Hi,

I have looked thru the forums for an answer to this problem.

The problem is this. If left the Magna (97 Exec) battery goes flat after a few days. my wife took it for a drive a couple of weeks ago at night (bout 10kms) all was well, but when she got there the car was dead.
I went back the following morning and jumpstarted it, and it went and i drove it home no worries, even re-started it after refueling on the way!!

The battery was replaced, and i have also checked the volts coming off the battery (running with A/C High beam and all acc's on) - 13.5v, and off connected - 12.8v's.

I have even tried disconnecting the battery overnight, and still have had a dead start??

and yes i have tapped the alt with a hammer!

Any help?

Cheers Guys

Al & Kate:kb::kb:

Does the voltage change when you rev the car?

didnt try that!! will give it a go in the morning thanks!

If it does, what does it mean?

PS - where did u find the nice headlights?

ok, first up i see you have - 13.5v to me thats reading (minus) 13.5v, if thats the case, you have an alternator problem, with it running in revers polarity. when you disconnected the battery, did you remove both leads, if yes, and the batters still went flat, then its the battery at fault. another thing to do if all those checked out is process of elimination, with your multimeter, have the car run, with all the electrical stuff off, CD player, lights, air-con, fan blower, everything, amplifier ever if one is installed, then turn one thing on and check for a massive voltage drop, turn it of, then turn on the next, ETC, if you get a massive voltage drop, then check the earths or power wires to that particular item shorting out to cause the drain.

No load engine idle voltage should be 14.2 to 14.5. Also at idle and headlights on the voltage should stay up there. If it drops a lot, you will need to fix the alternator.

Hi,

I have even tried disconnecting the battery overnight, and still have had a dead start??

Cheers Guys

Al & Kate:kb::kb:

Going on what you say above it would indicate a bad battery despite replacing it. However if the above is incorrect I'd say it could be due to either a bad voltage regulator or a bad diode in the alternator. The bad regulator can cause poor charging as can a bad diode which will also allow the battery to drain back through the alternator when the engine is switched off.
No chance it is a bad starter?

A bad diode that is draining the battery is easy to identify. The alternator will feel hot even when the engine is cold. You could also try using a multimeter set to current to measure current flow between the battery positive terminal to the lead (with the lead detached from the battery) when everything is off.

No load engine idle voltage should be 14.2 to 14.5. Also at idle and headlights on the voltage should stay up there. If it drops a lot, you will need to fix the alternator.

To add to the above you will find with our voltage regulators that it'll end up being about 13.8 volts when the cars running
Starts off high (14.4) then will drop down after the car starts to warm up

To the OP, when your cars hot and you go to restart it does the battery light show on the dash?

didnt try that!! will give it a go in the morning thanks!

If it does, what does it mean?

PS - where did u find the nice headlights?

If the voltage rises and drops alot when revving the car that will basically mean a stuffed alternator regulator, An easy enough fix if it is. If it is that then it explains the batteries dying as it will kill them very quickly :)

As for the headlights i do them professionally :) Look out for Loudz Creations section coming soon to AMC for more :)