Rc Plane Motor Current Draw

System Overview and Precautions

In the past electric flying wasn't every bit easy as it is today due to the weight of the older batteries and power of the older motors.  Older generation batteries like NiCads were heavy and the brushed motors produced less power than today'southward brushless versions resulting in marginally powered electric shipping.  Saving the weight of a second battery was critically important and thus the BEC (Battery Eliminator Circuit) evolved.

Fast forward to today and we have improved energy density of the batteries in Lithium Polymer and brushless motor with electronic exchange resulting in vastly improved thrust to weight ratios.  Since nosotros are now less weight constrained we take additional choices regarding electric shipping setup.   Eliminating a bombardment is not as important as it once was.

Today there are multiple ways to do an electric setup.

1. a.ESC does both jobs (motor and rx/servos) using BEC (Battery Eliminator Circuit).  Unmarried
2. b.Separate the ESC and BECSingle bombardment.  Achieves thermal separation.
3. c.Dual batteries, one for the motor and another for the receiver/Improved reliability.

Choices b) and c) become more prevalent equally models increment in size and the current draw from the servos increases.  Both solutions are more than weight than a) but every bit the model grows, the minor weight penalty has negligible overall effect.  Separate ESC and BEC is a step toward better reliability as the thermal limits of these two items are now divide so one doesn't touch on the other;  that is, a hot ESC cannot dethrone the RX supply or force information technology into thermal shutdown.

A movement to dual batteries is an additional step toward amend reliability as the motor battery or ESC can fully die and the wireless link remains intact so the pilot retains the power to country the plane dead stick.  Another potential reward is the elimination of conducted RF noise to rx.  More than details in the Electrical Details section.

 Ok, and so dual batteries give you better reliability.  Isn't that the stop of the story?  Well, no, it isn't.

While you might retrieve installing a dual battery setup is every bit simple as just plugging the ESC throttle connexion into RX, this elementary human activity can get you lot into trouble.  There are precautions that need to be observed on this connectedness.  If you just blindly claw up the throttle connection to the RX it might seem to work, but it is non unusual to get erratic throttle operation like spontaneous total throttle.  Clearly, this is dangerous.

First allow's constitute a couple of definitions to assist us be clear.

Domain is an "area of influence".  One example of this term in a dual battery context is the "motor ability domain".  This means all the circuitry powered by the motor battery.  This is complemented by the "receiver domain" which of form powers the receiver and the servos.

Power Domain segregation (Method 2 beneath).Segregation in this context means the stuff that needs to be separate is just that there is notwithstanding an electrical connexion between multiple domains.  In this case we utilise the same basis connection on both ability domains.  At the betoken where the 2 domains come together, precautions are taken so each side is a proficient citizen in the overall system.  This method can reach a lower cost installation than the fully isolated method described beneath.

Power Domainisolation (Method iii beneath).  Isolation means no electrical connection whatsoever.  This scheme has boosted racket advantages and is too a bit more than expensive than Method two.

The Rub

The fundamental application issue for a dual battery setup is that with two power sources, the potential exists that 1 can touch on the other.  The claiming is topreventane domain from affecting the other.  That is, the motor power domain cannot adversely affect the rx/servo power domain and vice versa.  These 2 domains are continued at merely one point, the throttle connection from the RX to the ESC.  Several methods exist to accomplish this end and are described beneath.

Method 1, Power Domain Segregation,  Disconnect ruddy wire in throttle connection

One method is to pull the red wire out of the housing of the ESC throttle connexion every bit shown below.  And so the housing is used to plug into the receiver without the reddish wire.  Be sure to embrace the exposed metal with tape.  This works for the needed domain segregation, but at that place is a downward side.  The down side is the USB programming method happens to need the scarlet wire to power the ESC.  So, if you're doing USB ESC programming method , you will demand to replace the wire each time y'all want to do USB programming.  Not the most convenient for programming.

Power Domain Segregation, Method  1

Ruby Wire removed from ESC Throttle connectedness

How do I do this?   If you expect at the dorsum of the connector, each of the wires has sort of barb on the connector and the housing has a flexible retentivity tab, the two of which mate and so that once inserted, the wire cannot pull out of the housing.  To remove the wire equally shown higher up, use a hobby knife and raise the plastic tab slightly while holding and releasing extraction tension on the wire.  When you pull the plastic tab up enough, the wire with connector will release and slide out as shown in a higher place.  If using this method make sure to use some electric tape to insulate the bare metal to prevent information technology from shorting to something inappropriately.

Method 2, Ability Domain Segregation, Modified servo extension with cut red wire

Another scheme, and one that I apply consistently, is to add a modified 6" servo extension between the ESC throttle connection and the RX.  A modified extension is shown in the picture below.

Ability Domain Segregation, Method two

Modified 6" servo extension

All I did here was to clip the cherry-red atomic number 82.  I actually cut a piece of the wire out (note arrow position) so it could not inadvertently get reconnected.  As you might imagine trying to tape this pocket-size stuff is tough and so I left a gap.  In this scheme I don't use insulating record at all.  This way I tin still use my USB programming tool directly to the ESC while also providing the needed power domain segregation to the RX.

Method 3, Power Domain Isolation, Opto Isolator

Still another method is to use an opto isolator shown below.  A W Mountain Radio version is pictured beneath only there are other vendors.  The opto method has an additional advantage of conducted dissonance isolation so that the ESC electronic switching dissonance is not conducted into the RX due to removal of all the electrical connnections.    This is installed between the ESC and RX and is a little more expensive than the other two methods.  More details in the Electric Details section below.

Power Domain Segregation, Method 3

Opto Isolator from W Mountain Radio

Yous can test the isolation if you accept and know how to utilise an ohm meter.  Measure between the gnd on ane end to the gnd on the other end and y'all will read an open, which is indicative of the isolation.  Actually you would get the aforementioned reading on any connectedness on one end to the other.  The data traverses one finish to the other via an optical path instead of a conducted path.  In add-on to the basis wire isolation, the other conductors are also not connected betwixt the ii ends.  See Electric Details department for farther insights.

Electric Details Viewpoint

Why is this of import?  The connectors seem to fit and then it should be ok.  Be Careful.

With two divide power sources (domains) in a single organization, care must be taken to make sure that the downstream circuits exercise not affect each other.  That is, each source should merely power the intended circuits and not circuits of the other power domain.  If the proper power segregation is non observed, and one source feeds the other or across dissimilar ability domains without precautions, unintended currents can flow which fully defeat the intended reliability enhancement.  In fact, fundamental reliability can be worse than using only one power source.  Clearly this defeats the purpose of the additional RX bombardment in the showtime place.

What is happening with dual batteries and no segregation or isolation utilized is that the two carve up power sources sort of fight each other.  Each wants to put out a specific voltage and does what it must to achieve that end to the best of its power.  The trouble is that each voltage is simply a little dissimilar, so in an attempt for each source to have its ain way, rather big currents tin flow.  These large currents cause excess ability dissipation of class but the real trouble is if 1 source overpowers the other, so current tin backfeed and cause boosted unexpected operational troubles.  It is hard to predict what specific things can happen because the result is controlled by the details of the mismatch and the strength of the relative sources.  Suffice it to say, nothing good can happen in this situation and it should exist avoided.

One might exist tempted to interchange the terms "segregation" and "isolation".  While doing this is non completely wrong, it's not completely right either.

In the electrical field, nosotros reserve the word "isolation" for ii circuits that have no direct electrical connection at all such equally the sides of the opto coupler, see schematic later on in this article.  This "no electrical connection at all" is termed "galvanic isolation" and is an important safety requirement in many areas.  This "galvanic isolation" can exist achieved by any of several methods, the about common of which are optical or magnetic.

The term "segregation" in this article is used to draw the stardom between the two methods (galvanic and non galvanic) and also point that interface precautions accept been taken.  With segregation (non galvanic isolation) in that location is a single electrical connexion which is the ground reference connection.  With galvanic isolation at that place is no conducted connexion between the sides, see opto coupler schematic at the stop of the schematics section in this article.

To BEC or not to BEC?

There is some other point of awareness that I think is important.  The BEC is aught more than a voltage regulator given an application specific name.  Below is a simplified schematic.

Simplified BEC connection schematic

A voltage regulator maintains a constant output voltage (Vout) regardless of its input voltage (Vin) for output currents (Iout) up to its rating.  So for example, a 5v, three Amp regulator will supply 5 volts out at a current up to 3A every bit long as adequate input voltage is supplied and the output current doesn't exceed its rating.  If either of these criteria is non maintained, that is an input voltage dip or an excess output current is required, the Vout volition also drop.  This tin be particularly bad in our application since the wireless RF connection depends on Vout existence reliable.

What is bad is that Vout is the supply for the RX every bit shown to a higher place and if Vin were to drib too low, the RX tin lose ability and the link to the TX is lost.  In today'southward 2.4GHz globe, it tin take seconds to reestablish the link and that is a long time.  Although I am seeing newer receivers like the Spektrum AR600 (full range) and AR6110  (park flyer) that offer a "quick connect" feature that is intended to minimize the reconnect fourth dimension so the outcome is known and features are being added to address this connect fourth dimension outcome.

There are a couple of things that can happen that can contribute to Vout dropping in voltage.

1. a.If inadequate Vin is supplied, so Vout will drib
2. b.If too much Iout is drawn, so Vout will drop
3. c.If the temperature of the regulator exceeds a set point, information technology will shut down meaning Vout will drop

Conspicuously none of these situations is good.  Our systems are rather robust confronting Vin dropping too depression, but potential Iout backlog tin quite easily occur;  consider a stuck servo for instance.  The Vin robustness is due to the voltage we typically run which in most cases is 3S (11.1v) and higher.  The minimum acceptable Vin is RX voltage + regulator drop (5v + 1.5v ) or 6.5v worse case, so nosotros have a lot of headroom before we get to 11v.

Integrated voltage regulators today have a couple of mechanisms for self protection.  One is that if the maximum Iout is exceeded, they volition provide rated Iout but at a reduced Vout ;  this functioning is called foldback and can be implemented in several ways .  Another machinery is that regulators accept an internal temp measurement method and, if maximum acceptable temperature is exceeded, indicating backlog power dissipation, the regulator will shut down.  The idea for both of these features is that a momentary short on the output will not outcome in regulator devastation but rather will invoke this mode and the regulator will recover when the short is removed, that is,  the regulator will tend to self preserve.  Proficient for the regulator that it might live to regulate another day, only this operation might not exist the best from the viewpoint of the plane.

Schematics

Here are some schematics to illustrate the points.

First is the classic unmarried battery

setup, ESC throttle plugs straight

into RX, no precautions are

necessary.  The motor drive

and BEC are linked thermally which means ane tin can affect the other.

Schematic i, Single Bombardment Setup, BEC inside ESC

Next is a single battery system using an external BEC where precautions are necessary because there are 2 separate ability sources.  One source is the battery, the other is the external BEC that is sourcing to the RX and servos.  In this schematic, the ability domain segregation method was used, annotation the lack of connection of the pwr(cherry) wire between the ESC and the RX throttle aqueduct.

Schematic two, Single Battery Setup Using External BEC

Adjacent is a dual bombardment setup where the rx battery voltage is ok for rx and servo to use direct.  Some run their rx/servos at iv.8v and others run them all the style up to 6v for a faster servo response.  The indicate here is that the RX battery itself is the source for the RX and the servos without the need to change the voltage supplied.

Schematic 3, Dual Battery Setup, Direct RX battery

Below is a dual battery setup where the rx bombardment is a piddling college than desired for the rx and servos, so it must be dropped down a flake prior to apply.  This schematic also shows the power domain segregation method.

Schematic 4, Dual Battery Setup,

with RX Battery Dropping Ways for

using Power Domain Segregation

Below is the same dual battery   scheme every bit schematic 4 above but using the opto setup for total galvanic isolation.

Schematic 5, Dual Bombardment Setup,

with Dropping Ways for RX Battery and Opto

And finally, here is a schematic of an opto isolator circuit below.  There are a couple of schematic variations depending on how the output needs to be driven.  The salient point here is that there is no conducted path (wire) between the diode side and the transistor side.

Schematic half dozen, Opto Isolator

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Source: https://www.eastbayrc.org/index.php/tims-tips/79-dual-battery-setup