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Mar 10, 2015, 04:21 PM
CSU Chico, Flight Club
Test Pilot Mafia's Avatar
Thread OP
Help!

LiPo 80% rule and my shallow charge rates.


Ive been looking in all the obvious places, so forgive me if theres a full explanation somewhere else.

Here's my problem, I have 2 Turnigy Nano-tech batteries. 3,300mAh, 3S. I love them working great after 50+ cycles. But . . .

- I get 3:30 minutes out of 3,300 mAh, to 11.1-ish volts.
- When I charge, I see 1,200-ish mAh put back in regularly
- my inflight watts up meter says 1,200mAh used in most flights.
- end of flight cell voltage seems to be 3.65 - 3. 7 volts, which is equally balanced.

** I don't want to puff them or over-discharge, so im cautious **

Is it ok to discharge down to 3.1 v per cell ? I Have an 80 amp continuous discharge LiPo, which I have pulled a max of 31 amps out in a super demand situation.

So may question is, am I discharging to shallow, Im not nearing the 80% rule. It seems im at 36 % ?
Last edited by Test Pilot Mafia; Mar 10, 2015 at 04:27 PM.
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Mar 10, 2015, 04:41 PM
Registered User
I think you're experiencing confusion of loaded vs. unloaded voltage.

In order to preserve maximum longevity, lipoly cells should not be below ~3.70 volts post flight with no load. This typically translates to ~3.0-3.5 volts under load and is dependent upon many factors (cell quality, current draw, ambient temperature, etc.). As such, I have always ignored loaded voltage and simply program the timer in my radio for each model such that my packs are no lower than 3.70 volts/cell after I remove them from my models.

If you are indeed measuring 3.65-3.70 volts with no load and are charging to 4.20 volts, your packs are nowhere near their stated capacity.

Mark
Mar 10, 2015, 04:56 PM
Space Coast USA
hoppy's Avatar
If you are going to shallow discharge you can really increase cycle life by only charging to 4.1V instead of 4.2V. Shallow discharges are very good for extending cycle life. The 80% rule does not give max cycle life, it does in most cases protect low capacity cells in a pack from over discharging.
Charging to 4.1V, discharging 1200mah and storing at 3.8V/cell should give you a long, long cycle life.
In fact, if you are only taking 36% out of the pack, you are probably right on storage voltage when you finish flying.
Mar 10, 2015, 04:58 PM
CSU Chico, Flight Club
Test Pilot Mafia's Avatar
Thread OP
Quote:
Originally Posted by mrforsyth
If you are indeed measuring 3.65-3.70 volts with no load and are charging to 4.20 volts, your packs are nowhere near their stated capacity.

Mark
So, my batteries bounce back in about 15 -20 seconds to 3.85-ish V per C, and lipos have a flat discharge curve, im not sure when to call it quits.

As for my Turnigy Nanotechs, 3,300 mah, are turnigy's known to be garbage? what batteries do you use?

does 3-4 minutes sound credible for a better battery of 250g ?


And im not interested in super long life, like 300 cycles, im really wanting about 100 or so cycles, without fires, as I do scientific flying. id like the longest flight time possible with out a boat-anchor-battery.
Mar 10, 2015, 08:17 PM
Registered User
Most of us time our flights. If we put back less than 80% AND the power still seems ok, then we can increase flying time---but again always monitoring the power back in. If power noticeably drops while flying, then come on down, you are getting over the edge. If it still takes less than 80% to refill, then the packs are over the hill.
Mar 10, 2015, 10:31 PM
Registered User
Quote:
Originally Posted by Test Pilot Mafia
So, my batteries bounce back in about 15 -20 seconds to 3.85-ish V per C, and lipos have a flat discharge curve, im not sure when to call it quits.
At 3.85 volts/cell resting, you've consumed only 45% of available capacity and your pack is at 55% remaining capacity. If you're only flying for 3-1/2 minutes, you can easily increase this to ~5-1/2 to 6 minutes and still be at or above 3.70 volts/cell.

Again, I'd recommend that you use an appropriate countdown timer (most transmitters have these built-in) that beeps to signal when it's time to land. Simply adjust the timer such that your packs are at or above 3.70 volts/cell resting voltage.

Refer to this chart to get a reasonably accurate assessment of remaining capacity:



More info here:https://www.rcgroups.com/forums/show....php?t=2245385

Mark
Mar 11, 2015, 02:10 AM
CSU Chico, Flight Club
Test Pilot Mafia's Avatar
Thread OP
heres the problem, i bought 3,300 mah turnigy's, but when i time the flights its 4 minutes that reaches 3.6 - 3.7 or abit lower (rested). theres no way i could go to 5-6 minutes.

I tried to stretch it a wee bit past 4 minutes on my timer, and judging buy my volt meter, crash and enormously puffed cell, id say i screwed up. My tricopters tail is in pieces.

hmmmmmmm, which brand are you guys using ?

theres something missing, you guys say at 11.1-ish it'd be ( 3,300 x 0.8 = 2,640 ) but my charger never gets beyond about 1,200 -1,400 mah put back in. my in flight measurements supports the lack of discharge.

were both of my batteries garbage from the day i bought them ? theyve been consistent.
Last edited by Test Pilot Mafia; Mar 11, 2015 at 02:19 AM.
Mar 11, 2015, 08:28 AM
Jaketheone46
Quote:
Originally Posted by Test Pilot Mafia
heres the problem, i bought 3,300 mah turnigy's, but when i time the flights its 4 minutes that reaches 3.6 - 3.7 or abit lower (rested). theres no way i could go to 5-6 minutes.

I tried to stretch it a wee bit past 4 minutes on my timer, and judging buy my volt meter, crash and enormously puffed cell, id say i screwed up. My tricopters tail is in pieces.

hmmmmmmm, which brand are you guys using ?

theres something missing, you guys say at 11.1-ish it'd be ( 3,300 x 0.8 = 2,640 ) but my charger never gets beyond about 1,200 -1,400 mah put back in. my in flight measurements supports the lack of discharge.

were both of my batteries garbage from the day i bought them ? theyve been consistent.
Are you saying your only charging your packs to 11 ish volts?? If so now wonder your only getting 3 minutes and only putting back 1200 mah. I may be misunderstanding you but Turnigy nano s are great packs if used only to there abilities. You only getting 3 min flight and using only 1200 mah almost sounds like your only charging to mid 11ish kinda. I am just kinda lost on reading this thread that your only using 1200mah on a 3300mah pack and ending up around 3.7 volts or so something is not right. What exact voltage are you charging your pack too. If your wanting to be super conservative 4.1volts per cell is fine. And also if your wanting a 100 or so cycles out of a pack you can get that out of a pack fully charging to 4.2 volts per cell as long as your taking care of the packs.
Mar 11, 2015, 08:32 AM
Jaketheone46
you do know a fully charged 3 cell pack is 12.6 volts right??
I'm only asking to try and understand myself.
Mar 11, 2015, 08:38 AM
Registered User
Quote:
Originally Posted by Test Pilot Mafia
So, my batteries bounce back in about 15 -20 seconds to 3.85-ish V per C
Quote:
Originally Posted by Test Pilot Mafia
when i time the flights its 4 minutes that reaches 3.6 - 3.7 or abit lower (rested).
Which is it? You can't have it both ways.

You'll need to provide accurate information in order to enable anyone here to provide any meaningful answers.

Do this:
1) Balance charge your battery, remove from charger and measure pack voltage with a DMM, and then write this number down.
2) Fly your model for 4 minutes.
3) Remove battery from model, wait 5 minutes, measure voltage with a DMM, and write this number down.
4) Come back here and provide the two numbers.
Mar 11, 2015, 08:56 AM
Registered User
ggcrandall1's Avatar
Quote:
Originally Posted by Jaketheone46
Are you saying your only charging your packs to 11 ish volts?? If so now wonder your only getting 3 minutes and only putting back 1200 mah. I may be misunderstanding you but Turnigy nano s are great packs if used only to there abilities. You only getting 3 min flight and using only 1200 mah almost sounds like your only charging to mid 11ish kinda. I am just kinda lost on reading this thread that your only using 1200mah on a 3300mah pack and ending up around 3.7 volts or so something is not right. What exact voltage are you charging your pack too. If your wanting to be super conservative 4.1volts per cell is fine. And also if your wanting a 100 or so cycles out of a pack you can get that out of a pack fully charging to 4.2 volts per cell as long as your taking care of the packs.
The OP is charging his pack to 4.20V/cell (12.6V/pack). When the pack has been flown the pack voltage is down to 11.1V. Voltage is a good indicator of "percentage" of charge, not actual capacity. Since his charger only puts back about 1200mAH into his 3300mAh battery, this indicates the actual capacity of his pack is not 3300mAh but only about 1500mAh. The pack is either worn out or was mislabeled.

I thought mrforsyth explained that earlier but perhaps you missed it.

Glen
Mar 11, 2015, 06:51 PM
Jaketheone46
Quote:
Originally Posted by ggcrandall1
The OP is charging his pack to 4.20V/cell (12.6V/pack). When the pack has been flown the pack voltage is down to 11.1V. Voltage is a good indicator of "percentage" of charge, not actual capacity. Since his charger only puts back about 1200mAH into his 3300mAh battery, this indicates the actual capacity of his pack is not 3300mAh but only about 1500mAh. The pack is either worn out or was mislabeled.

I thought mrforsyth explained that earlier but perhaps you missed it.

Glen
Yea he did but I was kinda wondering if this guy was still confused I guess.
If he is charging fully and only getting 1200 mah out of those packs that's just crazy. I've never seen a pack this much overrated.
I did experience a issue with a 2100 mah venom pack once but I found it on the charger before ever using the pack.
I had bought 2 2100 mah packs and discharged them to 3.7 volts at rest then charged them both. One of them took 1900mah the other 1460 or something around there. I stuck them both on the scale and the problem was there too.
The one pack was much lighter than the other. Venom replaced that pack.
I always charge a new pack by itself the first cycle to make sure it is what it's labeled before I go parallel charging this is info I like to know.
Mar 12, 2015, 01:00 AM
CSU Chico, Flight Club
Test Pilot Mafia's Avatar
Thread OP
i always charge to 12.6 V, puting in 1,200 mAh-ish.

Quote:
Originally Posted by mrforsyth
Which is it? You can't have it both ways.

You'll need to provide accurate information in order to enable anyone here to provide any meaningful answers.

mr forsyth,

Quote:
So, my batteries bounce back in about 15 -20 seconds to 3.85-ish V per C
This was at 3 to 3:30 flight time
Quote:
when i time the flights its 4 minutes that reaches 3.6 - 3.7 or abit lower (rested).
This was trying to stretch to flight time 4 min.

Quote:
Originally Posted by ggcrandall1
.... this indicates the actual capacity of his pack is not 3300mAh but only about 1500mAh. The pack is either worn out or was mislabeled.
Glen
it is definitely not worn out, nor abused. That really leaves them being mislabeled. Performance was uniform from being new till now, If mislabled, that leaves turnigy screwing me twice. How much should a 3s 3,300 mah weigh if a honest battery?

charging them supposedly fully, leaves each cell at 4.16 to 4.18 V. They're pretty predictable always reaching this level at about 1,200mah input. Both batteries discharge down to 11.1-ish volts, before i call it quits.

This is why i ask what brand others use and if this is known to happen to turnigy.
Last edited by Test Pilot Mafia; Mar 12, 2015 at 01:40 AM.
Mar 12, 2015, 05:41 AM
Registered User
ggcrandall1's Avatar
Quote:
Originally Posted by Test Pilot Mafia
i always charge to 12.6 V, puting in 1,200 mAh-ish.
May I ask what charger you are using?

Glen
Mar 12, 2015, 01:20 PM
Space Coast USA
hoppy's Avatar
Quote:
How much should a 3s 3,300 mah weigh if a honest battery?
Go to the Hobby King website and you'll find it there.


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