Dual BEC configuration

[Reezo]

OK, admittedly, I knew everything about this and was quite sure 'it all worked'. But trailing today with a friend, around here, he suggested what I am doing might not be the best way to handle things. I searched in the forum but could not quite find what I was looking for.

In most of my rigs, I use 2 BECs:
1) The first BEC is something quite powerful and set to a voltage of usually 9 V. I use Castle BECs a lot, for this application. I use this BEC for my servo. Power is taken from a JST connector at the XT60 male connector on the ESC, and sent to a Y-cable that sends +, - and signal to the servo, and then only the signal wire goes to the receiver
2) The second BEC is a less-beefy one, like a UBEC 8A that can "only" do 5, 6 or 7.4 V. I usually keep this at 5 V. It takes power from a JST connector at the XT60 male connector on the ESC (same as above, but a different JST, and its output (+ and -) and goes to a free slot on the receiver. This BEC is in charge of powering up the ESC, lights, winches and receiver.

My ESCs have no onboard BECs. If they do, I use them as the 2nd BEC.


Is what I am doing "bad"? Is it possible for the 2 BECs to interfere with each other in any way?

I like this setup as my lights don't get blown up, they all work at a nice 5 V, but the servo gets its dedicated power, without being pushed to direct power but it stays at 9 V which is over the 8.4 V most of my servos are rated, but still within safe limits.

I run 4S on all of my rigs, usually big 4000 mAh batteries.

I have had situations in which, when going from zero to the fastest FULL THROTTLE possible, my servo turns (left or right) even without any gyro setting etc. Usually though, it was either a faulty Y-cable or an ESC that I thought had no BEC, that was actually sending power to the receiver on top of the main BEC etc. - things like that, that I know are not right. But - exception made for these cases - am I doing something wrong?

I would run a single beefy BEC if I could, but 9 V for my LEDs is - I think - going to destroy their lifespan...am I right?

Thank you for your kind assistance!

 

[Col_Sanders]

Sounds overcomplicated. If I were dead set against running direct powered servos, I'd run everything at 8.4V and add a resistor to the LEDs do drop voltage.

BUT if you run two BECs or an external BEC and ESC with built in BEC, the + wire on both should not both be plugged into the RX. One is needed to power the RX, the other should just be used for servos or whatever.

 

[Reezo]

If you run two BECs or an external BEC and ESC with built in BEC, the + wire on both should not both be plugged into the RX.

One is needed to power the RX, the other should just be used for servos or whatever.

Precisely, this is what I am doing.
- BEC1 is for the servo, it gets power from battery, it goes to the servo with + and -. The servo goes to the receiver only with its signal wire
- BEC2 is for the rest, it gets power from battery, it goes straight to + and - on the receiver, and everything else connected to the receiver uses this BEC
- ESC gets power from battery, goes with - and signal to the receiver

Sounds overcomplicated. If I were dead set against running direct powered servos, I'd run everything at 8.4V and add a resistor to the LEDs do drop voltage.

It is, and I'd love to remove one BEC as it would streamline things, a lot (especially cable management alone). All of my lights, in all the rigs I have, have resistors inline but I have not calculated what it would take to drop 9 V to, say, 3 V, because the whole load would need to be calculated. That's why it was easier to just send a 5 V BEC for 'everything else'. This becomes exponentially easier a solution with rigs with tons of lights, winch etc. (e.g. my Gladiator), with the addition of lights that use the signal wire to change blinking effect etc. etc.

 

[HumboldtEF]

I like to use 12v LEDs and direct power servos, runing 3S. With that setup I can do direct power for both the lights and servo. I rarely have to use external BECs anymore.

This works out for me because I've started to make my own light kits and dont mind soldering them up. If you dont like to solder and make your own light kits this may not be as appealing.

The only thing you might have done wrong was to power the receiver twice with 2 BECs (on accident). I know you're aware but I'll say it anyway, you'd want to use a bypass adapter to avoid this (which you already mentioned doing).

 

[bgredjeep]

I soldered in a small step down voltage regulator in my 3v leds I installed in my old capra.

I don't want to install 1 external bec, let alone 2.

 

[HVACTeacher]

Everyone has their preferences.

In some of crawlers I use the internal BEC on my ESC's to run the RX if it cannot handle high voltage. Essentially doing what you're doing.

 

[Reezo]

I like to use 12v LEDs and direct power servos, runing 3S. With that setup I can do direct power for both the lights and servo. I rarely have to use external BECs anymore.

This works out for me because I've started to make my own light kits and dont mind soldering them up. If you dont like to solder and make your own light kits this may not be as appealing.

The only thing you might have done wrong was to power the receiver twice with 2 BECs (on accident). I know you're aware but I'll say it anyway, you'd want to use a bypass adapter to avoid this (which you already mentioned doing).

That makes perfect sense and I would be comfortable soldering that, if I were starting a new project but not for these I already have. Great idea though and solid.

Great advice on checking the common mistake of powering a receiver twice, it all checks though, I am not doing anything weird.

I've tried running direct power servos but 4s is a bit of a strain and even on 3s I haven't had good luck with those servos, they all burned sooner or later. So I'm staying at 9 V on servos that are rated 8.4 V, I get a bit more frisky performance without risking too much.

I'm thinking all I'm doing is legit, so far your tips are confirming it.

I soldered in a small step down voltage regulator in my 3v leds I installed in my old capra.

I don't want to install 1 external bec, let alone 2.

That's basically what I am doing with a small BEC like that, only I'm placing it after the battery, before the receiver, meaning all goes thanks to it, minus the servo. When winches are involved I tend to use a bit of a beefier one, not the push buttons ones, because winches seem to draw a lot when under stress. But maybe it's not that important and a 2A will be okay. I had them layering around so I preferred an 8A.

Anyway, so far so good it seems you folks are confirming that the layout is correct, regardless of how it might be not as streamlined.

 

[Reezo]

Everyone has their preferences.

In some of crawlers I use the internal BEC on my ESC's to run the RX if it cannot handle high voltage. Essentially doing what you're doing.

I missed your reply by some seconds

Agreed. I'm okay with taking the time to run a dual BEC system because I need to make a lot of ends meet, but there's nothing wrong with a simpler system. My rigs aren't that simple I realize that.

 

[HVACTeacher]

I missed your reply by some seconds

Agreed. I'm okay with taking the time to run a dual BEC system because I need to make a lot of ends meet, but there's nothing wrong with a simpler system. My rigs aren't that simple I realize that.

All good!

I personally enjoy wiring and soldering so I tend to run a heavier rig with electronics and wiring, too.

Good luck out there!

 

[Reezo]

All good!

I personally enjoy wiring and soldering so I tend to run a heavier rig with electronics and wiring, too.

Good luck out there!

Same here. 4s, Escape32 in my slower rigs, ESCs with not BECs, strong servos but not direct-powered, controllable lights, winches... I just cannot fathom how I could run a single BEC and the extra wiring is minimal in the context of things.