A car knows!!!!

[COLVERT]

Originally Posted by mantianak

Yes I'm aware of that. But even the AA recomend not connecting the negative to the battery but to a grounding point elsewhere. Although they don't state why. Also they say wait 3 minutes turn the car off then start them both without the leads. I assume this is due to voltage spike from cranking which could damage the electical systems (although probably the donor car). I'm sure the cars can handle it but I would rather play it safe.

http://www.theaa.com/motoring_advice...jumpleads.html

You will NOT get a voltage spike from cranking !!

[shane25]

i only wanted to know how to get my dash working

[COLVERT]

The three minute wait is to allow any explosive vapours generated whilst charging to dissipate. Therefore reducing the risk of explosion and maybe facial or bodily injury from acid or flying plastic.



Colvert.

[COLVERT]

Originally Posted by shane25

i only wanted to know how to get my dash working

Ooops, Sorry.

[COLVERT]

Originally Posted by shane25

I've had an offer on my R75 2.0 v6 (selling due to running costs), so as you would expect i went out go give it the once over as its been standing for a couple of months, i've been going out every week or so to start it, apart from the battery being flat its been fine before, starts first turn of the key and everything works fine.

Today giving it the once over i started up by jumping it from the missus foci, started up fine, so i looked at the dash and nothing was working, i had the normal lights (oil, battery etc) on the first turn of the key, but soon as the car was started they all went out and the dash was blank, so i tried everything else in the cab to see what wasn't working:
all dials/displays
elec mirrors
a/c
fans
rear screen heater
fob only unlocks but the button in the cab to lock and unlock the doors work, tried putting the key in to lock and only the drivers door locks.

So far i have checked:
Fuses
plenums
loose earth/cables

If any has any ideas or suggestions please do feel free to speak up

Anyway any little bit of info. about your car may be useful in the future. Lol.
Once I got started I couldn't stop.

[Martynp]

Brilliant analogy Colvert----
Guess that means water will not flow uphill either!

Babolonians managed it, with some extra mechanics

Had to smile at the OPs comment at post 12!
Hope he gets a quick sale, they don't like just standing around

[COLVERT]

Originally Posted by Martynp

Brilliant analogy Colvert----
Guess that means water will not flow uphill either!

Babolonians managed it, with some extra mechanics

Had to smile at the OPs comment at post 12!
Hope he gets a quick sale, they don't like just standing around

Thanks Martyn but now having re-read post 10 I think I could have worded it a little better. Lol.

Oh well, C'est la vie.



Colvert.

[HarryM1BYT]

Originally Posted by COLVERT

That is absolutely not true !!!!
To understand it you must think in terms of water !!!!
If you have a tank one foot in diameter next to a tank ten feet in diameter and they are both full to the same level in water.
Then connect the tanks together with a pipe, say halfway down, the water from the large tank will NOT flow into the small tank.
The surface level of both will remain EXactly the same.
Obviously the large tank will hold much much more water than the small tank.
Now back to batteries.
The voltage in the two batteries, in good condition, will be twelve volts whether they are charged or discharged. ( ie. the height of the two tanks of water ) no flow between them.
The capacity of the batteries (ie. their ability to do work ) will be the volume of water in the respective tanks.
There will be no flow between the charged and discharged battery because their voltage is the same !! ( Height of water in the two
joined tanks. )
So, little tank ( Discharged battery, will not have enough capacity to start the car )
And big tank ( Charged battery, will start the car with power to spare. ) Even though both have twelve volts. ( Pressure of electricity. )
So you cannot charge one twelve volt battery to another by joining them together.



Colvert.

That is generally true, but none the less some current will pass from the charged battery to the flat one - usually nowhere enough to be useful.

A fully charged battery at rest will be 12.5 to around 12.8. A completely flat battery will be 12.0v or maybe much less. If you try to crank the car on the flat battery, its voltage during cranking (if it will crank at all) will fall much more than that of a charged battery doing the same. Link the two with some good quality jump leads, then crank - the good battery will supply much of the crank current.

To actually get some charge current to flow, the engine on the second car will need to be run - where the voltage will rise to around 14.4 to 14.6v.