BEC or DC-DC converter.

[juandbotiva]

Hello everyone,

I've used a 5V switching BEC to power my Raspberry Pi using a 2S LiPo battery, now I want to power some Lego Mindstorm bricks and Arduinos with a single LiPo battery (4S or more) and control each output with a microcontroller. The idea is to have a BEC for each output (9V Lego or 12V Arduino) but I can't find any BEC schematics on the Internet to build them myself, I don't know if using a BEC is kinda overkill for what I'm using it and a DC to DC converter can do the job. I would like your help pointing me where I can find the required schematics for the BECs or converters and how can I control them from a microcontroller (do I need a relay ?). I've read in some forums that the converter itself needs a microcontroller to regulate the output, is this true ? Thanks in advance.

Regards

[Simon]

What is BEC supposed to mean ?

[fcb]

BEC=Battery Eliminator Circuit.

Just look for DCDC converter, or buck converter.

[Simon]

Oh my god, which version of moron dreamt that one up to market their shitty product with ?

[Refrigerator]

Oh my god, which version of moron dreamt that one up to market their shitty product with ?

Well, it's meant to be used in RC cars because before BECs came in the market people used separate batteries for ESC and the receiver but since BEC eliminated the need for a second battery it's been named a battery eliminator circuit.

[Simon]

So RC people can't be asked to use the correct terminology 

[MatCat]

So RC people can't be asked to use the correct terminology 

It's a very common term in RC, in-fact my primary product I sell is just named simply 12v UBEC, I sell them like hotcakes, it's just a word, and a simple DC-DC buck .

[Simon]

I bet you'd sell bugger all if you called it a DC-DC converter because they think it's something special 

[MatCat]

I bet you'd sell bugger all if you called it a DC-DC converter because they think it's something special 

Good old marketing wank, haha.

[Simon]

indeed

[fcb]

I bet you'd sell bugger all if you called it a DC-DC converter because they think it's something special 

AFAIK, the term BEC has been around since at least the 70's, certainly 80's.

And they tended not to be DC/DC, just a regulator - mainly because they powered the sensitive radio receiver and the power saving from DC/DC does not justify the weight/cost/complexity/size penalty.

[Riotpack]

I remember adding one to my RC car years ago. This was before LIPO, DC/DC converters and brushless motors were the norm. The car used a 7.2V NICAD pack for the motor and 4xAA batteries for the receiver. When I upgraded to an electronic speed controller, it had a "BEC" in it (probably a 7805 lol) so I no longer had to use the AA batteries.

[MatCat]

Most ESC's do indeed contain a BEC now, they usually are DC-DC bucks, but are also usually horribly inefficient and pick up a lot of noise from the main fets driving the motor.  The better ones are opt-isolated.

[Simon]

Pray, what is an ESC ? hopefully not an alternative name for something else

[MatCat]

Pray, what is an ESC ? hopefully not an alternative name for something else

Electronic Speed Controller, basically 3 phase driver for brushless motors.

[Riotpack]

You have to remember these acronyms are from the RC scene and not describing a certain technology. So for example a "BEC" or battery eliminator circuit could be a linear regulator, a buck or boost converter, or even a resistor and a zener diode.

The first speed controller that was in my RC car was a servo that had an arm which selected between 2 different values of resistance in series with the drive motor, or to have the battery connect directly to the motor at full servo rotation, reverse was the same in the servo CCW direction.

 I have attached an image showing such a beast, it is the plate with contacts seen in the middle. The resistors were high wattage wire wound so when the electronic speed controllers came out they were much more efficient.

My first real ESC was single phase PWM driving a brushed motor. Even with the antiquated technology the car had a top speed of around 60km/h.

[HackedFridgeMagnet]

Those ESC's sound great, I might try the one on my keyboard.