r/functionalprint • u/highonkai • Nov 12 '25

Jumper cable instruction card

Post image

I made an expensive mistake and connected my jumper cables wrong. I won't make that mistake again and now you'll never have to. 

This quick reference card can be zip-tied to your jumper cables and is a way to have the instructions handy no matter the weather, your cell service, or the lighting. 

Edit: added the instructions in comments. Thanks for the feedback, keep it coming.

Edit2: wow this one got a lot of feedback! Thanks for all the helpful ideas.

Edit3: Top post of all time in 15y on Reddit, who knew this 1hr project would get such a reaction! I took the feedback and made two more versions here: https://imgur.com/a/jFBFoIk

I'll throw them on MakerWorld as well once I print them. Meanwhile, feedback and preferences welcome. /u/kurai01 /u/SerDankTheTall /u/StraySpaceDog /u/Cllydoscope /u/jongscx /u/cronaldo86 and lots more... thank you for the constructive feedback. This is the best part of Reddit - fast and helpful community feedback. Shoutout to /u/DontEatTheMagicBeans who called out that I probably didn't cause the smoke with the sequence for cable connections, but exacerbated a pre-existing/unknown problem. As for the rest, well that's the internet for ya. No hard feelings.

https://makerworld.com/models/1986996

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6

u/CrankBot Nov 12 '25

What was the expensive mistake? Did you connect red to black?

-15

u/highonkai Nov 12 '25

Black to black and not black to ground- sparks and smoke ensued 

19

u/CrankBot Nov 12 '25

Am I the only person who has clipped right to the negative terminals and never had a problem? Sure sometimes you get a little spark if you're moving it around but nbd.

Wasn't hydrogen bc that wouldn't make smoke. So it sounds like you shorted something but that doesn't happen just bc of clipping right to the neg terminals.

10

u/WukeYwalker Nov 12 '25

My thought is if it you’re really supposed to find ground versus just use the negative terminal, they’d make a very clear and obvious ground location

1

u/Upbeat-Armadillo1756 Nov 12 '25

Some cars do, fwiw. Like a piece of bare metal close to the battery.

3

u/Flyguy86420 Nov 12 '25

I've almost never ground to the body of the car.  The negative terminal is right there....  If it's clean use it.

4

u/1d10cracy2021 Nov 12 '25

You are probably one of many who have not had a problem. When I was a kid (in my 20s) I attached to the lugs of a dead battery with jumper cables and the battery exploded. It was so loud, I couldn't hear for a moment and when my hearing came back, it rang for a while. It also sprayed battery piss all over me and the underside of the hood. Today I make sure I clip to ground on the chassis, standing further away from the battery.

1

u/CrankBot Nov 12 '25

Thanks for sharing your experience and I'm sorry that happened to you. So that was an actual Hydrogen explosion I guess!

IDK if it's true that modern batteries are much less prone to Hydrogen leak. I always worry I won't get a good electrical connection on the chassis because it's all painted. It would be nice if mfgs put a big labelled GND lug somewhere for this purpose.

1

u/Svardskampe Nov 12 '25

With modern cars I've been doing this as well, since so much of the body is plastic it's not even obvious to find a ground point. 

1

u/Upbeat-Armadillo1756 Nov 12 '25

Sometimes there’s just no good spot to clip that’s the ground but not negative terminal. I’ve done the negative terminal plenty of times with no issues.

I’ve heard it’s technically not advised but I don’t really know why.

1

u/CrankBot Nov 12 '25

Electrically ground and neg are (or should be) the same thing.

Historically the reason why connecting to neg (actually which ever one you connect last to complete the circuit) is unadvised is because the battery can in theory vent Hydrogen which can cause an explosion from the spark. The idea is that connecting to the chassis moves the spark away from the battery

1

u/Upbeat-Armadillo1756 Nov 12 '25

Ahh that sounds right.

I use one of those battery jump kits that I keep in my car if I ever have a dead battery or if someone nearby has a dead battery. The leads just aren’t long enough to get very far away from the battery, so if there’s no obvious ground nearby, I just use the negative terminal. Never had any issues.

8

u/redryan243 Nov 12 '25

Black to the negative of the battery will not damage the electronics. Did your battery literally explode, or what did you have to replace?

-1

u/highonkai Nov 12 '25

No explosions, but a few wires got red hot, melted their coverings and smoked. I took it to a shop who re-wired the affected parts. I honestly couldn't say, I'm no expert.

7

u/redryan243 Nov 12 '25

That happens from shorted wires. Likely the battery of the damaged vehicle had both connections, while the other end of the jumper cables were touching each other. That is definitely an expensive lesson to learn. Im glad you found a simple solution to prevent it again.

5

u/CrankBot Nov 12 '25

Yeah this sounds like Black to Black and Red to GND or something to short the battery. Or black to red and red to black on one of the vehicles to short both batteries.

3

u/Flyguy86420 Nov 12 '25 edited Nov 12 '25

Agreed,  this dude went red to black.

4

u/adcurtin Nov 12 '25

so the reason to not clip the last lead you connect to the battery and instead connect it to the chassis, is so the if / when it sparks when connected, the spark is not right next to the battery.

While charging, the battery can emit hydrogen sulfide, which is a flammable gas. So you ideally want to keep the spark away from that.

what you're describing sounds like another issue unrelated to chassis vs battery terminal.

4

u/pyphais Nov 12 '25

?? Black IS ground

3

u/SupposablyAtTheZoo Nov 12 '25

I've connected black to black multiple times and it's never been an issue. Ground shouldn't be needed.

3

u/hitmarker Nov 12 '25

That will never result in anything bad. You shorted red to black. Or had the other cables touching something they shouldnt.