Whats a BEC?

[Cralis]

My new heli, a Hurricane EP550, is arriving tomorrow. It has a BEC. What is that for? The heli uses 2 sets of 3 cell batteries (Lipos) but ALSO, seems to have another RX battery.

I'd have though it would be the same as my Trex450, which has no BEC. But my Trex doesn't have a separate RX pack.. so has this got something to do with it? I hear some speed controllers have built in BECs.

Mmm... To BEC or not....
I'll leave it..

[robgt]

BEC = Battery Elimination Circuit - it is basically a voltage step down.

Your Trex450 ESC will probably have an inbuilt BEC.
Those heli's with separate receiver packs have one pack running the motor, and the other (much smaller pack) running all the other electrics on the heli.
You need the BEC - the decision is whether to go for a 5 volt or 6 volt BEC
Unless the decision is made for you with the kit it's coming with!
Cheers,
Rob

[Cralis]

Mine comes with a BEC. But on watching the Finless Bob video on the build of the EP550, there were slight alarm bells when he mentioned the voltage of the GY401s servo, and the BEC. He mentioned 'Step down', but with my poor knowledge of electronics - I'm not sure if I am going to blow up my heli when I plug it all in...

[robgt]

I don't know what voltage the BEC you'll be getting is?
If it's 5 volts, pretty much everything will work fine.
If it's 6 volts (less likely...) then some servos won't like it.
If you have to use a step down from a 6 volt BEC to a tail servo, then the Align inline step down will work very well.

Cheers,
Rob

[moyesboy]

Most motor controllers (ESC) have an inbuilt BEC (Battery eliminator circuit).
This allows the motor power battery to also power the receiver and servos by cutting the voltage down from 11.1 (trex) or 22.2(550) to 5v, or 6v.
People use 6v to get faster servos, but some gyros and tail servos then need the 6v cut down to 5v using an additional inline step down just for the rudder channel with the gyro and tail servo on it.

On the BEC, the BEC gets hotter the more it is cutting the voltage down. For example on your trex450 you can use the BEC in the ESC fine with a 3 cell lipo - but if you used a 4 cell lipo the BEC would get too hot - it would be unable to power all the servos from 14.4v. The spec is just 2 servos from 14.4v.

Then you would fit an external BEC alongside the ESC. You tape off the red and black wire from the ESC by pulling the crimp out of the plug on the throttle channel, and then plug the BEC power into a spare channel, or put the red and black wires from the BEC into the throttle channel plug.

The idea was to explain this clearly - I think I've failed again...

The BEC needs to be a good one for the 550 running on 6 cells (22.2v). another solution would be to use a separate RX battery pack, but it would work out heavier.

[Sao]

And if you do have issues with your Esc not being able to cope with the input voltage or just struggling to power 4 digi servos and a gyro then look at the Castle Creations BEC. Adjustable output voltage and can take up to 10A!

That's a seperate BEC not the one built into CC Esc's

[Smoothound]

You tape off the red and black wire from the ESC by pulling the crimp out of the plug on the throttle channel, and then plug the BEC power into a spare channel, or put the red and black wires from the BEC into the throttle channel plug.

Just to play "Devils Advocate" here, and it's only a small point anyway


You would normally just pull the red wire from your ESC because some ESC's get upset if the black wire is pulled as well, doesn't always happen but it does sometimes...

[Cralis]

Thanks guys. Esp Moys. Nice. Understood 100%. Once my heli arrives, I'll see what it has and tell you. Hopefully nothing that needs new parts/additions to make it work. Will be starting mu build thread soon.

Thanks!

[moyesboy]

Smoothhound:
Yes it can be good to leave the black wire connected.

Usually the black wire from the lipo is connected to the black wire on the throttle connector inside the ESC.
Also on the BEC the black wire from the lipo is connected to the black wire on the output side of the BEC.
So it doesn't matter which of these two black wires are connected to the receiver, or if you connect both.