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How To  What is the difference between switched and non switched BEC's

Many people are confused by BEC's at the best of times, and in particular what the difference is between switched and unswitched BEC's.

Firstly a BEC is a Battery Eliminator Circuit (BEC) and was designed simply to provide a fixed and lower voltage output from a higher input, without needing to have a separate flight battery on board to supply the 5 volts we need.  Almost all Radio receivers today run at 5 volts, and some will accept 6 volts as well. The problem is that some servos, especially the higher priced ones, cannot accept 6 volts, so if you have a 6 volt feed, you need to drop the power that goes to those types of servos or they will burn out.

That is where the BEC comes in for it's first task.  All you need to do is to cut the power lead that goes to the servo, and insert the BEC into it.  The signal cable is left alone.

Most of us avoid this and prefer to insert the BEC into the circuit  before the receiver so that the receiver runs at 5 volts. To do so we take a positive and negative lead off the lipo before it reaches the ESC, and we run the 5 volt BEC output to the BATTERY connector of the receiver.  Then we need to cut one or both of the power wires that come from the ESC to the receiver to ensure that only the 5 volt supply is available.

Now lets move to the question of plain and switched BEC's

As part of the process of dropping the voltage, especially from the typical 11.1volt lipo that we run on 400-450 size helicopters, is that the BEC generates heat, and it can be quite a large amount of heat.  We can of course position the BEC where it gets lots of cooling from the fan to help this.

If we get ourselves a switched BEC, which are typically more expensive, we get a BEC that actually switches the input current on and off internally millions of times a second, which helps a great deal to reduce the amount of heat generated.

The BEC is also used to allow us to use 4 cell, 14/8 volt lipos on our 11.1 volts helicopters if we want to do so.  It may seem strange, but quite often we do want to do this to gain a bit more power to the motor, but of course, still provide 5 volts to our radio receiver.  If you want to do this, check that your motor can take the additional voltage.

So in future when you need a BEC, do yourself and your helicopter a favour and get a switched one

I do hope this was useful. ?

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