimum voltage saved on my computer.
Interesting. Your test sounds a bit more controlled than mine was. I used a watt meter in series so I wasn't measuring right at the board, it might account for the difference.

3.15V does make more sense though since your average pack IR is around the 0.15 ohm, at 4A (typical peak load) your looking at a 0.6V drop. 3.15+0.6V = 3.75V rest voltage after LVC is triggered!

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Yes. I tested my 35C (50C burst or something ) nano-tech's and they can't even hit 3A on my brushless Genius CP. Voltage drops way low of course.
It even more laughable how the Nano-tech 45C claim a burst rating of 90C = 27A!! At least the batteries that ship stock with v939 are reasonable and only claim 25C. Based on my tests, in reality most of these batteries (nano-tech included) only range between 10-15C 'true' c-rating!
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Old Feb 14, 2013, 12:07 PM
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i found the nanotech WILL supply 20 or 30 amps. for a few milliseconds anyway. you need a scope and fet to see this but its true. the point is these cells do perform better than any of the others ive tested. certainly better than any stock lipo. the truth comes out when you try using with a micro brushless quad. or temperature drops. even with brushed quad only got about 5 sec with stock cells and yet 1-2 minute with nanos when its cold out.

imo they are by far the best deal going. better than hyperion or any other afaik when you consider cost. specially if you buy them in 2s or 3s and dismantle the pack like i do.

also note that those protection boards do not really help you with inferior chargers. limits only kick in under extreme conditions like short, huge overvoltage, or total discharge. even those diode resistor chargers like the v911/v929 will not put out more than 4.2-4.3v which is perfectly safe. i like that v929 charger a lot because it will charge more cells in parallel faster than any of the others includng v939 which has a "real" charge ic. and its very compact and easier to carry around than my dc6. the v939 is nicer for doing one or two cells at a time but thats rare for me.

btw "danger" level for lithium cells is more like 2v not 3v according to technical papers. and far more important how long you leave it in that state. im convinced it is other forms of abuse that cause most hobbyists to damage their cells. like "quick charge" which is far more dangerous but everybody wants it.
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Old Feb 14, 2013, 12:29 PM
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It's really hard to get any sort of definitive answer on correct lipo handling. The technology is always changing and the various manufacturers are using different techniques even within their own brands. All you can do is find what works by trail and error then hope for the best.

I have nearly killed a couple of those 35C 300 mAh nano-tech's by letting them get too low. One went to 2.7 and the other to 2.58. The 2.7 one eventually recovered after about 10 cycles but the other one never did and now it has very weak power delivery and half the run time.

I also had a similar issue when I accidentally charged a few of them at 2C. They lost 50% capacity and one of them never recovered. I believe they are officially rated for higher charge rates even. Oh well... You never can tell.

Plus charger quality can make a difference. Also whether the voltages they hit were under load or at rest. A lot of variables at play.
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Old Feb 14, 2013, 12:54 PM
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Originally Posted by LittleMo View Post
It's really hard to get any sort of definitive answer on correct lipo handling.
true dat. lots of flotsam.

theres also an issue of cause and effect. ie it has been definitively proven neither chicken soup nor achinacea have any benefit for the common cold. try telling ma or the new age yippy down the street. they rarely take into accout that sniffles ALWAYS go away whether you use them or not.

with lipos its hard to pin down what actually killed them. some lots are cursed from the start and nothing you do will extend life. im convinced the cause most peple assign is often misplaced. i also believe there is no way to "revive". at least not in my exerience. apparently youve had much better luck.
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Old Feb 14, 2013, 03:18 PM
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I've been told, by the manufacturer themselves, that batches of lipos that had been sitting in storage needed a good cycling before they would meet their ratings. Their claim seemed spot on, as the first charge->discharge would only be about 80% or less of the rated capacity. The next charge->discharge would be closer to the rating, and the third met or exceeded capacity.

As long as it isn't puffy, it doesn't hurt to power cycle a time or two before declaring TOD.
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Old Feb 14, 2013, 03:23 PM
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actually that pertains to nixx more than lipo. they definitely need a few cycles after sitting or left in a continuously charged state (memory). capacity can double. for lipos its more relevant to brand new unused cells. there is a special chemical treatment applied at the factory to keep them inactive while on the shelf. i have seen 10% increase after first charge but nothing after that. never managed to improve a damaged cell though.
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Old Feb 14, 2013, 06:43 PM
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Originally Posted by dave1993 View Post
actually that pertains to nixx more than lipo. they definitely need a few cycles after sitting or left in a continuously charged state (memory). capacity can double. for lipos its more relevant to brand new unused cells. there is a special chemical treatment applied at the factory to keep them inactive while on the shelf. i have seen 10% increase after first charge but nothing after that. never managed to improve a damaged cell though.
Well, that is true about the damaged cell. Once a cell is truly damaged, it is gone. I think, though, that you can drain a cell to less than even 2V and it still doesn't guarantee damage.
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Old Feb 14, 2013, 07:01 PM
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yes. that was my point in the previous post:

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Originally Posted by dave1993 View Post
btw "danger" level for lithium cells is more like 2v not 3v according to technical papers. and far more important how long you leave it in that state. im convinced it is other forms of abuse that cause most hobbyists to damage their cells. like "quick charge" which is far more dangerous but everybody wants it.
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Old Feb 14, 2013, 08:17 PM
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Nice reading guys..Gives me ideas after i complete my V911 build..Ill be back
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