Hi all,
I am new to posting but have followed you all for a while, such a huge inspiration!
I have a foil assist diy kit which I’ve been adapting to a tow boogie.
I have a 6384 motor, HobbyWing ezrunmax6 and a 8s3p battery. Surprisingly, this combo got me up for a bit but was drawing such high current (80A) the battery BMS tripped. So I added my spare battery. With two 8s3p in parralel into the Hobbywing it worked with me foiling behind boogie for 15 min. Power was a bit weak but doable. (I am quite light 70Kg) However the sustained power was too high. I was passively cooling the Hobby wing on a massive ALU heat sink, but the output current was too high, the wires to motor got hot, and after another 10 min session the motor wiring melted. At first I saw rebuilding with 10mm2 cores to motor (!) but then realised the incident had taken out the hobbywing ( comes on immediately without switch to 4 green flashes failure mode).
So I want to reuse the batteries and motor, and wonder about putting batteries in series to make a compound 16s3p battery, (leaving the BMSes alone, just plugginf in serties. This 60v inout could potentially give more/same power for much less current? I am proposing to buy a VESC, eg flipsky 75200 watercooled.
I see many of you also use 6384 motors with upto a 12s config. I am not sure if there are different specs, but what I see say only use to 36v, (unless that is just for the cheaper $50 motors I have). The motor is underwater and so very well cooled, so is that why 12s (or more) is OK?
For my 16s would same logic hold, or otherwise could the VESC be set to limit motor power?
Does this seem like a reasonable rebuild or am I heading for failures (blown motor/VESC)? Im trying to minimise costs but also fed up of not much flying time between faults and rebuilds!
Thanks to all. This site has been a huge inspiration. I will happily put up photos/vid of my windsurfer based tow-boogie if there is interest.
That’s not entirely true. Far lower voltage can kill you if supplied current is high enough and it crosses your heart. Even as low as 7 volts. There’s just more power available in a higher voltage battery. There are ways to protect against it like design discharge paths etc.
Anti-shark devices push out pulsed 125V spikes but they have a dedicated shorting path to lower the current so that its always minute and just gives sharks a jolt. You can feel the shock if you place the electrodes close enough.
The motor does not really care about the battery voltage; the current is what generates heat in the motor. Also, the motor never sees the full battery voltage unless you are running at no load max rpms (100% duty cycle): the controller, in a way, converts the battery voltage down in proportion to the motor speed, so for the same motor speed, the voltage going into the motor is the same regardless of the battery voltage at the controller.
Aside from the safety concerns, this theoretically would work if you used a lower pitch prop, which would decrease the torque/current required to run. The higher voltage would then allow the motor to spin faster to achieve the same thrust.
One nice thing about the VESC is that it limits the current if it gets too hot, so you are far less likely to break it by running too much continuous current. The motor is a different story though: as you found out, you were running that motor at too high of a phase current. It’s rated by flipsky for a max phase current of 88A, and since your continuous battery current was 80A, the phase current would have been much higher, as evidenced by melting motor wiring. As said above, I would say to decrease prop pitch to reduce current and adjust voltage if necessary to achieve enough thrust. Hopefully some more experienced builders can weigh in on using 60v/16s; however, I think I have seen it multiple times on this forum and people usually warn against doing any higher than that, so you might be okay.