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ProModeler Scorpion Power
TailKiller

Senior Heliman

Panama City, FL

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Since I'm talking about a scale application, I thought I'd post here.

Ok, so I'm looking to get 2 pair of batteries for my As350 only. 5000mah 22.2 6s packs.I think the highest Current recorded in the Castle logger at about 28.0A and that was during a pitch pump or fast climb out. The higher the C rating the higher the price for the batteries. So this would mean I would need a 30C battery? Or since pitch pumps are not an every day thing with scale flying, could I get away with running 20C batteries?

,Dennis
http://pcrcheliclub.com/
700 Astar Super Scale T-600 Bell 206 Trex 600 Naza H DX8

12-16-2016 09:52 PM
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marc28

Veteran

new york

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20C is fine for scale flying. I use 15C 10000 in my 1/4 scale EC 135

East Coast scale helicopter Field Rep
Vario Team Pilot

12-16-2016 10:43 PM
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ICUR1-2

Elite Veteran

Ottawa, Ontario

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I think the highest Current recorded in the Castle logger at about 28.0A and that was during a pitch pump or fast climb out. The higher the C rating the higher the price for the batteries. So this would mean I would need a 30C battery
yes and no.. it means you need a battery capable of delivering 28 amps when depleted to avoid damaging your battery at end of flight.

however a lower c rated battery weighs less and may draw less amps because the model now weighs less.

from my experience I would not use anything lower than 30C for my style of aerobatic flying.

spending time, paying attention

12-17-2016 03:24 AM
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Andy01

Senior Heliman

Brisbane, Australia

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Well since 30C x 5Ah gives you 130A and you are peaking at 28A, I would be inclined to think that 30C is probably overkill. Bear in mind that 28A on a 5Ah battery is not even 6C.

An average 12s As350 (600 or 700 size probably) is likely to weigh around 15-20lbs maximum, and even at 20lbs x 50W/lb (on the high side) it should only draw around 1000W for normal scale FF. Now 1200W on 12s is around 22A, which means the system is pulling about 4.5C out of the lipos in normal use.

I suspect the difference in weight between a 20C flight pack and a 30C flight pack compared to the weight of a 12s scale heli is probably minimal and would have no impact on the overall amp draw, but I might be wrong.

I have run plain blue Turnigy 5000mAh 6s 25C for about 6 years now (always stored fully charged and frozen) and they are still going strong - only used in scale flying.

If I had to buy again I would buy 20C unless there was little price difference between 20C and 25C, but certainly no need for 30C unless you are doing some aggressive flying or sharing with a aerobatic model.

Colin

Vario Long Ranger 700e
Seahawk 600
UH-1N 500
Baumann EC-145 800+ (coming soon )

12-17-2016 08:10 AM
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TailKiller

Senior Heliman

Panama City, FL

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Thanks guys.. Colin, I had hoped you would reply. Question.. I know lipo like cold but, fully charged and frozen? Benefits?

,Dennis
http://pcrcheliclub.com/
700 Astar Super Scale T-600 Bell 206 Trex 600 Naza H DX8

12-17-2016 01:54 PM
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ICUR1-2

Elite Veteran

Ottawa, Ontario

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Well since 30C x 5Ah gives you 130A and you are peaking at 28A, I would be inclined to think that 30C is probably overkill. Bear in mind that 28A on a 5Ah battery is not even 6C.
This is true when the battery starts out fully charged. at the end of the battery when you're down to 20% -30% you will have 1000-1500mah at 30c is barely 30amps

My point is consider how many amps are required at end of flight to keep from damaging battery.

spending time, paying attention

12-17-2016 02:58 PM
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Peter Wales

Elite Veteran

Orlando Fl

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This is true when the battery starts out fully charged. at the end of the battery when you're down to 20% -30% you will have 1000-1500mah at 30c is barely 30amps
You are mistaken in your premise. The C rating of battery is related to its internal resistance, which does not change significantly from full to empty. So a 5AH battery at 30C will give 150 amps when freshly charged and when mostly depleted. Its terminal voltage will drop a little of course, but that depends on the voltage you determine as being the terminal voltage.

Just google LiPo discharge curves to see what I mean

Peter Wales
http://scalehelicopters.org

12-18-2016 02:54 AM
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Ace Dude

rrProfessor

USA

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You are mistaken in your premise. The C rating of battery is related to its internal resistance, which does not change significantly from full to empty. So a 5AH battery at 30C will give 150 amps when freshly charged and when mostly depleted. Its terminal voltage will drop a little of course, but that depends on the voltage you determine as being the terminal voltage.
IR is also highly temperature dependent. The temperature of a pack will increase based on the rate of discharge and as the temperature increases the IR will decrease.

Here's a chart showing IR vs. temperature for several different packs.

  

12-18-2016 03:20 AM
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ICUR1-2

Elite Veteran

Ottawa, Ontario

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So a 5AH battery at 30C will give 150 amps when freshly charged and when mostly depleted.
where does the battery get the mah to supply 150amps when mostly depleted ?

your logic seems flawed

1000mah X 30 c = 30amps max when depleted

spending time, paying attention

12-18-2016 03:28 AM
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TailKiller

Senior Heliman

Panama City, FL

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Thank you guys.. I have been reading on this curve thing for the last couple of hours. I have retain some of it but the reading headache has shut me down.. lol..
I am very carefull with my lipo's.. In fact Keyrigger has told me he that I can go further and not hurt my packs.
I run a 3.3 soft cutoff. I fly till to cutoff and set my flight time for that model accordingly and from that point forward I never over run but a few seconds. I feel I have good battery management. My 700 AS350 will always be flown in a calm fashion. I my nose it over in a long run but nothing to push it hard.
Now my 600 Jet Ranger is a different story.. I fly it fast and most of the time on the deck as if I had a gunship on my 6 shooting my tail off. But again 3.3 and adjust flight time according. I will recheck but I'm sure it never see's 30A. So if I can save money by getting lower c rated battery then so be it.
So knowing all this the question is... Can I fly the AS350 on 20c packs with my battery management style? Thanks.

Dennis

,Dennis
http://pcrcheliclub.com/
700 Astar Super Scale T-600 Bell 206 Trex 600 Naza H DX8

12-18-2016 04:42 AM
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TailKiller

Senior Heliman

Panama City, FL

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I said 3.3 cutoff but then I set the flight time so that I am 3.75 per cell at the time I shut down. So I no way abuse the packs.

,Dennis
http://pcrcheliclub.com/
700 Astar Super Scale T-600 Bell 206 Trex 600 Naza H DX8

12-18-2016 04:47 AM
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ICUR1-2

Elite Veteran

Ottawa, Ontario

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Can I fly the AS350 on 20c packs with my battery management style? Thanks.

only you will know in the end. everybody flies a little bit different.
plus other factors such as the models electronics.

if your battery get's hot and/or puffs then you are pulling too much out of it.
try to land with a standing voltage of 3.8v or about 30% remaining
for max life charge to 4.0v and stop at 3.8v or a range of 95% full to 30% remaining.

spending time, paying attention

12-18-2016 05:18 AM
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Peter Wales

Elite Veteran

Orlando Fl

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Take a look at the bottom red line, 25c discharge rate.

Peter Wales
http://scalehelicopters.org

12-18-2016 12:38 PM
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ICUR1-2

Elite Veteran

Ottawa, Ontario

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12-18-2016 01:58 PM
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Peter Wales

Elite Veteran

Orlando Fl

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I wouldn't trust rc-heli-review as a definitive source for battery information, but when I looked at the link you gave, I did not find anything which said that a battery will not provide its full amp output at anything than full capacity.

Batteryuniversity etc, is a more likely source of reliable information but I did not find anything to back up your claims on that site either. I confess I did not read the entire site, life is too short.

If you want to quote a source be more specific please.

I still maintain that your claim that a 5AH 30C battery which would give 150 amps when fully charged and only 75 Amps when 50% discharged is erroneous and if you had ever watched one of these 3D hooligans flying, you would know that they dont lose power at the end of their flight. They are just as annoying at the end as they are at the beginning

Anyway, as this discussion is totally academic as no one on this forum will be running 150 continuous amps, I am going to drop it and let those who care, make up their own minds based upon what has been said.

Merry Christmas, I got presents to wrap.

Peter Wales
http://scalehelicopters.org

12-18-2016 02:57 PM
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ssmith512

Key Veteran

Indianapolis, IN USA

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They are just as annoying at the end as they are at the beginning
LOL!!!

Steve

12-18-2016 03:03 PM
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ICUR1-2

Elite Veteran

Ottawa, Ontario

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can't teach an old dog new tricks

but the math is simple

spending time, paying attention

12-18-2016 03:35 PM
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Peter Wales

Elite Veteran

Orlando Fl

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Old Dog??

Hrrrmmph I resemble that remark! Ok, one last try, yes i promise, last try. Let's look at this THUNDER POWER discharge graph one more time

Look at the bottom red line, which shows the 25c discharge voltage

You will note that until it reaches the knee, it is almost constant. This immediately disproves your theory that the internal resistance dramatically rises as the battery gets discharged.

Now, if the voltage is a constant and the load is constant, from that quaint old formula from that other old dog, Mr Ohm,

Vk/Rk = Ik

Where Vk is a constant, Rk is a constant and therefore Ik must also be a constant

Quod Erat Demonstrandum (look it up, its something else us old dogs learned in school)

Peter Wales
http://scalehelicopters.org

12-18-2016 05:09 PM
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TailKiller

Senior Heliman

Panama City, FL

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Hooligans.lol
I'm going to fly my birds as normal and check the new logs and see what the high current is so i know what they are pulling and not rely on memory. I've been using Pulse 4500 45c's and they are well used. The JR is 6s where as the as350 is 12s.. I suspect the JR is the bigger current draw but I'm only looking to buy batteries for the as350. If i am 25A or under then 20c should work fine.
I didn't think this topic could get so heated.. but thanks.

,Dennis
http://pcrcheliclub.com/
700 Astar Super Scale T-600 Bell 206 Trex 600 Naza H DX8

12-18-2016 05:16 PM
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Phoenix NOTAR

Senior Heliman

State College, PA USA

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Here is my opinion if anyone is interested;

With a few exceptions (you know who you are Steve and Gary), most of us in the Scale heli community fly our helicopters somewhat sedately, meaning without drawing huge current / watt load from out of our batteries. But, there are times when you panic, or descend too quickly and need to ask for everything the helicopter may have to save it from an impact with the ground.

I have seen many pilots wondering why their scale helicopter seem so under-powered, when they have seen similar models zip around the sky. The answer is very often "batteries".

"C" ratings are not governed or mandated to be accurate, they are more of a marketing tool. So some generalities are needed.

Will your helicopter helicopter fly with 15C or 20C 5000 mAh capacity batteries? Sure it will. Will it fly as well as it could with the equivalent (rating accuracy) batteries with a 30C or 40C rating? Maybe. Will the 30C or 40C packs give you a definite safety advantage in a panic or emergency situation. Most definitely YES.

As the batteries age, they seem to loose capacity (my experience over 1000's of flights), and this will make even 30C or 40C packs seem under-powered to what they used to be. When you start with the "marginal" flying power of the 15C or 20C packs, and add in a number a flights over time, they start to perform poorly, so you buy new packs to replace them. It is now that the money saved on the initial investment of the lower "C" packs does not seem so wise (assuming you have not already damaged your scale masterpiece by not having the power at one time when you really needed it).

One reason that Marc may not have this issue is that he noted he was running 10,000 mAh total capacity packs, so his capacity load that the batteries can safely sustain is twice what a typical 5000 mAh system can tolerate. So in essence he is running the equivalent of 5000 mAh 30C packs at the beginning of his flights

For me, the lower weight/cost difference of 15C verses 30C packs is not worth it based on how my helicopters fly, and the confidence I have knowing that I have that little extra zing when I may need it.

Sandy

12-18-2016 05:28 PM
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