RCU Review: Greg Covey's Amp'd Issue 4: Why Regulate?

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    Contributed by: Greg Covey | Published: January 2008 | Views: 44022 | email icon Email this Article | PDFpdf icon






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    Issue 4
    Article By Greg Covey

    Print Issue 4 "Why Regulate?"

    One of the many advantages of electric flight is that we can tap into the main battery pack to supply power for the receiver and servos. Most Electronic Speed Controllers (ESCs) have a built-in Battery Eliminator Circuit (BEC) that eliminates the need for a separate receiver battery pack - thus reducing weight and adding the convenience of recharging only a single battery. The BEC is fed by the main flight battery and drops the voltage to a level that is suitable for the receiver and servos. This regulated output, typically 5v or 6v, is commonly fed from the ESC to the receiver via the control cable to the throttle channel. The receiver + and - bus then feeds the power to each servo so it is not necessary to connect to the receiver's battery input connector, if it even has one.

    The function of the regulation is to supply a steady voltage to the receiver and servos while the main flight pack is drained in flight. If the flight pack voltage becomes too low, the Low Voltage Cutoff (LCV) feature of the ESC will turn off the motor, saving the rest of the battery power to continue feeding the receiver and servos for a safe landing.

    The scenario described above is most commonly seen in parkflyers using up to 3-cell (11.1v) Lithium flight packs as the linear regulators in the BEC are not designed to handle more than 12 volts. What alternatives are available for higher voltage power systems? Why not just use a receiver battery like those used in glow-powered planes? What else can I do with an on-board regulator? In this month's issue of AMP'D, we explore the need and advantages of why we use regulated power.

    Choosing A Regulator

    Regulators are available in many sizes, both physically and functionally. Most can handle input voltages of 2s to 3s LiPo. Some can handle input voltages up to 6s or 10s LiPo or higher. (1s=1cell=3.7v)

    A typical regulator output will be 5v or 6v or selectable for either voltage. The advantage of using 6v on many servos is to increase the transition speed and torque. A 6v output is often used in 3D applications where quickness and precision of flight are needed. Note that not all receivers or servos are capable of handling a 6v supply.

    Smaller parkflyer and indoor models will almost always use a BEC that is part of the ESC. Weight is more critical in these smaller planes and most of them use 2 or 3 cell LiPo packs with a few servos. In cases where many servos are used, like full-house controls, retracts, or flaps, it is possible to exceed the capabilities of the linear BEC equipped ESC.

    The new CC BEC from Castle Creations is a little device that eliminates the need for a receiver and servo battery pack. It draws higher voltage from the motor batteries and drops it to a voltage level that is suitable for your receiver and servos. This is required in applications which draw high power for multiple servos or use more than 3-cell LiPo packs, as most ESCs with linear BECs are not designed for these more demanding applications.

    The CC BEC is a flexible design that can be used for many applications requiring a regulator. The switching regulation design, as opposed to a linear regulation, allows it to maintain a small package size and weight while providing up to 10amps of peak current. The input voltage can range from a 2s to 6s Lithium battery. The output voltage can be programmed from 4.8v up to 9v. As noted above, not all servos and receivers can handle more than 5v so you must check with the manufacturers specifications before using a higher supply voltage.

    Dimension Engineering has a series of regulators called ParkBEC and SportBEC. The ParkBEC series comes in 5v and 6v versions which allow you to run more servos on input voltages up to 8s LiPo. Weighing in at only 6.2 grams (0.22oz), these regulators are the smallest and lightest switching BEC on the market - providing a great enhancement for smaller 3D and heli models.

    The SportBEC offers additional capability over the ParkBEC at about twice the weight. Because it is an efficient switching regulator, SportBEC can supply its full rated current of 3.5A all the way up to a 8s input voltage. As many as 8 servos can be powered without worrying about an overheating BEC. SportBEC works great up to very high voltages, and is especially suited for "sport" aircraft and glow conversions. SportBEC is usually a necessity at 4s and above when running high torque or digital servos. SportBEC's output is selectable between 5V/6V using a small slide switch. The 6V setting gives more speed and torque to the servos, and is especially useful for helicopter flyers. A red LED indicates when 6V is selected. SportBEC installs between your ESC and receiver, so you don't have to modify your speed control to disable its internal BEC.

    What is a UBEC?

    For many years, the only option available to eliminate the receiver pack on a glow to electric conversion was the UBEC. The Ultimate BEC (or UBEC) is an external circuit that taps power from your battery pack and regulates the voltage to 5 or 6 volts to power your receiver and servos. It does not replace the speed control, however, it replaces the BEC function in a non-Opto-isolated speed control with much more capabilities or it provides the BEC function in any Opto-isolated ESC.

    Three UBEC versions are available to handle input voltages up to 35v (10s LiPo) or 45v (12s LiPo). They have either a 5v or 6v output rating of 3 amps continuous and up to 5 amps for 5 minutes which can power up to 8-10 servos.

    A UBEC allows you to use your flight pack to supply power for your radio and servos

    The "UBEC" has a set of input and output leads. The input leads are soldered on the input side of the speed control at the battery connector. The output lead plugs into the receiver where you would normally plug a receiver battery. The last thing to do is to disable the BEC function of your speed control if there is one. This is usually accomplished by pulling the red pin out of the servo lead on the speed control. Note that Opto-isolated ESCs do not have a BEC so there is no need to pull out the red pin.

    On most .40-size to .90-size models, the UBEC provides a lightweight alternative to using a receiver battery. It also eliminates the need to remember to recharge the receiver battery.


    Linear or Switching Regulation

    A voltage regulator is an electrical circuit designed to automatically maintain a constant output voltage level even when the input voltage changes. In our applications, we use the main flight pack to power the regulator and expect a steady output of 5v (sometimes 6v) to feed our receiver and servos. When this function is built into an ESC, we call it a Battery Eliminator Circuit (BEC) because it eliminates the need for a separate receiver battery pack.

    Linear regulators are based on devices (usually one or more transistors) that operate in their linear region. Linear regulator designs have the advantage of very "clean" output with little noise introduced into their DC output, but are less efficient and unable to step-up or invert the input voltage like switched supplies. A typical BEC in an ESC, being a linear regulator, can only handle input voltages up to a 3s LiPo (11.1v) and can only deliver regulated power to the receiver and a few servos. The linear BEC is an inexpensive feature to add to an ESC and satisfies the majority of smaller electric flight applications.

    Switching regulators rapidly switch a series device on and off. The duty cycle of the switch sets how much charge is transferred to the load. Because the series element is either fully conducting, or switched off, it dissipates almost no power; this is what gives the switching design its efficiency. Switching regulators are also able to generate output voltages which are higher than the input voltage ? something not possible with a linear design.

    When comparing linear vs. switching regulators, the two types of regulators have different advantages:

    • Linear regulators are best when low output noise is required
    • Linear regulators are best when a fast response to input and output disturbances is required.
    • At low levels of power, linear regulators are cheaper.
    • Switching regulators are best when power efficiency is critical.
    • Switching regulators are required when the only power supply is a DC voltage, and a higher output voltage is required.
    • At high levels of power (above a few watts), switching regulators are cheaper.

    In the past, our receivers were more prone to being interfered with by switching regulator noise. Newer dual conversion and 2.4GHz spread spectrum designs have greatly reduced the potential for interference. Further, newer switching regulator products like the SportBEC and CC BEC are designed to ensure they do not create radio interference. Components like shielded inductors and an optimized layout reduce the radiated noise so you can use it without fear of glitching.

    For more detailed information, visit "Voltage Regulators" on Wikipedia.


    Gas, Jet, Electric, or Glow Flight

    If the power source of your R/C airplane is not electric, you will need some sort of receiver battery. When the electric-powered model is big enough or expensive enough, most people consider using a separate power system on the receiver and servos for better safety. If you have a larger model with many servos, particularly digital servos that use a lot of current, you need a reliable power source of high capacity.

    The Duralite Regulators come with a failsafe switch that is pre-wired and ready for use. Should the switch or the wiring between the switch and regulator fail, the regulator will stay in the "on" position and continue providing power to your radio and servos. This type of design is essential for large aircraft safety and protects your investment in expensive gear.

    The DURALITE Regulator is designed to operate on input voltages from 5 to 12 volts, allowing you to power your receiver and servos with a high capacity, yet lightweight, Lithium Ion or Lithium Polymer battery pack.

    When flying larger, more powerful aircraft, it is also important to use redundancy in the receiver and servo power design. High capacity battery technologies like Lithium-Ion are used to provide 6-10 flights before requiring a recharge. Built-in safety circuitry insures that each cell in the battery pack stays in balance when charging.

    Key features of the Duralite PLUS System include:

    • Lightweight & Powerful - constant voltage to servos
    • High Energy Density - Long Cycle Life
    • Built in Pack Redundancy - Available In all 4 & 6 Cell Packs
    • No Memory & No cycling - Easy to Use
    • More Robust than Li-poly's - Cylindrical design can better withstand impact & vibration
    • Max Discharge Continuous - 2C
    • Dual lead system - choice of power output leads/connectors, plus charging lead w/yellow connector

    Redundancy creates a safety margin where if there is a problem with any cell in a pack, the pack will continue to operate at half of the packs rated capacity, at normal voltage. The larger and more powerful Duralite PLUS 4-cell packs are assembled with two 2-cell packs in parallel (2s2p). This paralleling creates "in pack redundancy" with four cells working together to allow higher current output for larger, more powerful aircraft.

    Big Power / Big Safety

    The "Power Force" VRLI2 Voltage Regulator from FMA Direct is designed specifically for powering high current flight electronics (receivers and servos) in radio controlled aircraft. It can be used in sport, giant scale, electric planes and helicopters. It is ideal for use in aircraft with dual radio systems and outputs are user selectable for either 5v or 6v. This extremely low dropout regulator maintains a maximum 0.15v drop, even if the battery voltage decreases under full load.

    The VRLI2 supplies up to 10amps continuous current which is sufficient for driving many high torque servos.
    Status LEDs provide a quick indication of battery condition. The VRLI2 includes an on/off switch with failsafe operation and will not drain the battery when switch is off. Since the VRLI2 is a linear regulator, it produces no noise interference and can safely be used with older receiver technologies.

    These dual-battery regulators from Smart-Fly provide the user with battery redundancy and a remote fail-safe on/off switch.

    The Smart-Fly SuperReg provides the user with battery redundancy and an adjustable regulator output from 5.2 volts to 6.5 volts. An optional remote failsafe switch can be used in aircraft with engines up to the 100cc size. The SuperReg combines several features into one lightweight unit. It has dual battery inputs with isolation between the two batteries. In case of a catastrophic failure of one battery the other can continue to supply power to the aircraft. All power input and output connectors are Deans Ultra Plugs to handle up to 7.5amps continuous current.

    The SuperReg also has failsafe operation with the optional remote on/off failsafe-switch. The switch turns the failsafe regulator on but does not carry the system load current. If the switch or wiring between the switch and failsafe regulator were to fail the regulator stays on until you unplug it from the battery.

    The Smart-Fly TurboReg is similar to the SuperReg but can supply a whooping 17.5 amps continuous current when the input voltage is 8.4 volts and the regulator is set to an output voltage of 6.0 volts. The TurboReg also uses a computer-grade brushless fan to provide active cooling of the regulator.




    Regulators in Action
    No need to keep multiple Rx. battery packs charged.

    Regulators can be used in many other functions besides providing power to the receiver and servos.

    By using dual UBECs, one UBEC can provide 6v to the receiver and servos while the second UBEC provides 5v for the retract servos. In this manner, the control surfaces will have the benefit of higher torque and speed from the 6v, 20 gram, UBEC and the added safety from the isolation of a retract jam. Most retract servos require a 5v supply and will not tolerate 6 volts.

    On a tip from Team Futaba's Dan Landis, I installed dual 10-amp Power Force regulators to provide more current to the dual rudder servos on my 33% Hangar 9 Edge 540. The regulators are positive controlled and they will work fine with common ground. Since they are push type only, they can also be paralleled on the positive side too. The second regulator tip from Dan is an easy solution to eliminate blowback on my two rudder servos.
    Dual regulators means more servo power!
    Light 'em up at night!

    LED and other illuminating products like this Night-Light Set for the Wingo are becoming very popular. By adding external regulators like the new CC BEC or ParkBEC to an airplane, you can power many lights on the wings, fuselage, and tail for some night flying fun!



    When it comes to small slowflyer and parkflyer models, we will almost always use the BEC built into the ESC. Weight is at a premium in these planes, and since most of them use two or three LiPo cells with several micro-servos, the inexpensive, low-noise, linear regulators are well within the capabilities of even the smallest ESC. Exceptions to this scenario might be needed by a 3D pilot wanting the servos to run on 6v for more speed and torque, or a full-house scale model with extra servos.

    Mid-size sport and scale aircraft also benefit from a BEC on non-Opto-isolated ESCs but it is possible to exceed the manufacturer's recommendations regarding cell count, maximum number of servos, or servo current. In this situation, or when using an Opto-isolated ESC, you must either use a separate receiver pack or take advantage of a more capable external BEC. Switching regulators are best when power efficiency is critical since they weigh less than linear regulators and accept a wider input voltage range.

    Larger sport and scale models typically need a BEC because the ESCs do not allow use of the BEC with more than 3 LiPo cells or they use an Opto-isolated ESC that does not have the BEC. When the model becomes sufficiently large or complex, safety is a main concern.

    In these photos of a turbine-powered T-bird, a voltage regulator can be seen on the left and the Spektrum DX-7 receiver with 4 JR MatchBoxes to run 11 digital servos and the main computer (ECU). The Duralite PLUS 4-cell pack creates "in pack redundancy" with four cells working together to allow higher current output for larger, more powerful, or complex aircraft.

    Added safety in larger or giant-scale models is obtained though redundancy, high-capacity battery technology, and fail-safe operation. New technologies like spread spectrum radios in the 2.4GHz frequency band offer even further safety from anti-jamming features, greater noise immunity, and reducing user error by forcing a match between the model and the transmitter programming.

    When you fly electric, fly clean, fly quiet, and fly safe!

    Duralite PLUS 4-cell pack redundancy

    Turbine-powered Jet Complexity




    This section of AMP'D covers some of the questions that our readers have sent in and I thought would be interesting for others.

    Andrew W. asks: "Hi Greg, I have a DX7 with the Ar7000 and running 4 DS821 and 1 JRes539 so five servo's in my H9 Funtana 50. With the supplied 1100mha flight pack, how will this battery handle the load as I have read alot of threads about recievers unbinding due to power problems? I have not flown this plane yet and am test flying the receiver in my foamy to check for any range problems. "

    Greg: As long as the receiver battery stays above 3.5v you won't have any problem with the AR7000. In other words, you need to keep the 4-cell 1100mAh NiCd pack charged to stay out of trouble.

    Since all your components can handle a higher voltage, you can also try a pack with both higher voltage and capacity like the new Spektrum 2700mAh 6.0v NiMH pack (right).

    If you are flying with electric power, you can eliminate the receiver battery along with the weight and charging issues by using an external BEC.

    Good luck!


    Ray L. asks: "Hi Greg, What a great article. Just what I've been looking for. My next question is "How do I get copies of Issue's #1 and #2"? Thanks a lot,"

    Greg: Thanks for the kind words. We are getting many requests for a printable version of the columns so I will now create a PDF file of each issue and put a printer image at the bottom of each column that you can click on.

    To get PDFs of the first three columns, you can use these printer icons here.

    Print Issue 1 "What is a Parkflyer?"

    Print Issue 2 "Arming the Big Boys"

    Print Issue 3 "What Motor do I use?

    Print Issue 4 "Why Regulate?"

    Ask questions by e-mailing me at greg@rcuniverse.com


    This section of AMP'D reveals some of the feedback or suggestions that our readers have sent in about previous issues.

    Bob A. writes:


    Your most recent RC Universe column, "AMP'd - issue 3, December 2007 that starts with -- What Motor do I use?" is probably one of the best electric articles I have come across to date. Between your comments along with the many references to additional data, this has to be something that electric modelers should keep on their PC desktop for constant referrals. I have every intention of mentioning this specific article in my next available FAQ column that appears monthly in Model Aviation. Great work!

    Bob Aberle, AMA 215
    Technical Editor
    Model Aviation

    Make suggestions by e-mailing me at greg@rcuniverse.com


    ElectriFly Silver Series High Power
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    Manage all your power needs more efficiently with the revolutionary DURALITE POWERBOX ROYAL. A giant step forward in the overall control and safety of large and expensive aircraft.

    Print Issue 4 "Why Regulate?"

    Comments on RCU Review: Greg Covey's Amp'd Issue 4: Why Regulate?

    Posted by: spaceweasel on 02/12/2008
    This article explains why to use an external BEC very clearly. Saved me time and trouble. Thanks Greg
    Page: 1

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