ktrainman

My Honda had a dead battery today, so I connected the 911 to jump start and it didn't work. Have jump started many cars previously without issue, got the little sparks when I finally made the connection and even heard the idle change a bit with the load. Lights in Honda came on when the cables were connected but the car didn't make any noise at all.

A jump start battery was brought out and started the Honda without any issue. The Honda does have a AGM battery if that makes a difference.

Any thoughts?

Edgy01

So you hooked it up positive to positive and neg to neg? Did you rev up the Porsche a bit to aid in starting the Honda?

I never heard of an issue like this before--although I have never had to try it. When you own 8 vehicles, you ALWAYS own a battery charger/starter!

Philster

The car with the dead battery gets the negative grounded to the car frame... not to the battery.

The car doing the charging: black to black and red to red on the battery.

My understanding of this procedure is to ensure the set up drops juice into the dead battery, rather than creating a loop that it trying to equalize both batteries' levels. Electricity in the setup above goes into the dead battery.

Dead battery: red to red. black to car frame/ground

Good battery: red to red. black to black

Petza914

Exactly correct. The one connected to the frame of the dead battery car is also the last connection made so that any spark that occurs is not around the battery where there could be explosive gasses lurking. Even better is if the car has a jump post where a large wire is run from it to the battery for very little loss, but still away from the battery.

3Series

I have a thought....Huh???? Little Sparks lol?? You shouldn't get sparks when connecting cables for a jump.

Besides the funky wiring my only other thought is that your cables may not be thick enough. But you mentioned it started up with a different "jump battery". Do you mean a starter pack? Did it use the same cables as you used for the jump between cars?

chuck911

Most likely explanation is you had a bad connection. It doesn't take much of a connection at all to get a spark, turn lights on or activate your alternator (which is what causes the idle change). But getting enough current to crank is a whole lot more. I've seen a car with a perfectly good battery act just like this. Everything seems to work but turn the key, nothing. Cleaned the terminals, fired right up. Probably you just needed to wiggle and adjust one or more connections and it would have worked.

Either that or, I dunno, space aliens?

911searcher

What is the definition of a dead battery ?
When I am jumping a car .... isn't the battery "dead" by definition ? (ie won't turn over the engine)?

For the battery that won't start the car, is it dead if there is no voltage in the battery ? ie. check by a VoltMeter ?

ADias

Watch out... I have seen my share of blown alternator rectifiers caused by a jump start. And usually one does not notice the damage right away, as what happens is one rectifier goes bad, a waving voltage ensues, causing a rotating alternator mechanical unbalance, which eventually destroys the alternator.

Much safer to call AAA or now use one of the light/high-current-capable battery boosters.

Ahsai

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Tsilnner

I agree, it is not worth it to use your 911 to jump another car unless it is a real emergency, as in a fire or flood is on its way.

I have a few simple rules regarding my 911S, bought new in 2009; allow as few people as possible to drive it, never say how much you paid for it and do not use it to jump-start anything other than your love of driving.

ocgarza

Or something similar .... Has jump starter, air compressor, alternator tester, etc, Quite a nice unit and while a bit heavy, can be put into a Pcar to help with jump starting buddies without risking your own electronics.