Alternator problems!!!!!!

[Sleepless i]

Hi guys,I am new! I am running a 172 on a 52 plate.Alternator was over charging,18 volts.Replaced alternator,and battery as it cooked!Ran for a few days ,battery flat.Took out all main fuses.Still losing current.Whilst disconnecting the battery,I noticed that a faint humming noise was coming from the alternator,when reconnecting.Connected a amp meter,in between alternator and battery lead and a current of 0.3 amps,shows up.Changed alternator again,still the same,discharging 0.3 amps again,with totally different alternator.And sometimes you still get that very quiet hum.I am pulling my hair out,has anyone got any ideas!!!!!!

 

[MicKPM]

Does it still do it with the charge circuitry "exciter" wire disconnected?

 

[Sleepless i]

Yes,it does.You can take the alternator off the car,and connect to a battery,putting an amp meter between big terminal and live and it still drains 0.3 amps at worst ,sometimes a little less.The exciter has battery voltage with ignition on and no voltage when off.

 

[MicKPM]

Its very strange that two alternators would both cause the same drain. I'd say its more likely to be, if it's 100% that circuit, more likely to be the starter motor/starter solenoid at fault.

You could try disconnecting this from the starter to see if the drain vanishes. Also, making the assumption that all the connections are clean?

Mick

 

[Sleepless i]

Thanks for showing an interest!The thing is Mick,the alternator still drains when it's totally off the car,on the bench,with just some jump leads and an amp meter . The thing is i cant be sure if the car made them fail or they both have a weakness with the diode packs!? Another alternator has arrived.Now as fair as I can make out nothing externally can damage the alternator ,if your exciter is good,and the engine earth is good,what could make it fail.I am trying to double check every thing before fitting another one.

 

[MicKPM]

The battery feed from the battery to the alternator splits in two somewhere in the loom to power the starter. If this is faulty then it will cause the drain even when the alternator is off the car... this is why I suggested taking the starter live off to rule it out.

 

[DTM Cars Ltd]

Mick.

You really are a wiring and electronic geniuses

Andy

 

[Sleepless i]

Sorry Mick,when I say "it still drains,totally off the car" what I was trying to explain is, if you disconnect the alternator terminal,the drain stops.As a check to show that the alternator was faulty, when I took it back to the motor factors,I could just connect a battery with jump leads and the alternator would show a drain,on an amp meter.I will check for a drain to the starter solenoid though .Thank you

 

[Sleepless i]

Just checked this morning,after your suggestion,I've got total battery drain of 0.5 amps.On the engine side I've got a drain of 0.2 amps ,this stops when you undo the large bolted terminal on the alternator.Showing no drain to solenoid.I' ve still got 0.3 amps draining to the fuse side of the battery.If you take out two of the fuses the drain stops. I 've got a drain to the small fuse in the passenger side fuse box,marked as a "key" and a drain the fuse marked as "picture of car with the doors open"

 

[MicKPM]

A small drain is to be expected but not quite that much. Without seeing it I'm kind of out of ideas now chap

 

[Sleepless i]

I ran the engine for a bit then checked the drain again,apart from the alternator drain,I had 0.02 drain to the heated seat fuse and 0.02 to the radio fuse,the radio is off ,but the digi display above radio centre of dash is on the same fuse.One other thing the lights come on with the ignition,even with the switch off.