Jump Start Neighbour's Car

[trufflehunt]

Odd thing happened today. A neighbours car had had a flat battery for several days.
She'd asked if I could jump start it this morning.

Cables out, engine running on my car, positive to positive.
Negative on her battery to engine block on her car.

She tried to start, loud ticking of her starter motor, nothing more.

I moved the negative from her engine block to negative of my battery.
Tried again. Nothing.

Eventually, I gave her a tow start, fired up OK.

Just wondered though, any ideas why the cables didn't work.
The battery in my car is a decent one, a Yuasa, about 4 years old
now. Not as strong as it was new, but OK , and no problems.

Her car was a Ford Focus, Fusion or something.

?

[GingerMagic]

I'm a bit confused about how you put the leads on, but I normally do positive to positive, slam panel to slam panel with the negative.
Maybe her starter is goosed too...

[steve_earwig]

Danger of frying ecu's using jump leads on moderns, unless you have a set with spark supressors in them or can fit a welding supressor across them.

Anyway, leads not up to the job? Did they get warm?

[lozz]

Modern fords are fitted with smart charge..
Some won't start off jump leads..

There not ordinary battery's..
Not well up on the smart charge thing..
I guess bailes will know..

[Bailes1992]

I'm not convinced the Fusion would have smart charge. I may be wrong, my 2003 Focus had it.
All smart charge does is vary the voltage output from the alternator from 12v-18v. A battery will charge more efficiently when it's cold. Therefore the car will monitor different sensors and judge when it would be best to charge the battery.
If you remove the 3 pin plug from the alternator it will revert back to a standard alternator and you could technically go back to a lead acid battery. You wouldn't want to use a lead acid battery on a smart charge system. I can't imagine it dealing with 18v very well. They have to be silver calcium.

Now jump starting modern cars is very tricky. My Fathers F30 320d has specific jump starting points. You can easily fry electrical components.
However there is an added danger when jump starting a smart charge system. Not for the car being jump started but the car jump starting... if that makes sense? If your car is designed to work on a maximum of 14.4v then once the car with the smart charge system has started it is straight away going to ramp the alternator up to 18v to get as much juice into that battery as possible which could quite easily do damage to the car that jump started it.

However I think more than likely in this case you had continuity problems. Either dodgey leads or bad connections. There's no reason why a Ford wouldn't jump start... it just shouldn't be jump started.

[trufflehunt]

Leads are brand new, never needed till now. Didn't notice if they got warm/hot or not. I just moved on to
my next idea , under the gaze of the woman. I got her to push the car, while I steered. It almost
started, so I gave it a good rapid tow.

Thanks for replies everyone.

Must admit, I do find the 'fried ECU's' stuff somewhat worrying. I wonder sometimes if there's an amount of internet
scaremongering/magnification of a 'possible but unlikely' scenario.

[Bailes1992]

Without a shadow of a doubt but repair costs for such items failing is eye watering! Is it worth the risk?

[steve_earwig]

I'm sure a car equipped with this smart charge (it's that "smart" word again, I've concluded it doesn't mean smart as in intelligent, it's more like a smart haircut...) will be protected against the voltage increase but not so your Pug.

Next time someone asks for a jump start tell them you don't have any leads (it works for me )

[Bailes1992]

If I needed to jump start a car with smart charge with a car that didn't have it then I would either unplug the 3pin connector on the alternator or just connect my jump leads to it for 15-20mins to charge the battery and then remove them before cranking. Although I'd much rather just bump start it.

[PhillipM]

Cables out, engine running on my car, positive to positive.
Negative on her battery to engine block on her car.

Is that a typo, or did you really not connect the negative back to your own car to complete the circuit?

[Bailes1992]

Wait... I didn't even notice that.

There would be your problem!

[trufflehunt]

Cables out, engine running on my car, positive to positive.
Negative on her battery to engine block on her car.

Is that a typo, or did you really not connect the negative back to your own car to complete the circuit?

Nope, not a typo.

The way I've always jumped , through umpteen years, though not too many occasions, is...
the red cable to both positives, and black cable to both negatives.

This time, semi-aware of the 'blown circuitry' talk, I checked various Youtube videos on jump-starting.
And I did what they said.

In the same way that water will always seek the lowest level, electricity seeks ground/earth. Any ground does it,
What's important here, I think, is that the electricity is going through the dead battery to get to ground.

[PhillipM]

Yeah, doesn't work very well if her battery is almost kaput anyway...especially as it sounds like it may have a dead cell (not starting even when connecting earth to yours)

[Welly]

I wonder sometimes if there's an amount of internet
scaremongering/magnification of a 'possible but unlikely' scenario.

My mechanic has a bin full of instrument clusters where kind customers helped* neighbours of moderns and received a nice spike in return. My Dad's 2011 Focus is always going flat through repeated short journeys and that has the smart* charge thing; which doesn't work for him obviously.