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What is damaging low voltage to LiPo?

Maverick3n1

Senior Heliman

San Diego, CA

I have lipo's that discharged to approx 3.33 per cell... Is that still in acceptable range? Easy to lose track of power when you are testing and making adjustments constantly.. I noticed my head speed started to drop without adjustments and that shot a red flag to throw it on the charger.. not sure what I'll put back in, but I know I got the 3s pack down to like 9.9-10v.

08-14-2009 Over year old.
HOMEPAGE  
Maverick3n1

Senior Heliman

San Diego, CA

Well it was a 3s 2200 mah battery, and I just put 2222 mah in it... hope it's ok.. =( Only used the battery twice maybe...

08-14-2009 Over year old.
HOMEPAGE  
Kamikaze Pilot

Senior Heliman

Marion, Illinois- USA

Its a tough and expensive lesson to learn but 3S min. voltage is 11.1V. I abused mine when I first got started...then $150.00 later I learned. It will charge back up to max. but when you use it, it will die within a minute. Time to break out the wallet

A.T. Quad-Rave 450-Trex 550

08-14-2009 Over year old.
Maverick3n1

Senior Heliman

San Diego, CA

"It's science, Holmes" to coin a phrase... What a battery can handle should be science based and fairly reproducable in results. Granted, not every cell is exactly the same, the science behind it is, and therefor there should be an average standard. You say you can't drop below 11.1v, but if that were the case, why would the battery be called a 2200 mah if you get to 11.1v at say 1800mah? Someone else told me in a PM that I'd be fine as long as under load I didn't hit 2.75v per cell. Others say as long as you don't go below 3v per cell with no load. Everyone has a different answer, and each one contradicts the other. LiPo's aren't new technology anymore. I'm sure there is someone out there who had the financial ability, and the desire to burn the money in attempts to find the limitations of these batteries, and how far you can draw or overdraw the battery before it doesn't function as intended. They sat there with a collection of chargers, charging and discharging batteries at different voltages, different rates etc.. Anyone?

You tell me that 11.1v is the max limit, and if you pass that, the battery is trash. So if I discharge that battery that I just discharged to 10v and re-charge it, and I draw 2200 mah out of it a second time, does that make you wrong? Why is it that the battery fail safe on ESC's standard is 3v per cell, if your cells are destroyed at 3.6v? Wouldn't they set the fail safe at 3.7v per cell? If you've already destroyed your battery at 3.0v, why setup a fail safe to cut power completely... if the battery is trashed, at least let me glide/auto my helicopter/airplane down and recover it, even if I have to throw the battery away.

08-14-2009 Over year old.
HOMEPAGE  
Kamikaze Pilot

Senior Heliman

Marion, Illinois- USA

Oh, I'm sorry, I didn't realize you wanted an actual scientific explaination. Just follow this formula:
%cell/output@nominalVxrms+2=11.1

In other words: experience= tribal knowledge

A.T. Quad-Rave 450-Trex 550

08-14-2009 Over year old.
TJinGuyrrProfessor - Socorro, NM - USA -

1) You can safely discharge a lipo to 100% if you discharge it very slowly. We use these in rc helicopters and we discharge them very quickly, that is hard on them and if you let the voltage drop too far, the voltage under load can drop into the mid-low 2V range. That will damage a lipo. So we are really watching the resting voltage and % capacity used as a method of keeping the under load voltage acceptable.

2) Look at a lipo discharge graph and you will see why we only discharge lipos to 80% of the rated capacity, usually resulting in a resting voltage around 3.7V.

3) When you use a balance charger, some of the mAh put back into the battery was bleed off for balancing. This can be as high as 10% of the total mAh.

4) Batteries are not rated for their total capable capacity but rather a capacity under certain circumstances. So it is very possible to discharge more than the rated capacity of a lipo.

Hope these thought help.

- Chris

Team New Mexico
TJinTech

08-14-2009 Over year old.
HOMEPAGE  
Maverick3n1

Senior Heliman

San Diego, CA

So if the ESC has a fail safe at say 3v, wouldn't that be cutting voltage off if under load the voltage drops below 3v per cell? Why wouldn't you be able to use that as your safety line? My resting state of my battery was at 3.3v per cell, but if under load, say it dropped to 2.9v per cell, wouldn't the ESC do it's job and cut power?

08-15-2009 Over year old.
HOMEPAGE  
stanc

Key Veteran

Conroe, TX

Lipos charge to 4.2v per cell and when a load is applied they drop to 3.7v per cell. I use a 3S pack in my TX and the voltage after a charge is 12.6 and stays above 12V for quit some time, I'll charge the pack when the voltage gets to around 11.6v. Since the TX doesn't apply much of a load, the voltage stays way above 11.1 or 3.7 per cell.
I've never seen a Lipo cells resting voltage at 3.3, unless that is the voltage after a flight.

Maverick3n1
So if the ESC has a fail safe at say 3v, wouldn't that be cutting voltage off if under load the voltage drops below 3v per cell? Why wouldn't you be able to use that as your safety line? My resting state of my battery was at 3.3v per cell, but if under load, say it dropped to 2.9v per cell, wouldn't the ESC do it's job and cut power?
I sincerely hope you don't have your ESCs Cut Off Voltage set at 3v per cell, unless you want to crash. The LVC is fine for a plane, since planes can glide. The LVC should be set as low as possible so the ESC won't cut off and the Brake Disabled.

If I were you I wouldn't worry about what the voltage is, but instead fly your heli for say 3 minutes and then charge the pack. See what Mah it took back and if it was say 50%, then fly it for 4 minutes and then charge it. When you find the flight time where the pack took 70 to 80%, then don't exceed that amount of time.
I've been flying Lipos for a long time and that is the way I and most others go about taking care of our packs and it works. If the pack is not over discharged, then the voltage will take care of itself.

Stan
2- Logo 500
Ion X2
eAvro90

08-15-2009 Over year old.
Maverick3n1

Senior Heliman

San Diego, CA

I've been in the process of trying to get my heli up and running, so I haven't had any solid flight to time with it yet. It's been a "Spin up the head.. spin down.. figure out where the vibration is.. spin up, spin down.. figure out why something else is happening.. spin up, spin down.. damn, another thing wrong" type of path with this bird so far. It's flying now, but the control is so sloppy, I'm considering doing an overhaul and replacing all remaining plastic parts in the head with aluminum. I just hate to do that if it's not going to fix the sloppyness. I'm used to my bigger bird with digital servos. The head holds rock solid, even being plastic, but of course it's all much thicker plastic than an electric MX-400. That's how I accidently discharged the battery as low as I did, as I was working on fixing issues, and it had been taken apart and rebuilt a few times on the same charge as I had only 30 seconds here, a minute there, and most of it never even left the ground, nor was it at full head speed.

08-15-2009 Over year old.
HOMEPAGE  
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What is damaging low voltage to LiPo?

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