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11-28-2017 01:43 AM  10 months agoPost 21
EEngineer

rrProfessor

TX

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C rating is a figure that's a measure of the pack's ability to source current....and not that of total pack capacity....nor max. capacity.

Logo 600SXs, 800XX, TDR IIs

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11-28-2017 01:48 AM  10 months agoPost 22
AirWolfRC

rrProfessor

42½ N, 83½ W

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Correct . . . it is a number that indicates how many times the mah rating it can deliver in current.

The spec that none of the manufacturers publish is what the output voltage is under that kind of current draw.

If you know what the internal resistance is, you can calculate that voltage.

. . . and then you can test it and find out who's lying

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11-28-2017 02:31 AM  10 months agoPost 23
ICUR1-2

rrElite Veteran

Ottawa, Ontario

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Flyin for Jesus
Where the C rating is not a factor of a pack's max capacity, but rather its current capacity.
Flyin for Jesus
I don't agree with your interpretation of the C rating.
I understand I might be wrong, but as of now, I don't agree.
That's what I'm trying to figure out for myself as well.
The discharge rate of a Lipo remains fairly constant until the "cliff" drop off point in the graphs. So going by the graphs my statement would be incorrect .
However looking at my old lipos they are like new.

spending time, paying attention

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11-28-2017 03:50 AM  10 months agoPost 24
EEngineer

rrProfessor

TX

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internal resistance
And, if the IR is "high", then discharging such a pack at a "high" C rate causes "high" internal power dissipation in the form of heat.

You cannot have a high C rating with high IR.

Logo 600SXs, 800XX, TDR IIs

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11-28-2017 05:29 AM  10 months agoPost 25
Flyin for Jesus

rrVeteran

Troy, IL. 62294

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Well ICUR1-2, You're not the first one to say that a 5000mAh 30c pack will output 150A at full charge but only 75A when it is half charged.
I get the fact that a fully charged pack will have some drop in voltage especially when you are drawing 150A from it. It would easily have to drop to 4.1v per cell under that kind of load.
I do get that when the pack is at 3.75v at rest, you may drop it down to 3v if you pull 150A from the pack at that state of charge.
But the graph cannot be linear, it has to be pretty flat at least until about the 75% - 80% discharged then start dropping pretty quickly.

However all that I say is just from my own observations and looking at my telemetry and ESC logs.

Back on the topic for the OP... the 25c pack would probably fly your heli just fine ( depending on heli weight, blades, HS, max pitch ) but when I buy packs, I buy the highest C rated quality packs I can afford. The C rating is really an inverse function of the pack's Internal Resistance.
If your heli flies well with a 25c 8000mAh pack, then if you buy a quality 50c 8000mAh pack, that quality pack will continue to fly your heli well when it ages. With age and usage, the IR will increase. Good care helps to keep IRs low, but they won't last forever.
So when you use your quality pack, it will take a while for it to degrade to the level of a new 25c pack. Now both are the same but you got a couple years use out of the quality pack already.
When the 25c pack degrades, it might not take long before it can't fly your heli.

Short of it, like others have said, buy a quality high C rated pack and enjoy many years of trouble free flying.

But $46 for a 6s 8000mAh is tempting.

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11-28-2017 09:42 AM  10 months agoPost 26
sean911sc

rrVeteran

San Diego

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Over time you'll learn the brand(s) and "C Rating" that work best for you.

I'm currently using Pulse 35/45C in a 12S setup and they've out performed previous Hyperion and TP packs in my experiance.

William S Harris

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11-28-2017 12:17 PM  10 months agoPost 27
mcfast

rrKey Veteran

Quebec Quebec Canada

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I was looking at the 6s 8000mAh mostly because of its weight, I want to run a single 6s, so to get the CG right I need something heavy out front, but I did see some hight C 5000mAh that would do the job, so I think I am going for some of those.

P.S. sorry for the spelling or the grammar I am dyslexic!

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11-28-2017 02:11 PM  10 months agoPost 28
EEngineer

rrProfessor

TX

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Any way to rearrange the battery(move it forward) to adjust your CG without adding needless weight?

Or remove weight from the tail end?

Or a combo of both?

Logo 600SXs, 800XX, TDR IIs

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11-28-2017 05:20 PM  10 months agoPost 29
Richardmid1

rrProfessor

Leeds, England

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Some of these replies are hilarious! Hahaha.

Sport flying a 700 on a single 6s pack assuming you are using stock 12s gearing with only average around 25A. An 8000mah 25C pack is good for 200A continuous AND 400A in 5-10 second bursts assuming it's a 25-50C pack.

So yes, a 25C pack will be more than enough! Heck even a 10C pack would be fine!

A lot of people forget we used to 3D helis on 20C and lower packs!

60% of the time, it works every time!

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11-28-2017 05:30 PM  10 months agoPost 30
revmix

rrKey Veteran

NJ

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700size main rotor Low Head Speed works just fine with 6s 25C

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11-28-2017 05:43 PM  10 months agoPost 31
EEngineer

rrProfessor

TX

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Low Head Speed
The OP never mentioned low head speed....

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11-28-2017 05:44 PM  10 months agoPost 32
Richardmid1

rrProfessor

Leeds, England

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LHS = low head speed.

Even if he was 3Ding at 2000rpm it would be fine!

60% of the time, it works every time!

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11-28-2017 05:52 PM  10 months agoPost 33
EEngineer

rrProfessor

TX

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I misinterpreted that, Richard...

I thought LHS stood for Local Hobby Shop.....

I stand corrected....

Logo 600SXs, 800XX, TDR IIs

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11-28-2017 05:54 PM  10 months agoPost 34
ICUR1-2

rrElite Veteran

Ottawa, Ontario

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Richardmid1
A lot of people forget we used to 3D helis on 20C and lower packs!
And what a time that was .
Almost everyone had an eagle tree to figure out their amp draw and gearing to compensate.

However higher C rated packs seem to take the abuse better

spending time, paying attention

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11-28-2017 06:00 PM  10 months agoPost 35
Richardmid1

rrProfessor

Leeds, England

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Must have been very early 20C packs and also when chargers weren't nearly as good and people's understanding of lipos was poor!

...also flybarred so more current draw!

Oh and also before they started putting metal plates round the packs to 'hide' the puffing! Haha

60% of the time, it works every time!

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11-28-2017 06:04 PM  10 months agoPost 36
revmix

rrKey Veteran

NJ

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building an LHS 700e heli
OP never mentioned

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11-28-2017 06:23 PM  10 months agoPost 37
RM3

rrElite Veteran

Killeen, Texas - USA

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An 8000mah 25C pack is good for 200A continuous
goood lord, the bars must be open in london early today... AND they have WiFi...

oh yeah? at what voltage Mr. Watt hour?... cause they sure as hell aint holding it at no 4.1v per cell when doing it.

showing a preference will only get you into trouble, 90% of everything is crap...

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11-28-2017 06:32 PM  10 months agoPost 38
Richardmid1

rrProfessor

Leeds, England

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Haha the drinks are way too expensive down in London!

Cells are tested till the voltage drops to 3v.

60% of the time, it works every time!

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11-28-2017 06:36 PM  10 months agoPost 39
Richardmid1

rrProfessor

Leeds, England

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NO pack we use can hold 4.1v at almost any load! Please don't confuse people!

60% of the time, it works every time!

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11-28-2017 06:47 PM  10 months agoPost 40
RM3

rrElite Veteran

Killeen, Texas - USA

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NO pack we use can hold 4.1v at almost any load!
so $hit... but thats the marketing gimmick now isnt it?

the fine print normally does not state what that voltage is...

So then what is it? whats the standard?

this is why many ESCs have a shutdown feature to prevent Lipo failure (below 3.2)

FROM CC website:
2. When I get to full throttle, my ESC cuts power to the motor. I have to throttle off then back on to get the motor to start, but it cuts off again at full throttle. Why is that?
The most likely cause of this problem is a lithium polymer battery pack that is not capable of providing the current the motor, gear ratio, and propeller are asking for. Normally the voltage curve for LiPo batteries is almost flat, but when overdrawn their voltage will fall below the cutoff point before the battery is discharged completely. The solution for this situation is either a higher gear ratio or a smaller prop, which lowers the current draw of the system. Or, if the performance is not wished to be lost, a higher mAh, or more capable brand of LiPo pack can be used. Another less likely cause for premature low voltage cutoff is too small or too high a resistance plug between the battery and the ESC. Also make sure the wires on the battery pack are at least the same size as on the ESC. If the battery pack is up to the task, and the wires and plugs are sized correctly, it is possible that a sudden motor cut off, with the ability to restart by going to the off throttle position, could be caused by the over current protection on that particular controller being too sensitive
http://www.castlecreations.com/en/h...esc-010-0109-00

this is why we go with packs that dont sag voltage wise at full draw below a safe point. And this requires packs whos true "C" rating is so... thats why I go with the 50% + rule.

So explain to me why my telemetry shows pack voltage kiss 3.2 or even drop below per cell at full draw on a 30C 5000mah pack?

thats why todays "C" rating is a bunch of bull.

showing a preference will only get you into trouble, 90% of everything is crap...

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