Disclaimer-I am not an expert! I do not recommend, or vouch for batteries in any way! I do not test batteries in any way! This is just a collection of data that I have compiled after hours of research. This is not everything you need to know, just what I have compiled. The data is presented to you for your own interpretation.
Lipo Battery Safety Links-Read these!
this list of safety links will be updated as I find more, to give the reader as much information as I can
http://thedronegirl.com/2015/02/07/lipo-battery/
http://www.icharger.co.nz/articles/ArticleId/3/Lipo-Lithium-Battery-Safety-Guide.aspx
https://www.maxamps.com/lipo-care.php
Lithium Polymer batteries come in many forms, chemistry, sizes, and capacities. Unlike our lithium ion battery sizing system, lipos have no standard size I've found so far. lipos also do not use the amp rating that we're all used to, but rather a C-rating. Lipo voltages vary wildly from 3.7v to over 22v, depending on the number of cells and chemistry used. And finally, battery ratings can be overrated just like with our 18650s, so please fully research any battery you plan on using.
In my research, I have focused on minicopter/drone style batteries. There are other batteries out there, but I chose this style because of their small size, high power output features. The concepts, formulas, terminology should generally apply to all lipos.
Lipo Varieties
Lipos are available in 1-6 cells. 1 cell can be between 4.2v-4.35v fully charged
Lipos come in standard voltage, or high voltage, see above. High voltage requires a charger that is capable of charging high volt batteries. High volt batteries are made to be charged this high, Standard LIPOs are not!
Some lipos use graphene. IN THEORY, graphene lipos have a lower internal resistance, which allows power to flow more freely through the battery, generating less heat. Also, IN THEORY, the graphene batteries can be thinner than a traditional lipo
What Is a C Rating?
a C rating is a multiplier used to calculate amperage. This is the formula:
Capacity(mah)*Crating=milliamps. this formula is found everywhere in the rc world, so here is just 1 link to show I did not make it up.
http://www.revolectrix.com/tech_data/lipoCalc/Battery_C_Rating.htm
C ratings are usually measured in 2 ways, continuous, and burst. Burst ratings are like our pulsed ratings we are used to.
MY OPINION!- When I consider batteries, I only look at the continuous daw, and never take any burst rating into account for any of my formulas. Why? because(opinion) I don't trust them. I refuse to give any comparisons, ratings, or recommendations on pulse ratings! Hell, I don't even trust the continuous ratings on batteries. When I do build my lipo mod, I will send a battery to mooch for testing before I put it in my mod.
So, what makes the c rating stand out in lipos, more than our 18650s?
Lets look at 2 theoretical batteries as an example
battery a has 1300mah and a 50c rating for 65,000milliamps, or 65 amps
battery b has 1800mah and a 50c rating for 90,000milliamps, or 90 amps
This should not look right for people only familiar with 18650s. In our confined battery dimensions, we know that the higher amperage batteries carry a lower capacity. But that rule does not apply when the batteries are different sizes. The 1800mah lipo battery is physically larger than the 1300mah lipo.
2s 3s 4s?
This is pretty straight foreward- 2(cells)s(series)=2 battery cells wired in series. A standard voltage lipo pack would look like this:
2s=4.2v+4.2v=8.4v(fully charged)
3s=4.2v+4.2v+4.2v=12.6v
something to note here is that there is a little bit of voltage drop when you stack batteries, due to internal resistance, but for theoretical purposes, I will refer to batteries by their maximum theoretical charge.
Series lipo batteries maintain the same Mah rating, no matter how many cells are in the pack. so similar sized (length and width) batteries have similar mah ratings, even if one is about 6mm thicker and carry an extra cell for a higher voltage. So the amperage ratings can remain the same with a 3s or 4s with the same c rating. But the number of cells has a huge effect on the final wattage.
Using these 2 theoretical batteries, we will see the effect cell count has on wattage (voltage*amperage=wattage)
3s- 1300mah*50c=65 amps *12.6v=819 watts
4s- 1300mah*50c=65 amps *16.8v=1,092 watts
THESE ARE THEORITICAL EXAMPLES!
THERE IS A VERY REAL CHANCE YOUR C RATING IS OVERRATED!
YOUR BATTERY HAS A VERY SERIOUS AND REAL THREAT OF FAILING WHEN USED AT ITS C RATING!
2s1p 2s2p 3s2p?
this is where it gets a little more complex.
2s1p= 2series, 1 parallel= just another way of saying 2s
2s2p=2 series, 2parallel= we all know the benefit os the para-series setups with the 18650s, this brings out that, only in lipo form.
With 2 batteries in parallel, the Mah rating is doubled, and 2 in series, the voltage is doubled.
The increase in mah is already on the label, though, so the math remains the same. But it is not uncommon to see very high ratings from this type of cell structure.
LIPOS puff under heavy load(not a fact for all lipos!)
most lipos of this variety(minicopter/drone) are soft packs, and (some) expand as they discharge. This characteristic, from my research, is common, but not guaranteed. They(usually)return to their origional shape after they cool. Some are damaged by this and must be discarded. This is not scientific. I have not found rhyme or reason for this. It is just another warning, and encouragement to do your homework before buying a battery.
Minimum Cell Voltage
If there is a standard for this, I have not found it. I have heard everything from 3.5v per cell(resting) to 3v per cell (resting). But the common theory here is that the lower the resting voltage gets, the more you will hurt your battery. This means your battery will take fewer recharge cycles before it will not take a charge anymore
Ohms law is the law
Can't i just turn down the pot to ease the load on the battery?
Yes and no. Most pwm mods Do Not Change The Voltage, they change the duty cycle- the number of times full power is applied to the atty per second. Ever wonder why your pwm fires massive coils at ridiculously low voltage readings? That's because it's not. Your voltage meter is giving you an average voltage, not the actual voltage. The actual voltage would be read so fast on and off that you are not capable of reading it, (pwms can pulse anywhere from 1 time per second to many tens of thousands of times per second).
This point will be clearly laid out in a later installment but for now, lets just focus on the fact that if your pwm adjusts the duty cycle, you are vaping at the same wattage, no matter where you put the potentiometer. So when you figure out the ohms you can build at safely, remember that there is no voltage regulation on an adjustable duty cycle mod, so treat it like a mech mod and select a properly rated battery(with a generous safety cushion).
So Who does battery testing?
So far, the only person I found that has tested lots of batteries in what appears to be a scientific manner is this guy:
I Do Not Vouch For Him
His methods might be flawed, he might be bias, he might be the Mooch of the lipo world I Do Not Know.
He appears to have tested a whole bunch of batteries and came up with data that may be considdered. But thats up to you!
Here is a spreadsheet of his testing results, and in some of his videos, he explains how to read the spreadsheet.
https://onedrive.live.com/view.aspx?resid=AC06B68F01DD1B5E!44168&ithint=file,xlsx&app=Excel&authkey=!AF8VSKcKJUWLi80
Thats about all I've got for now. I may update this as I learn more though.
I am up for crowdfunding a battery for mooch to test, if anyone else wants to pay for the piece of mind.
I know this post will cause controversy. If you disagree with anything I have said here, please feel free to comment. I only ask that we keep this to polite debate. I have the humility to admit when I am wrong.
If you think a warning or disclaimer should be added, let me know where and I will put it in
More info about lipos
http://www.rchelicopterfun.com/rc-lipo-batteries.html
Lipo Battery Safety Links-Read these!
this list of safety links will be updated as I find more, to give the reader as much information as I can
http://thedronegirl.com/2015/02/07/lipo-battery/
http://www.icharger.co.nz/articles/ArticleId/3/Lipo-Lithium-Battery-Safety-Guide.aspx
https://www.maxamps.com/lipo-care.php
Lithium Polymer batteries come in many forms, chemistry, sizes, and capacities. Unlike our lithium ion battery sizing system, lipos have no standard size I've found so far. lipos also do not use the amp rating that we're all used to, but rather a C-rating. Lipo voltages vary wildly from 3.7v to over 22v, depending on the number of cells and chemistry used. And finally, battery ratings can be overrated just like with our 18650s, so please fully research any battery you plan on using.
In my research, I have focused on minicopter/drone style batteries. There are other batteries out there, but I chose this style because of their small size, high power output features. The concepts, formulas, terminology should generally apply to all lipos.
Lipo Varieties
Lipos are available in 1-6 cells. 1 cell can be between 4.2v-4.35v fully charged
Lipos come in standard voltage, or high voltage, see above. High voltage requires a charger that is capable of charging high volt batteries. High volt batteries are made to be charged this high, Standard LIPOs are not!
Some lipos use graphene. IN THEORY, graphene lipos have a lower internal resistance, which allows power to flow more freely through the battery, generating less heat. Also, IN THEORY, the graphene batteries can be thinner than a traditional lipo
What Is a C Rating?
a C rating is a multiplier used to calculate amperage. This is the formula:
Capacity(mah)*Crating=milliamps. this formula is found everywhere in the rc world, so here is just 1 link to show I did not make it up.
http://www.revolectrix.com/tech_data/lipoCalc/Battery_C_Rating.htm
C ratings are usually measured in 2 ways, continuous, and burst. Burst ratings are like our pulsed ratings we are used to.
MY OPINION!- When I consider batteries, I only look at the continuous daw, and never take any burst rating into account for any of my formulas. Why? because(opinion) I don't trust them. I refuse to give any comparisons, ratings, or recommendations on pulse ratings! Hell, I don't even trust the continuous ratings on batteries. When I do build my lipo mod, I will send a battery to mooch for testing before I put it in my mod.
So, what makes the c rating stand out in lipos, more than our 18650s?
Lets look at 2 theoretical batteries as an example
battery a has 1300mah and a 50c rating for 65,000milliamps, or 65 amps
battery b has 1800mah and a 50c rating for 90,000milliamps, or 90 amps
This should not look right for people only familiar with 18650s. In our confined battery dimensions, we know that the higher amperage batteries carry a lower capacity. But that rule does not apply when the batteries are different sizes. The 1800mah lipo battery is physically larger than the 1300mah lipo.
2s 3s 4s?
This is pretty straight foreward- 2(cells)s(series)=2 battery cells wired in series. A standard voltage lipo pack would look like this:
2s=4.2v+4.2v=8.4v(fully charged)
3s=4.2v+4.2v+4.2v=12.6v
something to note here is that there is a little bit of voltage drop when you stack batteries, due to internal resistance, but for theoretical purposes, I will refer to batteries by their maximum theoretical charge.
Series lipo batteries maintain the same Mah rating, no matter how many cells are in the pack. so similar sized (length and width) batteries have similar mah ratings, even if one is about 6mm thicker and carry an extra cell for a higher voltage. So the amperage ratings can remain the same with a 3s or 4s with the same c rating. But the number of cells has a huge effect on the final wattage.
Using these 2 theoretical batteries, we will see the effect cell count has on wattage (voltage*amperage=wattage)
3s- 1300mah*50c=65 amps *12.6v=819 watts
4s- 1300mah*50c=65 amps *16.8v=1,092 watts
THESE ARE THEORITICAL EXAMPLES!
THERE IS A VERY REAL CHANCE YOUR C RATING IS OVERRATED!
YOUR BATTERY HAS A VERY SERIOUS AND REAL THREAT OF FAILING WHEN USED AT ITS C RATING!
2s1p 2s2p 3s2p?
this is where it gets a little more complex.
2s1p= 2series, 1 parallel= just another way of saying 2s
2s2p=2 series, 2parallel= we all know the benefit os the para-series setups with the 18650s, this brings out that, only in lipo form.
With 2 batteries in parallel, the Mah rating is doubled, and 2 in series, the voltage is doubled.
The increase in mah is already on the label, though, so the math remains the same. But it is not uncommon to see very high ratings from this type of cell structure.
LIPOS puff under heavy load(not a fact for all lipos!)
most lipos of this variety(minicopter/drone) are soft packs, and (some) expand as they discharge. This characteristic, from my research, is common, but not guaranteed. They(usually)return to their origional shape after they cool. Some are damaged by this and must be discarded. This is not scientific. I have not found rhyme or reason for this. It is just another warning, and encouragement to do your homework before buying a battery.
Minimum Cell Voltage
If there is a standard for this, I have not found it. I have heard everything from 3.5v per cell(resting) to 3v per cell (resting). But the common theory here is that the lower the resting voltage gets, the more you will hurt your battery. This means your battery will take fewer recharge cycles before it will not take a charge anymore
Ohms law is the law
Can't i just turn down the pot to ease the load on the battery?
Yes and no. Most pwm mods Do Not Change The Voltage, they change the duty cycle- the number of times full power is applied to the atty per second. Ever wonder why your pwm fires massive coils at ridiculously low voltage readings? That's because it's not. Your voltage meter is giving you an average voltage, not the actual voltage. The actual voltage would be read so fast on and off that you are not capable of reading it, (pwms can pulse anywhere from 1 time per second to many tens of thousands of times per second).
This point will be clearly laid out in a later installment but for now, lets just focus on the fact that if your pwm adjusts the duty cycle, you are vaping at the same wattage, no matter where you put the potentiometer. So when you figure out the ohms you can build at safely, remember that there is no voltage regulation on an adjustable duty cycle mod, so treat it like a mech mod and select a properly rated battery(with a generous safety cushion).
So Who does battery testing?
So far, the only person I found that has tested lots of batteries in what appears to be a scientific manner is this guy:
His methods might be flawed, he might be bias, he might be the Mooch of the lipo world I Do Not Know.
He appears to have tested a whole bunch of batteries and came up with data that may be considdered. But thats up to you!
Here is a spreadsheet of his testing results, and in some of his videos, he explains how to read the spreadsheet.
https://onedrive.live.com/view.aspx?resid=AC06B68F01DD1B5E!44168&ithint=file,xlsx&app=Excel&authkey=!AF8VSKcKJUWLi80
Thats about all I've got for now. I may update this as I learn more though.
I am up for crowdfunding a battery for mooch to test, if anyone else wants to pay for the piece of mind.
I know this post will cause controversy. If you disagree with anything I have said here, please feel free to comment. I only ask that we keep this to polite debate. I have the humility to admit when I am wrong.
If you think a warning or disclaimer should be added, let me know where and I will put it in
More info about lipos
http://www.rchelicopterfun.com/rc-lipo-batteries.html
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