I’m quite a newbie when it comes to electronics and all that. I think I have a basic idea of how they all work but need some clarification.
So, say my motor draws:
Maximum Amps: 93A
Maximum Voltage: 130V
Maximum Power: 13000W
My ESC has to have a larger current than the motor? Like this one.
Operation Current: 200A Cont, 250A peak 6-12 cell.
Then my batteries. I was looking at buying three of these -
so 20X5000/1000= 100AWhich isn’t enough current right? (C value X Capacity / 1000 )
Also, my main question -
Can the motor draw more current than the ESC is rated for from the batteries (If they produced enough current)
Say I used this motor, what happens when it’s in the water? Does it run off the current that is supplied to it or does it pull more current, increasing temperatures in the wires, raising the resistance and melting the ESC? Meaning if my ESC isn’t rated to a high enough current, it will fail to work because too much is being drawn?
Also, how do you calculate the wattage needed/produced and why is it important?
Sorry guys, I realise that it’s quite the task to respond to those questions but I would really appreciate some short answers if you have time! I’m only 17 so don’t have the experience from real world tests…
yes it is better that the esc is rated more than the motor
your motor can pull more than 93a , this value is the peak amp working before getting to hot and being destroyed, i am sure it needs more than 93A to stall
this esc 200A can work
-for the lipo : this is correct but the voltage decrease, capacity decrease and heat increase during riding, i would said count larger (2 times the max to be safe depending on battery quality)
yes the motor can “draw” more amp
you can run under water as long as the connector or solder between motor and esc are waterproof, it will dommage the bearings, rust the can, but it can last some times
the wattage we need ? good question, it depends on weight , board size… espacilly for take off, i would said at least 3000W to be safe
it is important in order to size correctly the wires plug and battery… to avoid fire to me, and maybe to spend more money at the begining and have something that works, than to try to built cheap again and again
Thanks, that’s really helpful. I will be in salt water so wont risk the rust. Instead, I think I will buy a cooling jacket for the motor to keep it cool and the ESC is water cooled.
I’m guessing you need a pump for the water to cool the system or can the water flow itself?
the water jacket on motor for a efoil is not the best solution, yes water can flow itseft as long as you are moving but you need to cool it all the time, heat doesn’t stop you stop riding
i think salt water is even worst for the motor (oxidation?)
first of all, all those numbers made up by sellers are more like suggestions or even less: euphemism ratings.
95% of the electronics won’t work at their “rated” specs under real world conditions.
Now to the basics of the electronics, how it should be:
You have a motor rated for a given power. This motor will pull approx. the rated power when working under designed condition (this normally is max. efficient operation point). But your motor also is just a (more or less dynamic) resistance. So when you drive your motor below this designed operation point, it can draw much more power (e.g. the SSS56114 has a winding resistance of about 12mOhm, so when feeding it 50V and blocking the motor this motor is theoretically able to pull up to 50/0,012= 4166A, don’t worry it won’t happen such extreme since even cheap ESC detect motor blocking).
So you have 2 options now:
limit the power/amps your motor can pull
design you electronics way stronger than the max rating of the motor and hope it will be enough
How to do 1.): Your ESC decides what you feed your motor, so if you get a controller which supports current control, you are fine and can just calculate/set how much power you want to give your motor (e.g. never get more than 80A so design your batteries for around 100A and be on the safe side).
How 2.) is done: many RC controllers (like the one you linked) only support dutycycle control which basically is not bad, but if you don’t have an additional current limit things can escalate quickly. What does that mean: by dutycycle control you are simply telling the motor “draw as much power as you can till reaching the corresponding rpm (-power-balance)” so each dutycycle level/percentage corresponds to an effective voltage and each voltage corresponds (through KV-number) to a rpm (but this changes under load so you get power-rpm-dutycycle balance levels). Because of the effective voltage your motor wont draw too much power in the lower trigger regions, but if push the trigger hard to max dutycycle, the ESC basically gets a wired connection to the battery and the motor can pull as much power till either the corresponding rpm-power level is reached or something will set fire.
So now to answer your questions directly:
Depends if you choose 1) or 2), for your ESC it can work, have at least an additional fuse and watch your temperatures.
If the battery is really able to deliver 20C constant, you would get 100A, under ideal conditions your motor wont pull more than 93A and you it would be fine. But, I doubt the battery can deliver 20C constant, better read a long the RC-Forums what the battery is really able to deliver (e.g. the popular multistar batteries are rated for 10C constant and 20C burst, but by pulling more than 3C they swell and at the rated 10C it needs active cooling and wont last more than 50 cycles).
Also the motor can draw way more than 93A…
Yes, it is quite simple, always the weakest point/part will break. But it also can be the connectors (which will get as hot till they start desoldering if you overcurrent them).
Hard to say, depends on the load the prop puts on it. 2 Extreme examples:
you try mini-prop and it will spin quite freely, nothing is heating up but not much power is drawn/given either.
you have much too large prop and the rpm-dutycycle-load-balance lies somewhere beyond 200A and your ESC will burn down (I guess it is the ESC since the motor is water cooled and the batteries are rated for 40C peak, so they wont like the 200A and might be dead after it, but there is a good chance they do not explode).
That is a quite hard one and I don’t have an answer for that. But here is some recommendation:
You have to differ between the max. wattage pulled by your motor and the wattage needed to get up foiling.
Both of them depend on the same factors (weight, prop, wingshape…), but if you have some over current protection, you only have to design your system for the wattage needed to get up foiling.
And to get this wattage needed I would simply compare the numbers posted in this forum. Best case would be something around 900-1500W (propeller, very efficient wing), worst case something around 3500-4500W (impeller, heavy setup, bad wing design).
Power = Current * Voltage,
also Heat losses = Resistance * Current * Current,
So if your motor + ESC combi supports higher voltage (not only by rating but also by designed RPM, you might need different gearboxes for a 8s (30V* 360KV=10800RPM) setup than for a 12s (45V* 360KV 16200RPM) setup) , then go by higher voltage and have less heat losses.
Wow, that was really really helpful, thanks Giga. You mention limiting the power/amps your motor can pull, is the ESC the thing that you can set a max current on or the remote you use to trigger the motor?
That depends on the ESC, so every ESC has some control mode. Some control the dutycycle (percentage of input voltage), some control the RPM (PID speed control) and e.g. almost every e-Bike uses current control.
So yeah, current control is the option where your trigger position corresponds to the current limit. (it works like: you set maximum current at ESC setup, then your trigger position is the percentage of maximum current your motor can draw maximum at the moment, e.g. you set limit at 80A at setup of ESC, then 50% throttle means you motor can pull up to 40A, “up to” because the motor will find its rpm-load-balance and if it lies under 40A it migh only draw 10A, if it lies over 40A the motor will just get 40A because of the limit and therefore will find a new rpm-load-balance which of course is lower than without the limit).
Ah right, so you’re saying that the more cells my battery has, the higher the voltage, times by the turns per volt = RPM. If this is too high, ill have to use a gearbox like a 5:1 for more torque?
Programmable Settings:
Reverse Type: Reverse lockout, forward only, forward / reverse*
Motor Direction: Normal*, reverse
Reverse Amount: 25%, 50%, 75%, 100%
Starting Power: Low, normal, high
Voltage Cutoff: Lipo 3.0V per cell, NIMH 40% of power up voltage
Motor Timing: Low / normal / high*
*Default setting
Specs:
Motor Type: Brushless, sensorless motors only
Input Voltage: NIMH 15-33 cell, Lipo 6-12s cell
Operation Current: 200A Cont, 250A peak
BEC: No BEC, seperate BEC required
Thermal Protection: 95°C
Lost RX Protection: Delay 0.5 second
Dimensions: 115 x 50 x 31.5mm
Weight: 290g
So the ESC mentions Programmable settings. Do I plug it into my computer and use software or do I typically have to buy a control box? And also, I guess reverse lockout is good so I don’t accidentally hammer reverse and snap something
I can’t see a control mode… Would it just not mention it? I think that’s the safer option
you have to differ between cells P (=in parallel) and cells S (=in series).
Cells P is increasing your capacity (run for longer because of more Ah) Cells S is increasing your voltage (just like every other battery like in your TV-Remote).
Well, to get up foiling you need Power = torque * rpm (*pi/30). But your prop size 1) limits the maximum RPM and 2) demands some torque at given RPM.
So basically yes you will need some kind of reduction, or use a jet impeller.
I guess both is possible, but normally those 5€ programming cards are much less hassle.
Also it is good, to not unscrew something accidentally…
I don’t think these RC-ESC have something else than dutycycle control.
I guess there are not that much current control ESC on hobbyking. Current control is basically acceleration control, which feels really nice. So since you cant feel the acceleration on a RC-Toy, they wont have it. So to name some popular examples for current control ESC:
VESC (used for skateboards), Kelly Controller (used for small EV, like golf caddy and upwards), almost every E-Bike controller, Kontronik-ESCs
So as you see, they are used for things where you can ride on. But they are also quite a lot more expensive…
lets put it this way, if you can build your own impeller, you can design it for a certain rpm range => the other way round, if you buy some impeller, it is already designed for some rpm range and should be used within to be efficient.
For a lot of fun accompanied by learning more than during the whole time you spent in school (that is also the argument used for sponsoring )
(that is also the argument used for sponsoring 
I do engineering and that meant to teach me this stuff but we always do AC circuits