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HelicopterMain Discussion › Safe low voltage lipo. Are we selling ourselves​short coming down at 3.8v per cell ?
03-12-2017 07:29 AM  8 months agoPost 1
joshreynolds777

rrApprentice

Willis, Tx

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I'm wondering about the ending voltage of the lipos. I feel like I'm selling myself short taking them out at 3.8v when 3.7v is half. 3.2v is safe. 3.0v is bad. So I feel like I'm loosing like two solid minutes of flight time at least by bringing it down at 3.8. Sometimes 3.88v. You agree ? Disagree? What voltage do y'all come down at?

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03-12-2017 02:20 PM  8 months agoPost 2
rpat

rrElite Veteran

Weirton, W. Va.

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I try to quit at 3.0 volts. Seems to work for me.

I was wrong on that statement. I go to 30% not 3.0 volts.

trex 700fbl cal30,minititan,, trx600fbl,trex250,logo 500,Velocity N2

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03-12-2017 02:56 PM  8 months agoPost 3
gmcullan

rrKey Veteran

Southbridge, MA

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Due to their cost, I'm very conservative in the way I handle my LiPos. I use 3.6 as my cut off point. I never charge faster than 1C, and my more expensive 6 cell packs are charged at only 1/2C.

Wimpy? Yes, but I average 500+ charge/discharge cycles for most of my LiPo packs.

Gerry Cullan,
Gaui 200, 255; T-Rex 250, 450 SE & SA, Mini-Titan, Blade 450

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03-12-2017 03:19 PM  8 months agoPost 4
DennisH

rrApprentice

Baton Rouge​Louisiana USA

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I try to quit at 3.0 volts. Seems to work for me.
I would be buying batteries every other flight running them down to 3.0v's.

3.80v's to 4.20v's are your normal LiPo cell operating range.

Anything over or under, you will be buying batteries every month.

Dennis

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03-12-2017 03:30 PM  8 months agoPost 5
Dan Minick

rrKey Veteran

Columbus, WI

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I set my cutoff at 3.3v using Kontronik ESC's and Thunder Power packs. Works great, I have packs that are 6 years old. When the cell draws to 3.3v under load I land and usually the packs recovers a tenth or two before I charge them again.

Team Synergy, Team FBL Rotors-------if its not broke...it will be!

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03-12-2017 04:48 PM  8 months agoPost 6
DennisH

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Baton Rouge​Louisiana USA

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I set my cutoff at 3.3v using Kontronik ESC's and Thunder Power packs. Wors great, I have packs that are 6 years old.
I might have to try the Kontronik's out. I use Pulse and GenAce, my alarm goes off @ 3.8v's, by the time I land, I am around 3.6v to 3.7v. I don't have any issues at these settings. When charging, my 406 cuts the balance charge off @ 4.17v to 4.19v's.

I might try 3.7v cut off and see what happens. But batteries averaging a little over $100.00 each, I try to be careful.

Dennis

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03-12-2017 06:51 PM  8 months agoPost 7
Andy from Sandy

rrElite Veteran

Bedfordshire, UK

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I would say what is more important is the low volt under load.

The longer you fly the lower this figure. If the pack is not strong enough for your application then it will get damaged.

Do you have a figure for that. If the voltage sags too much I believe that is when the packs start to puff.

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03-12-2017 10:36 PM  8 months agoPost 8
DennisH

rrApprentice

Baton Rouge​Louisiana USA

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I would say what is more important is the low volt under load.
The longer you fly the lower this figure. If the pack is not strong enough for your application then it will get damaged.
Do you have a figure for that. If the voltage sags too much I believe that is when the packs start to puff.
Again, my figure is anything close to 37.5v's per cell. In this area or "even" lower, you risk damaging your battery.

I have my alarm set up to go off @ 3.80v's. I usually land within 30 seconds or so after seeing the lamp flashing.

I always check the IR's of the battery cells while charging. You can determine when your battery is going south watching the IR's.

There are plenty of Videos on YouTube to watch showing how people charge their LiPo's. If you watch a few of them, you will see a pattern of the correct way to charge them.

Some batteries tend to puff, some will go dead real quick, but some will last several more weeks.

Always put your battery in storage mode if your not going to use them for a few days or so. Storing you LiPo at peak charge damages the batter as well.

JMO, Dennis

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03-12-2017 11:04 PM  8 months agoPost 9
Heli_Splatter

rrElite Veteran

USA

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I shoot for 3.6-3.7 under load on telemetry. I am talking about 6S 5000mahr batteries.

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03-12-2017 11:15 PM  8 months agoPost 10
Ace Dude

rrProfessor

USA

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I made this chart a while back. It applies to standard 4.2V/cell LiPos.

  

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03-12-2017 11:31 PM  8 months agoPost 11
DennisH

rrApprentice

Baton Rouge​Louisiana USA

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Nice chart!

Thanks for posting, Dennis

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03-13-2017 12:39 AM  8 months agoPost 12
doorman

rrProfessor

Sherwood, Arkansas

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Proper Amount Out....

There are a lot of different ways that people use their batteries..
Since I began using lipos back in the mid to late 90's, I was told to not let them go down past 20% capacity.. if you look at Aces chart you can see we agree... I set my timer lower then expected for the first flights.., when I recharge, I check to see how many mah I am putting back in... when I am happy with my timer, at the end of a flight I am putting back 75-80%. On a 5000 pack 4000 back in is 80% ...
I am not sure how tge batteries survive if letting the voltage drop to 3.0!! The way I do it, mine are 3.65-3.75 everytime...
I would much rather have a 30sec shorter flight, then to push the batteries harder then I do...

Stan

AMA 2918-Team JR, Spin Blades, East Coast Scale Helicopter,Castle Creations

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03-13-2017 02:50 AM  8 months agoPost 13
doorman

rrProfessor

Sherwood, Arkansas

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Proper Amount Out....

There are a lot of different ways that people use their batteries..
Since I began using lipos back in the mid to late 90's, I was told to not let them go down past 20% capacity.. if you look at Aces chart you can see we agree... I set my timer lower then expected for the first flights.., when I recharge, I check to see how many mah I am putting back in... when I am happy with my timer, at the end of a flight I am putting back 75-80%. On a 5000 pack 4000 back in is 80% ...
I am not sure how tge batteries survive if letting the voltage drop to 3.0!! The way I do it, mine are 3.65-3.75 everytime...
I would much rather have a 30sec shorter flight, then to push the batteries harder then I do...

Stan

AMA 2918-Team JR, Spin Blades, East Coast Scale Helicopter,Castle Creations

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03-13-2017 04:31 AM  8 months agoPost 14
DennisH

rrApprentice

Baton Rouge​Louisiana USA

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Proper Amount Out....
There are a lot of different ways that people use their batteries..
Since I began using lipos back in the mid to late 90's, I was told to not let them go down past 20% capacity.. if you look at Aces chart you can see we agree... I set my timer lower then expected for the first flights.., when I recharge, I check to see how many mah I am putting back in... when I am happy with my timer, at the end of a flight I am putting back 75-80%. On a 5000 pack 4000 back in is 80% ...
I am not sure how the batteries survive if letting the voltage drop to 3.0!! The way I do it, mine are 3.65-3.75 everytime...
I would much rather have a 30sec shorter flight, then to push the batteries harder then I do...
Stan
I quoted your message as it's showing up twice on my puter.

Stan, if you're doing that with your batteries, GREAT.

Which batteries are you using?

I could never put back 4000mAh's in a 5000mAh battery.

You state your battery level after flying is 3.65-3.75 which you might as well say is perfect.

I need to figure out your secret to drain a LiPo as stated above, then replace 4000mAh's.

That's Great.

What type of Heli are you flying? Weight? I am trying to figure it out.

Thanks,
Dennis

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03-13-2017 12:42 PM  8 months agoPost 15
rpat

rrElite Veteran

Weirton, W. Va.

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I have gone down to 3.0 volts forever and have never had a problem . you guys that are stopping at 3.8 must be flying only about 3 to 31/2 minutes. Is that correct?

trex 700fbl cal30,minititan,, trx600fbl,trex250,logo 500,Velocity N2

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03-13-2017 12:49 PM  8 months agoPost 16
Heli_Splatter

rrElite Veteran

USA

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I would like to know the source of the data/formula to create the table.

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03-13-2017 01:34 PM  8 months agoPost 17
KevinB

rrKey Veteran

Saskatoon,​Saskatchewan, Canada

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On a 5000 pack 4000 back in is 80% ...
Maybe....and only when they are new. The true capacity of a battery isn't necessarily what it says on the label. I always run a new battery through a few analyze cycles on the charger first to determine it's real capacity.

With every cycle, it will lose a small amount of capacity as well. I have some 5 year old 5000mah packs that only have a usable capacity of 4000mah now. As long as you fly to the lower capacity limit, they still work fine.

Checking the cell voltages after the flight is the only way to know if you are over-discharging or not. My target voltage is 3.77v/cell and I fly by mah used rather than time.

Whenever I see the after-flight cell voltages less than 3.77, I drop the battery's capacity setting in my VControl. It actually has an app to do that automatically.....I just haven't taken the time to set it up.

KevinB

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03-13-2017 01:35 PM  8 months agoPost 18
Ace Dude

rrProfessor

USA

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The basis for the data is the fuel table used by the PowerLab chargers which have been around for years.

  

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03-13-2017 05:37 PM  8 months agoPost 19
Pistol Pete

rrProfessor

Seffner, FL

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Ending Voltage vs Loaded Voltage

I'm wondering about the ending voltage of the lipos. I feel like I'm selling myself short taking them out at 3.8v when 3.7v is half. 3.2v is safe. 3.0v is bad. So I feel like I'm loosing like two solid minutes of flight time at least by bringing it down at 3.8. Sometimes 3.88v. You agree ? Disagree? What voltage do y'all come down at?
I've found that using a ($5) lipo alarm set at 3.6V, has pretty much used between 75%-80% of batts capacity. The type you plug into your balancer lead and will chirp when any-one-cell reaches set voltage.

Whatever you are charging back into the batt will determine if you're shorting your flight or not.

~~Enjoying the hobby one flight at a time~~

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03-13-2017 05:47 PM  8 months agoPost 20
Dr.Ben

rrMaster

Richmond, VA, USA

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I have gone down to 3.0 volts forever and have never had a problem . you guys that are stopping at 3.8 must be flying only about 3 to 31/2 minutes. Is that correct?
Set ups vary. My ultralight low(er) rpm 3D models fly for 6:45 to 7:30 and come down at 3.8 to 3.85 V/cell.

The greatest risk from pushing the limits of low cell voltage is that a weaker cell may go noticeably lower than the rest. When weak cells are pushed low, they often get hot and may readily puff. Landing with 5/6 cells at 3.8 and a weak cell at 3.7 is no big deal and might go unnoticed. Fly that same pack deeper into its capacity such that the five cells are about @ 3.0/cell, and the weak one is going to be hot and in the 2's. If you are the type that closely watches cell voltages post flight and during charge, this risk won't bite you. Get careless, and it will. I haven't worn that T-shirt, but I have friends who have.

Ben Minor

Team Synergy Team Futaba Team Kontronik USA
Progressive RC

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HelicopterMain Discussion › Safe low voltage lipo. Are we selling ourselves​short coming down at 3.8v per cell ?
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