quote:

ORIGINAL: bill_delong

Generally speaking, a LiPo is considered fully discharged at about 3.0V/cell. In tests that I have performed, I found that the effective punch of most LiPo's tend to drop at around 3.4V/cell under load. The time it takes to drop from 3.4V to 3.0V is extremely fast.

I have read that 3.0V is really a safety buffer and that the actual danger zone is somewhere around 2.5V which suggests that 10V would be a better value to program than 9V, but keep in mind that you are tempting fate at this setting and really aren't going to gain much extra run time, probably just a few seconds if that.

I have successfully drained and recharged cells that have dropped as low as 1.5V but those packs did not last very long, maybe only 100 cycles over a 9 month period.

What you are asking is very doable, but at the risk of shortening the life of your packs. Here is an article that is well worth a read:
http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries


*** EDIT ***
I would suggest using 12V as your LVC setting, then when the LVC hits, let the boat sit for a few moments at rest to let the cells bump up in voltage, then slowly drive your boat back to shore so you don't hit the LVC again.

Another option is to use a 3rd channel on your radio wired into a relay with a small booster pack to help you get back to shore (effectively giving you a spare tank)

quote:

ORIGINAL: srt10

quote:

ORIGINAL: bill_delong

Generally speaking, a LiPo is considered fully discharged at about 3.0V/cell. In tests that I have performed, I found that the effective punch of most LiPo's tend to drop at around 3.4V/cell under load. The time it takes to drop from 3.4V to 3.0V is extremely fast.

I have read that 3.0V is really a safety buffer and that the actual danger zone is somewhere around 2.5V which suggests that 10V would be a better value to program than 9V, but keep in mind that you are tempting fate at this setting and really aren't going to gain much extra run time, probably just a few seconds if that.

I have successfully drained and recharged cells that have dropped as low as 1.5V but those packs did not last very long, maybe only 100 cycles over a 9 month period.

What you are asking is very doable, but at the risk of shortening the life of your packs. Here is an article that is well worth a read:
http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries


*** EDIT ***
I would suggest using 12V as your LVC setting, then when the LVC hits, let the boat sit for a few moments at rest to let the cells bump up in voltage, then slowly drive your boat back to shore so you don't hit the LVC again.

Another option is to use a 3rd channel on your radio wired into a relay with a small booster pack to help you get back to shore (effectively giving you a spare tank)

I really wish some would stop giving BAD BAD advice!
running lipos to 3 volts resting is BAD
specially with FE boating...

quote:

ORIGINAL: guver

quote:

ORIGINAL: srt10

quote:

ORIGINAL: bill_delong

Generally speaking, a LiPo is considered fully discharged at about 3.0V/cell. In tests that I have performed, I found that the effective punch of most LiPo's tend to drop at around 3.4V/cell under load. The time it takes to drop from 3.4V to 3.0V is extremely fast.

I have read that 3.0V is really a safety buffer and that the actual danger zone is somewhere around 2.5V which suggests that 10V would be a better value to program than 9V, but keep in mind that you are tempting fate at this setting and really aren't going to gain much extra run time, probably just a few seconds if that.

I have successfully drained and recharged cells that have dropped as low as 1.5V but those packs did not last very long, maybe only 100 cycles over a 9 month period.

What you are asking is very doable, but at the risk of shortening the life of your packs. Here is an article that is well worth a read:
http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries


*** EDIT ***
I would suggest using 12V as your LVC setting, then when the LVC hits, let the boat sit for a few moments at rest to let the cells bump up in voltage, then slowly drive your boat back to shore so you don't hit the LVC again.

Another option is to use a 3rd channel on your radio wired into a relay with a small booster pack to help you get back to shore (effectively giving you a spare tank)

I really wish some would stop giving BAD BAD advice!
running lipos to 3 volts resting is BAD
specially with FE boating...

Bill is talking about loaded voltage , not resting voltage.

quote:

ORIGINAL: Thunder nut

 Hello all,

Is it ok to run my 30C 4s 5800 lipos with a cut off of 9 volts, becuase if I run them with a cut off of 12 volts my speed control won't allow me to run past half throttle and it cuts out. I reset the speed control to the 11.1 volt setting with a 9 Volt cutoff and it runs at full throttle, must be an issue with this chespish speed control?


Cheers

quote:

ORIGINAL: diy-pro

Guver is right you may want to get a new pack ''BUT'' if you pack is running fine with good run times with the lvc set at 9(im guessing there is no inbetween 9-12 because you would have tried) than get a secondary low voltage buzzer. Why Bill recommended leaving your lvc at 12 when its not working for you idk lol. And ouuuuuuu good stuff srt10 ive been looking a table like that. But those would be the voltages off a high quality pack with no voltage sag or memory damage right? What can he do than srt10 to ensure hes not over discharging his pack beyond the nominal 14.988V 80% discharged 4S pack?

quote:

ORIGINAL: srt10

I really wish some would stop giving BAD BAD advice!
running lipos to 3 volts resting is BAD

quote:

ORIGINAL: Thunder nut

The problem is with the standard setup of my Hobby king Libero, standard prop, plus a 150 amp speed control and 30C 4S 5800 lipo the boat will not go from stationary to full throttle , it just pulses once and cuts out, if accelerate slowly to about half throttle it runs fine, as soon as I go a little past half throttle, weather I dump it or progressively go past half throttle the boat cuts out immediately, I can then take it up to half throttle slowly and it will do the same thing again, this is with the speed control set to 4S 12 volt cut off, so I tried setting the speed control at 3S 11.1 Volts and 9Volts cut off and it runs fine, I do notice as the voltage drops during the run the boat gets slower and then I stop and use another lipo, I just want to know if running it this way is goping to ruin my lipo's?

I have bought a hobby king 12V low voltage alarm, waiting for it to arrive.

Cheers 

quote:

ORIGINAL: guver

There are many ways to determine what's damaging to a lipo cell , and a number of ways to hurt them. For figurin' out if running them will hurt them there are a couple of questions or ''ifs''

IF they aren't getting over 120 deg F by the end of the run then ok (no abnormal damage)
IF they come out of the run resting at over 3.5 volts/cell then ok (no abnormal damage)

ps. At least you know that low voltage is the trouble , right? It would be nice to know what that voltage is (at the cell taps during the run) You could very well have a wire,connection,solder issue causing a false low voltage seen by the esc.

quote:

ORIGINAL: srt10

yeah lipos can run upto 140* without damage
and about the only thing I've found to damage them is to run them to low in capacity..

quote:

ORIGINAL: bill_delong

quote:

ORIGINAL: srt10

yeah lipos can run upto 140* without damage
and about the only thing I've found to damage them is to run them to low in capacity..

you've got this backwards, heat causes far more irreparable damage than voltage. Here are the recommended target temps I try to limit with my electronics:

Battery < 120°
ESC < 140°
Motor < 160°

In a perfect world you want your LiPo's to be as close to 33° as possible along with a sustained voltage of 3.8V/cell.... you want to minimize the amount of time away from these two benchmarks to get the longest life of your battery packs.

quote:

ORIGINAL: bill_delong

quote:

ORIGINAL: srt10

I really wish some would stop giving BAD BAD advice!
running lipos to 3 volts resting is BAD

Not trying to get into a flame war but if you properly read my advice then you would've understood what I had to say. Please re-read my thoughts and maybe you won't be so quick to judge.

If you followed the link to the article I refereced earlier, then you would've read about the reasons why 3.0V is a safety buffer and that shunts slowly form over time (typically weeks) at voltages below 2.0V and there is no danger in over discharging, but if shunts are formed, then the danger occurs upon recharging the battery.  This is why many chargers will not charge a pack below 3.0V/cell. You can bypass this safety feature by boosting the cells in NiMh mode, but it's not a good idea to do this for more than 30 seconds so you don't overcharge a good cell in the case one of the cells has died and won't take a charge.

I know I shared a lot of information for you take in all at once, so please take the time to re-read several more times before you come back with another synde remark, thanks.

In this particular case for the OP, there is no opporunity for shunts to form and no immediate danger is presented if he draws 4S down to 9V, but I cautioned him that doing so will significantly reduce the lifespan of his pack.