I dont know if this is the correct place to post this but i thought it would be appropriate given the airplane im considering. Iplan to get a T-28 for my second a/c. From what i have read a 2200 mah battery will fit in the T-28 very easily. Ialso plan to get a F-27 Strkyer a/c afterwards and it recommends a 2200 battery. Iwas wanting to know what discharge rate i should use. Iwas planning on stocking up on batteries from Hobby king and ordering several 2200mah 25C. Iam open to any suggestions if im off the mark. Thanks in advance. Also can anyone recomment a good reciever for the stryker?

Higher C rating will be better for the stryker.

What radio do you have?

I have a gx5e.  I will probably get the gx6i in the near future but as of right now i will be using the 5channel.  I would like to be able to use both batteries in both a/c.  Is this possible?  I thought that the 25c would suffice.

It will. I use those same batteries in my Stryker and they are fine. They won't give you the best possible performance because they can't deliver the amps that a higher end battery can, but you won't overwork them in a Stryker unless you seriously upgrade the motor and esc to make more watts.

Jester,

Just for arguements sake, what would you consider as an optimal battery for the stryker>?

Higher "C" batteries of the same rating weight a bit more.

For instance a

2200mAh 30C pack will weight more than a 2200mAh 20C pack.

A 2200mAh 30C pack produces a theoretical 30 x 22 = 66 amps at peak.

However you can achieve the same thing another way...

A 3300mAh 20C pack produces 33 x 20 = 66 amps at peak.

However the latter may fly a plane drawing 22A far longer and with less wear and tear on the battery packs.
Higher capacity packs ( higher mAh ratings ) also TEND to keep the voltage levels higher. The higher "C" packs compensate by adding more plastic element windings to each cell, increasing the size and weight a bit.


In reality the max "C" rating of a battery should always be used as a MOMENTARY INSTANTANEOUS PEAK rating.

In actual practice you should design your power system to draw about 60% or so of max available current during hard/heavy use, for safety.


All of that said, you have to determine how you want to fly your planes and what works best for you.

2200mAh 20C packs tend to be fairly standard and used on many planes. So the 2200mAh 25C+ packs COULD give you better flexibility, if they fit other planes. Remember that the latter will be a bit larger too.

You can also gang packs together... so from two 2200mAh 20C packs you can make one 2200mAh 20c 22.2v pack or one 11.1v 4400mAh 20C pack.... using nothing more than removable connectors. As such I tend to use the 3200 or 3600mAh 11.1 packs where I can, knowing I can tie two together and fly a .60 sized airframe with the batteries doubled up.

Opjose,

I understood some of that but realized i have SOO much more to learn.

dont worry about the 25c it will be fine.

Optimal would be the battery that gives you the most amps at full throttle, is the lightest, and is the most durable. C ratings really don't mean much. Within a given product line they do indicate batteries with a little less internal resistance generally, but across brands there is no standard for what they really mean. So optimal would be one of the top shelf batteries in a 30c rating. Everyone has their favorites, but I'm thinking Hyperion, Thunder Power, and Maxamps will be near the top of most people's lists. What's really important for performance is the weight per capacity and amps delivered. The cheaper batteries work and are fine for just getting out and enjoying your plane, but they are heavier and simply won't deliver the same amps that the better brands will. Of course, you can have 5 Zippys for what one Thunder Power will cost, and the 5 Zippys together will probably last 3 times as long as the one Thunder Power before needing to be replaced. So it comes down to what gives you the most enjoyment out of your money spent.

Thanks guys, really appreciate the information.  Im ovbiously new in this and still learning.  I think i will get one top shelf and several cheaper ones and see if the differenceis worth the money for me personally. 

Just to clarify a point here.

You don't MAKE more watts, you CONSUME more watts. Wattage is a function of voltage times current. So, you don't make 'em, you use 'em. Larger capacity batteries at the same voltage are able to do two things: supply the same current for a longer time (watts over time) or give you more current for shorter time, (watts consumed over shorter time.. again, voltage times current).

CGr.

If you can afford to do it, this is probably the best way to find what you need.

This electric flight has so much to learn for everyone. It isn't just a matter of trying something. Unlike glow power, there is no magic "good enough" solution. It does take some calculation, some work in other words, to get things right.

Consider the watts per pound guideline:

You can determine the power requirements of a model based on the ‘Input Watts Per Pound’ guidelines found below, using the flying weight of the model (with battery):

50-70 watts per pound; Minimum level of power for decent performance, good for lightly loaded slow flyer and park flyer models
70-90 watts per pound; Trainer and slow flying scale models
90-110 watts per pound; Sport aerobatic and fast flying scale models
110-130 watts per pound; Advanced aerobatic and high-speed models
130-150 watts per pound; Lightly loaded 3D models and ducted fans
150-200+ watts per pound; Unlimited performance 3D models


So, if you have a plane that weighs in at 25 ounces. That works out to roughly 1.5 pounds. To fly this at sport aviation levels, it will take 1.5 X 110 watts or 143 watts. If you use a two cell LiPo, that's 7.8 volts (nominal). 7.8 volts works out to a battery capable of supplying at least 18 amps. So, a 2000 mah pack is pretty much minimum for this plane, and you have to consider how you want to fly it at that and that's where the C factor comes in.. how long and how much burst power do you want/need? A three cell Lipo will need less current.. but you get the idea, i'm sure.

It's not as simple as just putting a battery on the plane and trying it out. You chance burning up both the motor and the ESC with the wrong selection.

Remember that when making weight measurements (not estimates, unless you know exactly what each component weighs), everything has to be considered: airframe, motor, esc, battery pack, receiver, servos, everything.

Hmmmm... I wonder why I prefer/love glow power? Don't get me wrong.. I fly electrics, but prefer glow.

CGr

Have you tried the Nano's yet?

Methinks you'll change your mind when you do.

Not true.

Optimal can just as easily be cheaper packs of lower capacity, that can deliver the same or higher amps at a sustained voltage level, and often provide longer duration to boot.

It can go both ways dependant upon the application, and there-in is the problem for newbies. There are many things to consider.

However the basic stuff is much easier than it looks and newbies need not be intimidated by all of the numbers being thrown about.

CGRetired summed it up succintly.

I sent CGretired an email and hopefully he wont mind elaborating on this or pointing me to some literature that does.  I'll be honest i am literally so damn confused right now i dont know which way is up.  I dont understand how the voltage related to amps or watts or how they relate to selecting the proper battery for the application.  I have been reading through the batteries and chargers section and its about as clear as mud.  Truth be told i have always been a gear head and my pride and joy is a 69 Camaro.  I am pending orders to japan and i cant take my car.  I have always been intrested in R/C's since i was a kid and had the cheap ones from radio shack.  I had one glow truck that i messed around with but really would like to get into the airborn side of it.  I dont expect someone to babystep my through all this knowledge but im having a hard time find a place to read it so i can understand it.  I dont have acces to a club as i am currently deployed to afg.

I sent CGretired an email and hopefully he wont mind elaborating on this or pointing me to some literature that does.  I'll be honest i am literally so damn confused right now i dont know which way is up.  I dont understand how the voltage related to amps or watts or how they relate to selecting the proper battery for the application.  I have been reading through the batteries and chargers section and its about as clear as mud.  Truth be told i have always been a gear head and my pride and joy is a 69 Camaro.  I am pending orders to japan and i cant take my car.  I have always been intrested in R/C's since i was a kid and had the cheap ones from radio shack.  I had one glow truck that i messed around with but really would like to get into the airborn side of it.  I dont expect someone to babystep my through all this knowledge but im having a hard time find a place to read it so i can understand it.  I dont have acces to a club as i am currently deployed to afg.

I've written long explanations many times before and there are quite a few of them on these forums...

Here's a quickly I did for someone recently... he asked how to select a power system for his plane.

Snip -

Actually it's quite simple...

To get 1:1 you want around 120-130+ watts per pound maximum ( burst ) power.

So if your plane is going to weight 15.2oz ( as projected by the manufacturer ) then take a figure OVER this and multiply by 130watts...

So let's say the plane will weight 20oz AUW just for safety....

1.25lbs x 130w = 162 w

So a 180 watt motor will do the trick.

Assume that you'll use an 11.1v LiPo pack...

180w / 11.1v = 16.3A

A 20A-25A ESC will work fine

Thust HP says that a 8x6 prop spinning @ 11000 RPM produces about .234 HP

1HP = 745w

.234 * 745w = 174w ( right in the ballpark! )

So we can use an 8x6 prop and spin it at 11000 RPM.

11,000 RPM / 11.1v = 990KV or approximately 1000KV

I'd use an 1100KV motor to add a bit more power.

Finally let's find the battery we'll need... we'll want to drive it only to a maximum of about 15c if it is rated for 20C.

16A will be our maximum draw

16A * 20/15 = 21A @ 20c

So a 1000mAh to 1200mAh 11.1v 3S pack would be the smallest you can use... I'd go with something around 1300mAh+ for safety. 1800mAh would give you the flight times you want but adds weight.

So there you have it.

1300mAh+ 3S 11.1v LiPo
8x6e prop
20-25A ESC with BEC
1100KV Motor rated up to 180-200watts burst for 15-30seconds. ( look for a 150w motor or so ).

Snip

Knowing how to choose a power system affects your battery selections.

Very clear, opjose.

What seems very clear to you guys was clear as mud for me.  I have been doing a ton of reading but i finally made headway this morning.  It was like everything came togeher when i as looking at a battery.  I came back and read this again and i at least understand most of it.  THank for all the responses.

Well, I guess that answers your question from your Email. All in all, it's fairly easy to calculate given all the parameters. The most important part of this is getting the weights right, which always means a little research. Pretty much all of the vendors list such parameters.. weight of each item in the process, including the airframe, motor, prop, battery, esc, servos, and so on. Just add them up and work through it as Opjose did and you will come up with a solution for that combination.

Just remember that making a change, increasing the battery capacity, for instance, adds weight and the whole thing needs to be re-done again to make sure you remain within the 'envelope' for that particular type of flying and for that airframe.

I don't want to oversimply this and insult your intelligence, but, here is the basic math for watts, amps, and volts:

Ohm's law (algebra) [:@] :

Volts X Amps = Watts

Watts/Volts = Amps

Watts/amps = Volts

Easier stated, multiply volts x amps you get watts. 11.1 Volts - three cell LiPo multiplied by 20 Amps drawn = 222 Watts

222 Watts divided by 11.1 Volts = 20 Amps

And so on.


For OpJose's prop calculation, that comes already done for you. Ask him where he got the info.. it's on a web site somewhere.
CGr.

Thrust HP can be downloaded here:

[link=http://www.hoppenbrouwer-home.nl/ikarus/software/thrusthpv20d.htm]Click me for Thrust HP.[/link]

Bare in mind that it was written for gas/glow engine props, so you may want to assume the results are slightly over-optimistic for electrics.

Good stuff, José. Thanks for posting that link. You are both a Gentleman and a Scholar.. and there are damned few of us left!!

CGr (Dick)

There was a ton of information here that i found useful. Thank you all very much. I am happy to report learning has occured.