How close can you get to the current limit on a BEC?


#1

My FC supposedly has a 1.5A BEC to 5V. I’m powering my camera, VTX, RX off it for a total of 730mA. I want to power a cyclops DVR camera off it, which will probably raise the usage to 1.3mA.

From your experience, how close can you get to the BEC current limit without frying the BEC?

FYI, I could power the FPV camera and RX off my 3S to decrease the current draw to around 570mA.


#2

It’ll depend on the quality and tolerance of the vreg used, 10% tolerance is not uncommon in cheaper parts so that could put you close to the limit. Don’t trust values close to their limits. If you can run the fpv set up from vbat do that.


#3

If I run the FPV cam off VBAT ± and my VTX of the filtered 5V ± will that cause issues?

Also, will VBAT cause noise on my RX which may cause me to crash?


#4

I’ve never had success with getting anywhere near FC BEC limits.

What vtx do you have? If it accepts VBAT run it off that and run your camera off the vtx BEC (assuming it has one). Add a capacitor to VBat as well to clean things up a bit.


#5

I’m using the Eachine VTX03, which unfortunately does not accept 3S, so is it fine to run my Runcam MicroSwift 2 off VBAT and the VTX03 off filter 5V?


#6

Hmm. Generally speaking you want to share common circuits for VTX and camera so bit of a conundrum. If it was me i’d run your setup as is and just run the cyclops off a discrete BEC since that seems to be the big drain. That way you can remove easily if it doesn’t do what you want.


#7

I’ve done the micro-Swift on battery vtx03 on 5v thing, worked fine. Actually solved some issues.

The 5v regulators on cheap FCs are unlikely to be what China says they are. That said, that 1a regulator that is listed as 1.5a might be able to do 1.5a in flight in 45f ambient temps. Sit it on the bench in 75f temps and it might explode at 0.8a.
Heat is what kills them, more amps means more heat, if there is insufficient cooling it goes bang.

Once you go over the limit of the regulator’s MOSFET(s) and diode(s) you can expect a lot more heat for a small amount of current.

Linear regulators are just a disaster, thankfully they’re fairly rare on 5v circuits these days.


#8

Hmmm… So flying my micro in the summer in 95F+ weather may turn it into a fiery projectile?!? That’s not good lol!


#9

If I keep my set up the same and add a 5V regulator for the Cyclops DVR camera, would the wires going from my 3S VBAT to the regulator need to be 16AWG (because of high voltage) or can I get away with the following wiring (since it should maybe have low current):

24AWG wire from VBAT to a pico Molex Mollex connector to the 5V regulator to the DVR Cam?

I’m thinking of doing it that way so I can easily remove the DVR cam and regulator when I don’t need to record.

Thanks! Still not 100% sure on this wiring stuff.


#10

24 is fine, high voltage doesn’t require thicker wires, just more current.
You could probably run 30ga with no issues if you’re just powering the camera.


#11

Cool! I’ll probably try that. Do you have any recommendation on a lightweight 5V BEC (if you’ve used before)?

Thanks!


#12

I don’t remember where I got any of mine, these(and related models) seem popular though I haven’t actually tried them:

I’m sure Banggood has clones for less, too.


#13

Thanks for the help!

I saw some on BG for <$2 and weighing less than 1g. I just hope They don’t burn out quickly!