OK here is what I have and here is the problem I run into

I got the ultimate ultrafly and I am using a himax HC2808 brushless motor. The esc is a E-flite 20 amp brushless and the battery is a 3 cell 11.1v electrifly Li-Po.

The problem is when I go to fly and the throttle is about half way to full, everything shuts down.

I was tolled by a hobby store guy that to many amps are being pulled through and that I needed to use a smaller prop, well I tried an 8x6 which at half throttle barely moved the plain and then it shut down just like before.

What can I do??? I want to fly...

It sounds like you're drawing your battery down below 9 volts using too much current and the LVC, (low vlotage cut-off), is shutting the motor off. You didn't say what size prop you're using or how many amps your system is using. Are you sure the battery is fully charged? What condition is the battery in? i.e well used, brand new??? A watt meter will tell you exactly what's happening as you throttle up your system. If you don't have one yet, I'd suggest making it your next purchase. There are several reasonably priced units on the market. If the watt meter saves you from ruining one LiPo, it's paid for itself. Good luck.
Rick

The battery is brand new and fully charged. The interesting thing is that it's not the motor that shuts off, it everything. I have to off the battery and reattach it in order to reestablish power again. In other words if I was to take off and it cut out like it has been, I would have no control and it would drop like a rock.

WOW!! Now it's sounding like the BEC is malfunctioning. Is the ESC new? If so, it may be defective. Do you have another one to put in its place? Good luck
Rick

You might have a bad ESC? How long does it take before everything shuts off? Is the ESC hot? What capacity is your battery?

When the power shuts off, the Esc is not hot at all, and the power is only about half to 3/4 full throttle. And the ESC is brand new.

Well...actually what I meant by a bad ESC is maybe it's defective? How long will the motor run at half throttle?

It does sound like the battery is being pulled down below the LVC (Low Voltage Cut-off ) at high throttle settings, but the servos should still work, especially if the ESC is not overheating.

Which ElectraFly battery do you have? A 3 cell but of what capacity?

The motor will run at half throttle for as long as I keep it there. The batteries are 3 cell 11.1V 640mAH. Another thing that I forgot is that when I take the prop of there is no problem, but agian I have tried from a 9X7.5 to 8X6, which almost didn't move the plane.

O.K....it sounds like the 640 is too small a capacity to be able to deliver the amps required.

Is there a recommended battery size (mah capacity ) listed in the manual? I have a 2808 / 24 motor (AXi ) but a 2100 mah capacity battery. That would be too heavy for your plane, but maybe if you had a 1250 or 1320 mah.

The 2808 is capable of pulling a lot more current than the little 640 is capable of delivering.

Why don't you give MPi / Maxx products a call and tell them your set-up and what's going on and maybe they can give you a better recommendation for a battery?

I think that Proptop has it right in that the battery is to small for the load, but, why is the esc completly shutting down instead of just shutting off the motor? I know of no ESCs in which the BEC shuts down upon hitting the LVC. There may be two problems here, a battery not up to the task and a malfunctioning ESC.
Rick

Have you tried to reprogam the speed controller? Might be worth a shot..

not sure how to program the ESC, can you explain

AFAIK the only thing you can "program" on the E-flite 20A. is brake on or off?
Something is screwy somewhere...the only other thing I can think of is that the voltage is getting pulled down so low that it also gets below the min. for the radio to work? Doesn't seem very likely, but possable???

The low voltage cutoff makes sense because I have a 2 cell lipo that operates with 1050mAH and this problem doesn't happen. So I will just pick up a more powerful battery and see if that works.

Thanks every one