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View Full Version : lipo's for my wing,edumacate me?


trey3670
09-05-2005, 07:48 PM
ok guys I am considering makeing the change to lipolys from nimhs,here is what I need to know.
I am currentlly running an astro 20 brushless settup on my wing,swinging a 5x4 prop. what size lipo's do I need? how do you arive at the proper size? I have looked through some of threads on this and frankly I am cornfused! so talk slow for me!:D

ragbag
09-05-2005, 09:31 PM
Go to this site:

https://www.fmadirect.com/site/fma.htm?calc=true

It is the FMA lipo calc program that is available on line. Run your numbers at the top of the page and see what they say.

Of course I would expect them to recommend their product.:cool:

Sorry I'm not familiar with your setup so I can't be of more help.

By George

2dogrc
09-06-2005, 02:50 AM
Here is how you determine what size you need:
You have done the easy part you know what motor and prop you are using. Then you need to find out how many amps that motor draws with that prop at 7.4V (2 cell pack, 2S) and 11.1V (3 cell pack 3s). For example if your motor pulls 10A at full throttle, you would want at least a 1050 mAh battery rated at 10-12C continuos.

The math goes like this..1050 mAh equals 1.050 Amps. The battery rating, 10C means 10 times C, C being Capacity. So in this example 10C*1.050A=10.5A can be drawn form the battery continuously. That calculation will determine your min battery.

to figure out which batteries you can use, you know the minimum size, now it depends on weight and application. If you are going to be flying at full throttle pulling 10A, a 1050 will last under 10 minutes and be very hot! You are pushing it to the limit. In this case, try a 1350 rated at 10C. For this battery you can pull 10A and you are not at the max for the battery, which would be 13.5A. Your battery will last longer in flight and over time. Remember amps=flight time, and volts=power. Just pick a battery that won't be too heavy and will provide the flight time required.

Hope that helps..

trey3670
09-06-2005, 02:52 AM
ok cool i have a multimeter can you tell me how to check amp draw?

2dogrc
09-06-2005, 02:56 AM
sure!
hook one lead from the amp meter to the neg side of the battery. Then one lead from pos battery to pos of ESC.
Then another lead from neg of ESC to amp meter.

You need three wires..

questions?

Matt Kirsch
09-06-2005, 02:57 AM
Figuring out how many cells you need is easy. You simply replace Volts for Volts when going from NiMH to LiPoly, or come as close as you can.

What battery are you using now?

To figure out how many mAh you need in LiPoly, you need to have a good idea of how many Amps your setup draws now. Either measure the current with an Amp meter or Wattmeter, or look it up on an online resource. Astroflight.com posts their test data.

Every LiPoly cell is rated based on a value called "C." C stands for Capacity, as in the capacity of the pack in mAh. Multiply the capacity of the pack by the "C-number" to find out how many Amps the battery can handle. This value must be at least as much as the Amps being drawn by the motor.

777
09-06-2005, 03:20 AM
What if you're already running 12 cells of GP1100's. Any performance advantage to switching to 3s or 3s2p?

Brad

2dogrc
09-06-2005, 03:29 AM
What if you're already running 12 cells of GP1100's. Any performance advantage to switching to 3s or 3s2p?

Brad
Oh Ya!!

If you go 3s 1100 you WILL GET MORE PERFROMANCE GUARANTEED! You may ask guaranteed? Yes! You are getting about the same power to teh motor, BUT the weight of the plane has been greatly reduced! you will increase your thrust to weight ratio. Oh ya and you now will have a nice battery paper weight with your old cells:)

777
09-07-2005, 04:29 PM
Help me to understand, how can a 3s/11.1v lipo compete with a 12cell/14.4v NiMh pack as far as voltage delivery goes.

Brad

2dogrc
09-07-2005, 04:48 PM
Power wise it is less power,BUT! How much will your planes weight be reduced by using a lighter pack? How much does a 12 cell pack weight? A 3 cell 1050 pack weighs 1.58 oz..
Weigh your pack and compare. You can use the watts to pound to figure out if there would be an advatage...
W=Volts *Amps then divide by how much your plane weighs.
So for your NiMhsetup it would be 14.4*(amps your motor pulls at full throttle)/(weight of plane)
And for Lipoly it would be 11.1*(amps your motor pulls at full throttle)/(weight of plane)

I would be interested to see what you find out? Will the lipolys have the advantage?

777
09-07-2005, 05:25 PM
Keep in mind, if you're pulling big amps, you may need 3s2p to keep up.

A Polyquest 1800 3s weighs 4.8oz x2 = 9.6oz Add in some parallel connectors or Y connectors.....

A 12 cell pack of GP1100 weighs 9.12oz.

Brad

trey3670
09-07-2005, 09:55 PM
holy shnickys from what i can see the lipo will run me 95$

debhicks
09-07-2005, 10:23 PM
No one said they'd be cheap. If they are,.......beware......:)

777
09-08-2005, 12:00 AM
trey3670,
What kind & size of a wing are we trying to power?

Which Astro 20 do you have? When I go to
http://www.astroflight.com/e/env/0001WQ6wKIb8UN4VdQ1X716/index.html?link=/store/store-Brushless.html I see lots of motors.

Here's a cool & free motor/batt/prop calculator that may be useful; http://brantuas.com/ezcalc/dma1.asp Punch in your information and you get watts & amps at the bottom.

One thing for sure, unless you're flying a mini-wing of some kind, the 3s 1050 battery mentioned above will not provide sufficient amps. Even if it were to be 15c, then it would deliver about 15amps. Not very much.

If your application does not have to deliver big amps, from what I understand you may be able to get away with simply 3s (1p) of about 2600mah. That's similar to what some people are using with things like my 42" Unicorn with 16/15/4 and an APC 6 x 4. Makes about 30amps with 12 cells of GP1100.

I'm trying to run a 36" Wing Warrior with a 16/15/3 and an APC 5 x 5. Wing Warrior suggests 3s2p for that application, as I mentioned above. However it rips on 12 cells of GP1100. Makes about 40amps with 12 cells. Run-time isn't too long however.

Brad

rahtware
09-08-2005, 05:38 AM
By wing, do you mean pusher?

AF lists three direct drive 20 motors. The "Zaggi" pusher sucks 23 amps from a 3 cell liPo for 259W and 22,400 rpm on a MAS 5.5x4 prop. The same motor on 10 Ni cells draws 26 amps 312W and 23,500 rpm.

A 10 cell, 2000 mah (tower) NiMh pack costs only $29.99, but weighs 16.7 oz.

Tower has a Kokam 2000 3s pack that discharges at 15C / 30Amps continous for $79.99. It's weight is only 6.3 oz.

$40 gives you a saving of over 10 oz!!! I don't know about you, but I fly planes that weigh less than 10oz.