Hatchett Posted February 23, 2018 Share Posted February 23, 2018 I got given a 7.4v lipo battery however one of the cells is completely flat showing 00.0v. The other cell is almost fully charged at 4.19v. How can one cell drain so much on its own? Should they not discharge at a similar rate? Why does this happen? Also is this battery done with or can I recharge it safely? Cheers Link to comment Share on other sites More sharing options...
Supporters Esoterick Posted February 23, 2018 Supporters Share Posted February 23, 2018 If it's second hand and showing signs of being faulty I'd replace it, even if I knew the history of the battery I would personally chuck it. Might just be me but I'd rather not risk damaging a gun or anything else for the sake of £15. It could have previously been charged with a poor quality charger at a guess. Link to comment Share on other sites More sharing options...
Guest scalawag Posted February 23, 2018 Share Posted February 23, 2018 It’s finished, what ever you do don’t try to charge it. Just dispose of it safely. I have been using LiPo batteries now for several years in both my Airsoft guns and radio controlled stuff. LiPo batteries must not be discharged to 0v like NiMh batteries can be, they have a safe minimum voltage per cell of around 3v. If a cell in a LiPo is over-discahrged then charging it can be dangerous. Most of the horror stories of fires associated with LiPos whilst charging are attributable to someone charging a LiPo with cells with low voltages, or overcharging cells. This can also cause the cells to "puff up", and if then pierced, they will invariably spontaneously ignite due to the reaction caused by exposure of the built up gasses/chemicals to air. If you have a LiPo that has "puffed" dispose of it safely, and do not keep using it. In my experience one cell going dead like this typically happens when LiPos are not balance charged on a regular basis, and that usually happens when cheap chargers with no monitoring are used. You don’t need to balance charge every time , but it does need to be done on a regular basis. Balance charging is where a charger monitors all the cells in the battery individually, and makes sure that at full charge all the cell voltages match or are balanced. Thats what that little white plug on a LiPo is for, it gives a charger access to the voltage of individual cells in the battery. Typically a fully charged LiPo cell will be at 4.2v. When the cells are not balanced one cell will reach its safe minimum voltage of 3v before the other cells in the battery, but because the total voltage of the battery (all cells added together) is still above the the minimum then most protection circuits won’t cut in at this point because they monitor the total voltage of the battery, and will continue to drain the battery including the low cell. Eventually that low cell will go dead. So as an example, a 2s battery has 2 cells. The minimum voltage the battery can drain to is 6v( 3v per cell)and its typical full charge voltage will be 8.4v (4.2v per cell). If the cells are balanced and undamaged then they will both reach 3v at approximately the same time. But the cells in this battery are out of balance. Cell A has 4.5v (this is actually overcharged by a bit), and cell B has 3.9v, thats the usual 8.4v full charge (4.5v + 3.9v) at the point it begins to be used. As the battery drains cell B will reach 3v first, but cell A still has 3.3v. Because the battery as a whole still shows 6.3v (3v +3.3v) and a lot of protective cut out circuits will still think the battery is ok, the battery will continue to drain until it reaches 6v. When at 6v, Cell A will be around 3.15v while B will be 2.85v and at that point the protective cut out operates. Cell B is now below the safe minimum voltage for charging. When next charged Cell A will over charge a bit more to compensate for the lower voltage in cell B which will now charge a little less than before and drain a little quicker, and If this scenario happens often enough the effect is compounded until the B cell is definately useless and probably the A cell is too. Most LiPo cells damaged by being over-discharged will take less charge, and drain more quickly. You should always have some form of low voltage protection installed when using a LiPo as fully draining them not only damages them, it can render them dangerous to charge or even store. Using a LiPo without at least a low voltage alarm is really asking for trouble at some point in my opinion. Sure you can stop using the battery before you think it has drained to 6v but how will you know for sure that you have done that and how will you know how balanced the cells are keeping. Most mosfets these days have a low voltage cut out. This will typically monitor the total voltage of the battery and not the voltage of individual cells. In this case it is important to make sure the batteries are balanced before use or the above scenario can still occur. The protective circuits used in these mosfets assume that all the cells are charged to the same voltage(balanced) when they are first used in the gun and that they will drain at a uniform rate to one another. Or if you are not running a mosfet or you want extra protection, then I recommend using a LiPo low voltage alarm. This is a small circuit board that plugs into the balance lead of the battery and bleeps when any individual cell reaches its minimum voltage. An alarm like this will not protect your battery from over draining by cutting the power, but it will alert you that it is time to change the battery. They are really cheap to buy and will help you to get the most out of the LiPos you use. Most cheap chargers don’t allow you to monitor the balance of the voltage of the cells. Some do try to keep a balance to the cells of the battery when they charge, but none are very good at this in my experience. If your charger does not have a port to plug in the balance lead on your LiPo then it is not monitoring the individual cells voltage at all, just the total battery voltage and a low cell voltage and/or an over charged cell can still occur. I always recommend using a smart charger like the iMax B6. These allow you to keep an eye on the health of individual cells in a battery, and to balance charge when needs be, as well as a whole lot more besides. They really are a great buy if you are using LiPos. At the very least I recommend getting one of those small LiPo battery monitors which are available, as you will then at least be able to see the voltage of individual cells. Some even allow you to balance the cells by draining cells until all of their voltages match. They just plug into the balance lead and you can read the individual voltage of each cell. The voltages I have mentioned here are just to illustrate what I am trying to say in as simple a form as possible and actual voltages etc. may vary. sorry I didn’t mean this reply to be so long but I wanted to illustrate how this can happen, and its rather turned into a more general reply than one specifically for you Hatchett, I apologise. Additional Info I have added links from HobbyKings web site for the type of charger, low voltage alarm and battery checker I have talked about here as I thought that might be useful. iMax B6 Charger: https://hobbyking.com/en_us/imax-b6ac-v2-professional-balance-charger-discharger.html Low Voltage alarm: https://hobbyking.com/en_us/hobbykingtmlipoly-low-voltage-alarm-2s-3s.html Battery checker: https://hobbyking.com/en_us/hobbykingtm-battery-medic-system-2s-6s.html Link to comment Share on other sites More sharing options...
Hatchett Posted February 23, 2018 Author Share Posted February 23, 2018 2 hours ago, scalawag said: It’s finished, what ever you do don’t try to charge it. Just dispose of it safely. I have been using LiPo batteries now for several years in both my Airsoft guns and radio controlled stuff. LiPo batteries must not be discharged to 0v like NiMh batteries, they have a safe minimum voltage per cell of around 3v. If a cell in a LiPo is over-discahrged then charging it can be dangerous. Most of the horror stories of fires associated with LiPos whilst charging are attributable to someone charging a LiPo with cells with low voltages, or overcharging cells. This can also cause the cells to "puff up", and if then pierced, they will invariably spontaneously ignite. If you have a LiPo that has "puffed" dispose of it safely, and do not keep using it. In my experience one cell going dead like this typically happens when LiPos are not balance charged on a regular basis, and that usually happens when cheap chargers with no monitoring are used. You don’t need to balance charge every time , but it does need to be done on a regular basis. Balance charging is where a charger monitors all the cells in the battery individually, and makes sure that at full charge all the cell voltages match or are balanced. Thats what that little white plug on a LiPo is for, it gives a charger access to the voltage of individual cells in the battery. Typically a fully charged LiPo cell will be at 4.2v. When the cells are not balanced one cell will reach its safe minimum voltage of 3v before the other cells in the battery, but because the total voltage of the battery (all cells added together) is still above the the minimum then most protection circuits won’t cut in at this point because they monitor the total voltage of the battery, and will continue to drain the battery including the low cell. Eventually that low cell will go dead. So as an example, a 2s battery has 2 cells. The minimum voltage the battery can drain to is 6v( 3v per cell)and its typical full charge voltage will be 8.4v (4.2v per cell). If the cells are balanced and undamaged then they will both reach 3v at approximately the same time. But the cells in this battery are out of balance. Cell A has 4.5v (this is actually overcharged by a bit), and cell B has 3.9v, thats the usual 8.4v full charge (4.5v + 3.9v) at the point it begins to be used. As the battery drains cell B will reach 3v first, but cell A still has 3.3v. Because the battery as a whole still shows 6.3v (3v +3.3v) and a lot of protective cut out circuits will still think the battery is ok, the battery will continue to drain until it reaches 6v. When at 6v, Cell A will be around 3.15v while B will be 2.85v and at that point the protective cut out operates. Cell B is now below the safe minimum voltage for charging. When next charged Cell A will over charge a bit more to compensate for the lower voltage in cell B which will now charge a little less than before and drain a little quicker, and If this scenario happens often enough the effect is compounded until the B cell is definately useless and probably the A cell is too. Most LiPo cells damaged by being over-discharged will take less charge, and drain more quickly. You should always have some form of low voltage protection installed when using a LiPo as fully draining them not only damages them, it can render them dangerous to charge or even store. Using a LiPo without at least a low voltage alarm is really asking for trouble at some point in my opinion. Sure you can stop using the battery before you think it has drained to 6v but how will you know for sure that you have done that and how will you know how balanced the cells are keeping. Most mosfets these days have a low voltage cut out. This will typically monitor the total voltage of the battery and not the voltage of individual cells. In this case it is important to make sure the batteries are balanced before use or the above scenario can still occur. The protective circuits used in these mosfets assume that all the cells are charged to the same voltage(balanced) when they are first used in the gun and that they will drain at a uniform rate to one another. Or if you are not running a mosfet or you want extra protection, then I recommend using a LiPo low voltage alarm. This is a small circuit board that plugs into the balance lead of the battery and bleeps when any individual cell reaches its minimum voltage. An alarm like this will not protect your battery from over draining by cutting the power, but it will alert you that it is time to change the battery. They are really cheap to buy and will help you to get the most out of the LiPos you use. Most cheap chargers don’t allow you to monitor the balance of the voltage of the cells. Some do try to keep a balance to the cells of the battery when they charge, but none are very good at this in my experience. If your charger does not have a port to plug in the balance lead on your LiPo then it is not monitoring the individual cells voltage at all, just the total battery voltage and a low cell voltage and/or an over charged cell can still occur. I always recommend using a smart charger like the iMax B6. These allow you to keep an eye on the health of individual cells in a battery, and to balance charge when needs be, as well as a whole lot more besides. They really are a great buy if you are using LiPos. At the very least I recommend getting one of those small LiPo battery monitors which are available, as you will then at least be able to see the voltage of individual cells. Some even allow you to balance the cells by draining cells until all of their voltages match. They just plug into the balance lead and you can read the individual voltage of each cell. The voltages I have mentioned here are just to illustrate what I am trying to say in as simple a form as possible and actual voltages etc. may vary. sorry I didn’t mean this reply to be so long but I wanted to illustrate how this can happen, and its rather turned into a more general reply than one specifically for you Hatchett, I apologise. Additional Info I have added links from HobbyKings web site for the type of charger, low voltage alarm and battery checker I have talked about here as I thought that might be useful. iMax B6 Charger: https://hobbyking.com/en_us/imax-b6ac-v2-professional-balance-charger-discharger.html Low Voltage alarm: https://hobbyking.com/en_us/hobbykingtmlipoly-low-voltage-alarm-2s-3s.html Battery checker: https://hobbyking.com/en_us/hobbykingtm-battery-medic-system-2s-6s.html Wow thanks for this very informative reply. This helped clear a few things for sure. Link to comment Share on other sites More sharing options...
Guest scalawag Posted February 23, 2018 Share Posted February 23, 2018 2 minutes ago, Hatchett said: Wow thanks for this very informative reply. This helped clear a few things for sure. No problem mate, happy to try and help. Link to comment Share on other sites More sharing options...
LightningCh Posted February 23, 2018 Share Posted February 23, 2018 This thread just reminded to check my own LiPos ready for my game on Sunday lol. Link to comment Share on other sites More sharing options...
LightningCh Posted February 23, 2018 Share Posted February 23, 2018 So also just realised that 2 of my lipos are at the airsoft store... i hope the tech charged them slightly lol.... But my ones here are reading 3.81V in each cell so at least I have 2 out of 4 that are going to be fine lol Link to comment Share on other sites More sharing options...
Hatchett Posted February 23, 2018 Author Share Posted February 23, 2018 3 minutes ago, LightningCh said: So also just realised that 2 of my lipos are at the airsoft store... i hope the tech charged them slightly lol.... But my ones here are reading 3.81V in each cell so at least I have 2 out of 4 that are going to be fine lol You should be ok then, otherwise its going to be a long day of bayonet charging lol. Link to comment Share on other sites More sharing options...
LightningCh Posted February 23, 2018 Share Posted February 23, 2018 lol yeah, storage charge is always nice to see. As for bayonet charging, nah, not my thing lol, would rather just use my hi capa. Link to comment Share on other sites More sharing options...
smoorenator Posted February 23, 2018 Share Posted February 23, 2018 this thread actually made me buy a lipo alarm as i just started to switch over to lipo batteries Link to comment Share on other sites More sharing options...
Hatchett Posted February 23, 2018 Author Share Posted February 23, 2018 1 minute ago, smoorenator said: this thread actually made me buy a lipo alarm as i just started to switch over to lipo batteries Glad this thread has been useful for other people aswell lol. Link to comment Share on other sites More sharing options...
LightningCh Posted February 23, 2018 Share Posted February 23, 2018 29 minutes ago, smoorenator said: this thread actually made me buy a lipo alarm as i just started to switch over to lipo batteries I just carry a cheap battery capacity checker and plug it in to test after each hour of play, And I naturally swap lipos at lunch time anyway. Each to their own on it though, just I've seen it a few times with alarms when they start going off for no real reason lol. "why is that bush beeping?" Link to comment Share on other sites More sharing options...
Guest scalawag Posted February 23, 2018 Share Posted February 23, 2018 14 minutes ago, LightningCh said: I just carry a cheap battery capacity checker and plug it in to test after each hour of play, And I naturally swap lipos at lunch time anyway. Each to their own on it though, just I've seen it a few times with alarms when they start going off for no real reason lol. "why is that bush beeping?" Yeah it just needs something to make sure that the cell voltages do not drop too low, whether that is a system like yours or an alarm or a cut out via a mosfet. The aim is the same. I have seen a LiPo go up and they burn fierce. The cells tend to go up in sequence too so just when you think it is going out another cell catches and off it goes again. Link to comment Share on other sites More sharing options...
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