I’ve made a bolt on efoil with a 6374 motor, 12s battery and 100A maytech VESC.
I’ve cut a hole through my box and sealed the heatsink from the vesc to the outside to allow the cool outside air to run over it.
After around 10 minutes of cruising (only drawing 16-20A) the vesc overheats to 80 degrees and I’ve got to briefly sink the board to cool the heatsink underwater and I’m good to go again.
I would’ve thought this vesc would’ve run cooler especially with only drawing no more than 20A? Is a larger heatsink my only solution?
Best would be a bluetooth module and VESC app on phone. There you can see all parameters.
Battery current and motor current can be very different, at 20% duty cycle, when your motor draws 100A, battery will only see 20A (roughly). That would mean your prop is too big for the motor/voltage combo.
The motor has max power of 3200w (supposedly) so would have thought max possible current would be around 70A on 12s? That’s only at around 60% power as well, cruising at 18kmph. I can hit around 28kmph at 100% with a lot more battery current.
Thats what the motor is rated to. But that does not mean, that it will automatically limit to that.
If you prop is too big, it will draw so much current, that the “motor current limit” in the VESC will be reached. At that point, the VESC will simply limit the dutycycle to whatever value needed to keep the current below said maxiumum, therefore limiting the motor voltage (motor voltage = battery voltage * duty cycle (roughly). And as power = voltage * current, the power will also be limited.
If this is the case, the solution is to make the propeller smaller, so the current limit is reached later.
Think of it the other way:
The torque produced is proportional to motor current. If motor current is limited, also torque is limited. Lets say your prop is too big, needing a lot of torque to spin, therefore not coming up to speed.
Power = 2 * PI * torque * RPM
If the RPM are low and the torque is limited to some value, the mechanical output power will also be low.
Make the propeller smaller, then the max torque will be reached at higher RPM, so also mech. power will be grater (and the whole system much more efficient)
In order to estimate needed pitch of the propeller, you can use this tool: Propeller-Rechner
If you have the 190kV motor, you can reach up to 8000rpm at full duty. If you want to drive at 22kmh, you only need 2" of pitch on that propeller.
With a common 5" or 6" propeller you will overload the motor / VESC
To add to this, see below for a typical efficiency curve of a BLDC motor.
As you can see, the motor is most efficient at rather low torque, high rpm.
So again, if the prop is too big causing too much torque, efficiency will be low.
(X-Axis is torque)
What about a pad - like a dish sponge - under the head sink, it should give a bit more thermal mass to the heat sink as it will have to heat that volume of water as well.
Thanks for your explanation! I’ve ordered a bluetooth module that will hopefully be here soon. Today I limited the motor current to 50 amps in my vesc. I only just couldn’t get up on foil. I went up to 70 amps and could foil easily. I foil happily at 60% duty and reached 70 amps finally when I started to push it and got a bit of speed up around 75% duty.
Will my best bet be to change to current control with a 70amp max?
@Strongarm good idea! I thought about another heatsink but that may work quite well. Will try tomorrow and report back.
So with current control and max motor current set to 75 amps I can get on foil at 70% ( 52.5a) and cruise at 55%(37.5a). This still overheats the vesc rather quickly. I have found a sponge does not dissipate the heat enough. I can pump at 35% current and the temperature slowly drops.
Any ideas? Larger controller or will a larger heatsink help? Will a heatsink stacked on the existing be enough?
So I removed the aluminium enclosure and used a thermal pad to get good thermal contact direct from the mosfets to my external large heatsink. If I keep my motor amps really low (30 amps) the controller will stay cool. Anything more and it will gradual increase to 80 degrees before my thermal limit. At 50 amps motor current the controller will reach 80 degrees in under 1 minute!
I used the back half of the aluminium enclosure initially as a clamp however this got really hot! I printed a new enclosure for the rear so I could clamp it tight to my heatsink. This had minor improvements.
Lesson: the maytech 100a esc with heatsink will never stay under the temperature limit at over 30a regardless of contact with cold outside air. Only solution I can see is a custom water cooled enclosure.
Depends on how you use the controller, in regards of duty cycle. If your prop is too big, your duty cycle will always be in the 50-60% range, that is producing a lot of heat.
Interesting. With duty cycle at 50-60% I’m only going around 18kmph on a very efficient wing. I can easily go much faster and be with a higher duty cycle but this would increase motor current which I would think in turn would add heat?
I’m using current control on the remote so I could control the amps. 6374 (advertised as 6384) motor rated to 3200W. Max current set to 70amps (70 x 44.4 = 3108W). Attached is a graph from VESC tool which should show. Full throttle would see me at 70amps. I have only pushed it to around 85% as I’m using a large wing (Axis 1150 PNG) and struggled to hold it down at 28kmph.
I understand less pitch will mean less speed and in return higher voltage/less current to maintain same speed which would reduce heat? I just thought it wouldn’t be overheating at 40A motor current unless there’s something more I’m missing about duty cycle?
What is the cause of the current spikes? My propellers are only printed from PETG and will add carbon reinforcements during the week. I feel the slippage is rather low though to be causing such high spikes.
It seems like poor torque control to me, there is a difference of 250% (20A—>50A) on the output current on the 95% duty curve. Does it feel like it’s oscillating also on the riding?
I wonder if the motor and esc is not matched with the right settings when seeing the curves.
It does not feel like it’s oscillating. It’s really strange and I’m pretty certain it’s configured correctly in my vesc. Could it be the motor playing up with higher voltage? It is a cheap no name motor.
You could get current peaks and problems if there is a short in the windings but i think the VESC would shut down if this was the case.
I’ve had a shorted motor like that where the short was small enough to be unnoticable with a multimeter, controller refused to run motor and the short could eventually be proven with an isolation tester. I rewound the motor and then it worked as it should again.
