Discharge/Burst

[Knackered Sailor]

Being fairly ignorant of things electrical although gradually learning from knowledgeable people here, can one of you explain what is the meaning of the Discharge and Burst rate on the batteries? 

I've come across a battery same as the HZ one that came with the SC except it's rates are 25/50C does this matter? Or is it ok as long as it is 11.1V 1300mAh?

Thanks.

link

[flydiver]

A lot of C-Rating (discharge/burst) is marketing BS but it does have relevance, and needs to have some attention paid to it.
Read this: sites.google.com/site/tjinguytech/charging-how-tos/the-variable-c

I suggest that you bookmark the site and use it for reference.
Electric RC info, how-tos and such
sites.google.com/site/tjinguytech/charging-how-tos

This is one author that actually knows what they are talking about instead of the usual unsupported claims/opinions you find in forums.

Unfortunately since the C-rating is often an inflated number someone made up you end up stuck with not necessarily KNOWING whether it actually is a good battery or not unless you do some homework. Admittedly, the homework is difficult and often confusing.

[Knackered Sailor]

Thanks flydiver and I think I understand the calculations and I'v certainly bookmarked the guy's site. What I'm not sure of is if a battery has a higher discharge/burst C number than the one supplied with SC is it safe to use or could it burn out the Cub's motor
?

[flydiver]

Jan 20, 2014 18:23:54 GMT 1 @thingy said:

Thanks flydiver and I think I understand the calculations and I'v certainly bookmarked the guy's site. What I'm not sure of is if a battery has a higher discharge/burst C number than the one supplied with SC is it safe to use or could it burn out the Cub's motor
?

Probably not, the motor is pretty robust. Batteries don't PUSH amperage, they SUPPLY amperage. The demand is created by the motor+prop.
When the motor+prop says "give me X amount" IF the battery CAN supply it, it does. If the battery cannot...it shows some sign of failure. Mild failure is lack of performance. Complete failure is rapid voltage drop to LVC.
In all cases there is some voltage drop. A good battery will SUPPORT the voltage. A bad battery sags voltage.

The Cub stock battery (real) C-rating is kinda lame. The voltage will drop to some level when running at WOT.
Let's now put in a MUCH better High C-rated battery. The voltage will also sag at WOT...but not as much. As a consequence the better battery can supply a bit more current at WOT. If some part of the power system is marginal, it's possible that extra little bit my push it over the edge. In the stock Cub that's the ESC, not the motor. In a different system it could be either one.

NOTE-this is ONLY at WOT when you are pushing the system at maximum. At lower throttle it won't make much difference.

In most cases you need to get a C-rating that is HIGH ENOUGH FOR THE SYSTEM DEMAND. More mostly won't hurt. More generally costs more $$ and weighs a little more.

Same with ESC. ESC don't PUSH, they pass along the motor+prop demand. A larger ESC only costs you $$ and weight. Too small is not good. Too big doesn't hurt much.

[hghost]

See allot of that tho I read it over and over...and I Read ALLOT. Still is like reading a foreign language.

Simple English it may be, but Simple English to me is not C*850mah whatever....ya know?

I have an array of batteries, like i have an array of planes.

Each Battery reads different, rare to see any two exactly the same.

I have No Clue how to measure, read, figure,add, subtract,multiply,any of the C rates, WOT with an X or a Z.....times whatever it maybe.....lol

That is how I feel at times trying to understand allot of this stuff.
To me it can get frustrating.

And why I ask so much to get simple answers to get understanding.

I can tell you after i had health troubles my mind does not retain information as it once did, nor is my understanding as clear as it once was. Use to multitask allot, now lucky to understand the simply little things now days. So it takes me awhile to get it.

Here is a momentary READ about the C rating:

“C” rating.

What does it mean?

"C"-apacity begins with “C” so that should give you a pretty good idea. A battery with a discharge rating of 10 C would mean you could theoretically & safely discharge it at a rate 10 times more than the capacity of the pack, a 15 C pack = 15 times more, a 20 C pack = 20 times more, and so on.

Using our 1000 mAh battery as an example; if it has a 20 C discharge rating, that would mean you could pull a maximum sustained load up to 20,000 milliamps or 20 amps off that battery (20 x 1000 milliamps = 20,000 milliamps or 20 amps). From a purely theoretical time stand point, this equals 333 mAh of draw per minute so the 1000 mAh pack would be completely exhausted in about 3 minutes if it's exposed to the maximum rated 20 C discharge rate the entire time. Calculation as follows: 20,000 mA divided by 60 minutes = 333 mAh which is then divided into the 1000 mAh capacity of the pack giving us 3.00 minutes).

Most RC LiPo Battery packs will show the continuous C rating and usually a maximum burst C rating as well. A burst rating indicates the battery discharge rate for short bursts of extended power that. An example might be something like “Discharge rate = 20 C Continuous/40 C Bursts”

The higher the C rating, usually the more expensive the battery. This is where you can save some money. Getting an extremely high discharge rated pack when there is no way you could possibly pull the full amount of power is not required but it won't hurt either. The most important thing is you can't go with too low a discharge C rating or you will damage your battery and possibly your ESC (electronic speed control).
So how do you know what C rating to get when purchasing your LiPo RC Battery Pack? The easy answer most will give is to get the largest C rating you can... If money is not an object I agree with that 100%; but for most folks, especially beginners & intermediate or scale fliers who won't be performing power hungry 3D maneuvers and drawing much current - stretching your RC battery budget by purchasing lower C rated packs when you're first learning so you can get a few extra packs makes much more sense.

As a very general guide line, 25 C to 30 C discharge rated packs are the norm For larger birds, 25 C to 30 C discharge rated packs are a safe bet (again for normal to light sport). Once up to aggressive sport or 3D, that is where the 35 C and up discharge rated packs come into play.
RC LiPo packs are coming down in price all the time. If you find a 35 C pack for the same price as a 25 C when that is all you need, go for the 35 C pack - it will run cooler and have a longer life span. Like most things, pushing a Lipo pack hard close to its limits will wear it out and reduce it's useful capacity in very short order. If however you get a pack with a C discharge rating at least double of the maximum you intend to pull out of it, with proper care, there's no reason you shouldn't be able to get at least 400 charge and discharge cycles out of it with little degradation.

Heat ? taking a temperature reading of your packs after running them is another good way to gauge if you're using a high enough C rating. I'm afraid to say it, but just because a pack says it is rated at 30 C doesn't necessary mean it is in real world applications. Realistically, C ratings are somewhat meaningless because they are rarely verifiable. On top of that, as packs age the internal resistance gets higher making them run warmer and as your flying ability improves, chances are you will be pulling more current.
The general rule is if you can't comfortably hold a LiPo pack tightly in your hand after using it, it's way too hot. This equates to anything higher than about 50 C (122F). That is even way too warm as far as I'm concerned. Nothing higher than 40 C (about 104F) is what I consider safe and I rarely have my packs go much past 35 C (95F) unless it's also very hot outside as well. So - if you find your packs are getting warmer than this, it's a good bet you should consider moving up to a higher discharge rating for your next LiPo pack.
Leaving your packs in the car on a hot sunny day can certainly heat them up well past 40 C as well. Internal or external heat - both have the same negative effect, hot LiPo's are miserable and they won't last long.

The other thing that will heat a pack up fast is if you push it right down to or lower than 3.0 volts per cell under load. Even if you have a 40 C pack and can only draw one third that amount, if you push it hard right down to 3 volts per cell - it will become very warm/hot and will shorten its life substantially.
A very good rule to follow here is the "80% rule". This simply means that you should never discharge a LiPo pack down past 80% of it's capacity to be safe. For example, if you have a 2000 mAh LiPo pack, you should never draw more than 1600 mAh out of the pack (80% x 2000). This is assuming a healthy pack as well that has the full 2000 mAh capacity (as packs age, their capacity drops).

Computerized chargers pay for themselves many times over so you can see how much capacity the battery takes allowing you to adjust your flight times accordingly to stay within that 80% rule to get the most life out of your pack.
If you don't have a computerized charger to confirm the amount of capacity, another good indicator is to measure the open circuit voltage (no load voltage) of the pack or individual cells right after a flight/drive with a digital volt meter or other similar digital voltage measuring device. An 80% discharged LiPo cell, will give an approximate open circuit voltage of 3.72 to 3.74 volts. A 3 S LiPo pack therefore would show about 11.2 volts after a flight when it's about 80% discharged, a 6 S pack would be in the 22.4 volt region. The longer you wait after the flight/drive, the less accurate this voltage method of determining an 80% percent discharge works because as the pack rests after the flight, the resting open circuit voltage will increase slightly, perhaps up to 3.76 volts or so.

For instance you can use these little inexpensive LiPo battery monitors after most flights to gauge my flight times to ensure I'm not over discharging my packs much past 80%. These ones I use work with 2 S to 6 S LiPo packs.You can even attach one inside your Plane and set it to signal if and when the cell reaches the desired set voltage.The alarm will give a very loud beep that can be heard from a good distance to let you know your battery is at the 80% rule for that size pack. You set it at whatever rate you desire for your particular battery.( one like this is nice-http://www.amazon.com/Integy-C23212-Voltage-Checker-Warning/dp/B003Y6E6IE/ref=pd_sim_sbs_hi_3/178-7108851-5963303 )
(C discharge ratings), is used by the manufacturers to market their product or justify a higher price and realistically can't be verified, but they are still a good general guide line when choosing a pack.

One verifiable way and one of the best ways to monitor your RC LiPo batteries condition is Internal resistance. Most decent higher capacity and higher discharge rated LiPo cells will have roughly 2 to 6 milliohms (0.002 to 0.006 ohms) of internal resistance when brand new. To calculate the total internal resistance of a series wired pack, you would then add these numbers together so a 4 S pack with each cell having 4 milliohms of resistance will show a total internal resistance of about 16 milliohms (0.016 ohms).
As packs age, the internal resistance goes up and the warmer they run. Lower discharge rated packs and small capacity packs will generally have higher internal resistance readings. It is not unusual to measure internal resistance numbers in the region of 200 milliohms on smaller 100 to 200 mAh micro park flyer LiPo packs when they are brand new for example.
So the best way to use internal resistance (if your charger supports this very useful function) is to take an IR reading of your LiPo/s when it/they are brand new.
Write that number (or the IR of all the cells in the pack) somewhere on the pack with a permanent marker so you will always have a brand new IR base reference for that particular battery. As the packs age, You can simply reference how the resistance is increasing or if one cell for some reason is getting bad.
How do you measure internal resistance? This again is where good computerized chargers come into play. The good ones that support this feature with built in balance boards will check the "IR" of each cell as well as the entire pack. Internal resistance really opens up a huge and complex topic of how to accurately calculate voltage drop in the pack and the total amount of watts being expended in the form of heat within the pack.

The four main things that shorten LiPo battery life are: HEAT, OVER-DISCHARGING (voltage & current), OVER CHARGING (voltage & current) & INADEQUATE BALANCING.

I have been reading about heli's and this is one such read I came across in RC Helicopter Fun-Understanding Lipo Batteries.

Again some explain it simply some explain it with simplicity....and some of us understand it simply, but not with simplicity.............There ya have it.And why i still ask so many questions about it.

[flydiver]

Simplify? Try this pipe and bucket analogy. Ignore numbers except battery capacity and know that higher C-rating generally means a POTENTIALLY better performing lipo.

Capacity is simply that - how much is in the 'bucket'. A 2200mA battery has 2.2 Amps available.

C-rating: how big the pipe out of the bucket IS. NOT what is 'claimed', but what IS. Unfortunately unless you have the tools, figuring that out is more trouble than it's worth for the average flier. I look at the specs, then try to find some reports/reviews to support or refute the claims.

Pipe size = internal resistance. You don't NEED to measure the IR. Just be aware that great batteries have a high C-rating and a low IR...and vice versa.
Amp need is directly related to pipe size.
Age and abuse makes the internal resistance go up, ie pipe size go down.
In all cases given time all lipos will increase the IR until the battery is not longer worth using. You can tell, the plane won't fly right or hits LVC almost immediately on a charged battery. The uninformed then go....WTF? and start asking questions. "How come my battery doesn't work anymore?"

The motor+prop define what pipe size (amp need) you require. The capacity defines how long you want to fly, and is often part of the CG equation.

[Knackered Sailor]

Blimey gentlemen, I ask a two line question and get back a library lol Thank you very much indeed, made interesting reading which I've bookmarked. The reason I asked was that the battery I found (I put a link at the top of the thread) was actually cheaper than some with a lower Burst/Discharge C so I'l go for that one. Thanks again. :-)

[flydiver]

Turnigy nanotech.....mmmmm, maybe, maybe not.

Remember I said that a LOT of this is marketing BS. HK found if they put [nanotech] on a lipo people would sprain their wrists getting their wallets out.
SOME nanotech are quite good.
SOME nanotechs are crap.
The whole nanotech area is confusing enough that I made a personal decision a long time ago to just not go there. It's hard to know which is which. It seems to be size dependent and I don't follow them THAT closely.

Is it better than the Cub battery? I don't know. OTOH the Cub battery is not a great battery either. The nanotech is a better 'deal' as long as soldering is not a big issue.
Many people have found the basic Zippy and Turnigy (even cheaper) actually are better.
www.hobbyking.co.uk/hobbyking/store/__6308__ZIPPY_Flightmax_1300mAh_3S1P_20C.html
www.hobbyking.co.uk/hobbyking/store/__9493__Turnigy_1300mAh_3S_30C_Lipo_Pack.html
Personally I'd probably try this: www.gensaceusa.com/98p-25c-1300-3s1p.html

I think I'd put my $$ into one of those. Or, you could buy one of each and report back at the end of summer. That would not be a very expensive experiment, as long as you treated them pretty much the same.

FWIW the nanotech ARE batteries that do NOT take well to mishandling. Leave them charged for a couple months and they will be garbage. THAT seems to be true across the brand.

[Knackered Sailor]

Interesting. As it happens the battery in question on my link is, I have discovered, not available in UK as far as I can tell. I've now ordered a Parkzone one at reasonable price. Hope no one is going to tell me this one is crap. lol