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11-28-2017 06:58 PM  10 months agoPost 41
Richardmid1

rrProfessor

Leeds, England

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.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?

You answered your own question, you are at full draw. This will be for very brief periods but maybe your setup isn't optimal or your packs are getting weak.
.thats why todays "C" rating is a bunch of bull.
Your right about one thing.

60% of the time, it works every time!

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11-28-2017 07:11 PM  10 months agoPost 42
RM3

rrElite Veteran

Killeen, Texas - USA

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you are at full draw
with a 100A ESC on a 600e?

...exactly... so much for the 150A rating on the 5000mah pack huh...

therefore the simple C * Mah = Amps does not hold water...

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

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11-28-2017 07:27 PM  10 months agoPost 43
Richardmid1

rrProfessor

Leeds, England

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ESC ratings are continuous, a 100A ESC will easily handle bursts of 150A.

Look, it's a simple equation, the C is Capacity and the number is the multiple of the capacity. 25C means 25 times the capacity. If the capacity is 8Ah (8000mah) then the cells in that pack were tested at 200A continuous and delivered at least 80% capacity (6400mah) and stayed above 3v. If the cell dropped to 3v but DIDN'T deliver at least 80% of it's capacity then it didn't pass the test at that C rating.

60% of the time, it works every time!

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11-28-2017 11:23 PM  10 months agoPost 44
ICUR1-2

rrElite Veteran

Ottawa, Ontario

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I wouldn't argue over it guys but try a share your practical experience.

this is why I go by C rating X capacity at a % remaining
say 25% remaining of the capacity.
My batteries land warm but I don't fly very hard.... more like a planker with a heli

spending time, paying attention

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11-28-2017 11:52 PM  10 months agoPost 45
revmix

rrKey Veteran

NJ

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%
higher C rating gives more rotor RPM at the same T curve setting,
doesn't need crazy power for sport flying (scale like)

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11-29-2017 12:35 AM  10 months agoPost 46
EEngineer

rrProfessor

TX

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Cells are tested till the voltage drops to 3v.
Is that voltage a little too low?

I wouldn't take it down that far....but that's just me....

Logo 600SXs, 800XX, TDR IIs

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11-29-2017 12:37 AM  10 months agoPost 47
EEngineer

rrProfessor

TX

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TH setting
RPMs with Throttle hold?....

Logo 600SXs, 800XX, TDR IIs

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11-29-2017 04:41 AM  10 months agoPost 48
revmix

rrKey Veteran

NJ

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RPMs
of course if not 0 or -

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11-29-2017 04:53 AM  10 months agoPost 49
EEngineer

rrProfessor

TX

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LHS....TH....the jargon....

Merry Christmas to ya....

Logo 600SXs, 800XX, TDR IIs

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11-29-2017 11:48 AM  10 months agoPost 50
Richardmid1

rrProfessor

Leeds, England

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Is that voltage a little too low?
I wouldn't take it down that far....but that's just me....
It's just for testing and under load for brief periods it's fine.

60% of the time, it works every time!

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11-29-2017 11:50 AM  10 months agoPost 51
Richardmid1

rrProfessor

Leeds, England

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this is why I go by C rating X capacity at a % remaining
say 25% remaining of the capacity.
Remember that as the pack runs down you have decreased power so the current draw will actually decrease towards the end of the flight so you don't need the same C rating from start to end of flight.

60% of the time, it works every time!

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11-29-2017 02:58 PM  10 months agoPost 52
gwright

rrVeteran

Champaign Il

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Back to the original question,.. it all depends on his actual power config.
I seek out low C batteries,.. because the 15c~20c packs are generally much higher energy density (more gas in the tank for a given weight), and my setups are pretty low on the current. Attached is an image of a log from my 700 at b'ham last year. 12s/4350 packs, peak current 61 amps. Before RM3 points it out, yes there was a drop to a touch under 3.2v per cell,.. but at the very end of the flight. Capacity telemetry said 80% was used, so I hit full collective (16 degrees) and climbed up for an auto,.. which I normally do on most flights. Average voltage during the flight was over 3.7/cell which is normal. Unfortunately, these are 30c packs because I don't have any low C ones in the size and weight I need for that machine. This flight was roughly 15 minutes. If a pack is rated at 30C, that means the manuf says you should be able to discharge it in 2 minutes, which would be a 30C rate. I'd go conservative and not use a 30C pack in something that flies less than 6 minutes,.. which would be a 10C average draw, but most of my setups are very efficient and fly a lot longer than that, so C ratings are never a concern, except its getting more and more difficult to find those nice high energy density 10/15/20 C cells these days.

This is that machine in another flight, so you can see it's not just hovering around

Watch at YouTube

Gary Wright

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11-29-2017 03:09 PM  10 months agoPost 53
AirWolfRC

rrProfessor

42½ N, 83½ W

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Two reasons low C ratings are getting hard to find,

Marketing - the common conception is bigger numbers are better, so people are buying bigger numbers and manufacturers are catering to that perception.

More realistically - when flying and you need/want that burst of power, a higher C rating is more capable of delivering than a low C rating. - - like a small engine in a car, it's more efficient but doesn't have that "punch".

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11-29-2017 03:32 PM  10 months agoPost 54
gwright

rrVeteran

Champaign Il

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Agree on both counts, especially marketing. If a small number is good, a big number must be better!

If the setup is optimized with gearing and the right kv motor for your particular need, the current surges are lower, so while I agree with you, that can be somewhat mitigated.

Being all electric for the last 17 years (after 21 years flying glow) I think good batteries have made us all lazy. With nicads we worked hard to optimize things to get acceptable flight times. Lipos arrived, with 4 times the energy in the same weight battery, and we miraculously went from short but acceptable flight times to super long flight times (5c and then 10C packs were all we used and we were happy with them). people started coming over to electric and soon learned you can just spin it up, prop it to draw more current if it's fixed wing.. etc, and get more and more power, which wasn't possible with glow. They can only use their fuel at a certain rate. this continued untill we took those nice 20 minute acceptably powered electrics and made them 3 minute insane monsters. We all got lazy with configuring things efficiently because we had so much energy in the packs.

Gary Wright

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11-29-2017 05:04 PM  10 months agoPost 55
RM3

rrElite Veteran

Killeen, Texas - USA

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We all got lazy with configuring things efficiently because we had so much energy in the packs
good point... Im not sure its being lazy... more like really bad collective management... When I got Started the 10C packs were the norm, 20C packs came at a premium.

But noticed one thing in particular during the Heli craze in 08... the 3D moves were quickly becoming VERY aggressive on heli blade pitch and pushing the rotor past 1800 rpms on a 600 was seen as a requirement for many of the moves... even nitros that ran 90s were starting to show up with 120s... I quickly started seeing these low arc rainbows span an entire field, the Wall move, full collective climbouts, drag racing, tail dives with full collective saves at 3 feet, pitch pumping, tic tocs that minimal arcs (hovering tail stands?)...

it was the mentality that power was required for competition and to compete you needed both speed and power... the idea of collective management had no place anymore... and therefore C ratings, HV somehow translated to ability... hell even servos went HV.

I left alot of that behind and got into gassers when the Radikal came out... and the need for collective management hit me square in the face... so began the race AGAIN for more power... tuned pipes, bigger displacement, skeletonizing everything to reduce weight, exotic metals, CF everything...

Now Im about simply flying (when I can), no more chasing power, now its about improving my skill with what I have. C ratings for me are a minimum of 30C... not because i fly crappy (Im not great but not that bad either), but I want them to last a few years... low C packs just dont last for me.

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

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11-29-2017 05:36 PM  10 months agoPost 56
gwright

rrVeteran

Champaign Il

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Understand what your saying but i only see that as an anomoly, not a general rule with lower C packs. some packs that I regularly used during this flying season are some 20C packs (6s/5000) that are 5 years old. They're down a bit on capacity (4870 on one I checked last summer) but still work just fine to 4000mah used with capacity telemetry. Always discharged to 3.7~3.8 per cell, never stored when fully charged, and if not going to be used for a while they go in my battery fridge. That's a cheapie full size fridge that sits next to the beer fridge in the garage That's where most of my batteries go except the ones that are used at least weekly. They stay in an ammo can at 3.7~3.8/cell. Packs that go into cold storage for a week or two get pulled out the night before to warm back up before use.

Gary Wright

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11-29-2017 07:14 PM  10 months agoPost 57
Richardmid1

rrProfessor

Leeds, England

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. except its getting more and more difficult to find those nice high energy density 10/15/20 C cells these days.
There's more now than ever thanks to the drones! Check out the Turnigy Multistar packs.

60% of the time, it works every time!

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11-29-2017 07:26 PM  10 months agoPost 58
gwright

rrVeteran

Champaign Il

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Those are low c, but not the really high energy density I was referring.

Gary Wright

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11-30-2017 02:58 AM  10 months agoPost 59
rcflyerheli

rrKey Veteran

Granbury, TX USA

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After going thru this thread, one question (in my mind) seems not to have been addressed.

Just how big is this 8000mah pack? Will it fit in the heli? All the power in the world doesn't do us any good if the packs won't fit in our helis.

Logo 700, Specter 700, Goblin 700, Trex 700DFC, Gaui X7, Logo 690SX, Logo 600SX; Trex 470 Trex 500
Amain Team Rep

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11-30-2017 03:52 AM  10 months agoPost 60
RM3

rrElite Veteran

Killeen, Texas - USA

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depends... on a 700 that has a tray underneath... they should fit as most are simply a bit longer (for same brand)...ex: TP 6S lipos from 5000 are 160mm long, the 7600 are 195mm long... both share about the same Height and width which vary by about as much as 10mm...

http://www.znline.com/data/11697339..._power_prix.pdf

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

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