Lipo Voltage Question

[Brushless Moose]

What is the lowest safe voltage for a lipo cell after being taken out of the truck? Is the 3.0v/cell under load, or resting?

[freelife04239]

well thay say 3.6 is as low as you should go but I hear other stuff all the time i know i run my packs down to 7.1, 7.2 all the time I have also run down to as low as 6.8 befor and never had a problem. But now i have been told if i stop them at 7.2 that im going to get more use out of them in the long run so best bet is to read up this is some good reading on lipo read this it should tell you all you need to know

http://www.jconceptsevents.com/events/clash/Lipos.pdf

[Revo¹]

3.0V is the default setting on the MMM, but I wouldn't go any lower than 3.2 personally.

[freelife04239]

the 3V cut off is under load but to play it safe 3.2 is better just because if it drops to 2.9 under load then your hurting your batter and taking life away every time it his 2.9

[Hughes500Bob]

Kong Power 2.2 volts per cell ...so they say!
3.0v/cell is under load. I think Load Voltage Cutoff.

Under 3.7 resting is bad. A true "resting" is 12 hours after use.
4.20v = 100%
4.03v = 76%
3.86v = 52%
3.83v = 42%
3.79v = 30%
3.70v = 11%
3.6?v = 0%

Capacity below 3.7v "resting" is not usable.

Beter batteries today can be discharged safely to lower voltages .... but cheap batteries certainly can not.

Here is a link to Runryder forum (R/C helis) and an older thread. http://runryder.com/helicopter/t438903p1/
Look at the discharge curve shown in the first thread post. Take a look at the FMA Direct link and check out section 2 of the guide/handbook .... yes it is a 2005 document, but they do keep it up to date.

The BIG thing you will find is once a lipo goes into lower voltages the true danger is one cell getting lower than the rest. You will also see that lipo temp is another indication of charge state. Once it gets to the fall off point the temperture goes up rapidly.

A gallon of nitro fuel is $40 in my parts. If you are running $40 packs and get as much run time as the nitro while abusing them .... then I guess it makes no difference!! If you are running $100 plus dollar packs it makes sense to take care of them to get your money's worth.

[Brushless Moose]

conflicting opinions... When I pull them out of my truck, they are at 3.4 volts per cell. is that too low? They sit for about an hour, and then are recharged.

[freelife04239]

yea that must be with the defalt setting on mmm if you go in and turn it up to 3.2 it will get you up to 7.1 0r 7.2 when you pull the battery out. This cuts down on run time but gives you more life from your lipo

[Hughes500Bob]

What brand and size lipo?
How many mAhs are you putting back into the packs?
If you are putting more than 85% of their capacity back during charge you are running them too low. Yeah we all go too low occasionally and if it really is once every 50 runs it probably won't hurt too much.

[Brushless Moose]

So, you are saying that they should be 7.2 volts or more when they come out? uh oh. mine come out at like 6.6-6.8

[Deahttub]

So, you are saying that they should be 7.2 volts or more when they come out? uh oh. mine come out at like 6.6-6.8

Mine are the same Moose......if I charge my batteries right after a run it shows like you 6.6 to 6.8 volts (2 cells) but If I wait awhile they rebound on their own to 7.4(ish)....do you charge your batteries right after a run?

[freelife04239]

well on a 9000 mah battery i have recharged 7000mah-7500mah a few times dose that sound like im running mine down to low

[Hughes500Bob]

well on a 9000 mah battery i have recharged 7000mah-7500mah a few times dose that sound like im running mine down to low

You are doing great! 7650 would be 85%

True "resting" voltage is 12 hours after use.

[freelife04239]

You are doing great! 7650 would be 85%.

thanks im bad with math lol

[freelife04239]

yea coming out at 7.2v is best

[Bocephus]

3.0volts is the lowest, but you better stop at 3.2volts per cell, otherewise you run the risk of losing your battery.

[BrianG]

I set my LVC cutoff such that the battery voltage is around 3.6v/cell after around 20 minutes unloaded. If it's lower than that, I raise the LVC, and vice versa.

[2IS]

I think some people are being overly cautious. 3.2v/cell is a good and safe number. 3.0 would be fine in a perfect world, but many times cells don't dicharge at the same rate, so choosing 3.0v per cell could cause a cell to drop well below that if it discharges a bit faster than the other cells. Remember tha the ESC monitors overall voltage, not individual cells. I have yet to develop a bad cell using a 3.2 cutoff and my 2S packs come out around 6.8 volts after hitting LVC.

[1stGenCRXer]

You guys get really, really overly cautious.

A LiPo cell's nominal voltage is 3.7 VDC per cell. Full charge is 4.2 VDC/cell and maximum discharge is 3.0 VDC/cell. If you have your LVC set for 3.0 V/cell under load, your resting voltage will be above 3.0 V/cell IF YOU STOP WHEN LVC KICKS IN. Not, "oh, LVC just kicked in, one more jump, and then let me drive the truck back to me so I don't have to walk over to it."

The 85% rule with aircraft started with a safety measure to make sure guys could land their models while they still had enough juice, and above the 3.0 V/cell minimum, since a LVC would cause crashes.

The key to getting long life from your cells is to treat them well. Deep discharging breaks down the chemical composition, causing heat, and damages the cell. Too heavy of a load [too many amps] leads to deep discharging, heat, and damages the cell. Charging at too high of a rate, causes heat, etc. Don't push the limits of your battery's rating and you'll get as many, or more, cycles from your cells than following any other combinations of snake-oil "rules for lipo's".

If you feel better by bumping your LVC to 3.2V/cell, it's your money, and you're definately not hurting the battery by doing so. Setting your LVC to 3.7V/cell is only going to take away about 60% of your usable capacity, and not gain you any more cycle life.

[Mammuth]

You guys get really, really overly cautious.

A LiPo cell's nominal voltage is 3.7 VDC per cell. Full charge is 4.2 VDC/cell and maximum discharge is 3.0 VDC/cell. If you have your LVC set for 3.0 V/cell under load, your resting voltage will be above 3.0 V/cell IF YOU STOP WHEN LVC KICKS IN. Not, "oh, LVC just kicked in, one more jump, and then let me drive the truck back to me so I don't have to walk over to it."

You are right stating that but the built in erevo LVC when kicks in let you drive the car for couple of seconds via that peculiar on-off mode just for the will to let the car come to you by itself. It is intended just for that will, after that magic moment you will see the car completely stopping, also that on-off " fuel reserve " has gone and that's just the moment to walk over it cause the LVC is telling : " c'mon lazy man, come here fatboy ! "

[rupert]

Some are still confusing a loaded lvc setting with resting voltage. The chart that Hughes500Bob posted is right on the mark and there's not a lot of springback between 15 minutes and 15 hrs. He's also correct in that there isn't much usable capacity after 3.7 resting voltage. This can be anywhere from 3-3.5 volts on a particular lvc and set-up. It can be as much as 2-3.5 volts/cell.

I personally use 3.5 resting, but again there isn't a whole lot of capacity below 3.7 resting volts. It is not a great idea to use the lvc to determine "when to stop driving" unless it is set quite high.

First graph is a lipo that essentially can have it's lnv set anywhere from 3.5-2.5 volts. As you can see it is nearly a srtraight down drop (no capacity) the discharge is then stopped. Then , depending upon when you measure the voltage determines the reading you get. The samples are every second and notice that after 8 minutes or so there isn't alot of voltage springback , but the true resting voltage (after setting) for a long time is what we are after when determining remaining capacity. Second Graph is NIMH batts.

[1stGenCRXer]

The reason I worded it that way is because I've seen people try to drive around a LVC by changing their driving habits and avoiding starts from a stop, and keep rolling slow so the LVC isn't stopping the truck, since the load isn't as high. All this does is discharge the cells deeper without hitting the LVC voltage under load, instead it brings the cells down to the LVC almost at resting voltage.

[rupert]

This is true, at or near zero current the lvc and the resting voltage can be nearly equal. The higher the current the more differential between the two.