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Battery/alternator question

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Mark Jones

Mark Jones

Jedi Warrior
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This past weekend my wife and I were autocrossing/slaloming our Spitfire. Getting ready for my first run I went to start the car and all I got was some clicking of the starter solenoid (you should have heard the Lucas jokes). Thinking that it might be the solenoid I put a screwdriver across the terminals but got nothing. I was able to get the car running by boosting it and made my run. To me this seems to mean that I have a bad alternator but the red ignition light on the dash never came on.

After the run I parked the car and left it running. Within a couple of minutes the car just died. I tried to start the car but this time there wasn’t even the click of the starter solenoid. So I took of to Canadian Tire and bought a new battery so that we could complete our day of autocross. The battery in the car was a 60 mth battery and the battery was 6 years old.

Yesterday evening we went about testing the alternator to see if that was the culprit. First we check the ign light by turning on the ignition and grounding the brown/yellow wire at the alternator and the red ign light came on. Good, the light is working.

Next I disconnect a cable from the battery and checked the amperage draw with nothing on, but found there only to be a current draw of 40 mA – probably just the radio and not a bad diode pack right? Then I checked the voltage at the battery and it was reading 12.7 V. My wife started the car and revved the engine and the volt meter read 14.6 V at the batter. Next we turned off the car and turned on the headlights for 10 minutes to drain the battery a bit and then started the car again and revved the engine, and once again saw a reading at the battery of 14.6 V So it certainly seems that the alternator is working.

Could it be that the old battery had lived the good life? But why would the car just die when it was sitting idling, something that it would not normally do? Prior to this the car had always started easily – the battery never seemed to be labouring during starting.

Thanks for your help.
 
I always suspect less-than-ideal connections on the major cables when something like this happens. The battery clamps themselves might be ok now that the battery has been changed, but there's still the other end of the ground cable and the other end of the positive cable (to solenoid and/or wherever it ends up), and finally the cable from solenoid to starter.
 
Sounds like a simple dead battery. The new battery is operating as it should and the alternator appears to be charging it. The "charge" light works --- all good!

When your battery died, it ceased to accept charge from the alternator. Then it slowly wound down. The clicking starter is a symptom of a low battery delivering inadequate voltage/current to the starter. But there's still enough juice to run the motor. Then you kept driving it, discharging the battery further, until it wouldn't even do that anymore -- also no more clicks from the starter -- stone dead.

You're lucky. A battery in that condition can take the alternator with it. Yours is still charging, so that didn't happen -- but it can.
 
6 years is more than an adequate life for a battery. They don't last forever and your subsequent measurements confirm that the rest of the charging system appears to be in good order.

This is not a slight at you or anyone else. I think I'm just getting older. Over the past year I've noticed on several of the message boards that there have been similar threads to yours. A charging or starting problem in these threads is discussed at length without mentioning that the battery was old and could simply be dead. I believe this is a testament to how reliable cars have become. When I was a child, some shops still serviced batteries by opening them up and cleaning the plates. Back then it wasn't unusual for a battery to die in the first two years. The rare exceptions were some of the high-end German batteries that might last a decade. Clearly a lot of progress has been made when people no longer replace batteries at the first sign of a problem.

Regardless, you did an excellent job of diagnosing your car's problem and it sounds like everything is in order.
 
Thanks guys for your input; I appreciate it.

I guess one thing I forgot about is that the battery is what the car operates on, the alternator is there to charge the battery, hense once the battery could hold no more charge or had no more charge, the car just died. I guess the part that surprised me is that I had no signs that the battery was going until I got the clicking at the solenoid - lesson learned.
 
I received a phone call one day from my wife who was stranded at the gas station. Her car had been running fine until she went to re-start it after filling the gas tank. First she got the machine gun clicks from the solenoid, then nothing. There was simply nothing left in the battery at all and it died with no warning.

It really does amaze me how reliable charging systems have become.
 
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