|06-30-2009, 08:55 PM||#1|
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I am: Mike G
Join Date: Jan 2005
Location: Elmira Ont.
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Ok need to know when it says ESC with Bec (at so many A)does this mean it supplies power to run receiver and servos
A perfect ESC for those looking for something simple to use and economic.
Cells: 2-3S (Auto Detect)
Max Current: 35A
I use this same brand at 100AMP but use external power to run receiver and servos. This is for much lighter plane so unable to carry extra weight.
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|06-30-2009, 09:30 PM||#2|
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I am: Gary L
Join Date: Aug 2008
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Yes, the BEC part of the speed control is there to supply the power to run the radio system and servos. 3A should cover you for normal use, but be aware that if you are using them, many digital servos are power hungry and can push this limit.
There are other factors to watch for. That 3A rating may be for 2S, so hooking up a 3S pack can actually drop the output current capacity since they are power rated. What that means is that, to maintain the same total power output, raising the voltage means that the current level has to drop accordingly.
Another point is the type of BEC circuitry. Most lower end use a linear system to reduce the pack voltage down to the 4.5-6 volts and is accomplished by dumping the excess as heat. Due to this you need at least good airflow over the ESC and a heat sink is a good idea, although it can add some weight. I've sometimes bonded on a cut down sink from an old PC processor.
Better BEC's use a "Switching" type regulator, which actually turns the output on and off very rapidly to average the voltage you need. The rule of thumb there is creating the circuitry is 10% of the job, the other 90% of the effort goes into quieting the output so it does not send errant signals to the receiver and/or gyro.
In any case, installing a Ferrite Ring on the lead from the ESC/BEC to the receiver is a good idea. Some will already have one installed. If you see what looks like a covered blob on that lead it likely is there. You can install one yourself and I've been lucky enough to find a lot of them on old Casio Digital Diary PC link cables. The ones you see in computer power supplies are the same theory, but I find them too large and heavy.
|07-01-2009, 03:36 PM||#3|
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I am: Marc P
Join Date: Apr 2008
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JR x9303 2.4
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There are generally 2 types of BEC circuits: linear and swith mode.
A linear regulator drops high voltage down to a specified lower value (typically around 5V). The higher the input voltage, the more heat needs to be dissipated and the output current handling is reduced. So a linear BEC may be rated at 3 Amps, but only on a 2s lipo, on a 3s lipo the same linear BEC may only be able to provide 2 Amps.
The switch mode BEC circuit uses a DC-DC switching circuit to drop high voltage down to 5 to 6V (sometimes adjustable from a switch, sometimes programmable). The switch mode BEC is much more efficient because it does not dissipate the extra voltage as heat but uses a switching circuit to produce a lower DC output voltage. The disadvantage of a switch mode BEC is that if not properly designed it may produce interference with lower end receivers (typically 72Mhz) or some servos.
Very often high current / high voltage ESC do not have a built-in ESC. If your plane consumes near 100 Amps, then most likely you have fairly large servos, which most integrated BECs can't handle. An external BEC or battery would be advised.
Here are a few examples of external BECs:
Don't be fooled by cheap chinese imitations, many sub $10 external BECs cannot meet their posted current specs and will suffer from voltage sag under load. The same goes for BECs integrated with ESC. Many manufacturers post the peak Amps instead of the continuous Amps.
Ex: The Castle Creations CC Bec is advertised at 10Amps, but it can only handle 5 Amps continuous up to 24 V, 7 Amps up to 12V. The connectors cannot support more than 5 Amps.
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