Why hook up positive first

Regardless of your car-related knowledge, you should have no trouble recognizing the acid-based device. Now, before you rush at the poor battery with your combination wrench or socket and ratchet, a few words of advice. First of all, be sure to have the engine turned off. Secondly, check if there's any spillage from the battery.

You wouldn't want to get any of the sulfuric acid on your face or hands, so always wear goggles and a pair of rubber gloves. We didn't wear any because the battery was quite new and there was no danger, but you should, it's the safest way! Also, if you notice any severe leakage and corrosion signs, it would be wise to turn to a professional to get the job done. Assuming that you've done all of the above, proceed to disconnect the cables.

Hooking up the Battery Charger

As previously mentioned, there are two cables: Always remove the negative one first. Because that cable is connected to the car body and if you go for the positive one first and accidentally touch any metal part with the metallic tool you will short circuit the battery not to mention causing a shower of sparks. With the negative cable disconnected, proceed to the positive one. As a rule of thumb, the positive cable is usually red, while the negative one is black. However, it's best to check your battery markings just to be on the safe side. You can now go ahead and remove the battery from its place.

How to Jump Start a Car : Connecting Jumper Cables to the Dead Car Battery

By using our site, you acknowledge that you have read and understand our Cookie Policy , Privacy Policy , and our Terms of Service. When jumping a car battery the standard advice is to connect the red positive cable first. What's the physics explanation for this? This question is a bit vague and not obviously entirely confined to physics. In order to make it a physics question, I'll focus on which order is better if the main concern is what happens to the circuit if we accidentally drop one of the cable's connectors.

Suppose we connect the black cable first, i. Suppose also that the minus terminal is connected to the car chassis. Now suppose we connect the red cable to one of the batteries, and then accidentally drop the other end of the cable on somewhere on the car chassis.

Now we've shorted the battery, so lots of current will flow. There will probably be sparks etc.

How to Charge a Car Battery - Easy Instructions | Meineke Blog

If you drop one of the connectors, it's easy for it to touch the chassis of the car because the chassis is big. On the other hand, dropping a connector onto the positive terminal of the battery is much more unlikely. Therefore, if our main concern is what happens if we accidentally drop the cable, it's better to connect the red one first. The reason you connect the reds first is to minimize the likelihood of a short. Remember that you're typically in control of one clip at a time, so one of them is not fully in your control.

The particular trouble case is the last clip that you put in place. If you attach the negative sides first, then one positive clip, the other positive clip is now at 12V with respect to the "ground" of the other car's body. If the other red clip touches the other car almost anywhere in the engine, you'll create a short circuit. This is really easy because there's a lot of metal in an engine compartment! If you connect the positive clips first, and then one negative clip, the other clip is now at roughly 0V with respect to the "ground" of the other car's body.

If it touches anything in the engine, it's no big deal.


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The only way to create a short circuit here is if you explicitly touched the black clip to the red one, and that's a lot harder to do by accident. According to IIRC an old Haynes manual for an MG Midget, the true reason for connecting the reds first is that lead acid batteries produce hydrogen, and when you connect your jumper cables to the battery terminals there may be a spark in the event of a potential difference between the batteries one of them is probably somewhat dead, so this is likely. I have heard a first hand account of this causing an explosion, but did not see it with my own eyes.

Damage was said to be limited to singed body hair, but surely this is better avoided. Connect the red cable to both positive terminals, in whichever order you like.

How to Charge a Car Battery

No spark, as there is no difference in potential. Connect one end of the black cable to the negative terminal of the good battery.


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  • Now connect the other end of the black cable to some part of the engine block away from the battery of the dead car. The engine is connected to the negative terminal of the battery by a large cable, so you will still make a good connection.

    How to Replace Your Car Battery

    Depends on how careful you are with your wrench, I zapped myself a few times by using a wrench which accidently made a connection between the positive pole and the car body. Disconnecting the negative first is better. This is for removing the cables. For setting up, connect the positive cable first.