Installing a Kill Switch


I want to add a Kill Switch to my build, however it is specified to 12V / 15A so I cannot disrupt the powerflow directly from the batteries. Would it make sense to disrupt the power flow to the RC receiver?



You’ll have to test how your ESC responds to not getting any RX signal mid-flight. With some ESCs this would basically do the exact opposite of what you intend: it cuts the throttle signal to the ESC which will then remain at the current throttle indefinitely and you board will go off to the horizon, some ESCs at least keep the motor spinning for a few seconds.
This is not the best solution, I guess.

okay thanx, any suggestions?

You could use the switch to trigger a relay that would drive the receiver input to ground instead of triggering the failsafe. That way it’s guaranteed you will switch the board off.

You could also use the kill switch to switch a heavy duty relay that is capable of directly cutting the motor power, e.g. a forklift relay - I think @MaxMaker uses one. But I think he uses it to connect the batteries before start, not as kill switch. Cutting the battery power completely is not a good idea as it may destroy the ESC.

My idea behind installing a Kill Switch is to avoid falling into the turning prop when I have to bail. Is this a justified fear or does this not occur? I have no experience yet in riding an e-foil so I don’t know. My build uses a duct.

Anyone have an opinion on this?

I have to admit I didn’t foil yet either but I have read here that this is not a completely unrealistic case.
But I highly doubt that you would be able to stop the prop until you hit it. Then the leash would need to be really short and you would need to actively brake the motor instead of putting it to idle, which would kill the gearbox sooner or later (more likely sooner).
But still a leash is a good thing, it prevents - if done right - the board from taking off and will at least reduce the damage potential of the prop because it doesn’t have torque anymore.

okay, I’ll continue to think about how to manage this and post my solution.

Dont you release the trigger when you know you will fall?
I used to have a safety switch, used it 3 times, it is very uncomfortable and breaking the power will not make the motor stop, at least it develops no torque anymore. Anyhow, the follow up situation is bad. Your surfboard with our without foil -but surely now without you- drifts around in the waves and currents. How do you stop it? I kicked away all my earlier solutions and make it work. There is a main switch connected like a safety switch easily operated, mounted and glued in watertightly into a hole in the battery box. There is no use of it but switching on and off the main relais. This relais is bypassed by a fet and resistor to precharge the caps of the ESC in advance before the relais contacts close (20-30 milliseconds with around 60 Amps). I have tested it with the VESC under full power, the vesc was not damaged.

So the normal situation when i fall of the board, is that i push away the board with my feet to gain distance and not fall onto the board. To reach the board again i have to swim normally two strokes, align myself to the board, climb on, knee, stand up, align and restart. What is really bad, if you are in rougher seas: The board could drift away, probably forwards with a speed you cannot reach by swimming. This is really painful!
For this reason i configured the vesc to have a slow backward movement, when i command it by the remote. This makes the board stop or at least it becomes quickly slower . It wont hurt you too bad, and its not dynamically at all. I also let the board drive forward by remote to reach it quicker. Be careful!

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Very well done with that backward movement.
The waves are great at aligning the board, and then lift it, let it glide away from you, lift it, let it glide… fast!
I got in trouble a couple times because of that when foiling with a kite on choppy water…

What about a regular coiled leash, that’s what i use when surf-foiling? any one had issue with leash+efoil?

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I was thinking of a tiny rudder that would trip when you pulled the safety cord (along with 98% power drop) and cause the board to come around and pick you up like I think jetski’s do.

Of course this requires the electronics to be coherent since it’s a soft stop and not a hard power off.

Epoxy 2 hall sensors into your board. These can then be used as waterproof switches that can drive 5v /12v relays with a magnet. One relay cuts the power to 48v 200a relay the other cuts power to the reciever so will totally disable your motor. You need diodes across the relay coil to stop ant currentflowing backward when the coil collapses. A 50 ohm resistor across the 48v solenoid will allow the capacitors on the esc to fill up before the solenoid switches thus stopping it sparking and destroying itself.

Why do you all want to cut the power?
Cutting the power of a running ESC can damage the ESC. Also you can not brake anymore. Why not just set the throttle to 0 (and maybe even have active breaking so that the propeller doesn’t even spin anymore…)

in my setup, the killswitch will release my main relay and disconnect my batteries from the ESC.

That is just in case something goes wrong. Like some sort of shortcircuit, water in electronics, smoking electronics, error in transmitter, reciever making disco, :tada:… maybe leading to an uncontrollable board…

normally you set the throttle to 0 at your transmitter or put it under water and the ESC will stop, but if that doesnt work, I want a way to stop my board, and I want a way to competely disconnect the Batteries anytime…

But I m still looking for the best way to trigger my Killswitch… :joy::see_no_evil:

just my opinion… :sunglasses:


well these cases should be handled by a fuse, I doubt you are fast enough to press the button/pull the string what ever to prevent a shortciruit…

thats what you have the fail-safe for in the ESC…

well, during idle many things may work…but under load mosfet switches die
also I don’t think relays do work reliable under load…why? watch this

So I can understand, you want to have the power over your board and take the power from it, but I doubt that capping power during load is the right solution…

I use an albright relay to cut the power around 2kW, used it several times for a vesc 4.12 when it was failing to cut power with an enertion nano-x. Nano-X with VESC provides full gas permanently - Electronics (ESC, remote, batteries) -
The vesc shuts down without damage so far. From developers view it is a normal situation.
Of course you should not cut the motor, always only the powersupply.
I think you should be able to cut the battery power from esc actively in some way regularly. Even under full load.


Looking for wiring guidance from @MaxMaker or anyone else using one of these forklift relays as a kill switch. My biggest concern is spark. Can I place a resistor across the contacts? If so, what size? Also I assume it should between the battery and the esc. Finally I am running 4 each 5s batteries (2 in parallel x 2 in series) at 37 volts. My relay is rated at 24 volts but seems to work fine on 18.5v. Can i pull power for it from one half of the battery pack? Thank’s in advance!

I do it this way:

I use a FET Transistor with a resistor, a nice mechanical waterproof switch and an albright to build my own antispark. It uses the effect, that the albright has some switching time. During this delay i precharge the capacitors of the ESC by the resistor and the FET which switches on almost immediately compared to the relay.
By this i limit the inrush current to ~50A.

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My one is a 12v relay that gets power from a 9.5v UBEC. Make sure you add a diode between the coil terminals. There is a strong back EDF that can break electrionics.

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Looks like a great solution. Can you tell me which FET transistor and resistor you used? I’m a novice when it comes to reading these schematics. Thanks!