Lipo C rating figured out?!?!

[#ARRMArcfanboy4life]

I think I figured out lipo C-rating. Most batteries charge at 1C. If the battery is 5000mah a safe charge rate is 5A. You can charge batteries can charge above 1C, but if you do, it will reduce life of the battery and increase likelihood of fires. If you have a battery that has a discharge rate of 50C (same unit) it means the amps draw limit is 50*mah. Many members of this forum say discharge C-rating doesn't mean anything. I think they are wrong. If you "can" charge about recommended limit for the battery, you increase likelihood of problems.
If I am correct, it is the same with discharge rates. You can discharge about 50c, but if you do, you will increase damage to the battery. If you do it enough

Do you think I am correct?

 

[LicketySplit]

No.

 

[Moonstonemike]

The battery C rating is the discharge rating times capacity. So for simplicity say a 1,000miliamp battery at 10c would have a Max 10,000miliamp draw rating or 10amps

 

[Diem Turner]

No.

 

[gotnitro]

Imagine having a constant volt and amp supply in a RC. Yes, its plugged into a wall and you are dragging a long wire. Every time you stab the throttle, you get the same thing, same speed, same punch, same everything, the same power is endless.

Now imagine having a battery in the car with the same volts and amps to start as above. Every time you stab the throttle, you get just a bit less power, less speed, less punch until the battery is drained.

If a manufacturer has a sticker with a discharge rate of 20c and the pack is 5000mah, that would = 5000mah=5amps, 5amps x20c= 100 amps total continues discharge. But wait, as you continue to use the battery, everything is falling because you have no continues power supply like when it's plugged into a wall.

Volts are pushed
Amps are pulled
Watts are created (horsepower)

If that motor wants the power, amps will supply it, but amps also create all the heat.

Sometimes C "ratings" are all flubbed by manufacturers to sell the packs. Most of the time they are called out pretty quickly due to the pack's performance and private testing equ. Lots of times the same manufacturer will produce great packs and sh!tty packs under a different label but it's all the same banner (owner). You only have a handful of manufacturers coming out of china.

 

[Hector_Fisher]

I think I figured out lipo C-rating. Most batteries charge at 1C. If the battery is 5000mah a safe charge rate is 5A. You can charge batteries can charge above 1C, but if you do, it will reduce life of the battery and increase likelihood of fires. If you have a battery that has a discharge rate of 50C (same unit) it means the amps draw limit is 50*mah. Many members of this forum say discharge C-rating doesn't mean anything. I think they are wrong. If you "can" charge about recommended limit for the battery, you increase likelihood of problems.
If I am correct, it is the same with discharge rates. You can discharge about 50c, but if you do, you will increase damage to the battery. If you do it enough

Do you think I am correct?

You're getting there.

The reason why C ratings are all made up is because there is no standardized way to test for capable c rating. How long does the battery need to hold the sustained amps for in order to pass the test? What is an acceptable voltage sag when the battery is subjected to a 50c load? Does that battery survive much more life after a 50c load?

For an example, a 5ah (5000 mah) battery means 5 amps over an hour. When you fully charge it at 1c, it will usually take about an hour to charge. Hence 5ah. A 50c discharge means discharging all that in 1/50th of the time. So that would mean a continuous discharge of the battery in just over a minute (1.2 minutes).

Knowing that. How many batteries do you think could, in real life, survive a full 50c discharge in just over a minute and 1) not explode or 2) survive for more use? Now imagine a "120c" battery that should be able to be discharged in half a second.

So you are right on about the math of c ratings, but the numbers are still made up by the manufacturer and mean very little.

 

[jkflow]

I think I figured out lipo C-rating. Most batteries charge at 1C. If the battery is 5000mah a safe charge rate is 5A. You can charge batteries can charge above 1C, but if you do, it will reduce life of the battery and increase likelihood of fires. If you have a battery that has a discharge rate of 50C (same unit) it means the amps draw limit is 50*mah. Many members of this forum say discharge C-rating doesn't mean anything. I think they are wrong. If you "can" charge about recommended limit for the battery, you increase likelihood of problems.
If I am correct, it is the same with discharge rates. You can discharge about 50c, but if you do, you will increase damage to the battery. If you do it enough

Do you think I am correct?

The battery C rating is the discharge rating times capacity. So for simplicity say a 1,000miliamp battery at 10c would have a Max 10,000miliamp draw rating or 10amps

You are both right, but also a little off point.
The 1C charge rate is recommended, but independent of advertised C rating. Everything else you state is correct.

Your math is correct, the 'milli' is a simple European(?) standard for 1/1000.

Discharge C -rating, this is literally made up by the people marketing the lipo. Those numbers are always inflated, as there is no standard. In their own mind, it's correct, in reality it will damage the lipo when you do follow that label but most likely it can handle it for 1s.

Unfortunately, there is no guarantee that a vendor that had good packs in one batch has good packs in the next batch. There are about 5 manufacturers of lipo cells, you are getting premium vs lower class, that is all.

 

[Moonstonemike]

You are both right, but also a little off point.
The 1C charge rate is recommended, but independent of advertised C rating. Everything else you state is correct.

Your math is correct, the 'milli' is a simple European(?) standard for 1/1000.

Discharge C -rating, this is literally made up by the people marketing the lipo. Those numbers are always inflated, as there is no standard. In their own mind, it's correct, in reality it will damage the lipo when you do follow that label but most likely it can handle it for 1s.

Unfortunately, there is no guarantee that a vendor that had good packs in one batch has good packs in the next batch. There are about 5 manufacturers of lipo cells, you are getting premium vs lower class, that is all.

Yes I should have clarified, the C rating for the charge is multiplied by the capacity. So if the battery is rated at 1C charge rate and it is for example 5,000 milliamps then you would be able to charge it at 5,000 milliamps which is 5 amps. If it was rated at 2C you would be able to charge it at 10amps.

Personally I am only comfortable charging at maximum 1C.

I did find a handy calculator Here
That lets you input the batteries internal resistance and capacity and gives you a more conservative / realistic value of the batteries actual discharge C rating.

 

[Jerold]

+1 on https://www.radiocontrolinfo.com. He has lot of good stuff and he does the math for you and I love math... However, the math is not the real world.

Your math is right from a one dimensional perspective. The problem is this is multi-variable function that uses, charge, time voltage, current, heat, internal resistance, in chemical reaction and probably a few other things I forgot.

SMC Racing does a pretty good job of explaining how they create their C ratings. Mathematically the C rating is a function of the current demand (Amps) and the mAH of the battery. C=Amps/mAH. So if you have large battery it can have a lower C rating and sill deliver the same current.

For example an 8000 mAH battery rated at 65C can provide 500A. Likewise a 5000 mAh battery rated 100C also can provide 500A.

If the battery is 5000mah a safe charge rate is 5A.You can charge batteries can charge above 1C, but if you do, it will reduce life of the battery and increase likelihood of fires.

Damage maybe; although, I don't know if you will get a fire from this? I've seen over voltage will create a fire, I'm not sure about over current? If someone has done this please post back​

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The manufacture will give a maximum charge rate. It's not uncommon to see max charge rates at 2C or even 10C for LiPo. For other technologies it might be less than 1C. Exceeding the manufactures recommendation will void your warranty and may damage the battery. Read the manual and follow the instructions.​

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If you have a battery that has a discharge rate of 50C (same unit) it means the amps draw limit is 50*mah.

The maximum current it can deliver is 1C * 50. If you have a 3000 mAh battery, then 1C is 3A. If the C rating is 50C then you you can in theory get 150A (3X50) from the battery. But there is no time value, so it could be 150A for 1ms or 1min or 1 hr, I dunno. However, most test are done with a constant current draw to see the voltage degrade. That's were you need to see the discharge curves. Other than SMC I don't typically see the curves published.​

This is still a test, in a lab, under controlled conditions. In the real world the current demand is not an absolute singular number. The conditions are changing constantly when you drive. Your current requirements change and the voltage from the battery changes as well as the amount of charge left.​

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You can charge batteries can charge above 1C, but if you do, it will reduce life of the battery and increase likelihood of fires. If you "can" charge about recommended limit for the battery, you increase likelihood of problems.

Remember this is a chemical process and it takes time to happen. Theoretically the slower the charge rate the better it is for the battery. Since our batteries don't have a built in Battery Management System (BMS) it's up to us to ensure they are treated well and kept healthy. Back to follow the instructions.​

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If I am correct, it is the same with discharge rates. You can discharge about 50c, but if you do, you will increase damage to the battery. If you do it enough.

Batteries can only provide so much current. If you ask more they typically just tell you "Sorry Dave, I can't do that". Could you damage it, perhaps but it has to be extreme like a dead short (Infinite current). The big limiting factor is the internal resistance. Current and resistance means heat. Heat is not a friend of your battery. Increasing the internal resistance can limit the the ability to provide current.​

​

If you look at better quality batteries they will give you a continuous C ratting and a Maximum burst C rating.

So in theory, yes you can ask for 200C (1500 Amps) from the battery for a very short undefined period of time. The average discharge rate would be 130C (975A). That is the average of the times you are doing nothing and the times you have the throttle pinned. Either way it's a ton of juice that your car is unlikely to ever need. And if you did ask it to give you 975A, your run time would be very short, like 7.6Mins in this case.

So why do they put this number on there - Marketing. It's kind of BS in the end. See what other's are running and buy good batteries.

 

[jkflow]

From a site linked below,

Testing reveals mAh is a variable governed by the Load
Therefore the expression "A = Ah * C" can never be resolved unless the load is known. At the factory mAh is determined by discharging a cell at 1C down to 3.0v. Unfortunately averaging a 15C - 20C load causes lipo to start cooking off when voltage drops to ~3.55v. "C" in actual practice is the measure of a packs ability to resist discharging before running out of juice (Ah). The true measure of this "resistance" is the voltage measured during the given load profile. The true measure of a packs "juice" (mAh) for this given load is how long before voltage drops to 3.5v. After that it's like driving on flat tires, it serves no useful purpose and causes damage.

So "mAh", "C" and "Load" are all interdependent. Weight generally influences temperature rise vs. power over time and can add an element of durability and robustness.


https://www.rcgroups.com/forums/showthread.php?1767093-Battery-Load-Test-Comparisons/page970

 

[RedOctobyr]

View attachment 260328 The average discharge rate would be 130C (975A). That is the average of the times you are doing nothing and the times you have the throttle pinned. Either way it's a ton of juice that your car is unlikely to ever need. And if you did ask it to give you 975A, your run time would be very short, like 7.6Mins in this case.​

Very well said.

But just to clarify something where I think the math came out wrong. If you discharged at a constant 130C (975A in your example), the discharge time is not 7.6 minutes. It's 0.46 minutes, or just under 30 seconds.

A 60C discharge is 1/60 hours, or 1 minute. A 120C discharge is 1/120 hours, or 0.5 minutes.

Put differently, if you discharged your battery in 5 minutes, that's an AVERAGE discharge current of 12C. Spikes of current during actual driving will be higher, of course. But if you just drove in big consistent circles, hard enough to kill a battery in 5 minutes, that's a 12C load.

 

[Jamhu]

Very informative thread so far! I have been struggling to understand the details relating to C rating

 

[jkflow]

Very well said.

But just to clarify something where I think the math came out wrong. If you discharged at a constant 130C (975A in your example), the discharge time is not 7.6 minutes. It's 0.46 minutes, or just under 30 seconds.

A 60C discharge is 1/60 hours, or 1 minute. A 120C discharge is 1/120 hours, or 0.5 minutes.

Yes, must be a typo.

 

[Jerold]

"C" in actual practice is the measure of a packs ability to resist discharging before running out of juice (Ah). The true measure of this "resistance" is the voltage measured during the given load profile.

I'm not sure I follow this? C is the batterie's ability to give charge. I suppose you could invert that (1/C) and say it's in ability to resist charge/discharge (changer energy states) but it doesn't make sense. When it gives energy the baseline is a rate of 0C, no current flows and all the values are positive.

Here is a C rating calculator if you're interested.
https://www.batteriesinaflash.com/c...) Examples of Different C Rating Calculations

They also say "1C rating is the base time which is always equivalent to 1 hour or 60mins." Keep in mind that this is the standard charge rate, where 1C is 1/1000th of your battery capacity.

I think C is often confused or mixed with capacity. Bigger batteries hold more charge and means they can give more energy over time.

So "mAh", "C" and "Load" are all interdependent. Weight generally influences temperature rise vs. power over time and can add an element of durability and robustness.

Correct, if you know your max current required, then you can calculate your required C rating for the capacity of the battery. Assuming they all measured them the same... big if.

Current = (Battery mAh/1000) *C​

These batteries can all deliver roughly the same current with very different C ratings. The difference is how long can they do that.

It turns out if you have a very large battery you don't need a high C rating, because the C rating is a % of the total capacity. This is why parallel configuration are current providing beasts.

If you think of this like a fuel tank - That's what cars had before ya'll bought a Tesla.

Capacity is the size of the fuel tank.
C rating is the flow rate of the fuel with respect to the size of the tank.

If you have two tanks, 1 gal and 10 gals and both have the same flow flow rate. The smaller tank has a higher C rating because it flows more fuel relative to the size of the tank. i.e. it will empty quicker.

 

[#ARRMArcfanboy4life]

If you think of this like a fuel tank - That's what cars had before ya'll bought a Tesla.

Me with my ice swapped tesla...

 

[jkflow]

I'm not sure I follow this? C is the batterie's ability to give charge. I suppose you could invert that (1/C) and say it's in ability to resist charge/discharge (changer energy states) but it doesn't make sense. When it gives energy the baseline is a rate of 0C, no current flows and all the values are positive.

No, offense, your use of analogies is what gets you pointed in the wrong directions. They are good for a certain amount of accuracy, but you would have to adjust your analogies to reality as well. Your pipe diameter is all of a sudden variable, and the reservoir size as well, even the flow rate changes due to teh change in internal resistance and rising temperatures.

The entire point of the article is that the C-rate is always advertised and printed on the Lipo as a fixed value. That is horribly misleading in real world applications.

The equation stays, but they are not fixed values as we always assume. The magic threshold of 3.5V always stays and anything below is causing Lipo damage, no ifs or 'buts' about it, it simply does even if the Lipo recovers to a higher value once the load is gone.
All that is backed up with verifiable real world data, while the manufacturers (many) continue to mislead with printed values. Even the best distributors have to follow this labelling in order to maintain market share, as the typical consumer just looks at high numbers, while in reality these can either never be achieved or only for 1-2s while others truly achieve these values over 1 min (max loads) on a Lipo that is marked exactly the same. Technically, they are the same, but which one would you buy, and how would you know without prior testing?

Next problem, these values are never constant between manufacturing batches, and they will change based on market availability, hence, last batch high performer can be next batch worst performer. There are ~4-5 distributors that consistently stay in the high performance world, while you have the tail end wagging all over the place, but none of them come close to the top performers.

The guy at the linked article is doing yearly testing based on given real world loads and relies on donations.

Personal example, Zeee (~2 years ago), very good performer and had advertised capacity with horribly overrated C rating. Last year, bought a new batch, absolute junk and barely got 60% of advertised capacity and can barely use them in cars but impossible in boats.

 

[Jerold]

No, offense, your use of analogies is what gets you pointed in the wrong directions. They are good for a certain amount of accuracy, but you would have to adjust your analogies to reality as well. Your pipe diameter is all of a sudden variable, and the reservoir size as well, even the flow rate changes due to teh change in internal resistance and rising temperatures.

The entire point of the article is that the C-rate is always advertised and printed on the Lipo as a fixed value. That is horribly misleading in real world applications.

The equation stays, but they are not fixed values as we always assume. The magic threshold of 3.5V always stays and anything below is causing Lipo damage, no ifs or 'buts' about it, it simply does even if the Lipo recovers to a higher value once the load is gone.
All that is backed up with verifiable real world data, while the manufacturers (many) continue to mislead with printed values. Even the best distributors have to follow this labelling in order to maintain market share, as the typical consumer just looks at high numbers, while in reality these can either never be achieved or only for 1-2s while others truly achieve these values over 1 min (max loads) on a Lipo that is marked exactly the same. Technically, they are the same, but which one would you buy, and how would you know without prior testing?

Next problem, these values are never constant between manufacturing batches, and they will change based on market availability, hence, last batch high performer can be next batch worst performer. There are ~4-5 distributors that consistently stay in the high performance world, while you have the tail end wagging all over the place, but none of them come close to the top performers.

The guy at the linked article is doing yearly testing based on given real world loads and relies on donations.

Personal example, Zeee (~2 years ago), very good performer and had advertised capacity with horribly overrated C rating. Last year, bought a new batch, absolute junk and barely got 60% of advertised capacity and can barely use them in cars but impossible in boats.

I totally agree. It's constantly changing, even the voltage changes just from environmental conditions. I use the analogies as something that is relatable. It's a chemical reaction that depends on a lot of variables, well beyond any modeling you can do with an on-line calculator.

However, if we understand the high level on what to look for it helps sort out the BS from reality. Not need to dry lab the chemistry and look for the last microvolt.

 

[Hector_Fisher]

Capacity is the size of the fuel tank.
C rating is the flow rate of the fuel with respect to the size of the tank.

If you have two tanks, 1 gal and 10 gals and both have the same flow flow rate. The smaller tank has a higher C rating because it flows more fuel relative to the size of the tank. i.e. it will empty quicker.

Something that is worth reiterating here that I'm not sure is being understood is that the specs and math in Lipo calculations are not fixed. Even knowing the discharge amperage and labeled capacity won't give you the full picture about how a lipo performs or what the actual capacity will be. Returning to an early quote:

So "mAh", "C" and "Load" are all interdependent.

Thus, Mah is not the full picture about the size of the fuel tank since the size of the fuel tank (or rather how much you can extract out of it) for lipos depends on how hard you drive, or the load.

As stated in the rcgroups forum:

"Testing reveals mAh is a variable governed by the Load
Therefore the expression "A = Ah * C" can never be resolved unless the load is known. At the factory mAh is determined by discharging a cell at 1C down to 3.0v. Unfortunately averaging a 15C - 20C load causes lipo to start cooking off when voltage drops to ~3.55v."

End user testing is really the key to determining which lipos are the best. And understanding how LOAD affects the picture is really necessary for understanding C rating and capacity. We could not trust the manufacturers or companies to provide accurate info on this only because the performance of their cells is depends on how you use them.

A couple of takeaways you can make:
- all batteries can discharge at crazy high amps once. The question is whether "repeatability" is possible afterwards. Better lipos are more likely to repeatedly be able to produce high amperage discharges.
- battery voltage less than 3.5v per cell is bad for the lipo. This applies for resting voltage (ie, after you take the lipo out of the RC and head home and check on your charger) and transient voltage from voltage sag during load. Poor cells will have shorter life spans and continue to perform worse and worse because voltage dips much lower during load than high quality cells.
- high quality, well designed cells are more efficient than poor quality ones, and will produce less heat under load. Excessive heat is another reason for declining lipo health.

 

[jkflow]

Something that is worth reiterating here that I'm not sure is being understood is that the specs and math in Lipo calculations are not fixed. Even knowing the discharge amperage and labeled capacity won't give you the full picture about how a lipo performs or what the actual capacity will be. Returning to an early quote:

Yes, you said it very well and are spot on.

The gas tank comparison is where most people get confused, as they believe it is a steel container that is fixed, and they just suck out the juice.
In reality, tank size is variable if you increase the 'suck' i.e. it literally deflates in capacity and your 10 gallon tank turns into a 3gallon one, if you discharge at high rates. It does not mean that I sucked out 7 gallons, those don't exist anymore, that is the difference between physical objects and chemical reactions. Rest just turns into heat. This reaction is catastrophic at high rates and below 3.5V.

The tank is empty when the lipo crosses 3.5V, end of story. Many ways to get there, and you get closer to the advertised values at low discharge rates.

Without external damage visible, this is how it looks on the inside:
https://www.arrmaforum.com/threads/anatomy-of-a-dead-lipo.47738/

By all means, I do not understand all these details 100% either, honestly I haven't met a person yet that does. This is based on real world though.