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        Discussion Please how can i chose a c rate of a lipo for my specific plane ?

#1 FedericoA Mar 07, 2012 06:12 PM

Please how can i chose a c rate of a lipo for my specific plane ?
 
Let'say i have to choose for a lipo is more suited for let's say a most kowed plane like the PARKZONE T 28 TROJAN.....Now should i choose a 3s 2100 20c or is best 25c or even more a 30c...and so on what should i expect from the difference of these c rates on my plane ....more performance maybe ?......same performance ?
will burn my motor with higher c rate ? or maybe burn my esc.....
I believe that most of the rc modelers think tha 20c will be less power and faster than a 25 c....BUT WHAT IS THE CORRECT BEHAVE OF THOSE C RATE ?

#2 ggcrandall1 Mar 07, 2012 06:26 PM

Quote:

Originally Posted by FedericoA (Post 20969150)
Let'say i have to choose for a lipo is more suited for let's say a most kowed plane like the PARKZONE T 28 TROJAN.....Now should i choose a 3s 2100 20c or is best 25c or even more a 30c...and so on what should i expect from the difference of these c rates on my plane ....more performance maybe ?......same performance ?
will burn my motor with higher c rate ? or maybe burn my esc.....
I believe that most of the rc modelers think tha 20c will be less power and faster than a 25 c....BUT WHAT IS THE CORRECT BEHAVE OF THOSE C RATE ?

1. A 3S 2200mah 20C is fine.

2. You could go with a 25C or even 30C if you want to spend the extra bucks.

3. You should expect very little difference between any of the various C rates.

4. You will not burn up your motor or ESC by using a higher C battery.

If you do not agree with any of the above, or even if you do, you should get a wattmeter and measure the differences, if any, for yourself.

Glen

#3 FedericoA Mar 07, 2012 06:37 PM

Quote:

Originally Posted by ggcrandall1 (Post 20969270)
1. A 3S 2200mah 20C is fine.

2. You could go with a 25C or even 30C if you want to spend the extra bucks.

3. You should expect very little difference between any of the various C rates.

4. You will not burn up your motor or ESC by using a higher C battery.

If you do not agree with any of the above, or even if you do, you should get a wattmeter and measure the differences, if any, for yourself.

Glen

So what is the poupouse of use a 20c or a 30c instead,,,,?

#4 C₄H₁₀ Mar 07, 2012 06:45 PM

Using batteries with higher C ratings will normally mean an increase in power, RPMs, and current draw, and the difference can indeed be very significant. The higher discharge capability leads to less voltage sag under load which directly causes the motor to spin faster. Obviously the current and total power must increase as a result.

As Glen said, a wattmeter is a must for this stuff. Most well-matched power systems shouldn't be at risk of frying simply because of a higher C rating, but if you're pushing your gear for performance then it can be something to be careful of.

#5 hoppy Mar 07, 2012 06:46 PM

1 - They may be available if a more suited one is not.
2 - You can use them in higher amp draw situations if ever needed.
3 - They usually can be charged faster.
4. - You need to get rid of some money.

I agree with Glens assessment.

The plane you mentioned will easily fly for 10 min with a 2100mah pack which would be a 6C average draw from the pack. With that low of a stress on the battery, a higher C-Rating than 20C would not buy you much more performance.

#6 C_Watkins Mar 07, 2012 06:47 PM

Quote:

Originally Posted by FedericoA (Post 20969362)
So what is the poupouse of use a 20c or a 30c instead,,,,?

Without getting into a bunch of other related items like internal resistance, manufacturers overrating their cells, etc...
Roughly, the C rating times the mAh of the battery is the maximum continuous draw the battery can handle.
ie... 20c 2000mAh would be good for 40A sustained; 30c 2000mAh is good for 60A sustained, etc.

Since you're pulling considerably less than 40A sustained with the T-28, a 20C battery is fine for that application.

#7 C₄H₁₀ Mar 07, 2012 06:53 PM

Ooh, I forgot to mention...

The "C" rating determines roughly how much current the battery can safely put out. A 2200mAh 20C lipo can handle (2.2Ah x 20C) = 44A continuous current. It's more of a ballpark figure than a solid number, and you're best off just staying well below it.

Either way, running a battery at just 10C constant draw will mean you get 4.8 minutes of runtime. 20C continuous means less than 2.5 minutes. Most power systems never get anywhere near this kind of continuous power, so the only real advantage of a higher C pack is less loaded voltage sag (at the expense of higher cost, usually more weight, and often bigger physical size).

#8 C₄H₁₀ Mar 07, 2012 06:53 PM

Jeez, y'all are fast :rolleyes:

#9 ggcrandall1 Mar 07, 2012 08:03 PM

Quote:

Originally Posted by FedericoA (Post 20969362)
So what is the poupouse of use a 20c or a 30c instead,,,,?

An example:
A 2200mah 20C drawing 40 amps is working at 90% of it's safe capacity. (44 amps)

A 2200mah 30C drawing 40 amps is only working at 60% of it's safe capacity (66 amps)

A good rule of thumb is to not work a battery at greater than 80% of it's maximum capacity.

Glen

#10 FedericoA Mar 08, 2012 04:43 PM

Quote:

Originally Posted by ggcrandall1 (Post 20970126)
An example:
A 2200mah 20C drawing 40 amps is working at 90% of it's safe capacity. (44 amps)

A 2200mah 30C drawing 40 amps is only working at 60% of it's safe capacity (66 amps)

A good rule of thumb is to not work a battery at greater than 80% of it's maximum capacity.

Glen

Well now is more clear thank you to you and thank you to all of you who helped me-


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