Go Back  R/C Tech Forums > General Forums > Electric Off-Road
Lipo cutoff, Voltage or Capacity >

Lipo cutoff, Voltage or Capacity

Lipo cutoff, Voltage or Capacity

Reply

Old 01-03-2009, 07:29 PM
  #1  
Tech Fanatic
Thread Starter
iTrader: (20)
 
brofroe's Avatar
 
Join Date: May 2008
Location: Cleveland, TN
Posts: 877
Trader Rating: 20 (100%+)
Default Lipo cutoff, Voltage or Capacity

I read most places that lipo cutoff should be 3.0 volts per cell maximum. I have also read in one place to only discharge them to like 80% of capacity. Which is right?? I'm new to electric much less lipo. I ran my 6s 5000mah pack to @ 3.5 volts per cell the other day and it still had plenty of punch. When I charged it it took 3980 mah to charge it, which is right at 80%. Some of you pro's staighten me out please If you do use voltage is it under load 3.0 volts or what? I currently have my MMM set at 19volts which is 3.17 volts per cell. HELP please, I don't want to waste my battery.
Thanks in advance.

Last edited by brofroe; 01-03-2009 at 08:58 PM. Reason: typo
brofroe is offline  
Reply With Quote
Old 01-03-2009, 09:13 PM
  #2  
Super Moderator
 
Join Date: Oct 2007
Location: Rochester Hills Michigan
Posts: 7,232
Default

They are both right, just saying different things. Need to stay above 3 volts per cell minimum. Go below this the battery may not charge back up. Immediate failure concern.

The 80% discharge comes before that, and is recommended for longer battery life and fewer out of balance issues. More of a long life issue.

Last edited by Dave H; 01-04-2009 at 07:07 AM.
Dave H is offline  
Reply With Quote
Old 02-16-2009, 06:28 AM
  #3  
Tech Fanatic
Thread Starter
iTrader: (20)
 
brofroe's Avatar
 
Join Date: May 2008
Location: Cleveland, TN
Posts: 877
Trader Rating: 20 (100%+)
Default

OK I've set my LVC to 3.5 volts per cell and don't even ever reach the LVC point. However i'm still using over 80% of capacity. In fact, once I recharged to over capacity. Info please.
brofroe is offline  
Reply With Quote
Old 02-16-2009, 06:39 AM
  #4  
Tech Champion
iTrader: (96)
 
whitrzac's Avatar
 
Join Date: May 2008
Location: WI
Posts: 5,794
Trader Rating: 96 (100%+)
Default

Originally Posted by Dave H View Post
They are both right, just saying different things. Need to stay above 3 volts per cell minimum. Go below this the battery may not charge back up. Immediate failure concern.

The 80% discharge comes before that, and is recommended for longer battery life and fewer out of balance issues. More of a long life issue.
common misconception, damage happens under 2.5v


don't worry about the batt, leave the lipo cutoff at 3.5 and your good to go.


the 80% is so it "supposedly" puts less stress on the batt
whitrzac is offline  
Reply With Quote
Old 02-16-2009, 07:45 AM
  #5  
Tech Addict
iTrader: (11)
 
Miller_Time's Avatar
 
Join Date: Jan 2008
Location: Charlotte, NC
Posts: 678
Trader Rating: 11 (92%+)
Default

Originally Posted by brofroe View Post
OK I've set my LVC to 3.5 volts per cell and don't even ever reach the LVC point. However i'm still using over 80% of capacity. In fact, once I recharged to over capacity. Info please.
It sounds like your LVC is either not turned on, not set correctly, or not working properly then. 3.5v per cell should be a pretty early cut off and if you still can put back in more than it's listed capacity something is wrong. It's also possible that the cells are very much under-rated and their actual capacity is higher than listed, but to be that far under-rated would be suspect.

If you have a digital multimeter, check the total pack's voltage next time after a run, and divide that by the number of cells. If that's lower than 3.5v then your LVC is not on or not set at 3.5 volts.

It's important that you check it as soon as possible after a run and with no load. The cells will "bounce back" and gain some voltage as they sit without a load. Also the cells will drop under a heavy load and quickly regain some voltage even before you can get a meter on them, so the actual voltage under load would have been lower than what you read.
Miller_Time is offline  
Reply With Quote
Old 02-16-2009, 11:12 AM
  #6  
Tech Regular
iTrader: (10)
 
Join Date: Mar 2008
Location: Plainfield, IL
Posts: 458
Trader Rating: 10 (100%+)
Default

Dont use the LVC to tell your runtime at all. Set it at like 3.2 which is still safe. If you set it to high and you punch the throttle the voltage could drop that low depending on how much juice is left and the ESC is cut power while your driving. Use a timer and find the magic time that keeps in at the safe 75-80% range.
Speed_Freak_039 is offline  
Reply With Quote
Old 02-16-2009, 11:34 AM
  #7  
Tech Master
iTrader: (17)
 
rearviewmirror's Avatar
 
Join Date: Nov 2008
Location: Melbourne / Austin
Posts: 1,844
Trader Rating: 17 (100%+)
Default

3.0 is safe... Damage begins < 2.7v per cell.
rearviewmirror is offline  
Reply With Quote
Old 03-23-2011, 09:32 AM
  #8  
Tech Initiate
 
djroberts's Avatar
 
Join Date: Mar 2011
Posts: 22
Default

It also seems like it would depend on the performance of the battery. For instance setting LVC at 3v on a Thunder Power would go way beyond the 80% rule due its ability to hold voltage. They hover around nominal voltage for a long time then slowly decrease to about 3.5. After that the voltage tanks and the battery is almost dry.

At 3.5v however its still got some capacity left but on cheap batteries that don't hold their voltage it may cut out too early.

I'm operating on uneducated logic here so please correct me if I'm off base.
djroberts is offline  
Reply With Quote
Old 03-23-2011, 10:56 AM
  #9  
Super Moderator
 
Join Date: Oct 2007
Location: Rochester Hills Michigan
Posts: 7,232
Default

Originally Posted by djroberts View Post
It also seems like it would depend on the performance of the battery. For instance setting LVC at 3v on a Thunder Power would go way beyond the 80% rule due its ability to hold voltage. They hover around nominal voltage for a long time then slowly decrease to about 3.5. After that the voltage tanks and the battery is almost dry.

At 3.5v however its still got some capacity left but on cheap batteries that don't hold their voltage it may cut out too early.

I'm operating on uneducated logic here so please correct me if I'm off base.
To some extent yes. Itís mostly about maintaining sufficient resting voltage from all of the data I have seen. A lot depends on the load the battery is under, how much the voltage is sagging under load. This impacts the actual state of discharge. Higher amp discharge rates (relative to battery size) can tolerate a lower voltage under load. Conversely lower loads need a higher shutoff.
Dave H is offline  
Reply With Quote
Old 03-23-2011, 11:02 AM
  #10  
Super Moderator
iTrader: (31)
 
racer1812's Avatar
 
Join Date: Nov 2008
Location: RIP 'Chopper', 4/18/13 miss you bud:(
Posts: 15,058
Trader Rating: 31 (100%+)
Default

Originally Posted by Dave H View Post
To some extent yes. Itís mostly about maintaining sufficient resting voltage from all of the data I have seen. A lot depends on the load the battery is under, how much the voltage is sagging under load. This impacts the actual state of discharge. Higher amp discharge rates (relative to battery size) can tolerate a lower voltage under load. Conversely lower loads need a higher shutoff.
I understand this but I'm betting you get some questions...
racer1812 is offline  
Reply With Quote
Old 03-23-2011, 11:04 AM
  #11  
Super Moderator
 
Join Date: Oct 2007
Location: Rochester Hills Michigan
Posts: 7,232
Default

Originally Posted by whitrzac View Post
common misconception, damage happens under 2.5v


don't worry about the batt, leave the lipo cutoff at 3.5 and your good to go.


the 80% is so it "supposedly" puts less stress on the batt
Originally Posted by rearviewmirror View Post
3.0 is safe... Damage begins < 2.7v per cell.
With all due respect I sure would like to see some hard proof of these claims with some cycling (the 2.7 & 2.5V part). I’ve seen a lot of lipo data, 300 cycles using ~3.2V or higher cutoff is not uncommon with little reduction in performance with quality lipos. I’ve never seen very good life taking cells that low (again 2.7 & 2.5V) regularly. Not to mention due to the way lipos dump there is very little run time difference, and going that low frequently results in at least some if not considerable imbalance. Take a 2S to 5.4V and I strongly suspect one cell is well below 2.7V for example, a 4S would likely be worse, etc.

Last edited by Dave H; 03-23-2011 at 11:26 AM.
Dave H is offline  
Reply With Quote
Old 03-23-2011, 11:06 AM
  #12  
Super Moderator
 
Join Date: Oct 2007
Location: Rochester Hills Michigan
Posts: 7,232
Default

Originally Posted by racer1812 View Post
I understand this but I'm betting you get some questions...
No doubt, the left flank is rather exposed eh?
Dave H is offline  
Reply With Quote
Old 03-24-2011, 02:27 PM
  #13  
Tech Initiate
 
djroberts's Avatar
 
Join Date: Mar 2011
Posts: 22
Default

Originally Posted by Dave H View Post
To some extent yes. Itís mostly about maintaining sufficient resting voltage from all of the data I have seen. A lot depends on the load the battery is under, how much the voltage is sagging under load. This impacts the actual state of discharge. Higher amp discharge rates (relative to battery size) can tolerate a lower voltage under load. Conversely lower loads need a higher shutoff.
Makes sense to use voltage since we're concerned about electric potential and its affect on capacitance. I guess I guess the variable here is performance and run-time. Personally based on my analysis I'd probably set my LVC at 3.4v. Currently I have a VXLs so I'm not sure what it uses.

Usually when I'm ready to take a break there's still about 3.6 on my Gens Ace so I rarely hit the LVC.
djroberts is offline  
Reply With Quote
Old 03-24-2011, 05:46 PM
  #14  
Tech Rookie
iTrader: (1)
 
jamminroger's Avatar
 
Join Date: Dec 2010
Posts: 13
Trader Rating: 1 (100%+)
Default

i use zippy 4 cells 30c 5000mah on my sc8e and my mugen mbx5t. i used to have my lvc at 3.0v per cell and my batteries would puff. now i have them at 3.6 volts per cell and my batteries are not even hot. i know 3.6 is probably too high, but i would rather save my batteries. they also charge much sooner than 3.0 lvc. so, if you have enough batteries, higher lvc is not a bad idea. i have seven batteries and it lasts me 4 hours at the track.
jamminroger is offline  
Reply With Quote
Old 03-24-2011, 05:55 PM
  #15  
Tech Elite
iTrader: (9)
 
bigben1165's Avatar
 
Join Date: Aug 2010
Location: grand rapids, michigan
Posts: 3,068
Trader Rating: 9 (100%+)
Default

Originally Posted by Speed_Freak_039 View Post
Dont use the LVC to tell your runtime at all. Set it at like 3.2 which is still safe. If you set it to high and you punch the throttle the voltage could drop that low depending on how much juice is left and the ESC is cut power while your driving. Use a timer and find the magic time that keeps in at the safe 75-80% range.
agree completely, also the comment on the rebounding of battery voltage is very good advice too. you will hear many different variations on a similar theme. i err on the side of caution, worse case scenario is that you dont get as much run time, best case, you get to keep an expensive lipo useful for 200-300 cycles.
bigben1165 is offline  
Reply With Quote

Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service