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Batteries & Chargers Discuss Li-P, Li-Ion, NiMh, Nicad battery technology and the chargers that juice 'em up!

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Old 03-10-2017, 04:50 AM   #1
dereckbc
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Default LiPo C-Rate Testing Protocol

OK this is not a debate or pissing contest, just me sharing test results and trying to find a Test Protocol to find the true C-Rate. Most of you likely know there is no defined test standard by BCI or the battery industry to test C-Rates. It is purely an arbitrary number manufactures give their batteries they feel is a safe thermal limit. As such all xC Rates vary widely under load. I am a bit of a battery nerd, and an electrical engineer with 40 years experience working with batteries. I have worked with all major industrial, commercial, and consumer batteries used in telecom and utilities. I even sat in IEEE battery committee to develop battery practices and standards. Thus I have access to a lot of professional lab quality battery test equipment. I can measure all battery parameters with excellent accuracy to see what is going on inside.

OK C-Rates is a function of the batteries Internal Resistance and the amount of current flowing through the battery in charge and discharge modes. Example if you have a 20C 3S Lipo battery is useless if you apply a 20 C load current and the voltage drops 3 volts or 1 volt per cell. So where I have drawn the line to test C-rates is to apply a load, increase the current until I achieve a .3-volt per cell voltage drop. There is some data or sources to back up a .3 volt drop. So if you have say a 3S Lipo with an open circuit voltage is 12 volts, apply the load current until the battery voltage drops to 11.1 volts.

I have several brands of LiPo and three of them pass the mustard and meet my test protocol. Thunder Power and Gens Ace are excellent and if they are rated 30C, the test results say they are under rated and will do better than spec. To my surprise the third one is Glacier sold by Buddy RC. I think I have heard Glacier is made by Gens Ace, but I do not know that as fact.

Of the other brands testing I did find one honorable mention. Strangely enough is a Chi-Com product from Turnigy under the Nano-Tech. They come close, and for the money is a very good value.

In the losers category and no surprise is any of Horizon Hobby brand names like Eflite and Park Zone. If you load them to the claimed C-Rate you get .8 to 1 volt sag per cell. Totally unacceptable.
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Old 03-10-2017, 09:51 AM   #2
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Great analysis and thanks for sharing. My 2 best friends over the last few years have been China Hobby Line and more recently Roaring Top (www.rcjetwerx.com)

The RT's are made on the same line as Thunder Power. Talking to a friend who has actually studied the mfg. process for several lipo makers, the key difference amongst them is QC.

Some are assembled in dusty open air conditions while others are assembled in lab environments. After all, there's not much difference in the chemistry. No one has a secret sauce.

What I like about the RT's that is most meaningful, is their power to weight ratio. Given the same C rating and mah, the RT's are typically lighter than most brands. Check it out.

I believe the Gens Ace, TP's are in the same category.

So what is the reason that one has better IR characteristics than another? IMO it's how they pack them. Why is a mfg like RT less weight than many given the same C and mah ? It's how they are packed.

You really do get what you pay for when it comes to lipos and there's a good reason some appear to be dirt cheap. Eflight gets away with putting out garbage because of their name in the hobby. HH should be ashamed of themselves. High price / low quality.

I agree 100% with your findings with the exception of the Nano's. I just never liked them and it's mainly based on longevity. That's just me though.

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Old 03-10-2017, 06:08 PM   #3
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Originally Posted by dahawk View Post
I agree 100% with your findings with the exception of the Nano's. I just never liked them and it's mainly based on longevity. That's just me though.
No problem and I cannot speak to longevity as of yet. All my Turnigy Nano-Tech are just a year old. I wil say I have no puffing problems like I have seen on Glazier packs of the same age. At one year the Internal Resistance has not gone up any meaningful amount. Long term I would say at this point are better than Glazier.

What surprised me is they come close to the manufacture claims. I only bought 4 of them because of the price at the time, and they are good value. My conclusion especially for folks on tight budgets the Turnigy is a good pick.

However I will not be buying anymore because in the last 2 years I have learned Gens Ace put the model I use on sale twice a year for less then what Turnigy cost. I got smart early IMO because I only use 3S 2200 mah battery. Although my new EF 540 EXP can use 3S 2200 mah, they do best with 4S 2200 which I have now obtained 4 of them.

Lastly folks my testing is not an authoritative analysis. I have only tested a few brands that I own and of those only 3S 2200 to 3S 2600 mah. What I can say in those limitations Thunder Power and Gens Ace are the best followed by Glazier. Personally going forward Gens Ace is my favorite because they are less expensive than TP with like performance. and if you catch them on sale are excellent value.

But I am open minded and if someone has something similar I will try one. Got so many batteries now I had to buy a small dorm size fridge to store them in.
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Old 03-10-2017, 07:30 PM   #4
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If you really want to know the true C rating of your lipos, this is the best tool on the market for that:

http://www.progressiverc.com/univers...sis-meter.html

I have one and it has really been eye opening. So far the best packs I've tested personally are the Turnigy Graphenes. The 45C rated pack is good for true 30C. That means my 4000mAh packs are good for 120 amps no problem, and they have been living up to that no problem.

I need to get some RTs and try them too.

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Old 03-11-2017, 02:16 AM   #5
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Originally Posted by crxmanpat View Post
I have one and it has really been eye opening. So far the best packs I've tested personally are the Turnigy Graphenes. The 45C rated pack is good for true 30C..
If that is the case then the Turnigy battery is greatly exaggerated. 45C should be 45C minimum, not 30C
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Old 03-11-2017, 10:50 AM   #6
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The Wayne Giles meter posted my Pat is a good tool, but it measures IR, not C rating. There is no 'industry standard' conversion from IR to C rating. End users have come up with some methods but it's just 'made up', so you need to take with a pinch of salt.
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Old 03-11-2017, 05:18 PM   #7
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Originally Posted by JetPlaneFlyer View Post
There is no 'industry standard' conversion from IR to C rating. End users have come up with some methods but it's just 'made up', so you need to take with a pinch of salt.
True there is no industry standard, it would have to come from BCI (Battery Council International). I do not think I would call it made up. One thing for sure it is NOT a performance specification. I will say it again, IT IS NOT A PERFORMANCE SPECIFICATION.

So if you buy high C-Rate batteries because you think they work better, you just wasted your money and took the bait.

All the C-Rating means is an arbitrary Thermal number the manufacture is comfortable with. In other words if you pull say 30C current, the battery will not burst into flames. Strictly a manufacture liability issue, NOT PERFOMANCE.

C-Rate and the battery Internal Resistance are related and also associated with the thermal mass of the battery. I checked that meter out and it measure a battery Internal Resistance, and then uses a formula to determine C-Rate. Still working on what that formula is. They are not saying.

But ask yourself this. What good is a C-Rate if say you have a 4S, 2000 mah, 30C battery and if you pull 60 amps and the voltage drops from 15 volts to 10 volts?

It is not worth a Flip. That tells you the battery Internal Resistance including the wiring = [15 volts - 10 volts] / 60 amps = .083 Ohms. Guess what happens as the battery ages? The resistance goes up.

IMHO it needs to be a Performance Based specification. Something like CCA or cold cranking amps. CCA tells you something. FWIW CCA means how much current a 12 volt battery can deliver for 30 seconds, at 0 degrees F, at 7.2 volts. Again that is an Internal Resistance function. We can calculate the resistance of an 800 CCA battery = [12.6 volts - 7.2 volts] / 800 Amps = .00675 Ohms.
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Old 03-11-2017, 06:38 PM   #8
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Originally Posted by dereckbc
IMHO it needs to be a Performance Based specification. Something like CCA or cold cranking amps. CCA tells you something. FWIW CCA means how much current a 12 volt battery can deliver for 30 seconds, at 0 degrees F, at 7.2 volts. Again that is an Internal Resistance function. We can calculate the resistance of an 800 CCA battery = [12.6 volts - 7.2 volts] / 800 Amps = .00675 Ohms.
You are our grand prize winner today! I believe that your voltage drop criteria needs to be combined with a temperature limit of 130 at maximum C rated draw. And then you need an independent certifying entity, like DereckBC Inc!

I don't know how you make that a profitable enterprise, but I would hope reputable battery manufacturers would be willing to pay for valid evaluation.

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Old 03-11-2017, 08:35 PM   #9
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Well RR if it happens will come from demand of the EV Industry to put pressure on BCI and manufactures. Don't anyone take this wrong but BCI, IEEE, and ANSI are not to concerned with Toys and that is how they view RC LiPo's because no one life or property are put at any significant risk.

If I were the Czar it would be both Performance and Thermal with 2 ratings similar to what we have today.

1. A performance rating of continuous C-Rate @ 0.3 volts per cell meaning you could run the battery from fully charged to exhausted and not over heat or loose more than .3 volts per cell.

2. A thermal or Burst rating of 10 seconds and 60 seconds rest.

So it might look somethin glike C20/60. The EV industry with large format cells already do something like that but is done behind the scenes. EV's do not need as much as our planes. An EV battery is rated more like 3/10 and that is a lot of overkill. An EV at cruise speed on uses C/2 to C/5 as high C rate is only for acceleration.
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Old 03-11-2017, 10:06 PM   #10
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I, for one, would love to see this happen, at least in a respectable independent fashion. It wouldn't have to even be anything official, just an independent rating of hobby batteries.

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Old 03-12-2017, 03:16 AM   #11
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I just pulled 45 amps leak out of a 20c rated 2200mah 3 cell hobby king battery. It was way above the 30 amp rating of the esc, over propped a bit I guess. I was surprised by it though. I dont think ive had a battery that wouldnt hit peak amperage unless it was seriously abused.

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Old 03-12-2017, 04:34 AM   #12
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Originally Posted by hayofstacks View Post
I just pulled 45 amps leak out of a 20c rated 2200mah 3 cell hobby king battery. It was way above the 30 amp rating of the esc, over propped a bit I guess. I was surprised by it though. I dont think ive had a battery that wouldnt hit peak amperage unless it was seriously abused.
Most any battery can do that. The issue is how much voltage drop there is. That 45 amps does not do much good if your pack voltage sagged to 5 volts.

One specification you rarely see published, and if it were is invaluable information called Short Circuit Current. Mathematically SCA = Open Circuit Voltage / [Internal Resistance + Circuit Resistance] . For a 3S 2200 mah battery could be as high as 200 amps just before it explodes. However the voltage would be 0 volts. 0 Volts x Any Current = 0 Watts.

SCA would be very useful because it tells you the battery Internal Resistance.
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Old 03-13-2017, 01:25 AM   #13
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Practical exercise in light of your previous comment (I'm in total agreement) regarding Eflite batteries.

I just bought an Eflite UMX Waco BL with an Eflite 280mAh battery. I was at the hobby store, my favorite online store, Heads Up RC, doesn't carry anything close to a 300mAh 2S battery and can't justify ordering only a couple of batteries from Hobby King.....I pulled the trigger on the Eflite 280mAh 2S 30C battery.



So check out the little sticker on the battery. Glad to see they employ comedians: "3C Maximum Charge Rate (2.1 Wh)"


How much trust do I put in the company who thinks it's appropriate to charge 130mAh 1S 20C batteries at 4C for my UM T-28 and Vapor? Just look at the charger settings. 1C for this baby and not a half C more! Yikes.

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Old 03-13-2017, 02:41 AM   #14
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Originally Posted by Rockin Robbins View Post
Practical exercise in light of your previous comment (I'm in total agreement) regarding Eflite batteries.

I just bought an Eflite UMX Waco BL with an Eflite 280mAh battery. I was at the hobby store, my favorite online store, Heads Up RC, doesn't carry anything close to a 300mAh 2S battery and can't justify ordering only a couple of batteries from Hobby King.....I pulled the trigger on the Eflite 280mAh 2S 30C battery.



So check out the little sticker on the battery. Glad to see they employ comedians: "3C Maximum Charge Rate (2.1 Wh)"


How much trust do I put in the company who thinks it's appropriate to charge 130mAh 1S 20C batteries at 4C for my UM T-28 and Vapor? Just look at the charger settings. 1C for this baby and not a half C more! Yikes.
For whatever reason I cannot see the image.
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Old 03-13-2017, 05:27 PM   #15
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The Wayne Giles ESR meter actually does give you a C rating for each cell based on IR, in addition to how many constant amps that cell can safely provide. I have found it a very useful tool for deciding with batteries to use in which setups.

I have switched to using the Graphenes in most of my jets now. And even pushing the pack with a lot of WOT flight, the packs barely come down warm (whereas some of my others pack that claim a higher C rating still get very warm). This way I don't push the packs by using them in setups that demand more amps than the battery can handle without damaging the pack.

The key to getting a good IR reading (and subsequently a good C rating) is to let the packs "soak" in ambient 73 temps for a couple of hours. Otherwise, it will throw off the readings. I keep my house at 73, so it works out.

Pat Gagnon
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Old 03-13-2017, 07:28 PM   #16
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Originally Posted by crxmanpat View Post
The Wayne Giles ESR meter actually does give you a C rating for each cell based on IR, in addition to how many constant amps that cell can safely provide. I have found it a very useful tool for deciding with batteries to use in which setups.
So how does it calculate C rating? Do you have to manually input the mAh capacity? (C rate cant be calculated without knowing battery capacity).

Even if that is the case it's still only giving Wayne Giles' opinion on what the C rate is, because as pointed out in this thread there is no industry standard way to work it out.

***EDIT*** yes, you are right, the C rate calculation was added at the last version of the meter, previous versions didn't do it... And yes, you have to manually input the mAh capacity, and yes it's just based on the heat build up rule (derived from battery weight and energy input) that was dreamed up by end users, it's not an officially recognised calculation.... (That's not to say it's not a realistic figure)
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Old 03-13-2017, 07:37 PM   #17
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It's also funny that there's some mfg's who claim they are using Graphene but are actually not. Buyer beware?
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Old 03-13-2017, 08:28 PM   #18
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Originally Posted by dereckbc View Post
Most any battery can do that. The issue is how much voltage drop there is. That 45 amps does not do much good if your pack voltage sagged to 5 volts.

One specification you rarely see published, and if it were is invaluable information called Short Circuit Current. Mathematically SCA = Open Circuit Voltage / [Internal Resistance + Circuit Resistance] . For a 3S 2200 mah battery could be as high as 200 amps just before it explodes. However the voltage would be 0 volts. 0 Volts x Any Current = 0 Watts.

SCA would be very useful because it tells you the battery Internal Resistance.
If it would have gotten close to the 3.5 volt pet cell cut off, then the esc woukd have throttled it down due to the low voltage settings. I was using a watt meter attached to the plane.

Realistically, you wont be doing 100% for more then a few seconds and amp draw is generally lower in flight then it is on the ground.

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Old 03-13-2017, 09:57 PM   #19
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Originally Posted by JetPlaneFlyer View Post
So how does it calculate C rating?
I think you already answered your own question, but for those folks asking the same question it does it with a math formula calculation using the Internal Resistance, Number of Cells, and amp hour capacity. They will not divulge the formula because if you had it would not need to buy their meter. Any good Hobby Charger wil give you the Internal Resistance.

This is the whole point of this thread. It is not a Performance spec, it is an arbitrary number the manufacture is comfortable with. It is a Thermal Calculation WAG.

Like I said a 2200 mah cell rated at 20C continuous is not worth a damn if cell voltage falls off a cliff to 3 volts if fully charged pulling 60 amps. Example that would be 9 volts on a 3S pack.

Heat generation is a product of resistance and current. Watts = Current x Current x Resistance. If you have a pack with say .02 Ohms with 60 amps load, the battery is burning 72 watts as waste heat and that would make a 3S 2200 mah battery hot real fast. Put that all together with a fully charge battery of 12 volts, and the voltage drops to 10.8 volts to the ESC. 72 watts as wasted battery heat and 650 watts to the ESC. Before you even consider the ESC/Motor efficiency you have already lost 11% of power. Throw in ESC/Motor losses and you have lost 30 to 40% of electrical power as waste heat.

IMHO as an EE the C-Rate needs to be a performance based Spec of how many Amps can the battery supply until you reach a voltage drop/sag of 0.3 volts per cell. In effect that would bring to C-Rate down considerably. Using the above example that 30C 2200 mah pack would drop to .9 volts / .02 Ohms / 2.2 = 20C. That would tell you as the user the battery will perform OK up to around 40 to 45 amps. Not the 65 amps the manufacture leads you to believe.

I base that .3 volts per cell on test results and some data I have read. TP and Gens Ace meet that criteria. Otherwise from what I have seen is you can slash 1/3 to 1/2 off lessor quality cells.
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Old 03-13-2017, 10:16 PM   #20
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Originally Posted by dereckbc View Post
For whatever reason I cannot see the image.
Anybody else not see the image? It's hooked to photos.google.com and displays fine on my machine.

In the meantime, Dereck, I'm charging at .3 Amps for a very slightly over 1C rate. No trust for Eflite here!

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Old 03-13-2017, 10:52 PM   #21
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Originally Posted by Rockin Robbins View Post
In the meantime, Dereck, I'm charging at .3 Amps for a very slightly over 1C rate. No trust for Eflite here!
Well butter my but and call it a bisquit. Around 4 years ago when I got into the hobby I seem to recall someone on another forum calling me a shill because I did not have nice things to say about HH and my Apprentice SAFE RX Brown Outs and causing me to crash.
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Old 03-14-2017, 01:34 AM   #22
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Well, I think aerodynamically their planes tend to be excellent. Had the chance to fly an Apprentice S for the first time last month and was astounded what a great flier it is.

But Horizon batteries and servos tend to be merely adequate. You can fly a plane with them and they won't let you down........often. But when the charger for my Vapor charged the 1S battery in fifteen minutes, I figured out the charger was more an oven than a charger. And then this 2S 30C battery recommended at 3C charge? Yikes. I'll bet it's at best a 20C battery and a 3C charge cuts its life in half.

I can't deny it. Four years ago I thought you were a clown short of a rodeo with your denunciation of the Apprentice S and I thought Horizon was due some cooperation and a chance to fix it. Well it turned out you knew what you were talking about and got the problems worked out. I was the idiot in that exchange, no doubt about it. Being an idiot is a tough job and somebody's got to do it once in awhile. Who better than me?

I've discovered over the years that you're one who figures things out and has a level head on your shoulders. I'd fly with you any time!

Hey, I'm really impressed with my UMX Waco BL. It's quicker than I am but what a fabulous flying plane! I have to learn how to land all over again with all that biplane drag!

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Old 03-14-2017, 02:40 AM   #23
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Originally Posted by Rockin Robbins View Post
I can't deny it. Four years ago I thought you were a clown short of a rodeo with your denunciation of the Apprentice S and I thought Horizon was due some cooperation and a chance to fix it. Well it turned out you knew what you were talking about and got the problems worked out. I was the idiot in that exchange, no doubt about it. Being an idiot is a tough job and somebody's got to do it once in awhile. Who better than me?
RR we are good. I was just poking fun at you. The joke was an inside one just between you and I.

I have mixed feeling with HH. To their credit their customer service is second to none. Yes the Apprentice is an excellent plane and I still recommend it to any beginner. Granted being a Private Pilot I have a heads up on beginners, but I learn how to fly RC with no instruction, just the Apprentice. My Radio is Spektrum and all my RX are Spektrum.

FWIW to you charge no battery faster than 1C. They will last longer and a lot less chance of letting the Magic Smoke out of them. The benefit of faster charge time IMO does not counter all the negatives. But I do have one advantage, I am semi-retired, never need to work another day in my life, and primarily only use 1 battery, a 3S 2200 mah 30C battery. I have a lot of them. I take 6 to the flying field along with a charger. I can fly all day long.

I still have the Apprentice, it is in 1 peice, and air worthy. I train kids and prospective members with it. I have a Boy Scout Troop coming next weekend to earn their earn their Airman's Patch. They have to bring their parent$.
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Old 03-14-2017, 07:44 AM   #24
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Originally Posted by dereckbc View Post
I They will not divulge the formula because if you had it would not need to buy their meter. Any good Hobby Charger wil give you the Internal Resistance.
The main point of the Wayne Giles meter is to do accurate IR measurement (as opposed to chargers which aren't considered accurate and give widely varying results).
The C rate conversion was only added as 'icing on the cake' at the most recent version of the meter and the conversion itself is a freely available utility found here: http://jj604.com/LiPoTool/

The formula is very simple based on P=I^2.r plus an empirically derived 'fudge factor' of 6 (at least it used to be 6 when they first made the tool, it may have been tweaked since). My version in Excel is attached.


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Old 03-15-2017, 12:51 AM   #25
dereckbc
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Originally Posted by JetPlaneFlyer View Post
The formula is very simple based on P=I^2.r plus an empirically derived 'fudge factor' of 6 (at least it used to be 6 when they first made the tool, it may have been tweaked since). My version in Excel is attached.
Well thanks for sharing, it does shine some light on the subject.

The website calculator does not reveal the formulas anywhere that I can find. Now from your spreadsheet it appears you do have the correct formula in Cell D8 for Maximum Continuous Current. However I do not see the relationship of power in the equation. Perhaps I am missing something.

SQRT (mah/Ri *6)

That appears to be some kind of Constant someone came up with. I have no idea what the Factor of Merit is at this time although I suspect if greater than 1 indicates a reasonable model.

After running some numbers initially on your spreadsheet and the website calculator I was liking what I seen. But it falls apart as the cell Resistance goes up, and the FOM falls below 1.

As i opened with I think C-Rate based on .3 volt per cell is a good and safe specification. Also extremely easy to measure and calculate. Where I was liking the formula was using low Resistance.

Example I added a calculation to your spreadsheet so I could observe what was happening. In cell D9 I entered the formula =D8*D9/1000 or Maximum Continuous Current x Cell Resistance so I could see what the Voltage Sag is. If you use a Resistance of 7 milli-ohms or less you get a voltage drop of .3 volts or less. Once you go above 8 milli-ohms the formula falls apart.

That may not sound like a big deal until you realize there are very very few 2200 mah LiPo's out there with less than 7 milli-ohms. Plug in 10 to 16 where most fall and you are looking at unacceptable voltage losses IMO.

Now the industry and users can debate what an acceptable voltage loss should be. The higher the loss, the more destructive heat you generate. At .3 volts you are at 8% loss, and if you twist my arm I could settle for 10% or .37 volts. But that may exceed thermal limits.

So I conclude C-rate is extremely easy for anyone to measure. All you need is the Internal Resistance of the cell under defined test condition of room temps (25C or 77F)at 50% SOC.

Maximum Continuous Current (MCC) = .3 volts / Internal Resistance
Max C-Rate = [MMC / Battery mah Capacity] x 1000

So easy any kid can do it and understand. A pure Performance Spec and HONEST.

Of all my Gens Ace 2200 mah 20C batteries mean average Ri = 6.2 millohms. That would generate a MCC = 48 amps C = 21.8. Spot on Spec. That would work great with a 45 to 50 amp ESC. and what I use.
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