Battery Internal Resistance Measurements

[bapgood]

Retested the 1200 round nano's after charging and they were about the same ~42mΩ.

However DrMA brings up a good point that I overlooked.....break in

All the batteries tested except for the round nano's should be good and broke in. The nano's haven't really been used, so that might skew the reading.

 

[DrMA]

Retested the 1200 round nano's after charging and they were about the same ~42mΩ.

However DrMA brings up a good point that I overlooked.....break in

All the batteries tested except for the round nano's should be good a broke in. The nano's haven't really been used, so that might skew the reading.

Most I've seen IR drop after break in is about half the virgin value, but generally it's much less than that... FWIW

 

[mikepetro]

I dont have any experience in the R/C realm, where most of these LiPos have their roots. I am still trying to grasp the nuances of using them. Please bear with me if I am asking stupid questions, I promise that I learn fast.

In our application, how much does the "C" rating matter. Case in point:

Is there any advantage (in a mod) to using a 60C versus a 25c. For discussion sake, lets assume a 3000mAh bat. The 25c would allow a continuous current of 75 amps, the 60C would allow 180 amps. Both are way more than the measly 5-10 amps that even a DNA30 would use. It would seem to me that even 10C would be more than adequate???

I get that having a bat that can "comfortably" handle the current , i.e. not at its top range, will prolong the life of the bat by not stressing it as much. But is there any advantage to "us" over 25C?

I ask because I am shopping for my next bat, and it is pretty clear that the higher the C rating the more the bat costs, I even see 100C bats out there now, albeit at about $100+.

 

[BJ43]

I dont have any experience in the R/C realm, where most of these LiPos have their roots. I am still trying to grasp the nuances of using them. Please bear with me if I am asking stupid questions, I promise that I learn fast.

In our application, how much does the "C" rating matter. Case in point:

Is there any advantage (in a Mod) to using a 60C versus a 25c. For discussion sake, lets assume a 3000mAh bat. The 25c would allow a continuous current of 75 amps, the 60C would allow 180 amps. Both are way more than the measly 5-10 amps that even a DNA30 would use. It would seem to me that even 10C would be more than adequate???

I get that having a bat that can "comfortably" handle the current , i.e. not at its top range, will prolong the life of the bat by not stressing it as much. But is there any advantage to "us" over 25C?

I ask because I am shopping for my next bat, and it is pretty clear that the higher the C rating the more the bat costs, I even see 100C bats out there now, albeit at about $100+.

Just from my RC experience (I am no expert on batteries or anything else for that matter) but, the higher the C rating the longer my run time on the same mAh rated battery and most seem to take many more charges before going bad. Why? IDK...

 

[bapgood]

In general the higher the c-rating the flatter the discharge curve is going to be.

In planes/helis its more about power to weight ratio, in cars/trucks its less about weight and more about max power that your able to achieve and stay within the racing class requirements.

In our application I would be surprised to see a major difference between a 30c and 100c with the same mAh. (as long as your well over the amp limit)

Remember A x C-Rating = Max Amp

 

[bapgood]

Just from my RC experience (I am no expert on batteries or anything else for that matter) but, the higher the C rating the longer my run time on the same mAh rated battery and most seem to take many more charges before going bad. Why? IDK...

I believe this is due to the low internal resistance and the batteries ability not to keep the internal resistance lower over many more charges. The hows and whys I don't really know.

 

[mikepetro]

I may have to swallow my pride and go back and try HobbyKing again. They do seem to have the best prices on non-Team-sponsored LiPos. I see lots of nice bats out there, but I learned pretty quick that if a bat is sponsored by a "Team" it will be pricey.

That being said, the form factor of this bat keeps grabbing my attention, at 69 x 47 x 18.5 mm it is pretty Mod-friendly.

CRC 4200mAh 1s (3.7v) 65C Shorty Lipo Battery, 4mm Bullets, CRC3703

 

[BJ43]

I believe this is due to the low internal resistance and the batteries ability not to keep the internal resistance lower over many more charges. The hows and whys I don't really know.

On RCs I might charge (fast charge) 3 or 4 times in a weekend, then go a month or more without using the battery. With ecigs I basically recharge (slow charge) every night. Even so I have had some Zippy batts in th 20C rating last only a few months... Also have had to jump start a few after sitting for a month or more.

 

[BJ43]

Those shorties can be very expensive...

Why not just 3 1400 mAh cells? Much cheaper.

Or this converted to parallel. 3900 mAh

http://www.hobbyking.com/hobbyking/..._1300mAh_3S_30C_Lipo_Pack_USA_Warehouse_.html

 

[mikepetro]

Those shorties can be very expensive...

Why not just 3 1400 mAh cells? Much cheaper.

Or this converted to parallel. 3900 mAh

Turnigy 1300mAh 3S 30C Lipo Pack (USA Warehouse)

Good idea. Still skittish about soldering these things, but I am sure that will dissipate with experience.

 

[mikepetro]

On RCs I might charge (fast charge) 3 or 4 times in a weekend, then go a month or more without using the battery. With ecigs I basically recharge (slow charge) every night. Even so I have had some Zippy batts in th 20C rating last only a few months... Also have had to jump start a few after sitting for a month or more.

Explain "Jump Start" please.

Is that where a bat is over discharged?

I have read something about hooking up a ni-cad charger to them to get the min-v up high enough to take a charge.

Is this what you are referring to?

 

[Visus]

On a side note Traxxas has an electric RTR that does 100mph out the box because of these new batts.. They are powerful...

Some people homes still run on a 50 amp service.... In 1920 OMG awesome, we'll never need more than 50amp service for most homes..

Its just wow I also am an ol school r/c guy back in 80's and 90's and I remember the new lithium ion 2500mah battery being the biggest buzz and inflated price. It was an amazing battery, I was king of the hill at the track lol--- Thank you cell phones which gave more R&D for this and helped bring the price, and size, down..

 

[mikepetro]

If only cell phone bats had a higher C rating this would be easy.

Sent from mobile, excuse brevity

 

[DaxFX]

Ive being flying RC helis , planes , and running cars before lipos get into market, just for let you know, "C" will not give more runing times, mAh do that, "C" stands fo "C"apacity that means how many times the capacity in mAh the battery can discharge,

mAh = miliamp/hours tells you how many miliamps will take to drain the bateri in a continous load of 1c in 1 hour

1000mAh = 1amp

So lets say a 1600mah battery at 30c discharge that 1600mah = 1.6amp, 30c = 30 times the Capacity, so 1.6x30=46amp safe,

Hope this clarify some of you,

Here is a link you can use for calculate your C rating and safe amp based on your IR reading.

http://www.jj604.com/LiPoTool/

I do have the megameter from hobbyking, i use it for reading the watts of my machines and rpm os the propellers, is pretty acurate and a good tool

You can find my aerial videos to have a bit of fun on youtube/daxfx




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[DrMA]

Those shorties can be very expensive...

Why not just 3 1400 mAh cells? Much cheaper.

Or this converted to parallel. 3900 mAh

Turnigy 1300mAh 3S 30C Lipo Pack (USA Warehouse)

Doing surgery on live LiPo's is extremely dangerous. I would not recommend this approach - there are plenty of inexpensive alternatives available that do not require taking apart a live multi-cell pack.

 

[bapgood]

Dax, your information is mostly accurate.

My point is that higher c-rated batteries are typically higher quality cells and see less voltage sag under load.

mAh doesn't mean a thing if the voltage is dropping to an unusable level. So to say "just for let you know, "C" will not give more runing times, mAh do that" is not 100% accurate. I know first hand from RC and vape experience that I can get longer run times out of higher c-rated batteries with a flatter discharge curve, the usable voltage stays higher longer....thus longer run time.

 

[mamu]

Thanks for the testing, bap!! I KNEW the Efest and MNKE batts were pos and you proved it.

..Is there any advantage (in a Mod) to using a 60C versus a 25c.

As long as the 25C battery can supply enough current for the demands of the load, there is no advantage for having a 60C rated batt vs a 25C rated batt.

BUT you have to look at the whole picture for that 25C rating - you may find a 25C rated batt may not be adequate for you and your vaping needs.

First, look at the batt's capacity to determine the amp value of that 25C rated batt:
500mAh x 25C = 12.5A
1000mAh x 25C = 25A
2000mAh x 25C = 50A

As you can see at certain capacities you can opt for a lower C rating, and at certain capacities you may need a higher C rating.

Then determine what demand (load) you require. I normally pull around a 4A - 5A load @ 15W, sub ohmers are pulling 2x that and some are pulling a LOT more and @ 30W - 50W. You want to choose a batt with a rating that far exceeds your load requirement to have it operate efficiently without stress.

Then consider the max current of the converter you're using. For the Raptor which can push a 20A output, I choose batts with a discharge rating that either equals, or more preferrably exceeds, the max capable of the Raptor. For me and my vaping needs, that's overkill, but for sub ohmers and their vaping needs, it's not. BUT that converter has the capability to output 20A if the vaper pushes it to that - and the batt should have the capability to keep up without stress.

Lastly, and this prob should be firstly look at the internal resistance of the batt. A batt with a high internal resistance, no matter the C rating, is going to give you shorter vape run times and cut out at higher volts than a batt with lower internal resistance. And more especially so if you vape at higher watts or volts.

For example, as bap shows us in the OP, the MNKE batts have horribly high internal resistance - the Efest batts do too. Those batts are going to cut out on you at 3.8v - 3.9v unloaded (drops to 3v loaded) because of their high internal resistance - no matter it has a high amp capability - vs a batt like the Sony with the exact same amp capability that has a lower internal resistance and will cut out on you around 3.2v unloaded (drops to 3v loaded).

I don't know how many times I've been asked what's wrong - the DNA won't fire and the batt has lots of volts left at 3.8v. Then I find out that they're trying to push the DNA at 17W with an Efest batt.

So you can see with internal resistance, a 30A Efest batt that cuts out at 3.8v is going to leave you frustrated vs a Sony 30A batt that cuts out at 3.2v. BUT they both have the same 30A rating.

 

[bapgood]

Well written Mamu!!!!

Someday I will figure out how to better articulate these things

 

[DrMA]

I guess the one thing that comes out of this discussion is that there is no standardized way of determining C-rating for a LiPo, and most manufacturers tend to overstate the true capabilities of their product. In reality, C-rating should be very closely tied to the pack IR, as shown by the calculator linked by Dax above (Lipoly Objective Performance Calculation Tool REV5.xlsx).

High IR, not only causes excessive voltage sag under load, but also heats up the battery when in use, which in turn accelerates wear on the battery. That's why low IR packs tend to have a longer service life.

 

[DaxFX]

Dax, your information is mostly accurate.

My point is that higher c-rated batteries are typically higher quality cells and see less voltage sag under load.

mAh doesn't mean a thing if the voltage is dropping to an unusable level. So to say "just for let you know, "C" will not give more runing times, mAh do that" is not 100% accurate. I know first hand from RC and vape experience that I can get longer run times out of higher c-rated batteries with a flatter discharge curve, the usable voltage stays higher longer....thus longer run time.

Higher C rating does not mean a higher quality battery, they are batteries with same brand same mah same qualities at diferent c rating, that depends on your needs, they are cheap battery with high c rating that you can use 10 times and thr IR shoots to the sky making unusable, they are batteries with low c rating that after a year of use the IR stay were is suppose,

For example, i have one of my planes that need 30amps @ 12v so a 2200mah 3cell 30c would be enough for my plane, in this case a higher c rating means a hevier bigger cell with same internal quality of the lighter smaller cell and the higher c will be hevier so my plane will draw more amps and reduce flight times, my point is not higher c rating the better the quality,

Higher c rating yes retain the nominal voltage longer than lower c rating but is irrevelant in the vaping world, the diference you will get in this small bateries is not noticable, just use what ever you need to supply the amps you need

By the other hand, in my helicopter that use 2x 5000mah 6 cells in serie a drop in every cell when you multyply by 12 cells will make a real big diference

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