Li-Ion battery info.

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Greywolf74

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I know that in RCs we rarely if ever use Li-ion batteries but I get asked about them on my youtube cahnnel/facebook from time to time because my interest in electronics was born out of my love of RC which means I tend to find myself using all manner if batteries for all sorts of reasons these days and its amazing how many of them (99.9%) can be charged/cycled with a good CCCV charger. Thats the type of charger that our LiPo chargers are in case you werent familiar. Anyway, someone asked me about some Li-Ion packs they were trying to build and I ended up writing a fairly lengthy response so I figured I would also share his question and my response here incase any of you might happen to need this info or were maybe just curious.

@Rolex I was thinking that maybe this post would be good to add to the sticky about batteries if you think it warrants it.

Question:
You seem to know about these batteries let me ask you this. I have 4 - 18650 batteries connected in parallel per cell. I have 12 cells connected in series starting with negative from cell 1 to positive in cell 2 and so on. Should be 4V x 12 cells = 48V. 4, 8, 12, 16, 20, 24, 28, 32, 36, 40, 44, 48V. Why do I have = 72V? Thanks

Response:
Well first lets address the power ratings for Li-ion batteries. The nominal charge of a Li-ion battery is 3.7V per cell. Their peak charge, in the case of a new battery, will be 4.2 V/C. Occasionally you'll get a cell or maybe a brand that will have a max charge of 4.1V/C but if you measure it with a multimeter it will most likely end up being closer to 4.2 than 4.1V/C but anyway, I digress. The maximum discharge point of a Li-ion cell is about 2.8V/C although you should be able to use it down to about 2.6V/C without damaging the battery. Deeply discharging the cells will damage them and in rare cases can cause them to catch fire, leak, deform, etc. Li-ion batteries that are not going to be used for extended periods of time (6 months or more) should be stored at about 60% of their max charge which is right around their nominal voltage. This is generally accomplished with a CCCV charger (let me know if you want more info on CCCV chargers) that will have a "storage" mode that will charge or discharge the battery down to the appropriate storage level.

Now that we have the basics covered we'll tackle the series and parallel problems. Connecting batteries of any kind in parallel increases the mAh rating (or capacity) of the battery pack. In your example of 4 cells wired in parallel you would start with the nominal voltage rating of the cell (3.7V in this case) and lets say they are 1000mAh capacity for the sake of the math being easy. In this example youve taken four 3.7v 1000mAh batteries and created a 3.7V 4000mAh battery pack because when wiring in parallel the only thing that increases is the mAh or capacity rating.

When it comes to wiring a pack in series its basically the opposite of parallel. In other words you add the voltages but the mAh value stays the same. In your example you have twelve 3.7V, 1000mAh, Li-ions wired up in series so your pack would be 12 x 3.7V and the mAh would stay the same so you would have a pack that was 44.4V, but still only 1000mAh.

**Footnote 2** List of nominal, max, and minimum volatges for various common battery types.
Type | Nominal | Maximum | Minimum |
NiXX | 1.2V/C | 1.5V/C | 1V/C |
LiFe | 3.3V/C | 3.4V/C | 3V/C |
Li_ion| 3.6V/C | 4.2V/C | 2.6V/C |
LiPo | 3.7V/C | 4.2V/C | 2.8V/C (a lot of people will typically say anything from 3.0 to 3.5V/C but one of the battery technicians from www.onlybatterypacks.com told me that 2.8V/C is completely safe and that real damage doesn't start until about 2.6V/C. That being said my recommendation is no lower than 3.0V/C since this is a proven safe number and still lets you get the vast majority of the capacity out of the pack. I've never had an issue using 3V/C)
 
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I've been checking through the battery info on the forum, and once I get a few things checked out I probably will add this to a sticky.
It's good info to have available.
 
I see one basic mistake. C is the rating is the max Amp Draw and has nothing to do with Capacity. mAh is your capacity.

1000mah is 1 ah and 10c would mean you could draw 10 x 1 = 10 amps. You would get about 6 minutes of run time at that amp draw.
3.7 Volts x 1ah = 3.7 Wh that is capacity. You can use Watt Hours to compare any battery to another.

I am not sure how you would get 4.2 x 12 to = anything higher then 50.4 Volts but maybe you have your meter set incorrect.

I hope this informs someone. LOL
 
I know that in RCs we rarely if ever use Li-ion batteries but I get asked about them on my youtube cahnnel/facebook from time to time because my interest in electronics was born out of my love of RC which means I tend to find myself using all manner if batteries for all sorts of reasons these days and its amazing how many of them (99.9%) can be charged/cycled with a good CCCV charger. Thats the type of charger that our LiPo chargers are in case you werent familiar. Anyway, someone asked me about some Li-Ion packs they were trying to build and I ended up writing a fairly lengthy response so I figured I would also share his question and my response here incase any of you might happen to need this info or were maybe just curious.

@Rolex I was thinking that maybe this post would be good to add to the sticky about batteries if you think it warrants it.

Question:
You seem to know about these batteries let me ask you this. I have 4 - 18650 batteries connected in parallel per cell. I have 12 cells connected in series starting with negative from cell 1 to positive in cell 2 and so on. Should be 4V x 12 cells = 48V. 4, 8, 12, 16, 20, 24, 28, 32, 36, 40, 44, 48V. Why do I have = 72V? Thanks

Response:
Well first lets address the power ratings for Li-ion batteries. The nominal charge of a Li-ion battery is 3.7V per cell. Their peak charge, in the case of a new battery, will be 4.2 V/C. Occasionally you'll get a cell or maybe a brand that will have a max charge of 4.1V/C but if you measure it with a multimeter it will most likely end up being closer to 4.2 than 4.1V/C but anyway, I digress. The maximum discharge point of a Li-ion cell is about 2.8V/C although you should be able to use it down to about 2.6V/C without damaging the battery. Deeply discharging the cells will damage them and in rare cases can cause them to catch fire, leak, deform, etc. Li-ion batteries that are not going to be used for extended periods of time (6 months or more) should be stored at about 60% of their max charge which is right around their nominal voltage. This is generally accomplished with a CCCV charger (let me know if you want more info on CCCV chargers) that will have a "storage" mode that will charge or discharge the battery down to the appropriate storage level.

Now that we have the basics covered we'll tackle the series and parallel problems. Connecting batteries of any kind in parallel increases the mAh rating (or capacity) of the battery pack. In your example of 4 cells wired in parallel you would start with the nominal voltage rating of the cell (3.7V in this case) and lets say they are 1000mAh capacity for the sake of the math being easy. In this example youve taken four 3.7v 1000mAh batteries and created a 3.7V 4000mAh battery pack because when wiring in parallel the only thing that increases is the mAh or capacity rating.

When it comes to wiring a pack in series its basically the opposite of parallel. In other words you add the voltages and the C ratings (see footnote below for a brief explaination of C-Ratings) together but the mAh value stays the same. In your example you have twelve 3.7V, 1000mAh, 10C (again just picking the number 10 out of thin air) Li-ions wired up in series so your pack would be 12 x 3.7V, 12 x 10C, and the mAh would stay the same so you would have a pack that was 44.4V, 120C, but still only 1000mAh.

**Footnote** C-Rating is (without going really in depth) basically just a way to calculate the maximum amp draw of a battery or battery pack. example a 10C 1000mAh battery can produce 10,000mAh or 10Ah of electricity (10C x 1Ah = 10A) consistently for the duration of the batteries charge. so if you were to pull lets say 10Amps out of a 10Ah battery the battery should last approx 1 hour. if you put 10A out of a .1Ah battery (or in other words 1000mAh) it would last for 6 minutes roughly (one tenth of an hour). C-Rating isnt really used to much in conjunction with Li-ion batteries but it is used much more commonly in LiPo (lithium polymer) batteries. All batteries will have a C-Rating but in most batteries its pretty low and isnt really a big factor and generally isnt even listed.

**Footnote 2** List of nominal, max, and minimum volatges for various common battery types.
Type | Nominal | Maximum | Minimum |
NiXX | 1.2V/C | 1.5V/C | 1V/C |
LiFe | 3.3V/C | 3.4V/C | 3V/C |
Li_ion| 3.6V/C | 4.2V/C | 2.6V/C |
LiPo | 3.7V/C | 4.2V/C | 2.8V/C (a lot of people will typically say anything from 3.0 to 3.5V/C but one of the battery technicians from www.onlybatterypacks.com told me that 2.8V/C is completely safe and that real damage doesn't start until about 2.6V/C. That being said my recommendation is no lower than 3.0V/C since this is a proven safe number and still lets you get the vast majority of the capacity out of the pack. I've never had an issue using 3V/C)

One thing that I have found out about lipo batteries is you hace to habve a high enough C ratting for your application. I had a excavator and ran 6000 mah 30C batteries and they got hot. I then went to 8000 mah and 70C and the batyteries stay cool. The c ratting is what made the differance. Ed
 
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I see one basic mistake. C is the rating is the max Amp Draw and has nothing to do with Capacity. mAh is your capacity.

1000mah is 1 ah and 10c would mean you could draw 10 x 1 = 10 amps. You would get about 6 minutes of run time at that amp draw.
3.7 Volts x 1ah = 3.7 Wh that is capacity. You can use Watt Hours to compare any battery to another.

I am not sure how you would get 4.2 x 12 to = anything higher then 50.4 Volts but maybe you have your meter set incorrect.

I hope this informs someone. LOL
I'm not sure what your talking about on either count. I never claimed that C rating has to do with the capacity of the battery. In fact the excerpt that you quote here specifically demonstrates how to use C rating find find you maximum amp draw. and then shows how you use the capacity and the amp draw to determine how long a battery would theoretically last. BTW, did you even read the footnote? very first line of the foot note states and I quote "C-Rating is (without going really in depth) basically just a way to calculate the maximum amp draw of a battery or battery pack."

As for 4.2v x 12 I never did that calculation so I'm clueless as to what you are talking about here, unless you are referring to the part where I posted the guys question to me. If you are then that means you didnt really read the post which would explain your post in its entirety. please READ next time.

One thing that I have found out about lipo batteries is you have to habve a high enough C ratting for your application. I had a excavator and ran 6000 mah 30C batteries and they got hot. I then went to 8000 mah and 70C and the batyteries stay cool. The c ratting is what made the differance. Ed
Very true. Higher C rating the better up to a point. If you're using 5000mAh packs then around 40C you start getting into the area where the max amp draw is going to be more than any ESC can take anyway and thereby sort of makes buying a LiPo with a very high C-Rating a bit of a waste. There are a couple of minor factors that could be said about having very high C ratings but usually the cost outweighs the gains at that point.
 
Your FOOTNOTE Quotes this in your original Post. That is what was not correct. The basics you have are correct.

C-Rating is (without going really in depth) basically just a way to calculate the maximum amp draw of a battery or battery pack. example a 10C 1000mAh battery can produce 10,000mAh or 10Ah of electricity (10C x 1Ah = 10A) consistently for the duration of the batteries charge.

C Rating just stands for Current Ration x Capacity = Max Current Draw Rating
 
Your FOOTNOTE Quotes this in your original Post. That is what was not correct. The basics you have are correct.

C-Rating is (without going really in depth) basically just a way to calculate the maximum amp draw of a battery or battery pack. example a 10C 1000mAh battery can produce 10,000mAh or 10Ah of electricity (10C x 1Ah = 10A) consistently for the duration of the batteries charge.

C Rating just stands for Current Ration x Capacity = Max Current Draw Rating
my bad...I put h's on the ends of mAh and Ah when I meant mA and A. you could have just said that so I wasn't sitting here scratching my head trying to figure out what you were vaguely referring to.

Typos have been corrected
 
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lol, whatever. I'm pretty sure that most people who spend time writing up paragraphs of information in order to try to help people understand something dont appreciate being "messed with" about it. Either be a part of the solution or keep it to yourself.
 
Hey greywolf, just had a quick glance through so don't k ow if you rectified it, but the C rating is from the cell,not the pack. Any way you connect them up the C rate stays the same in this case 10C not the 120C quoted.
 
Oh thats right....I dont know what I was thinking there. Thanks for pointing that out. I'll change it. So I guess there was a genuine mistake in my write up beside the two typos after all.
 
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Cool, I remember a few year back trying to find the voltages of the different lithium and struggled to find much info. Basic battery info can be quite a complex thing when you get into it. And normally get a few corrections along the way. Because don't forget their is high voltage lipos now just to add some more confusion into the mix.
 
lol, Yeah, thats right. I havent even looked at the HV lipos twice yet. IDK if I'm gonna go there or not unless they turn into the new norm.
 

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