I just bought my first plane (a NextStar EP) and after having read the thread here about VoltWatches I had a chat with a flight instructor about them and he also brought up a possible option of using a BEC instead of a receiver pack. I use a BEC in my converted brushless REVO but that does not leave the ground, well, not intentionally, well, thats not exactly true either. Anyways, what do you use to power your electronics? What are your thoughts?

The only electrics I don't use a BEC in is my gliders, and most of the better brushless ESCs will allow you to program the cut off voltage. Plus, you would be essentially lightening the plane by the weight of a battery pack.

For any electrics that do not require lots of current for the servos, the BEC is usually the best choice. However, on large electrics using 4 or more servos or servos drawing high current, the BEC is usually not capable of supplying sufficient power. Then, you must use a seperate receiver battery to power the receiver and servos. When you do this you must also disconnect the red wire from the ESC to the throttle channel on your receiver. As to the Voltwatch, it would only be beneficial when using a seperate battery for the receiver and servos.

I had a feeling that if a 600mah receiver pack could handle multiple flights then a BEC run from a fresh pair of 3600mah packs should not impact flight time much.

To clarify Rodney is talking about the built in BEC in the ESC, which is why he says it is good for planes that do NOT require a lot of current for the servos.

Hypersprint may be talking about using a seperate stand-alone BEC.

These typically CAN and DO handle higher power output requirements of higher torque servos.

I use standalone high power BECs with electric planes that have larger control surfaces and/or have a higher power ESC...

e.g. anything OVER 40 Amps.

Typically the higher the amp draw the less capacity available for the BEC's output to the servos which is why a standalone BEC is usually advised... and if you go higher, say to 80A esc's... these often do not have an on board BEC.

Sorry, I should have stated this more clearly. Yes, I was talking about an external BEC. The Castle Creations 10AMP Peak. I guess I just figured that if a RTF plane came with a receiver pack then the ESC probably did not have an internal BEC, why would a company spend the money to include something if they didn't have to.

Using a UBEC do you get any indication that you are about to run out of battery and if so what is it and how long do you have to get your plane down?

Nope no indication.

That is why you should always check the battery state after the first few flights.

I use a rough estimate... for freshly charged packs.

800mAH battery pack = check after 2 flights and thereafter
1200mAh battery pack = check after 4 flights and thereafter
1800mAh battery pack = check after 6 flights and thereafter
etc.

Check with the plane switched off and a voltmeter that places a load on the batteries.

Sorry opjose, I guess I was not clear again.

When using a BEC there is no receiver pack to check, but how do you know when your motor batteries (the NextStar EP recommends (2) 3600mah 8 cell nimh) are about to die? If there is no indication that your batteries are going to die soon wouldn't using a BEC be a bad thing in a plane? Batteries dieing, would mean no controls, wouldn't it?

Let me jump in if I may, most ESC have a low voltage cut out, meaning your engine will shut down but you will still have power to the RX and servos. End result DEAD STICK, just as if you ran out of fuel or some other thing caused the motor to quit on a glow or gas Airplane. Although with the electric you might get just enough engine back after a short pause to assist in landing. Good luck with your new Nexstar.

aaaah, I see the light.

TRKDRVR, Do you drive local or long haul?

Rodney, What part of FL? I'm a snowbird here in Eustis until April 18th then heading back to VT

You can also often set the ESC to "soft cut" the power, which I prefer.

Couple this with a higher cut voltage too, to protect LiPo's if you use them...

What happens is that you will suddenly notice a marked decrease in power available on the plane.

The prop will still spin and you will have enough power to go around and land, but you'll notice that the plane will not want to climb as before no matter what you do.

This indicates that it is time to bring it down ASAP. 2 minutes later you end up at full cut off.

Normally way before I hit this point, the gradual voltage drop from the batteries becomes very apparent.

I find that ( depending upon the plane ) I can tell that soft cut is 2 to 4 minutes away...

Rodney, Do you have to kill the BEC power from the ESC?
I have an ESC that pushes 5V (max) 2 Amps back to the receiver.
If were to add a battery pack also(4.8v with AA nimh's) I don't think it would kill the servo's or ESC. Do you think it would harm the receiver?
thx

You would be effectively dumping the built-in Bec's output back into the battery. which is one reason this is not done, without some form of isolation or switching.

I am going to start by using the provided BEC from the ESC.

What will I notice besides poor servo performance? Hot ESC?

One or two servo's are high torque, so I could Y cable the power to them and to a battery pack to provide for them separately. Then the ESC BEC will be sufficient.

thx