In my 700 size Compass 7HV helicopter, I did some tests on the jeti mezon130 bec, similar to the tests at Mikado (
www.vstabi.info/de/node/1316 or
www.vstabi.info/en/node/1327)
The bec voltage is programmed to 5.5V.
The pitchpump of Mikado Vstabi is used to maximize the movements of all connected servo’s during fast pitchmovements.
The used servo’s are : JR DS8915 (=JR DS8717), tail is the JR DS8900G.
In this system I have measured peakcurrents until 23A ! During this condition the BEC voltage will drop, without any extra capacitors, until 3.5V, which is not good. According Mikado the critical supply voltage for Vstabi equals 3.7V minimum .
If extra capacitors on the BEC output are connected, starting at 2x2200uF/16V (in parallel), then the bec voltage drop is significantly less. Increasing the capacitorvalue doesn’t give a big improvement anymore. The ESR of the capacitor seems also not dominant in this matter.
The minimum values are now between 4.2V and 4.4V which is safe.
So it is recommended to use at least 2x2200uF as extra buffer for Vstabi. Of course the value can vary when other servo’s are used.
Furthermore I did some tests with extended bec cables of 35cm, of which the diameter of the leads are the same as the original BEC wires.Of course this influences the bec voltage at the side of the vstabi/receiver.
Now it revealed that the extended bec cable can give an extra voltage drop of 0.5V, of which the main cause probably is the series resistance of the servoconnector. When soldering the extended wire, this should be almost zero (but beware of the void of the warranty when doing this !).
So please take this into account when using extended bec cable !
regards/mfg
Sebastien