Use BEC or no?

[Tony]

Should i use BEC that comes with ESC, or use a seperate RX pack?

[AndyKunz]

Depends on your power system, the ESC, and what type of running you do.

Andy

[Tony]

Depends on your power system, the ESC, and what type of running you do.

Andy


9XL Feigao
ETTI 125 amp ESC +BEC
2p3s 11.1v 5000mAh series
x442 or x642 prop

I'm thinking about using a seperate RX pack, and Lipo Low Voltage Cutoff device.

[Fluid]

You forgot to tell us the type of running you do.....also knowing the type of radio would be helpful.

WIthout knowing everything, it is tough to go wrong with a separate receiver pack as long as you keep it charged - get a 1400 mAh 5-cell pack and you will have fewer risks. A LiPo cutoff is a great investment, especially for sport boaters.


.

[Tony]

You forgot to tell us the type of running you do.....also knowing the type of radio would be helpful.

WIthout knowing everything, it is tough to go wrong with a separate receiver pack as long as you keep it charged - get a 1400 mAh 5-cell pack and you will have fewer risks. A LiPo cutoff is a great investment, especially for sport boaters.


.

Fluid

It will be sport running. Its a Futaba 2pk am radio that came with the boat. Gonna change to 2.4ghz soon. Whats a good lipo cutoff i should get. How about Lipo Shield Low voltage cutoff?

[Fluid]

I have used the LipoShield and liked it. With the cheap radio it is even more important to have clean receiver power - go with the Rx pack. The 2.4 radios seem to do better with 6.0 volts, another reason to go with a 5-cell pack. Another option is to use an external opto-BEC, but that's even more cost. Just call me old-skool....


./

[azjc]

I have always used a BEC with my land vehicles but I make sure it is a quality one though.I use the Western Robotics HV model which I am pleased with...I would stay away from Castle BEC, there have been reports that when they fail they allow the full amount of current to pass through. This will fry either your servos/Rx. I suppose the only safe method is a RX pack

[ApacheDude]

So what are you really improving by use an external RX pac?

1) Reduced draw on main batteries
- Is this significant? What about the added weight?
2) Stable RX voltages. No need to worry about sudden voltage drops during peak power draws?

3) Other?

[Fluid]

The increased draw on the drive packs is meaningless. The real advantage is eliminating potential interference to the receiver through the ESC. This has been a real problem in the past with BECs, but seems less of a problem with modern BECs.

The other advantage is the higher voltage with a 5-cell pack. Many BECs only put out 4.8 volts, yet most modern radios and servos work better with 6 volts.



.

[ApacheDude]

The increased draw on the drive packs is meaningless. The real advantage is eliminating potential interference to the receiver through the ESC. This has been a real problem in the past with BECs, but seems less of a problem with modern BECs.

The other advantage is the higher voltage with a 5-cell pack. Many BECs only put out 4.8 volts, yet most modern radios and servos work better with 6 volts.



.

This make sense. I never thought about interference.

[Simon.O.]

Here is a bit of interesting reading on the subject.

http://forums.offshoreelectrics.com/showthread.php?t=5025

FWIW I now use a 9V square cell in a couple of hulls and a standard 4 cell nimh in the other 2.
If you can take the wieght and room a 5-cell pack like Jay suggests is the go.
After all that I am now seriously looking at a UBEC as neither of my BL speedies have bec output and as far as I am concerned nor should they.
I have had the world supply of problems before when I ran mostly brushed setups with speedies that had no opto on the signal line and a BEC to boot. RF all over the place and a few very close calls with the pond edge.

IMHO opto's in the speedy are a must whether it is BL or Br.
I am happy to take the weight of a Rx pack or UBEC if the reliability is the there.

Your boat
Your call.

[785boats]

Hi Tony.
Just to confuse you a bit more I'll add my experiences on this topic.

If the ESC comes with internal BEC, I've always used it. Both brushed & brushless. Never had a problem.

If the ESC did not come with an internal BEC, I always use an UBEC. This one.
http://www.r2hobbies.com/proddetail.php?prod=rcps81706_ub
As you can see it has up to 42V input, a 3A output, & can be switched to 6V output.
I've never used a seperate battery pack in either my FE or scale boats.

If you are using a voltage higher than 12 cells or 4s Lipo, you should use a seperate battery pack or UBEC. This is because at the higher input voltage the BEC circuit has to work harder to drop the voltage to the 4.8V & thus generates more heat & can fail.

NOTE If you do run a seperate battery pack or UBEC with an ESC that does have an inbuilt BEC, you should disconnect the red (center) wire from the reciever plug.
Otherwise you have two voltages supplying the reciever. This can cause a failure of the reciever as the two different voltages try to balance themselves through the reciever rails. At least that's how it was explained to me.

Hope this helps a bit.
Paul.

[Tony]

Hi Tony.
Just to confuse you a bit more I'll add my experiences on this topic.

If the ESC comes with internal BEC, I've always used it. Both brushed & brushless. Never had a problem.

If the ESC did not come with an internal BEC, I always use an UBEC. This one.
http://www.r2hobbies.com/proddetail.php?prod=rcps81706_ub
As you can see it has up to 42V input, a 3A output, & can be switched to 6V output.
I've never used a seperate battery pack in either my FE or scale boats.

If you are using a voltage higher than 12 cells or 4s Lipo, you should use a seperate battery pack or UBEC. This is because at the higher input voltage the BEC circuit has to work harder to drop the voltage to the 4.8V & thus generates more heat & can fail.

NOTE If you do run a seperate battery pack or UBEC with an ESC that does have an inbuilt BEC, you should disconnect the red (center) wire from the reciever plug.
Otherwise you have two voltages supplying the reciever. This can cause a failure of the reciever as the two different voltages try to balance themselves through the reciever rails. At least that's how it was explained to me.

Hope this helps a bit.
Paul.


Paul
Thanks for the infos. You've just sumed up why my other esc failed. :flammes-09:
I am going to use 2p3s 11.1v in series. I bought a LipoShield low voltage cutoff device, and use it instead of the built in BEC. I'll use a seperate 6v 5c pack for the RX as well.

[785boats]

I am going to use 2p3s 11.1v in series. I bought a LipoShield low voltage cutoff device, and use it instead of the built in BEC. I'll use a seperate 6v 5c pack for the RX as well.

Hi Tony.
I'd just like to clarify something here. It may just be a typo on your part, but it is the 6V battery pack that replaces the BEC, not the Lipo Shield as stated above.
Cheers.
Paul.

[Tony]

Hi Tony.
I'd just like to clarify something here. It may just be a typo on your part, but it is the 6V battery pack that replaces the BEC, not the Lipo Shield as stated above.
Cheers.
Paul.

Paul,
It was a typo. The device is for lipo low voltage cutoff. 3v/ cell