greigmckean1

Have a problem with this subject. I understand that a BEC can Power 2-3 Servos safely using a 3s LiPo. Is this standard sized servos or any type of servos? Is this the same for UBECs? Can somebody tell me how many servos I can use for each type of LiPo for BECs and also UBECs.

Can someone fill in the blanks?

For example

BEC

3S LiPo = 3 Servos
4S LiPo = x Servos?
5S LiPo = x Servos?
6S LiPo = x Servos?

UBEC

3S LiPo = x Servos?
4S LiPo = x Servos?
5S LiPo = x Servos?
6S LiPo = x Servos?

MrMulligan

My Feedback: (314)

Depends on the kinds of servo and the rating of the BEC. You use generally less digital servos than with analog ones. Right now I'm using a Castle Creations BEC with a Castle Phoenix 45 ESC. This is because I'm using a 4cell A123 battery. There are also switching ESC's like from EFlite, the Pro. These are good for up to seven analog servos and 6 digital servos, I think. You can also use over three cells in the battery, also.

larrysogla

The BEC's that I have seen range from 1.5A for the 10A-30A ESC and then up to 3A BEC for the 35A-50A ESC. Above 50A ESC there is no BEC as the 18.5+V ESC usually produces a lot of heat to bring down to 4.8V-6V for the receiver. The ESC without a BEC is called opto ESC. The stand alone BEC is called the UBEC. I have bought UBEC's(stand alone) that are 8A up to 15A in short bursts. The smaller BEC and UBEC(25A or less) are usually linear mode(produces more heat) and the larger UBEC is usually switching mode(less heat but more interference with the radio). I use a UBEC because it allows me to use the dozens of lipo batteries that I use to fly my 1 pound foam airplanes. I do not have to buy NiCads or NimH for the receiver.
larry

-pkh-

My Feedback: (2)

Linear BECs handle less servos (i.e. less current) with higher input voltages because they just drop the excess voltage across the output device and dissipate the extra energy as heat. The linear BEC can only dissipate a given amount of power (before it overheats), and since power = voltage x current, the higher the voltage that it must drop, the lower the current it can support for a given power dissipation. Linear regulator efficiency is roughly Vout/Vin, so if you have a 11.1V 3S LiPo, and you have a 5V BEC output, then the efficiency is about 5/11.1 or 45% (pretty lousy, huh?). This means about 45% of the total power used from your battery is actually used by your receiver and servos, while 55% of it is just heating up your BEC.

Switching regulators/BECs are typically about 95% efficient, so the higher input voltages don't degrade the output current capability very much. This allows them to deliver much more power to your RX/servos and dissipate much less heat.

The BEC vs. UBEC nomenclature doesn't really mean much. A BEC is just a voltage regulator, and it is often included in the design of an ESC or receiver. There are also stand-alone BECs. Some manufacturers use "BEC" and some use "UBEC" to describe their standalone BECs.

larrysogla

The 1.5A BEC will handle 4 micro servos(servos weighing 5-10 gms.) and 1-2 standard servos( servos weighing 20-50 gms.) and the 3A BEC will handle 3-4 standard servos. The 8+A UBEC will handle 8-10 standard servos. The BEC and UBEC have a short burst capacity to handle slightly higher loads for a few seconds. For an electric brushless/glow powered flyer that has both lipo and glow airplanes, the BEC and UBEC makes the most sense allowing the receiver on both the electric and glow plane to utilize the lipo batteries that are used to power the brushless motors on the electric planes. It is very convenient for a combo electric/glow flyer like myself.
larry