Cheap BEC mod

[BrianG]

Now that most of my ESCs have switching regulators built-in, I have several external BECs not doing anything. I modded one in a recent project, but thought others might have something similar.

I have a few $5 Chinese BECs I got from eBay a while back and they are supposedly switchable from 5v to 6v via a jumper. With the jumper in place, I do get pretty much exactly 5v, but without the jumper, I get something around 5.5v. Well, I want 6v dammit!

The untouched BEC. Note the voltage, which is on the 6v setting:



With the shrinkwrap off and the capacitor bent out of the way, you can see the components I will remove (circled in red):



With those parts removed:



A little trial and error later, I found a 2.2k ohm resistor gets me a little over 6v. Here is the resistor in place. I just reused the jumper pin holes:



The end result. All I need to do now is re-heatshrink it and I'm ready to go!



I also like to add a little heatsink to the back of the PCB to help cooling a little. These are efficient, but they do still dissipate heat. If you do add a heatsink, make sure it's only on the ground trace and do not bridge any other traces.

This is just one specific type of BEC, but most based on this main IC will be very similar. These BECs are not technically designed to be adjustable. So, don't try to get voltages that are too high because the inductor used is sized specifically for a certain voltage. According to the datasheet, they are good for a range, but I would change the voltage no more than ~20% max.

[What's_nitro?]

Might as well add a trimmer pot and make it adjustable. Cool mod.

[squeeforever]

Think you could figure out what resistor to use for ~7V? I have one and would love to be able to get more voltage out of it.

[BrianG]

Squee, after using a few resistor values and analyzing the results, it appears the formulas are:

R=(V-5)/0.000533

V=R*0.000533+5

V = the output voltage you want.
R = the resistor
5 = the base regulator rating


So, for 7v, the resistor needed is 3752 ohms. The closest common value is 3.3k, which would give you around 6.75v. If you want exactly 7v, find some way to shoehorn a 5k ohm pot in there, adjust it, and then glue it so it doesn't move. I would prefer an actual resistor to prevent the pot from getting dirty and causing issues (like the output going to full input voltage). A 3.3k ohm in series with a 470 would work.

Be warned, the inductor value does play a critical role. If you choose a voltage too far away from 5v, "bad" things may happen. From what I've seen for the datasheet for the adjustable versions, each inductor value is good for a range. I would definitely bench test it under load to make sure it's ok before you risk a servo/receiver.

[suicideneil]

Theres no stopping this man- nice work dude.

[lincpimp]

Originally Posted by suicideneil

Theres no stopping this man- nice work dude.

I bet a nicely prepared meal would slow him down... For a few minutes anyway!!

Good stuff Brian, but back to work on that flux capacitor, I want to go back to 1988...

[BrianG]

After playing with the few BECs of this style, I have found a whole bunch of applications where they can be used. So, if anyone has any extra of these, I'll take them off your hands for a decent price. PM me.

I also ordered several samples of the adjustable versions of the 2596 IC (TO-220 style) for other interesting projects, but it would be nice to have a few more of the completed circuits when space is crictical since they are surface mount.