walbertonio Posted November 10, 2013 Share Posted November 10, 2013 Tried searching through some threads on this but I'm so mechanically inept that I can't put two & two together, so here goes: Had a problem where after a 10 minute drive, I came to start the car again and it died completely before turning over. Got a jump start, and car ran OK for next 10 minute journey. Had the battery checked at Halfords and they advised it was about 75% and didn't need replacing, just needed a good charge. So, jumped it again and went for a 20 minute drive this time, that was fine. Came out later on to start up, dead again - jumped it again, kept it connected for much longer this time and managed to get home OK. Comes to this morning - I go to start the car, fires up first time. Bemused, I decided to go straight out for a 90 minute drive to (hopefully?) fully charge the battery. Now, the funny thing is I have the car booked into JM next week to look at a potential issue with the aux belt tensioner (makes a half second squeak at start up, or pulling away when cold etc) and I've read that this kind of issue can cause additional problems for that alternator? Does it sound like the alternator is goosed? Or do I have an wiring gremlin that just hates Saturdays? Quote Link to comment Share on other sites More sharing options...
SteveC Posted November 10, 2013 Share Posted November 10, 2013 Putting a voltmeter across the battery when the engine is running would give a good indication if the alternator is OK or not and if the belt is sufficiently tensioned to turn the alternator enough. A voltmeter should indicate 14 - 14.5 volts with the engine running. I'd of thought that Halfords would have done that for you. If the belt was that loose, you'd have a warning light on the dash. You may have something on the car that's dragging the battery down whilst it's stood. Again, a fairly quick in-line current test with a meter would let you know if that was the case. Your battery could still be on it's way out even though Halfords say it's 75%. The battery may indicate OK shortly after stopping the car (like at Halfords), but it could have an internal partial short so it goes flat of it's own accord. Personally I doubt the alternator itself is faulty. Can't recall reading about any that have failed. Regardless of the above, however the battery is being flattened, repeatedly flattening it will definitely end it's life very quickly. Quote Link to comment Share on other sites More sharing options...
walbertonio Posted November 10, 2013 Author Share Posted November 10, 2013 Thanks for that SteveC - I'll have a search for recommended batteries and start there. Quote Link to comment Share on other sites More sharing options...
Guest Roger NE Posted November 10, 2013 Share Posted November 10, 2013 If you don't have a Multimeter to check the voltage when the engine is running, just turn the headlamps on at night against a white wall/garage door . . . when you increase the revs to about 2500 rpm they should be slightly brighter . . . . then go back to tickover . . . then cut the engine - the lights should be slightly dimmer than tickover. If that's what happens, your Alternator is almost certainly OK. Before rushing out to buy a new battery, I would check nothing is draining it while the car is parked. A common problem is aftermarket high power audio amps, wired permanently to the battery . . . or it could be a faulty alarm . . . even something silly like a faulty boot light switch so the light stays on. What you really need is a meter to measure the current taken from the battery when everything is switched off. Certainly what Steve said about repeatedly flattening a battery is correct (and especially leaving them flat) - it KILLS lead/acid batteries ! Quote Link to comment Share on other sites More sharing options...
walbertonio Posted November 10, 2013 Author Share Posted November 10, 2013 Think we might have a multimeter at work I can swipe and try out with the car off and indeed see if it's being drained from anywhere. Cheers for the suggestions Roger & Steve. Quote Link to comment Share on other sites More sharing options...
walbertonio Posted November 11, 2013 Author Share Posted November 11, 2013 Alternator was OK, was showing 14.36 with the engine running, so all good on that front. Tested the battery again after the car had been stood for 5 hours, and it's showing 12.6, so again seems OK. Bit of a mystery then. Guess my Supra just hates Saturdays. Cheers for the suggestions fellas. Quote Link to comment Share on other sites More sharing options...
Guest Roger NE Posted November 11, 2013 Share Posted November 11, 2013 Measuring the battery voltage WITHOUT putting a load on it isn't really much of a test . . . . turn your full headlamps on (without the engine running) and then measure what the voltage is But also, you really need to put the battery on charge for about 12 - 15 hours to fully charge it (if it was previously pretty flat) If you only use the car once a week, that will be part of the problem (as people on here frequently post!) . . . car batteries don't like being left without getting regularly topped up with charge . . . and it will gradually be drained by the Alarm/Immobiliser . . . on top of that they hate the cold weather! Quote Link to comment Share on other sites More sharing options...
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