Do I need an external BEC?

[clockworks]

Building a Venom with 2 Hitec 7955 steering servos, 2 miniature unbranded diff lock servos and a Novak Goat brushless setup.

IIRC, the Goat's BEC is rated at 5A. Will this be enough, or do I need an extra BEC? Seems to work OK on the bench.

[TattooKenny]

Running all of that I would def add a Castle BEC! Just the 2 regular servos you are running I would run one! Spend the $20 and get one

[Scattman]

Yes, you will definately need one.

[Rock Queen]

I suggest running it without the bec first and then put it on. This way you know exactly what the bec changed and you can learn exactly how it helps. It really makes a big difference for a small fee. Castle all the way!

[clockworks]

OK.

A couple of things made me ask this question:

I fly electric planes. Some of these are fitted with 4 Hitec HS55 servos. They are perfectly happy using the BEC in the cheap ESCs that I use. These BECs are rated at 1.5 to 2A.
It's quite possible for 3 of the servos to be in use at the same time (2 for ailerons plus one for elevator). Although the servos are obviously a lot smaller than the 7955, I read an article a while ago that was looking into the relative current draw of a range of servos. Large servos generally don't take more current than small ones.
The difference is, steering servos are under a lot more load than aircraft servos (unless you are DS-ing), so the amp draw will be higher.

Most BECs are rated at 5 to 7A. My ESC's BEC is rated at 5A.
The Castle BEC is rated at 10A, but the default output voltage is 5.1V. To change it to 6V you need to buy a Castlelink - more expense.

Finally, my usual suppliers don't stock the Castle BEC, even if they sell other Castle products.

[BigB_117]

Originally Posted by clockworks

OK.

A couple of things made me ask this question:

I fly electric planes. Some of these are fitted with 4 Hitec HS55 servos. They are perfectly happy using the BEC in the cheap ESCs that I use. These BECs are rated at 1.5 to 2A.
It's quite possible for 3 of the servos to be in use at the same time (2 for ailerons plus one for elevator). Although the servos are obviously a lot smaller than the 7955, I read an article a while ago that was looking into the relative current draw of a range of servos. Large servos generally don't take more current than small ones.
The difference is, steering servos are under a lot more load than aircraft servos (unless you are DS-ing), so the amp draw will be higher.

Most BECs are rated at 5 to 7A. My ESC's BEC is rated at 5A.
The Castle BEC is rated at 10A, but the default output voltage is 5.1V. To change it to 6V you need to buy a Castlelink - more expense.

Finally, my usual suppliers don't stock the Castle BEC, even if they sell other Castle products.

The BEC is more important in a crawler because when the servo's and motor get bound up and are working hard they draw so much power that the reciever doesn't get enough juice to keep running and it shuts down. Also if you're running 11.1v on say a 3 cell lipo the ESC's build in BEC becomes a lot less effective. I don't really understand why, but it has something to do with the ESC's BEC not being a digital switching unit or something like that.

If you order up your Castle BEC from HolmesHobbies.com he can program it for 6 volts for you before he sends it out.

Trust me when I say the $25 CC BEC is worth 3 times that in a crawler. Personally I wouldn't build a crawler without a BEC unless it was something really simple like a 1 servo scaler running on a 2 cell lipo.

[clockworks]

Good point about stalling/binding. You've convinced me - I've ordered a Castle BEC. I looked at the link for HolmesHobbies, but, by the time I've paid international shipping and UK customs charges, it'll cost me the same as buying the BEC and the programming kit here in the UK.

[Scattman]

You won't be disappointed.

[clodbuilder99]

Originally Posted by Scattman

You won't be disappointed.

X2!!

I have one in all my rigs

[Duuuuuuuude]

There should be a default answer to a "Do I need a BEC" question.

If you think you need a BEC, you need a BEC. :-P

[clockworks]

Well, I found a UK supplier who listed the CC BEC on their website. Unfortunately they don't have any stock. Can't find anyone in the UK with stock.

Apparently the UK importers have stopped handling Castle products. The new importers (Horizon Hobby?) aren't up to speed yet.

[clockworks]

UK suppliers still have no stock, so I ordered from Holmes Hobbies - thanks JRH.

I want to use the CC BEC to power the 2 steering servos, but stick with the Goat's BEC for the Rx and difflock servos. I assume that I need to connect the + and - servo wires to the BEC, and the servo signal wires to the Rx?

Will the servos behave themselves with power from the BEC, but no signal from the Rx? I'm wondering if the servos will move unexpectedly after I connect the battery, but before I switch on the ESC.

[JohnRobHolmes]

Since you are using one main pack, you can run just RX signal from RX to servos with no issue. The red and black coming from the CC BEC will provide power, and the ground will still be a viable reference for proper operation.


What I would do is get one Y Harness and one extension. Hack them together so that the CC BEC plugs in and powers the servo side, and only signal goes from RX to servo. It will look like a five legged mess.

[NovakTwo]

Novak believes that an external BEC is so important that we include it with our new Goat 3S controller.

This is the module that we include:

3-Amp Universal BEC

[clockworks]

Excellent. I'll make an adaptor.

[clockworks]

Adaptor to run 2x servos from CC BEC:

[Mnster]

Nice job, that sucker is clean.

[Cableman]

Originally Posted by NovakTwo

Novak believes that an external BEC is so important that we include it with our new Goat 3S controller.

This is the module that we include:

3-Amp Universal BEC

I have the havoc 3s ballistic for my slash, have you heard of any issue's with it while running 3s? I read somewhere of some problems and an external BEC was needed. Ill be getting a 3s soon and wanna make sure it will work correctly. Thanks

[JohnRobHolmes]

Yes, very nice!

[NovakTwo]

Originally Posted by Cableman

I have the havoc 3s ballistic for my slash, have you heard of any issue's with it while running 3s? I read somewhere of some problems and an external BEC was needed. Ill be getting a 3s soon and wanna make sure it will work correctly. Thanks

Our Goat 3S is sold with the external BEC module included. Most crawler users are running high powered servos. Some of these servos are expensive/high quality but more are cheap/unpredictable quality. This is primarily why we provide the module.

I encourage you to contact tech@teamnovak.com with specific application questions. In most 3S applications (regardless of the esc brand,) users find they require the external BEC.