W126 Battery Drain

hiram

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I have a 91 300SE that is draining the battery in about 5 hours if the car is unused. I have tested the alternator and it appears to be ok. Have done a drain test on the fuse box and it shows a 0.7 amp drain on fuse 2, also done a drain test on the battery with above fuse removed and it showed a 3.2 amp drain. Would be grateful it yous had any ideas of the cause of this problem.
Thanks
 

xavierx

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3.2 amps with the fuse removed? so do you mean testing in series across the fuse points?

3.2 amps is a huge drain, frankly it should be creating a significant ammount of heat somewhere in the electrics and maybe that will help you pinpoint the problem (would be even easier if you had a thermal imaging camera :D)
 

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I will give a hand in the morning
 
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hiram

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Re Drain

Yes I do mean testing across the fuse points. the battery I tested by disconnecting the positive terminal and had the meter on the wire terminal and the other on the battery terminal and that is were it was showing 3.2 amp drain. It didn't matter if the fuse was in place it still showed 3.2 drain at battery as tested above.
 

television

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I have checked to night and my info is too poor on the 126

The normal way to find drains is to put the ammeter is series with the battery,and leave it there,,you then take out the fuses one by one till you find the one where the drain stops, what ever is not working will show where the fault is.

Some thing must be quite warm with that drain
 
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hiram

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Thanks Very Much
Will try it that way. Will let you know tomorrow what happens.
 

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Thanks Very Much
Will try it that way. Will let you know tomorrow what happens.

If you have the fuse chart, then it makes it easier,,I have them somewhere but I have so many to sort
 

xavierx

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Yes I do mean testing across the fuse points. the battery I tested by disconnecting the positive terminal and had the meter on the wire terminal and the other on the battery terminal and that is were it was showing 3.2 amp drain. It didn't matter if the fuse was in place it still showed 3.2 drain at battery as tested above.

That is the correct way to test, however, if you are seeing the drain still with the fuse removed then it is nothing to do with that fuse.

As has been said above, pull out all the fuses one by one until either the drain stops or there are no fuses left. If you still have a drain then there are usually some fueses in the engine bay on most cars for high load electrical items.

Check the back of the fuse box for shorts, corrosion or water damage.

Failing that it is probably a failed blocking diode on the alternator turning one of the alternator windings into a small heater!
 

xavierx

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any progress on this one? Would be nice to know if you fixed it
 
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hiram

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Done all the above tests and still had drain. So disconnected the Alternator and the drain went away. so am thinking it must be the Alternator. Will replace the Alternator next week when I have the funds to do so and let you know the results with the new alternator in place. Hopefully the drain will then be gone for good. Let me know if you think that I am right to replace the alternator?
 
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television

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There is nothing in the primary of the alternator that could do this, as this is all AC, by just replacing the regulator pack that should do it and only £10. A said before this is not a known fault with the 126 and 3.5 amp would show up with something getting hot, but not with the alenator
 
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hiram

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Where is the regulator pack, and I take it that AC you mentioned is the Air Con?
 

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The regulator is 104 in the link and it just bolts onto the end of the alternator. As before only 2 screws and cost about £10-20 max from any Bosch Service center in the uk.

The alternator gives AC, this AC is alternating current, and the reg pack converts it to DC direct current, and a fault in this little device can cause the fault that you have.
 
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hiram

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Will try that,thanks. I'll let you know if it works and fixes the prob. Thanks again for your help.
 
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hiram

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Replacing voltage regulator in alternator sorted the problem and only cost me £10.98. Great advice thanks to you all for your help.
 


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