Possible Alternator Problem.

[motrroc]

I just bought a new battery for my 1994 mini cooper but the car is still dead when i try and start it in the mornings.
I manage to get it started using a portable booster pack but this is obviously not ideal.
If i am driving with the radio on, the power to the radio can switch off straight away and then come back again.
This happened the other night except all power went from the car and it cut out while sitting in traffic.
There is some sizable enough speakers under the back seats and wonder are these draining all power.
I have an idea that the Alternator might be giving trouble but looking for further advice if anyone has any.

Thanks a mill.

[keith]

this time of year the big loads on the battery, after cranking, are lights, heater & wipers. HiFi/radio etc only drains a fraction of what your lights do.

check that the alternator/water pump belt is not too worn and correctly tight - if its loose it the alternator wont provide full charge.

then check that with the engine running, all lights etc off, you are getting 13.5v at the positive side of the battery. if not, then check for 13.5v at the big terminal on the starter motor (careful, moving parts!)

if you have 13.5v there but not at battery, you have a battery cable problem - check for clean connections.
if you haven't got 13.5v at the starter, you most likely have an alternator issue.

if you have 13.5v at the battery, start turning on lights, heater, de-mister, wipers, radio etc. checking the voltage at the battery every time - if it drops suddenly that helps you find where the problem might be.

another thing if all the charging/voltages are ok it could be discharging overnight through the alarm or other accessory.
to test for that look at current flow (amps) at the battery with everything turned off, and then set the alarm. remember to bypass or neutralise the boot sensor as you will need the boot open to read the current at the battery.
if its discharging a new, fully charged battery overnight (say 12 hours) you are looking for a substantial current flow (woody can do the maths!) id say in the region of 5 to 10 amps...

[woody]

The fact that you lost all power when the engine was running would look like a connection problem(rather than a drain). The car should have been running on the altenator so I would think the engine earth strap may be the problem which would tie in with not charging.
There are 3 main cables to check.
Engine earth strap.
Battery earth strap
Battery to starter cable.
Checking involves removing the end of the cable and clean it. Clean whatever it is connected to (bear metal) and refit securily.
With a fully charged battery and engine off measure the voltage at the battery with the lights on (12volts or less)
Then start engine and measure again at the battery with lights on (13.5 volts)

[motrroc]

Thanks for the advice lads. I will check out what you have mentioned.

Cheers