Thread: BEC question
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Old 06-15-2013, 06:06 PM
  #11  
Wildflyer
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"AMPS, low voltage less resistance more amps, higher voltage more resistance less amps, its the amps that does the Heavy work. thats why using a switching UBEC is better. most esc/bec are Linear, they use a resistor, and are weak, and not a true Amp rating, switching becs are much better, as they use electronics to govenor the amps and volts better. some ESC have switching Becs, but they have to contend with the heat the ESC generates, thats why its better to have a seperate UBEC, Hope that helps, Chellie"
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Sorry Chellie, it doesn't quite work that way.

The BEC is putting out the same voltage to the servos, with either battery.

Lower or higher voltage, does not control resistance, that is a property of the load.

It is really watts, that do the heavy work. Thats why we use watts to predict motor proformance.

Back to the original question;

Using a 2 cell battery,
you would have an input voltage of about 8 Volts (+/- still the same math)
output to servos should be 4.8 volts
that means the regulator has 3.2 volts across it
if the load is pulling 2 amps,
the regulator is then generating 6.4 watts of heat, which it must dissipate or burn up

Using a 3 cell battery,
input voltage would be about 12 volts
output to servos is still 4.8 volts
the regulator now has 7.2 volts across it
if the load is pulling 2 amps
the regulator is then generating 14.4 watts of heat, which it must dissipate or burn up

I know it would seen you could drive more of a load with a higher voltage battery, but the problem is the extra amount of heat that a linear type BEC must get rid of.

In this example, the 14.4 watts with a 3s, is 2.25 times the 6.2 watts the 2s battery would cause.
The BEC may simply not be able to get rid of the extra heat, that will cause a failure.


Switching BEC's operate much differently inside, and do not create the heat that kills the linear type,
Basically a linear BEC operates like a resistor as Chellie says, it is really a variable resistor controlled by the BEC circuit.

In the simplest terms a switching regulator, is either on or off, this happens at a very high rate. When on it is a very good switch, with very little resistance causing heat, when off, there is no current therefore no heat. The circuitry sort of fills a capacitor to the correct voltage, then shuts off. It constantly checks the voltage output level and keeps refilling the cap as the load draws it down. This happens so fast that we see a constant voltage out, regardless of load ( within the ability of the BEC )

I know my description of a switching BEC is very basic and not exactly correct, but it is close enough for our use.
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