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Higher C advantages and disadvantages

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Old 03-27-2011, 06:02 AM
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fheppenheimer
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Default Higher C advantages and disadvantages

I've been told a 20C battery is appropriate for my planned installation, will "overkill" by using a 45C battery confer any immediate performance advantages or disadvantages? For example, will my setup run cooler or with less strain with the higher C?

I do understand that higher C means greater weight and cost, and offers faster discharge (not needed right now I'm told). Also, 45C will give me greater versatility for use in a future different setup where 45C is needed. Is there anything else?
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Old 03-27-2011, 07:29 AM
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Default RE: Higher C advantages and disadvantages

This is a great topic.

I'm starting my second season of electric flight. My first set of batteries was 30C, and later I was told that (for pattern flying) 20C was adequate and no need for the extra weight. Due to beginner's misuse (storing at full charge for any period of time) those batteries now perform more like 20C batteries or worse.

What is your planned application, and what's your experience level? Do you want long flights? Higher C batteries will have less resistance to dumping power, so you'll feel more power, but you'll also use the battery faster.

There are many things to consider. For example, 45C batteries at 5000mah can dump 225 amps. That would destroy my motor and my speed controller. I'm limited to maybe 80A continuous and 120A peak. This is why 20C is adequate. So it's important to look at your setup and see if the higher C batteries make sense.

I also chose to use higher voltage (more cells) to save current discharge, which gives me pretty long flights at good power. I could drop from 10S to 8S, but would need to use considerably more current to have the same power, and thus flight times would diminish. If I only wanted 5-6 minutes of all-out flying, a high current (80-100A), 8S setup would save a bunch of weight. 60A on 10S gives me the same performance for 10 minutes. Obviously it adds weight so you have to decide if like how the weight affects the flight characteristics.

My suggestion is to go with 20C. There is a learning curve so I think spending less early on is a good idea (of course I'm stubborn and don't always practice what I preach!) Also, lipos decay over time. Your 45C battery won't perform like 45C in the future, so it's probably a good idea to wait until you need them to buy them.
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Old 03-27-2011, 09:35 AM
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Default RE: Higher C advantages and disadvantages

Thanks Joe. I'd be grateful for your additional thoughts taking into account my ability and planned application =

3d Hobby Shop Osiris. I have the plane and am planning on using Futaba 9650 and 9551 which were 3DHS recommended servos. Based on the 3DHS website recommendations and forum threads, I was planning to use the following power equipment Hacker A50-12S motor, CC Ice 100A [not Lite], CC BEC Pro (20A), Prop APC electric prop 15-10, 15-12 or 16 x 10, 5S 5000 mah Lipo. All but the batteries were just ordered but it's not too late to change things around.

I am inexperienced with electrics and am a poor flyer even on glow. Slow, stable and long flights are perfect great for me: I still fly like a beginner and I will want to fly slow and practice and will not push the plane hard, no 3d or IMAC at all, I'll use this more like an old man's Sunday flyer and will want to fly sportsman pattern occasionally. (Actually, I'm trying electrics hoping the lack of fuss will let me get to the field more often.)

Based on the threads and website I was planning to use Thunder Power 5S 5000 mah batteries and had the choice boiled down to 20C [G4 Pro Lite V2] or 45C [apparently a G6 Pro Power 45C is coming out in April, less costly than the current 30C and 45C's). I have hopes of flying 2M electric someday and thought that the 5+5 configuration was appealing.

Are you saying that I'd be better off with a 6S battery ? The website also mentions using a 6S for use with a Hacker A50-14S or 16S and a CC 85 HV speed control? [I have no idea how 5S on A50-12S compares to 6S on A50-14S or A50-16S or even what 12, 14 or 16 are distinguishing] It's not too


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Old 03-27-2011, 11:14 AM
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Default RE: Higher C advantages and disadvantages

First off, I must say that is a wonderful choice of airplane!! I have flown against them in contests, and have the video that relates to the plane (which I recommend! covers building, setup, and basic pattern skills). I may get one too as I can use my 5S packs and try to preserve my Wind a little.

Knowing who designed that airplane (Andrew Jesky) I would go with the suggested setup, for everything. The plane was designed for pattern fliers as a backup or practice plane, and thus was designed to run on 5S batteries (we use two 5S batteries as a pair for flight). He flies one in the video on 5S and it flies fantastic.

That being said, moving to 6S is an option for that airplane, but you have to decide if it's for you. You can go to Castle Creation's webpage and play with the flight calculator; you can enter your motor, battery setup, speed controller, and prop, and see the current draw, power in and power out, estimate flight times, etc. The only issue I see there is Hacker motors are underrated, so you might get some premature warnings about power or current.

Again, experimenting can cost you money and flying time. I didn't listen to people who told me this (I'm stubborn) and it cost me lots of down time, trying different motors, buying more props, buying new hardware to install motors, etc. etc. Use the calculator as a learning tool, start with the recommended 5S setup, and decide when your comfortable and successfully flying if you want to make changes; you probably won't

Here's a link to the calculator; I suggest playing around with it and experimenting to see what happens when you change things, like number of cells or propeller:
http://www.ecalc.ch/motorcalc_e.htm?castle

Another suggestion, which is totally up to you, is that I would order Rhino or Zippy batteries from Hobbycity.com; they are something like 1/4 of the price of Thunder Power. There basically is no customer support, but many (like thousands of people all over the world) of us are using them successfully. For the price you can afford a bad pack here and there, but more importantly you can afford the learning curve with cheaper batteries. You will probably want to have at least 3 packs to show up to the field with. Unfortunately this is the time of year where everyone is stocking up, so they are often out of stock:
http://www.hobbyking.com/hobbyking/s...idProduct=7654
http://www.hobbyking.com/hobbyking/s...idProduct=8581 (in stock as of the time I posted!!)

An upgraded battery from that would be from F3Aunlimited.com. This is the store of a fellow American pattern flier who is dedicated to supporting our electric needs:
http://www.f3aunlimited.com/webstore...&products_id=7

So these are my suggestions based on my first year of flying an electric pattern plane. Please listen to whatever else people tell you, and make your own decisions. I'm here to offer advice and am happy to do so, but there are always other thoughts and opinions. If you have questions, ask away and feel free to send a PM. I have learned a lot (obviously not everything!) and love aviation and flying these planes, and like to share my experiences to help others enjoy as well.
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Old 03-27-2011, 11:32 AM
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Default RE: Higher C advantages and disadvantages

So Joe, staying with the AJ recommendation of the A50-12S and 5S 5000mah, should I go 20C [i think that's what he uses in the video I believe] or higher? from your post it sounds like 20C will give me a little more flight time than a 45C. Again, will one of them tax the motor and speed control less?
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Old 03-27-2011, 03:04 PM
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Default RE: Higher C advantages and disadvantages

Neither one will tax the speed control; it's only if you set up a system that actually draws 45C, but using the recommended setup you won't be anywhere close.

You may notice a small increase in power with the 45C, but based on where you're at with your flying and what you're trying to do, probably not. I would stick with the 20C. You will learn to love electric and most likely be buying more batteries in the future, so wait until (if) you actually need the 45C batteries to spend the money on them.

The difference in flight time between 20C and 45C will be small, but people say that since the 45C discharges more energy quicker, it uses up the battery faster. I'm still trying to prove this mathematically, but I'm not the best at EE.

20C will do you fine. You will be very happy with that plane and setup.
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Old 03-28-2011, 06:15 AM
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Default RE: Higher C advantages and disadvantages

Here is another opinion based on what I see with my 6s powered Osiris and AngelS50. I notice a significant increase in power from my 30C versus 25C packs. Flight times are actually a little longer with the 30C packs. This is a result of the 30C pack holding voltage under load much better than the 25C pack. That means I do not have to use as much throttle as I do with the 25C packs. The difference should be even greater between 45C and 20C packs. I have some new Turnigy Nanotech 6s 5000 45C packs to try next weekend. I would go with the higher C rated packs, I would not be too concerned about a little extra weight in a pattern plane.
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Old 03-28-2011, 06:19 AM
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Default RE: Higher C advantages and disadvantages

Just because a battery is 40c capable doesn't mean that its going to burn anything up if your setup doesn't demand it.

If you're setup is trying to over pull a 20c battery it will puff up the battery and possibly catch fire. That doesn't mean if you up the C rating on the battery you're going to burn anything up. Actually the battery will just run cooler and last longer (cycles, not flight time)

Upping the C rating does NOT effect flight time. Using more amps effects flight time.
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Old 03-28-2011, 06:37 AM
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Default RE: Higher C advantages and disadvantages

30C holds voltage better than my 20C, use less amps for same power. I always fly 7.5 min. The 30C packs have a higher measured voltage after a flight and take less mah to charge. So I could fly longer with the 30C packs.
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Old 03-28-2011, 06:47 AM
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Default RE: Higher C advantages and disadvantages

Here is some data from flying the end of year contest least season. I used 30C, 25C, and 20C batteries, and there is hardly a difference (One set 30C, One set 25C, and Two sets 20C). If a setup is only going to draw 60-70A and you're using 5000mah batteries, 20C is more than adequate. Especially in the case of slow and stable flying or starting out in basic aerobatics. I still say there is no need for extra money and weight on a first electric power system. If you were talking about trying 3D I might have a different opinion, but 20C is enough for me, and is enough for most of the guys I work with at contests, including internationally ranked competitors.

I don't disagree that higher C gives better performance somewhere, I just don't think it makes sense in this application at this time.

I'm glad there are some other responses. I have my opinions and experience, but ultimately it's up to anyone to make their own decisions

If you decide to go with the higher discharge batteries, the only thing it will hurt is your wallet and if you go with the Chinese it may not be that bad. I started out with 30C batteries but found out after I didn't need the extra weight and really don't need the extra discharge. To me it was a waste; should have went with a decent set of 20C to save money. And I still go with 20C based on the data above, plenty of power for contests.
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Old 03-28-2011, 07:05 AM
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Default RE: Higher C advantages and disadvantages

Joe, Interesting that your packs show no difference. My 30C packs draw just under 2000 watts static and the 25C packs about 1600 watts static. As I recall the numbers were similar when logged with eagletree. I like power!
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Old 03-28-2011, 07:29 AM
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Default RE: Higher C advantages and disadvantages

Something to keep in mind, the "C ratings" on some battery brands are optimistic to the point of imaginative.
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Old 03-28-2011, 08:25 AM
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Default RE: Higher C advantages and disadvantages

When I charge my batteries, I generally put the same amount into each one. I fly on a timer, 9.5min, and put in between 3400 and 3700mah back to the battery, regardless of the C rating.

I agree that it's half a fictitious number
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Old 03-28-2011, 11:54 AM
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Default RE: Higher C advantages and disadvantages

Upping the C rating does NOT effect flight time. Using more amps effects flight time.
I'm still trying to figure this one out. Some people are saying they are getting more power out of their higher C batteries, and thus using up the battery a little bit faster. I don't know if C rating is a direct function of internal resistance or not. More power means either your pulling more current, or running at a higher voltage. Less internal resistance would mean less voltage drop in the system (really across the battery terminals), thus higher voltage used for more power but equal current. I haven't played with any 45 or higher C rated batteries, and the internal resistances on my batteries are all similar, whether 20C or 30C, so I'm not sure if the i.r. is what has the effect or not.

Regardless, the difference in flight times one way or another would be very small. As stated, using more amps decreases flight time, so to extend flight times you'd use a bigger battery, run a more conservative system/prop, or increase your voltage (more cells, which is the route I chose based on the unusually large wing area for my size pattern plane).
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Old 05-10-2011, 02:18 PM
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Default RE: Higher C advantages and disadvantages

First let me say that "C" is a measure of how fast a battery can be safely discharged. It has nothing to do with the total (total being the operative word) amount of power a battery can supply. For example, at 1C a 5000mah battery will supply 5 amps for 1 hour regardless of it's C rating. At 20C this same battery will supply 100 amps for 3 minutes. Get the picture? The amount of current (amps) is controlled by Ohms Law - Current = Voltage/Resistance. As effective motor resistance goes down amps go up. If the battery sees 0Ohms, amps go to as much as the battery can supply. This is a "short" circuit, much smoke, fire, and other bad stuff. Aside from motor resistance, the primary contributor to current draw in any e-power system is propeller size. Bigger props increase amps drawn. So where does C come in? In any particular battery, motor, prop combination certain maneuvers can cause rapid changes in current draw. C is chosen to allow safe operation through these rapid changes. My 2 cents.
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Old 05-10-2011, 02:22 PM
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Default RE: Higher C advantages and disadvantages

Sorry but thats not correct at all.

The C rating IS the internal resistance of the battery. Well its a number that represents it in any case.

The higher the C rate the lower the internal resistance.

The motor/prop is the load.
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Old 05-10-2011, 07:12 PM
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Default RE: Higher C advantages and disadvantages


ORIGINAL: BarracudaHockey

Sorry but thats not correct at all.

The C rating IS the internal resistance of the battery. Well its a number that represents it in any case.

The higher the C rate the lower the internal resistance.

The motor/prop is the load.
The term C is stands for Capacity. Internal resistance is stated in Ohms (miliOhms for batteries). Battery internal resistance is not static. The value of internal resistance is dependent on the battery's state of charge. Maximum charge is minimum resistance. Minimum charge is maximum resistance. Please do some research before declaring something "is not correct."
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Old 05-11-2011, 04:30 AM
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Default RE: Higher C advantages and disadvantages

I'm good on the research thing thanks, but I should probably have been more specific.

First let me say that "C" is a measure of how fast a battery can be safely discharged. It has nothing to do with the total (total being the operative word) amount of power a battery can supply.
Both correct.

For example, at 1C a 5000mah battery will supply 5 amps for 1 hour regardless of it's C rating. At 20C this same battery will supply 100 amps for 3 minutes. Get the picture?
Not really. It CAN supply that, not that it WILL supply that simply because it has a higher C rating.

I have no idea what you edited.

The lower the internal resistance of the battery the higher its C rating will be.

As I said before, its more marketing than science though.
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Old 05-15-2011, 01:38 PM
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Default RE: Higher C advantages and disadvantages

Another point of view:
The C rating is basically dependent on the heat generated by the internakl resistance and secondly the ability of the pack to tolerate and dissipate the heat generated under normal (air temp and glow) conditions.

I suspect this second factor accounts for some of the different opinions expressed.
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