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標題: Lipo 40C vs 50C [打印本頁]

作者: xiang 時間: 2010-1-28 01:30
標題: Lipo 40C vs 50C
Anyone with any experience playing 40C and 50C lipo batteries...

I've played 25C, 35C and 40C.
With 40C I can really feel the power difference compared to 35C.
Am i right in assuming that there is a limit to how much power your ESC will draw from the battery.

Does a 50C battery really give/feel a lot more powerful than 40C?

作者: rcray 時間: 2010-1-28 02:02
do a easy experiment.

you can connect two 35C battary in Parallel.
Then you can have a 70C battary.

作者: xiang 時間: 2010-1-28 02:36

do a easy experiment.

you can connect two 35C battary in Parallel.
Then you can have a 70C battary.
rcray 發表於 2010-1-28 02:02

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Interesting idea... but i think you'll find that adding batteries in series or parallel will not effect the C rating. The total C rating for adding batteries in series or parallel will still be the same as each individual cell.

作者: rcray 時間: 2010-1-28 03:42
本帖最後由 rcray 於 2010-1-28 03:45 編輯

Interesting idea... but i think you'll find that adding batteries in series or parallel will not effect the C rating. The total C rating for adding batteries in series or parallel will still be th ...
xiang 發表於 2010-1-28 02:36

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you are completely wrong.
Please study what is parallel connection and the definition of "C".

if two 30c battary are connected in Parallel, the total output to your ESC is 60C.

作者: xiang 時間: 2010-1-28 12:05

you are completely wrong.
Please study what is parallel connection and the definition of "C".

if two 30c battary are connected in Parallel, the total output to your ESC is 60C.
rcray 發表於 2010-1-28 03:42

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lol rcray...you had me question myself there for a second.
From my understanding Discharge rate = C rating x capacity

My "completely wrong" calculation
For a single 40C 5,000mah battery:

Discharge rate: 40C x 5000mah = 200amps
Capacity: 1batt x 5000mah = 5ah
C Rating: 200amps / 5ah = 40C

For 2 batteries 40C 5,000mah in parallel:

Discharge rate: 2batt x 40C x 5000mah = 400amps
Capacity: 2batt x 5000mah = 10ah
C Rating: 400amps / 10ah = 40C

Please do correct me if I'm wrong.

Can we now get back to my original question: Anyone care to give their opinion on 40C vs 50C lipo batteries.

作者: xiang 時間: 2010-1-28 13:27
本帖最後由 xiang 於 2010-1-28 13:28 編輯

thinking about it more...
if Discharge rate = C rating x capacity.
then by increasing the capacity the discharge rate will increase... which i presume will lead to more power.

so maybe my initial question 40C vs 50C is a bit stupid, as the capacity of the battery needs to be conisdered too!

10C 5,000mah will have the same discharge rate as 50C 1,000mah

Does that make sense to anyone?

作者: hardmankam 時間: 2010-1-28 18:51
本帖最後由 hardmankam 於 2010-1-28 18:58 編輯

Let me try to get into this...

Think of 'C' as a straw.  The larger (in diameter) the straw, the larger the 'C' (ie flow)
'C' is a discharge rating

Think of mAh as a cup.  The larger the cup, the larger the mAh (ie reserve)
mah is the capacity

10C 5,000mah = small straw, large cup
50C 1,000mah = large straw, small cup

the method of delivery of current is total different in these 2 cases.

If you need a very high current flow in a short period of time, it is a must to have a high 'C' value in making sure the 'flow' is enough ... otherwise, the straw may burst because there is too much pressure in the straw.  (low turn motors)

On the other hand, if you only need small current in a long period of time, it is better to have more mah or more 'reserve' providing the a smaller straw can sustain the pressure.  (stock motors)

This is only my opinion, so I could be wrong.

As for 40C vs 50C, I think you may find a performance difference, but like anything else, there is a diminishing return. So it's not like 50C is 25% 'better' than 40C. But in theory, 50C is better than 40C.

作者: xiang 時間: 2010-1-28 19:35
I'm getting completely lost thinking about this.... so....

C is a discharge rating... but in relation to capacity.
C = Discharge rate / capacity

Then perhaps its the Discharge rate that i should be looking at and not the C rating.
10C x 5,000mah = 50Amps discharge
50C x 1,000mah = 50Amps discharge
10C x 4,000mah = 40Amps discharge

so using your cup/straw example, even though both have the same Amp discharge, 50C can provide the current faster?

作者: rcray 時間: 2010-1-28 21:01
8# xiang

Xing,

LoL. Be Smart!. Dont screw up yourself.

What you need to make your Car/ ESC moew powerful is Current.
i.e. the Max discharge rate.

40C x 1000maH = 40A discharge rate.
40C x 2000mah = 80A discharge rate.

** Which discharge rate will make your car more powerful? Please re-think about it.

You will need a 80C , 1000mah battary to achieve 80A discharge rate.

作者: ryancmlam 時間: 2010-1-28 21:41
yes. the key is the max. rate of discharging.

作者: xiang 時間: 2010-1-28 21:58

8# xiang

Xing,

LoL. Be Smart!. Dont screw up yourself.

What you need to make your Car/ ESC moew powerful is Current.
i.e. the Max discharge rate.

40C x 1000maH = 40A discharge rate.
...
rcray 發表於 2010-1-28 21:01

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rcray,
Firstly my username is xiang and not Xing.
Secondly, I havent "screwed myself up", and i thought i was being smart by not listening to your nonsense about increasing C rate.
Thirdly, i created this thread to get useful answers/thoughts to my question, not some random drivel telling me i am completely wrong and need to study.
If you want to contribute to this thread, i suggest you do so in a constructive way.

You obviously do not understand the comparison of:
10C x 5,000mah = 50Amps discharge
50C x 1,000mah = 50Amps discharge

my last question was... both seem to provide the same discharge rate, however it appears that C is only important in relation to capacity.
As usually when you think of lipo batteries and someone says they have a 50C battery... you immediately think it is very powerful... however it appears that this may not be the case if it has a low capacity.

作者: Aurora 時間: 2010-1-28 22:40
For the original questions, both 'C' rating and capacity of the cell would matter in real-life application.  The 'C' rating is relevant to the cell capacity, and therefore, even with the same capacity, higher C rating cell will allow a higher current drawn from the cell.

And yes, given the same capacity, higher C rating cell will prevail in a race.  Unless, a really low-end ESC+motor combo is used, then one might not feel the difference; since it might be drawing too little current from the battery for driver to notice the speed difference.

This kind of comparison is often time hard to make--mainly because different battery manufacturers might advertise their cell differently(and not always true to their real spec), and cell chemistry/manufacturing process would also affect the performance vs runtime as well.  For example, great performance in the first 30 sec does not mean the cell will remain punchy for the rest of the 5 min race...

作者: rcray 時間: 2010-1-28 22:51
11# xiang

There are two important terms that you need to consider:
1) Max discharge rate (5~10 sec only). It is important for starting up your RC car.
2) Max continuous discharge rate. It is important for continuous run.

For example, a 2000 mah x 40C.
The max discharge rate is 80A.
However, the max current only can be kept for a few sec (5~10s). it is depending to the battary quality.

The most important value is continuous discharge rate. it will be much lower than Max discharge rate.
But most of battary manufacturer will not release this parameter to end user.

Both 10c x 5000mah and 1000mah x 50c battary can get the same max discharge current in very short period of time.

However I do believe the 50c x 1000 mah battary can have much higher continuous discharge rate.

That's why we found that the 50c battary do the job better for sure.

作者: rcray 時間: 2010-1-28 22:56
Here is the A123 spec. for your reference.

Nominal voltage: 3.3V
Nominal capacity: 2.3Ah
Core cell weight: 70 grams
Internal impedance: (1kHz AC) 8 mΩ typical
Typical fast charge current: 10A to 3.6V CCCV
70A continuous discharge
120A, 10 sec pulse discharge
Cycle life at 10C discharge, 100% DOD: over 1,000 cycles

作者: xiang 時間: 2010-1-28 22:56
本帖最後由 xiang 於 2010-1-28 23:18 編輯

Thanks Aurora, thats very useful!
how about if the C rating is the same for both batteries, but one has more capacity than the other?
Would that mean the the battery with higher capacity would perform better as it would then have a higher discharge rate?

Its just seems very strange to think that just because a battery has a larger capacity, it means it will perform better...ie. have a higher discharge rate.

what i mean is if you would compare
50C 5,000mah
45C 6,000mah
one might initially think that the 50C battery would perform better, but in actual fact the 45C battery has 20Amps more discharge.

作者: Aurora 時間: 2010-1-28 23:58
Xiang,

Given the exact same chemistry/manufacturing process, with the same 'C' rating, the battery with the higher capacity will allow more amp draw.

And taken what RcRay and I have said earlier, it is kinda difficult to compare batteries nowadays since all the advertise spec are not on the same ground(pulse vs continuous, con't amp draw vs volt, how long are the pulse...etc).

For the last comparison, yes, on the paper, the 45C 6000mah might allow 20A extra discharge....but the question will then be--can a driver notice that 20A difference when driving? And are the cell chemistry(etc) exactly identical to make the comparison fair?

Back to the very original question, the best way to tell is probably to measure your best/avg lag time on a familiar track.

作者: xiang 時間: 2010-1-29 13:57
I completely agree that its not fair to compare batteries on paper (based on spec), as there are so many other factors to take into account. However, many beginner RC players like myself, should take note that the capacity of a battery not only plays a part in run time, but also performance. Something as i mentioned previously i was unaware of.

Testing a battery based on average lap times seems like the best way to test performance, however, this may not be ideal to purchase so many batteries to test for the average hobby player.

Back to my original question 40C vs 50C.
I would like to elaborate further and ask regarding the ESC. Surely there is a limit on how much current the ESC can withstand/draw, so with batteries having larger C values at what stage will the C value be obsolete.
ie. if a you had 2 batteries, 90C and 100C. would it be the case that there would be no performance difference as the ESC would be "Maxed out"?

so my original question 40C vs 50C, for those players who have tried both. can you feel the difference between the 2?

作者: r003 時間: 2010-1-29 14:08
本帖最後由 r003 於 2010-1-29 14:12 編輯

so my original question 40C vs 50C, for those players who have tried both. can you feel the difference between the 2?

其實之前d ching 都解左比你聽. 唔明點解仲要問.
50c 同 40c 一定有分別.
玩到 40c ~50c電一定比多幾分錢, 先多一分貨

有冇分別都同esc, motor有關.
如果你用60a 就冇
120a 3R 有.

作者: xiang 時間: 2010-1-30 01:31
thank you r003.

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