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choice of lipo

Old 04-03-2019, 06:03 PM
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jangodog
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Default choice of lipo

Hi. What's the difference between 30C and 45C lipos? Both 2200mah and 2800mah has this number in the end? Is the 45C better then 30C?

I'm getting the Turbo Timber plane next week and know the lipo specs for the plane is 2200 to 3200 both 3S and 4S lipos. But wanna know which lipo, 30 or 45C is the right one?
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Old 04-03-2019, 08:55 PM
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ron_van_sommeren
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For same measurement method, same criteria and same manufacturer fantasies/optimism/lies, both packs should be able to deliver same current:
2200mAh×45C ≈ 3200mAh×30C ≈ 97A

Without number of cycles specifications, C-value is pretty much useless. Better stay below half of C-specifications.

Higher C-value for same capacity means: lower pack internal, resistance Ri, slightly heavier, and more expensive.
And you will fly longer on the 3200mAh pack of course.
Real tests, wheeding out sticker-tuning, nonsense and lies, active thread:
Battery load test comparisons - RCG


Note that going from 3s to 4s packs, batterycurrent wants to increase by factor (4/3)² = 1.7, 70% extra current. You probably have to prop down to keep current down.
extra current with one or two cells added, simple table - RCG

And it is even 'worse' for changes in Kv and prop-diameter.
The 'full' story:
Motorcurrent is proportional to pitch¹, voltage², Kv³ and diameter⁴.
Power-drawn is proportional to pitch¹, voltage³, Kv³ and diameter⁴.

Without the exponentation
extra current with one or two cells added, simple table

So, changes in setup (and lousy Kv specifications!) can have surprisingly considerable/huge effects.
E.g. doubling voltage will four(2²)fold current, doubling Kv will eight(2³)fold current, and doubling prop diameter will sixteen(2⁴)fold current.
Even a small 10% change/difference in Kv will already lead to a 30% difference in current.

Last edited by ron_van_sommeren; 04-04-2019 at 07:37 PM.
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Old 04-04-2019, 09:48 AM
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Well, a lot of math there Guess the 30C is okay for both 2200 and 2800mah lipos.
Thank's though, Ron
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Old 04-04-2019, 10:41 AM
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My hat of to Ron ... excellent data.

But a simple answer :

Take the capacity of the battery and multiply by the C rating - this is the technical maximum amps the battery should be able to deliver without undue harm. So lets take your packs :

2200mAh at 30C ..... mAh convert to AH .. 2.2AH ... >>>>> 2.2 x 30 = 66 Amps
2200mAh at 45C .... >>>>> 2.2 x 45 = 99 Amps

3200mAh at 30C .... >>>>> 3.2 x 30 = 96 Amps
3200mAh at 45C .... >>>>> 3.2 x 45 = 144 Amps

But in all honesty ... think about those battery leads .... to handle such currents as those would need much larger capable leads. So its a theoretical maxim. It really becomes important when in smaller sizes or in high power setups such as EDF etc. Where batterys are pushed to limits.

If its the Horizon Hobby Turbo Timber model ..... https://www.horizonhobby.com/product...pnp-p-efl15275 .... it has a 50A ESC. With HH usually being a company that sells compatible items in its setups ... indicates that the 30C LiPo in either 3S or 4S is OK.

Note that there are two things that increase a battery weight :

Capacity and / or C rating.

It is common if a low C rating is good for a model and extreme vertical is not called for - to increase capacity by reducing to that C rating and keeping similar weight. Gives you more flight time.
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Old 04-04-2019, 11:26 AM
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Okay. Hope the 2800mah and 2200mah 45C lipos i just purchased will do just fine
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Old 04-04-2019, 01:18 PM
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Can I ask if you have flown RC before this ?

Have you bought a Wattmeter ? It really is THE TOOL we all use literally every day ...
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Old 04-04-2019, 09:12 PM
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No don't have a wattmeter. maybe somebody at the field has one. I did get a lipo buzzer/checker for the lipos But the 2800 and 2200 3S will be good for the Turbo Timber?
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Old 04-05-2019, 09:09 AM
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Please get a Wattmeter ... they are not expensive. It is the most essential tool the Electric modeller can ever have.

The Wattmeter can measure :

Voltage
Amps
Balance
% capacity remaining

It can help you to decide prop / motor / battery / ESC combinations.

Watch this video and you will see what a Wattmeter can do ...


When you buy one - make sure it has at least up to 100A capability ....

Here's a page on eBay with a large selection ...

https://www.ebay.com/bhp/rc-watt-meter
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Old 04-05-2019, 11:21 AM
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Hi. Thank's for the useful info and links. I will defintely get me one of those
Have a nice weekend my friend
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Old 04-05-2019, 11:41 AM
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You will not regret getting a Wattmeter.

This weekend I hope to be flying :
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Old 04-05-2019, 10:33 PM
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ron_van_sommeren
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Those watt-meters are all similar. This one comes with very good explanations: current, voltage, power, resistance, energy ..
www.rc-cars-planes.com/docs/wu100v2_user_manual.pdf
Chapter 4 Basics of electricity
→ page 7-10

Watt-meter simulator, lets you play with throtle, voltage, current, resistance, power, capacity (Ah), load etc.
www.rc-electronics-usa.com/ammeter-simulator.html
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Old 04-06-2019, 10:01 AM
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solentlife
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At end of day ... all wattmeters are similar .... just some like to have a fancy name or case on it. Of course there are odd bad cheapo's but they tend to be in the under 100A category.

My $15 TRAKKER Wattmeter has been providing excellent service for years now ... the only item I had to replace was the Balance fly lead. $2 and it was back in service again.
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Old 04-10-2019, 09:54 AM
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I just purchesed me an HK 010 wattmeter. So now i can meassure power on my lipos.
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Old 04-10-2019, 10:42 AM
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Good news.
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