I am building a hybrid drone, using a VESC controlled Flipsky 80100 7kw motor as a generator. I hope to generate 5kw of useful power. I have a 12s1p 35 amp 4000 mah Lion battery (in parallel with the load and with the VESC output) to both buffer the power for big manuevering surge loads, and provide an emergency source should my gas engine die.
I plan on using FOC control, but need to ensure my generator voltage never, ever goes above 50.4 volts (12x4.2v). So, with that in mind,
1: Do I need a Mosfet-zener type voltage limiter at the VESC output, or is there a way in software to limit output to 50.4 volts? I do have a mosfet that handles 150 amps. If I limit the max amps in the VESC seems like I am defeating the purpose of the generator providing most of the power since that is outputting 100 amps vs battery max charge of a much lower number
2: Do I need a diode to prevent power from the battery going back into the VESC? I also have a monster diode, but not sure if needed
There is a potential problem...
In order to charge a 12S battery, the Voltage applied to the battery (Regen voltage if you will) must be HIGHER than the battery Voltage. Current obviously flows "Downhill" due to the voltage drop across the load (the battery in this case).
What you could do is possibly use a VESC BMS which I believe could help with the Voltage handling. Most Drone Generators these days only keep the battery at 80% or so, in order to avoid this very issue that you mention.
12S voltage at 80% State of Charge is maybe 48 Volts whereas Full State of Charge is obviously 50.4 (12 x 4.2v per cell). So You could write a script to generate power until 48V is reached and then cut out.
Great insight, thanks. I may do what you suggest with a simple mosfet-zener circuit to limit voltage to 48v. For something so potentially dangerous, I trust hardware more. I follow your projects on Discord. Great ideas you have
I diode in the battery circuit is not a very good idea. In FOC mode the current needs to flow freely forward and backwards. Regeneration should also never happen when you can't dump the power. It is best to go for a software solution here and keep the battery at a certain level by using the battery when it reaches say 90% charge level.