minimum gauge required for jumper cables? - BMW M5 Forum and M6 Forums

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Old 5th January 2010, 08:32   #1
freakshoww
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minimum gauge required for jumper cables?

I just picked up some jumper cables and was told by a friend to make sure that they're thick enough to jump my car. I don't wanna find out they're not if my battery actually dies. The cables are 12ft, 6-gauge...
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Old 5th January 2010, 14:20   #2
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12 ft is quite long. The thicker and shorter the better otherwise the volt drop will be significant. Minimise the effect by turning off all unnecessary electrics of the dead car. Depress the clutch to remove the load on the starter motor.

BMW have used 4AWG from the battery to the starter and that must be 15ft or more. Should be OK then

As with all jump starts you should connect the cars together with the donor engine running above idle to get the voltage up to 14 to 14.5V. If the dead car has a really flat battery then you should allow the battery to charge up for a few minutes.

Only jump for a few seconds at a time. Make sure the jump leads don't get too warm and you'll be fine.

I had to start a dead car using nothing but bellwire once. I just left the wire connected for 30 minutes at which point there was enough juice in the battery to start it.

Last edited by m3matty; 5th January 2010 at 14:32.
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Old 5th January 2010, 20:57   #3
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Originally Posted by m3matty View Post
...As with all jump starts you should connect the cars together with the donor engine running above idle to get the voltage up to 14 to 14.5V. ...
I'm assuming this is just poor English, but to be clear, you connect the cars together FIRST (donor + to dead +, donor - to dead ground) and THEN start the donor vehicle. Hold the donor vehicle at about 2K rpm while starting your car. Remove cables in reverse order of attachment.

For the record, that method is called "boosting" a car. Jump starting, which is the preferred method of starting the M5, involves getting the car moving, jumping into it, and releasing the clutch in 5th gear. "Boosting" should be your last resort since it is a good way to fry your nav unit.

d-
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Old 5th January 2010, 21:43   #4
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Jump starting, which is the preferred method of starting the M5, involves getting the car moving, jumping into it, and releasing the clutch in 5th gear.

d-
pardon my ignorance Douglas but if you depress the clutch in 5th gear going what I can only presume is 5-8 mph how would that start the car? Wouldn't the car just stall immediately or am I missing something?
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Old 5th January 2010, 21:56   #5
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The AWG of the wire should be sized at least be 6 gauge. (I think the industry wires are sized as such) The gauge is not very important for jump starting since continuous current is not flowing through the cables for longer than 15-20 seconds.
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Old 5th January 2010, 22:14   #6
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pardon my ignorance Douglas but if you depress the clutch in 5th gear going what I can only presume is 5-8 mph how would that start the car? Wouldn't the car just stall immediately or am I missing something?
5th might be a little high, but i dont know. I used to jump my beater (98 neon) in highschool because the starter died, but i used 2nd or 3rd gear. I cant remember which one.

Its a bit of a balancing act as you need to push the clutch back in when the engine turns over.
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Old 5th January 2010, 22:54   #7
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pardon my ignorance Douglas but if you depress the clutch in 5th gear going what I can only presume is 5-8 mph how would that start the car? Wouldn't the car just stall immediately or am I missing something?
5-8 miles per hour is more than enough to turn over the engine in 5th gear when the clutch is released. You use a higher gear because it is easier on the transmission. Remember, all you need to do is cause enough a spark to start the engine. You release the clutch, the car starts, and you depress the clutch again to let it idle.

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Old 5th January 2010, 22:59   #8
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Quote:
Originally Posted by DouglasABaker View Post
I'm assuming this is just poor English, but to be clear, you connect the cars together FIRST (donor + to dead +, donor - to dead ground) and THEN start the donor vehicle. Hold the donor vehicle at about 2K rpm while starting your car. Remove cables in reverse order of attachment.

For the record, that method is called "boosting" a car. Jump starting, which is the preferred method of starting the M5, involves getting the car moving, jumping into it, and releasing the clutch in 5th gear. "Boosting" should be your last resort since it is a good way to fry your nav unit.

d-
Yeah, poor english although I did make an assumption that it was commonly accepted knowledge that you connect the cars together first and then run the engine as I described. I should have been clearer.
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Old 5th January 2010, 23:03   #9
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Originally Posted by Jan2000_M5 View Post
The AWG of the wire should be sized at least be 6 gauge. (I think the industry wires are sized as such) The gauge is not very important for jump starting since continuous current is not flowing through the cables for longer than 15-20 seconds.

The gauge is important. If the cable is too thin then the voltage drop across it will be high. Several hundred cranking amps will cause 3-4 volts drop along a 12 ft jump lead.
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Old 5th January 2010, 23:05   #10
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Quote:
Originally Posted by DouglasABaker View Post
I'm assuming this is just poor English, but to be clear, you connect the cars together FIRST (donor + to dead +, donor - to dead ground) and THEN start the donor vehicle. Hold the donor vehicle at about 2K rpm while starting your car. Remove cables in reverse order of attachment.

For the record, that method is called "boosting" a car. Jump starting, which is the preferred method of starting the M5, involves getting the car moving, jumping into it, and releasing the clutch in 5th gear. "Boosting" should be your last resort since it is a good way to fry your nav unit.

d-
In the uk this method is called jump starting hence the name jump leads. Boosting is a term used in the US. Bump starting is the term given for pushing the car and lifting the clutch to get it started.
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