Chronos comments on Procedural Knowledge Gaps - Less Wrong

126 Post author: Alicorn 08 February 2011 03:17AM

You are viewing a comment permalink. View the original post to see all comments and the full post content.

Article Navigation

Comments (1477)
Tags: cooperation instrumental

Comments (1477)

You are viewing a single comment's thread. Show more comments above.

Comment author: Matt_Simpson 07 February 2011 05:11:04PM *  7 points [-]

To my knowledge, this is how it works, but I might be missing a detail or two (never had to do it completely on my own).

1) Start with the car with the dead battery first. Expose the terminals of the battery - usually there are plastic covers to prevent anything from touching the metal terminals. Connect the jumper cables to both of these terminals. Jumper cables have a red side and a black side. You don't have to match red with the positive or negative terminal, but you will have to remember how you matched them. I.e., remember whether red is positive or negative.

2) Now go to the car with the good battery and make sure it's started and running. Connect the jumper cables to the terminals of the battery of that car in the same way that you connected them to the first car. I.e., if the red side was connected to the positive terminal on the first car, do the same on the second car.

3) Wait. It takes a few minutes to recharge a dead battery.

4) Try to start the car with the dead battery. You can do this with the jumper cables still connected. If it doesn't work, return to 3)

5) If it starts, disconnect the jumper cables.

A couple of things: don't touch the metal ends of the cables or the battery terminals. You could be in for a shock.

If the battery of a car dies, it's likely because the alternator, which recharges the battery, went out. Because of this, it's a good idea to give the dead battery a decent charge before disconnecting so that the car you're giving a jump can make it to wherever it's going (hopefully a mechanic!).

edit: and it's not my fault if you use these instructions and get caught in an infinite loop :)

Comment author: Chronos 21 February 2011 09:47:10AM *  0 points [-]

I was taught a slightly different procedure, which is the same as the one listed as the first result on Google for "jumper cables":

  1. Line up the cars, pop the hood on both cars, get out the jumper cables, make sure both cars have their engines turned off, check that the dead battery looks safe (no cracks, leaks, or swelling), and try to scrape off any corrosion on the terminals.
  2. Connect one red clip to the positive (+) terminal of the dead battery.
  3. Connect the other red clip to the positive (+) terminal of the good battery.
  4. Connect one black clip to the negative (-) terminal of the good battery.
  5. Connect the other black clip to the exposed metal of the engine or chassis of the car with the dead battery. The chassis is connected to the negative terminal ("grounded"), so this will complete the circuit while minimizing sparks near the battery itself. A malfunctioning battery might be venting fumes of flammable/explosive hydrogen gas, so don't risk sparks near the battery.
  6. Start the "donor" car. Let it run for a minute or two.
  7. Start the "acceptor" car. It should crank and run normally.
  8. Disconnect the cables in the reverse order (undo steps 5, 4, 3, 2). If the order is reversed exactly, then the cables can be disconnected from the two running cars with no sparking near the battery. You'll get some sparks when you disconnect from the chassis, but that's OK.
  9. Wait a few minutes (3 to 5). The acceptor car should continue to run. If it dies a few minutes after disconnecting the cables, then it's a problem with the alternator and not just the battery.
  10. Put the cables away, close the hoods, and thank the owner of the donor car (who can now leave).
  11. Leave the acceptor running for a while. You can drive it as much as you like during this period; just don't shut off the engine until the alternator has had time to recharge the battery (say, 10 to 15 additional minutes).

The site I linked to makes the point that steps 6-7-8 in my procedure can damage the acceptor's alternator. It recommends letting the donor run for a bit longer than my step 6 requires, then (8a) shutting off the donor, (8b) disconnecting the cables entirely, and only then (7) starting the acceptor. Whether or not this method works would depend on the state of the battery (it may fail for a poor but working battery) and the weather (it may fail below, say, 10°F / -12°C).

(Note: lead-acid batteries are damaged by letting them discharge fully, because the cathodes and anodes are both transformed into the same material, lead sulfate. Once that happens, it becomes far more difficult to recharge the battery and you're better off just buying a new one. Even if your battery won't take a charge, a jump start can get you to a store that sells new automotive batteries -- the battery is only needed to turn the engine through the first few cycles, and the alternator will provide all needed electricity once the engine is turning fast enough.)

Powered by Reddit Powered by Reddit