Risk for electrocution?

Blue Robotics Products Batteries and Chargers
1

Hello,

I’m almost finished building a waterscooter, and have worries about personal safety with regards to electrocution.

I would like to get some help with knowledge with my particular case.

I have already tested my build in a lake and not felt any symtoms of electrocution like tingling sensation and muscle cramps (symtoms according to this source: Electrocution In Water: Everything You Need To Know - Electrocution Lawyers, PLLC ).

However I wasnt using the max current in the escs at that time due to “low rpm protect” on in the ESC firmware.

Some info about the electronics in my build:

I am powering 4x M100 motors with 4x 20A ESC (Little Bee FVT 20A Pro 2-4S OPTO BLHeli) and a 11.1V Lipo battery (7800mAh, 40C).

The minuspole of the battery is exposed to water in the “emergency off pin” (see image) as a way to break power quickly if needed.

The solder connections of the motors are covered in epoxy (Power epoxy loctite). But small parts of the wire are exposed after having bent the cables after the adhesive hardened.

The 3 switches are waterproof and the enclosure have been tested to be waterproof when submerged. Not depth tested.

Should I be worried?

Btw. This source claims that its although the current needed to kill a person is small, its voltage we should be worried about when it comes to electrocution, and 12 VDC isnt enough to harm you.
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Hi @AquamanProspect,

Sounds like an exciting project :slight_smile:

The short answer to this is that battery-operated products with low voltages are generally not dangerous from an electrocution standpoint. The main dangers are instead to do with pressure, heat, and/or shrapnel that can occur if the battery is short-circuited and ends up exploding due to overheating from excessive current draw.

This article discusses a variety of potential electrocution risks, but they’re all either for high voltages or for alternating-current supplies, or both. As a brief summary, they discuss that direct current (DC) supplies only cause shock on contact and release, whereas alternating-current (AC) supplies cause continuous shock and muscle contraction.

A wet human has an approximate resistance of 300Ω, which with a 20V supply results in a maximum current of 20V/300\Omega \approx 67mA. The main risk for low voltage DC is ventricular fibrillation (irregular heartbeat caused by unexpected electrical impulse(s)), but that generally isn’t a concern until >100mA, so your proposed 11.1V battery shouldn’t be an issue on that front.

The worst effects would be potentially a brief ‘electric shock’ feeling (like you may get from static electricity when touching a metal doorknob after sliding your feet on carpet), and possibly feeling a bit warm. If your mouth is open you may feel tingling on your tongue and cheeks, and taste sour (assuming it gets past the salt of the water), like if you lick the terminals of a 9V battery (not recommended).

I would note that this source has a couple of sections on protecting yourself from electrocution, one of which mentions:

That should work, although be aware that exposing conductors to salty water will start to corrode them, which will reduce the current that you can run the rest of the system with, so I’d recommend rinsing the contacts in fresh water and then drying them if the pin gets pulled, and you’ll you’ll likely need to change the pin if it gets activated more than a few times.

Not entirely sure what you’re saying here, but if you have conductors from your wires exposed to the water then I’d definitely be concerned about them corroding and ruining your system’s efficiency, and water potentially travelling along the conductors inside the cable and getting into your enclosure.

Current and voltage are very much linked, but current is drawn based on the electrical potential (voltage) applied to a load (resistance). Voltage is the determining factor for what could happen (it’s called a ‘potential’ for a reason), whereas the current that is drawn determines the likely effects.

Hope that’s helpful! :slight_smile:

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