Sharing eBike batteries can hurt you post! Not me (Unpleasant picture)

rich c

Well-Known Member
This was posted on reddit ebike forum today. His comments' "Sloppy. I was doing some headlights and very stupidly wanted to test out before terminating properly. Held a bare wire to terminal...." and "Was a total arc very bright. I was hooking up headlights and had a bare wire touch the terminal. My sloppy mistake. Battery is a beast still works and the controller still work. My hand is very crispy. That black Is all chared skin." I have no other details, just made me wince to see this. By sharing his experience, I thought it might reinforce the caution needed around DIY mods. Be careful!
 

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rich c

Well-Known Member
Ugly, but better than being killed dead by 120 VAC that didn't leave a mark.
Guy in our woodworking club had 460vac go through his arm. It actually blew flesh away, but didn't kill him. He really never had use of that hand again. Even after a lot of reconstruction surgeries.
 

Sierratim

Well-Known Member
Lithium battery packs have an extremley low internal resistance which makes working with their unprotected terminals obviously very dangerous. It also makes them useful for powering EVs.
 

Kayakguy

Member
Shouldn't underestimate the power in some of these packs, they can push the same amperage as your mains electricity at home (even more in many cases!). Its the amps which kill you.
Disagree. It's the volts that kill you. You can grab both terminals on a 12 volt car battery, rated at several hundred amps, and you won't feel a thing (which is why I laugh when a movie shows guy being tortured by hooking him up to a car battery). Compare to a stun gun, a tiny thing that can knock you flat with very high voltage. (Okay, I admit I"m not sure of myself here, so someone smarter than I am chime in with another view).
 

Sierratim

Well-Known Member
Disagree. It's the volts that kill you. You can grab both terminals on a 12 volt car battery, rated at several hundred amps, and you won't feel a thing (which is why I laugh when a movie shows guy being tortured by hooking him up to a car battery). Compare to a stun gun, a tiny thing that can knock you flat with very high voltage. (Okay, I admit I"m not sure of myself here, so someone smarter than I am chime in with another view).

There's no doubt that enough volts can drive enough current through you to cause issues (burns, cardiac arrest,etc), but high currents are also dangerous (arcs, more burns, etc). Independent of immediate health issues due to voltage lithium batteries have fire hazards that can be caused by their high discharge currents, almost regardless of their voltage. These high currents can cause high temps that ignite the battery causing all sorts of negative consequences.

FWIW, 24Vac is defined as Class II voltage, generally considered as safe for dry conditions for a healthy person. So, you're generally OK grabbing the terminals of a 12V car battery, but only in dry conditions and with a healthy person.

That aside, dropping a wrench across the terminals of a car battery is ill advised...
 

Kaiede

New Member
Disagree. It's the volts that kill you. You can grab both terminals on a 12 volt car battery, rated at several hundred amps, and you won't feel a thing (which is why I laugh when a movie shows guy being tortured by hooking him up to a car battery). Compare to a stun gun, a tiny thing that can knock you flat with very high voltage. (Okay, I admit I"m not sure of myself here, so someone smarter than I am chime in with another view).

Current ratings for batteries are more about how much current the battery can provide based on the load, before the chemistry either reaches its limits, or starts having a really bad time.

Voltage by itself is not really able to do anything. It’s a measurement of potential. Current is what kills you, but you can’t have high current (I) without high enough voltage (V) or low enough resistance (R). I = V/R, after all. And since current flows along paths depending on the resistance, having multiple paths for the current to flow, where one is much lower resistance than you, helps avoid electric shocks. It’s this last principle that lets birds sit on very high voltage electrical wires.

But there’s no real good rule of thumb here, high voltage isn’t always going to be able to deliver fatal current, and low voltage isn’t always going to be safe. For me, the better rule of thumb is to treat this stuff with the respect it deserves and not operate on live circuits.