Mk4Gaz Posted January 25, 2014 Share Posted January 25, 2014 Hi guys, is there anything else you can think of, that I can test first, before replacing my alternator ? I removed it whilst tidying up the engine bay recently, and today I started the car to go out for it's first drive since doing all the work, and I had the warning lights of doom on the dash ! The alternator doesn't appear to be charging the battery - a multimeter has confirmed this. I've checked all the charging circuit fuses, and they're all fine. I've got battery voltage at all three alternator plug wires with the ignition on, and battery voltage at the main 12v cable on the alternator. Could it just be good old fashioned bad luck that it's just happened to fail, or am I missing something ? Any help greatly appreciated Quote Link to comment Share on other sites More sharing options...
T14PPA Posted January 25, 2014 Share Posted January 25, 2014 An easy way of testing it is to start the car and undo the earth on the battery and see if the car switches off Quote Link to comment Share on other sites More sharing options...
Mk4Gaz Posted January 25, 2014 Author Share Posted January 25, 2014 That's a good idea, might try that tomorrow. I'll have to set the sodding head unit up again though, one of my pet hates. Must get a power saver! Quote Link to comment Share on other sites More sharing options...
Guest Roger NE Posted January 25, 2014 Share Posted January 25, 2014 (edited) undo the earth on the battery NOT a good idea ! The Alternator doesn't supply smoothed DC . . . it's output is rectified AC, so it relies on the Battery to fill in the gaps between the pulses. Running without the battery connected could therefore blow up the various ECUs in the car . . . it can also damage the Alternator itself (if it's not already damaged) So when you say it's not working, are you saying the battery voltage is the same whether the engine is running or not? (you'll see about 12V across the battery when engine is off . . . if the Alternator is working OK this should rise to about 14V with the engine running) If it DOESN'T, then yes your Alternator is faulty. Most likely a transistor in the Regulator circuit has blown, so you should be able to get it repaired quite cheaply. (if you don't know a place that repairs/reconditions them, ask at a local Motor Factors who they use) Edited January 25, 2014 by Roger NE (see edit history) Quote Link to comment Share on other sites More sharing options...
Benjy Posted January 25, 2014 Share Posted January 25, 2014 With the car running, check the voltage at the battery. Should be 14-14.4v. If it's below that, test it at the main live at the alternator. That too should be 14-14.4v. If it's a good voltage but not at the battery, you have a problem in between. Don't disconnect the battery. 1, it can damage electrical components, and 2, unless the alternator's putting out less than 8 or 9v, it will still run. Quote Link to comment Share on other sites More sharing options...
Mk4Gaz Posted January 25, 2014 Author Share Posted January 25, 2014 Cheers guys. With the engine running, I only have battery voltage at the battery, and the main live feed on the alt ( 12.5v ish). I'm pretty sure the alternator must be dead, which is odd as it was perfect before I removed and refitted it. All charging circuit fuses are fine, and I have battery voltage at all 3 wires on the alternator plug, with the ignition on. So it looks like good old fashioned bad luck has caused it die. I've tried to repair alternators before, and never been successful! I'll take it to a local place, and have it refurbed I think. Always something eh! Quote Link to comment Share on other sites More sharing options...
Guest Roger NE Posted January 25, 2014 Share Posted January 25, 2014 You've obviously checked the right things . . . Bizarre if it was working fine before you took it off, but it's faulty now. You did put the fan belt back on? (just kidding!) As you say, must just be bad luck Quote Link to comment Share on other sites More sharing options...
Mk4Gaz Posted January 26, 2014 Author Share Posted January 26, 2014 Lol, I fitted a brand new belt! When the dash lit up like a Christmas tree, I figured it was an alternator fault. I put my multimeter across the battery, and was getting near 16v. I shut the engine down, checked for ignition voltage at the alternator plug, plugged it back in and when I started the engine back up, I wasn't getting any output on the charging circuit. I should've mentioned that earlier, but I'm guessing the voltage regulator has gone bad, and killed it? Quote Link to comment Share on other sites More sharing options...
Benjy Posted January 26, 2014 Share Posted January 26, 2014 Where are you based mate? I've got an autospark mate that works in Croydon. Quote Link to comment Share on other sites More sharing options...
Mk4Gaz Posted January 26, 2014 Author Share Posted January 26, 2014 I'm near Southend dude. I'll whip it off, and get it tested Quote Link to comment Share on other sites More sharing options...
Benjy Posted January 26, 2014 Share Posted January 26, 2014 Test it as i said above. Just the engine running, should be around 14v Load it up with headlights, heated rear screen, blowers etc and the lowest you should see should be around 13.6v Anything below either of those voltages, it's goosed. Quote Link to comment Share on other sites More sharing options...
Mk4Gaz Posted January 26, 2014 Author Share Posted January 26, 2014 Yeah did that mate, the battery voltage doesn't increase with the engine running, and when I loaded it up with heaters and lights, it dropped to under 12v. I'll order a new one tomorrow Quote Link to comment Share on other sites More sharing options...
keron Posted January 26, 2014 Share Posted January 26, 2014 Have you checked if the crank pulley is goosed? When they fail, the outer part spins and can cause a loss of power/battery drain... Tip ex trick should see weather it's goosed... However the alternators failing are a very common thing on these now... Quote Link to comment Share on other sites More sharing options...
Mk4Gaz Posted January 26, 2014 Author Share Posted January 26, 2014 Crank pulley is fine thanks bud, it's pretty much brand new - only installed it last week. The belt is definitely travelling correctly. Just really odd how it was fine, then I removed it to replace the water pump and cambelt, then refitted it, and now it doesn't work. Quote Link to comment Share on other sites More sharing options...
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