BEC battery?

[celter]

I am sorry for this noob question, but why do I need a separate battery for a BEC? (7.4 V) in some larger helis? Why can't the main battery supply the power to the BEC?

[Hughes500Bob]

A BEC is a Battery Eliminator Circuit. A ESC is an Electronic Speed Controler which takes the main battery power and controls the motor speed. Your Rx needs power as well. A BEC uses the main power battery to provide power to the Rx and servos. A Trex450 usually uses a BEC/ESC combo module to use 1 LiPo to power everything. A larger heli may want a large battery to an ESC to provide motor control and a seperate smaller LiPo or NiMh to power the Rx and servos.

You may need a high voltage to run a large motor ..... and if you need to reduce that voltage significantly to power servos and Rx you will waste power in the form of heat when you reduce it to a lower voltage. It is more efficient to use a second battery at a lower voltage.

[celter]

I understand what you are saying, but wouldn't a UBEC be able to power the servos and the receiver?

[LITHIUMSTATIC]

I understand what you are saying, but wouldn't a UBEC be able to power the servos and the receiver?Yes it will.

Option 1. Some people like to run a UBEC/BEC (really the same thing) off the main pack to power all their radio equipment. I do it this way on my big heli without any problems.

Option 2. Some like to use a BEC tighed into a 7.4 Lipo battery pack and leave the main pack to power only the ESC (Electronic Speed Control) & motor.

On smaller helis it's a little different because you use a smaller ESC. A lot of smaller ESC's have the BEC built into them. A most people use the built in BEC without any problems. I just got a sepate BEC on my Mini-Titan E325 so I could use a 4s Lipo battery and not a 3s. The BEC inside the ESC on my heli gets way to hot on a 4s setup and running a separate BEC makes everything run nice and cool.

If you decide to buy a BEC get a quality brand like a Kool flite Systems, Medusa or Quark.

Hope this helps.

Jeremy

[celter]

Thank you Jeremy. I understand, but what is the advantage of using a separate battery for the BEC?

[LITHIUMSTATIC]

Some say that it helps them to have a cleaner radio signal. Some do it to have a battery they can move around to fine tune Center of Gravity. Some do this to run a cheaper BEC that only accepts 7.4 input voltage.

I use a Kool flight systems UBEC/BEC on my big 620 heli and love it! It's connected to the main battery pack on my heli and I prefer it this way so I'm not charging 2 batteries. On my Mini-Titan it will be connected this way as well. I will be using a Medusa BEC on it.

[skishing]

Amother good reason for a seperate BEC battery is so you can power up and test-Range test your radio RX/TX, without the fear of a runaway prop.

[Pinecone]

You can do the same thing by putting a connector between the BEC and the main connector. I use a Micro Deans. That way I can plug in a pack with a Micro Deans and power just the electronics.