One morning the car would not start so I fitted a new battery and it started immediately. However, the next morning the battery is completly dead again - not even enough power to turn the interior light on or operate the central locking.
I know to check the obvious such as the boot light etc, but I would appreciate it if anybody has any ideas or advice on how to track the source of the power drain.
I've heard that this could be a bad earth or the alternator - any advice appreciated.
Edited by Dynamic Dave on 14/01/2010 at 13:33
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I would have thought that anything running the battery down that quickly would produce heat, so feel you alternator in the morning and see if its warm. If when you have finished with the car, you disconnect one battery terminal and connect a ammeter or multimeter with an amps range, between the terminal you have removed and the battery post you can read the current being drained, to flatten the battery overnight it will need to be drawing three or four amps or more, whereas it shouldn't be more than 100ma - 1/10th amp. Dont try and start the engine with the meter in circuit.
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Thanks Peter. Do you have any advice on how to track down the cause of the current drain?
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Only by removing the fuses one by one - in the hope that you have a handbook that tells you what they all do.
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Doubt it is a bad earth but alternator diode packs can fail and drain batteries. Also a faulty diode pack won't allow it to charge the battery properly. If you've a multimeter, check the charging voltage. You should have 14.4 - 14.6 volts or so across the battery when the engines doing a couple of thousand revs. If that's ok, remove the battery earth strap, put the meter in series with it and check the current drain with the engine off. Modern cars will draw a few 10s of milliamps - say 50mA or so - that's normal. If it's higher (and it would need to be much higher to drain the battery overnight)pull fuses/ disconnect items like the alternator until you isolate the item drawing the current.
JS
Edited by John S on 15/01/2010 at 16:32
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can adampbrown email me his mobile number at timorridge at tiscali dot co dot uk please?
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This is the course of action I'd follow.
Turn ignition off, turn interior light off.
Disconnect the positive battery lead.
Connect a multimeter from the battery terminal to the disconnected lead in Ammeter mode.
Most multimeters willl read up to 10 amps, any more than that and the fuse will blow - you'll need a shunt. Do not at anytime during testing turn the ignition back on.
Once connected you'll have a reading of amps being drawn by the electrical system which should be from 0 to a few milliamps for a healthy car - of course in your circumstance it will be quite a drain to flatten a new battery overnight.
Unplug the alternator - check the reading, if there's a big change then your alternator is duff. No change then move on...
One by one pull out each fuse in turn checking the reading - if there's no drastic change plug it back in and move on to the next fuse.
After the fuse box you'll want to unplug and plug in each relay you can get your hands on.
Hopefully you will find the drain that way or at least isolate it to what circuit is causing the drain.
If you do not find the current drain using the above method then you are likely to have a short upstream of the fusebox - call an automotive sparkie in - this is potentially dangerous in terms of a fire hazard.
Good luck.
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It will be the alternator diode (rectifier) at fault here. These are one way devices and allow power from alternator to battery but not the other way round, and now because this has failed the battery is losing power back through the system or charging the coils of the alternator. Unfortunately the cost of replacing these means that a new alternator at £80 (maybe less for exchange) is the only way forward and maybe 2-3 hours removal/fitting. Good news they are easy to get to and replace on the Rover 200.
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The alternator has indeed been identified as the offending component (admittidly I did use an auto electrician)! There was a fluctuating drain of between 2-4 amps. He suspected that it was the rectifier, but it turned out more cost effective to replace the whole alternator than to re-condition the exsiting unit.
Thanks to everyone who responded.
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