Feeding Orel 20 ESC with 21V power supply

Hi! I see in docs 19V max power supply is stated. But want to know is it even possible to feed it with 21V (using 5S LiPo)?

Because I faced with situation when 4S at maximum RPM on my octocopter makes battery voltage drop by 2 Volts itself and 0.7 Volts gets lost on wires and 1.5 Volts lost in motor itself at max current. This makes my copter work only at fully charged battery. And as battery lost couple of volts I have not enough voltage to keep flying reliably as thrust has quadratic dependance on RPM.

Thus 5S could solve all my problems if it possible to use more or less safely with Orel 20 ESC. Maybe there is some margin for power supply voltage available?

Using Orel 20 at 21 V is unsafe. I would recommend you to use Myxa instead.

I wish I sourced this part instead of Orel beforehand. But now Im trying to figure out what can I do with parts I have.

How unsafe it is? Is it like there are some small chances something could go wrong? Or is it something like: you will be lucky if it will work at all.

What is max input voltage for internal step-down power supplies and what is max voltage for MOSFETs used? Maybe some over voltage protection will prevent Orel 20 from working at 21V?

It should work in a lab environment; however, voltage variations under load may cause its power electronics to fail (violently). You are free to give it a try, but the result is not guaranteed.