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TROOPER88

Original Poster:

1,092 posts

62 months

[news] 
Wednesday 2nd February 2011 quote quote all
Hello
I posted on here with a great response a few weeks ago regarding my new purchase; an E30 325i Convertible.

I have managed to sort most problems and have now strated to investigate what the previous owner called a 'slow battry drain'.

Ok; I collected the car and used it for a week or so with no problems. I then tried starting it on the weekend and it would not start; just the 'clicking/ticking' noise. Today I purchased a multimeter having never used one before but am happy to learn!

I tried the multimeter on my other car and on my partners BMW. Set it to 20v and put the black end on the negative and the red on the positive terminal of the battery. Both came gave similar results of 12.5 volts with engine off and 14.5 volts with engine running.

So now I turned my attention to the 325i; with the car as it was (apparant flat battery) I had a result of about 11.3v. I was surpsied by this as I thought it would be much less if it was flat? Any way 11.3 volts and it would not even turn over.
I put the booster pack on to get the car running and got a maximum of 13.32v (this was after a long motorway run).

I then switched the battery from the 325i into our other BMW to try and remove the battery from the problem. It worked; 12.35 off and 14.06 running.

I am now unsure where to go? I guess the alternator is at fault as should it be getting the output upto 14+ volts with the car running; is this correct?

But even if I replace the alternator it is not going to prevent/stop a battery drain.....

I did unbolt and remove the aftermarket amp connection form the positive terminal. With this amp terminal now hanging loose I tried the multimeter with the black on the negative and the red on the amp terminal and was getting a reading of 0.9 volts. What does this mean; that it was draining this amount or that it needs that amount to run?

My electrics knowledge is extremely poor.


Any advice would be great.


mmm-five

6,269 posts

167 months

[news] 
Wednesday 2nd February 2011 quote quote all
Your alternator might just not be providing a full charge. This can be due to a simple fault with the voltage regulator, the brushes, or some of the diodes.

If you can, get the alternator off and take it to an alternator specialist who should be able to bench-test it and refur/recon it back to spec - although I would counsel getting the slip-ring checked for ovalisation - otherwise you may find the same thing happens again and again.

TROOPER88

Original Poster:

1,092 posts

62 months

[news] 
Wednesday 2nd February 2011 quote quote all
mmm-five said:
Your alternator might just not be providing a full charge. This can be due to a simple fault with the voltage regulator, the brushes, or some of the diodes.

If you can, get the alternator off and take it to an alternator specialist who should be able to bench-test it and refur/recon it back to spec - although I would counsel getting the slip-ring checked for ovalisation - otherwise you may find the same thing happens again and again.
Or could I try the alternator (if its the same) from the other E30 BMW?

This would not account for a battery drain causing the car not to start after a period of not being used would it?

Thanks

mmm-five

6,269 posts

167 months

[news] 
Wednesday 2nd February 2011 quote quote all
Batteries do not maintain there charge indefinitely, and cold weather, parasitic losses, etc. will all contribute to the speed of that drain. The age of the wiring won't help either, and with the amount of splicing into the loom that's probably been done over the years won't help either.

The only way to see if the other alternator will work is to try it.

E30M3SE

7,599 posts

79 months

[news] 
Thursday 3rd February 2011 quote quote all
Maybe I missed this in your post, but what voltage do you get on the 325i Cab with the engine running at 2-2.5K rpms?

What is the voltage if you then turn on lights, rear screen blower, fan etc?


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TROOPER88

Original Poster:

1,092 posts

62 months

[news] 
Thursday 3rd February 2011 quote quote all
Hello
I did not try it with the engine under any load; just with it ticking over and nothing running.

I checked the battery this morn very quickly with nothing on and engine off and got 11.70 v.

When I try it on 2-2500 rpm and blowers etc on, what should I be getting volts wise?

Cheers

E30M3SE

7,599 posts

79 months

[news] 
Thursday 3rd February 2011 quote quote all
2-2.5K RPMS should produce a reading of 13.5-14.4V.

With the electrical circuits loaded you should still see circa 14V, anything less than 13V is an issue.

On the back of the alternator there is a blue wire, often called the 'exciter' wire, if this wire has a poor connection or a break it will not allow charging to occur, something to check before you get an new alerantor if the V's are low.

To test for drains on the system disconnect the earth terminal on the battery and wire in the multimeter in series, i.e. connect the +ve terminal of the battery multimeter to the -ve on the battery and the -ve of the meter to the -ve lead of the battery or the earth post on the suspension turret.

Ensure the multimeter is set to read AMPS or mA and the ignition is switched off, all of the doors & boot are closed and bonnet courtesy light disconnected.

If the meter reads more than 0.05A then would have a excessive drain on the system, typically on your car it should read 0.02-3 amps.

If the draw on your car is more than 0.05amps then remove the fuse box cover and remove 1 fuse at a time, each time you remove a fuse wait about 30 seconds to see what change if any occurs on the mA reading, if no change then the drain is not on that circuit and the fuse can be replaced.

If removal of a fuse reduces the mA reading to an acceptable level then one of the items running off that fuse is the possible culprit, if you look in your owners hand book there is a map of the fues box telling you what runs of each fuse.

HTH.

Edited for major correction. Thank you Gruber thumbup


Edited by E30M3SE on Thursday 3rd February 15:54

Gruber

4,977 posts

97 months

[news] 
Thursday 3rd February 2011 quote quote all
E30M3SE said:
i.e. connect the +ve terminal of the battery to the -ve on the battery
OP - I'm pretty sure he didn't mean this...

TROOPER88

Original Poster:

1,092 posts

62 months

[news] 
Thursday 3rd February 2011 quote quote all
E30M3SE said:
2-2.5K RPMS should produce a reading of 13.5-14.4V.

With the electrical circuits loaded you should still see circa 14V, anything less than 13V is an issue.

On the back of the alternator there is a blue wire, often called the 'exciter' wire, if this wire has a poor connection or a break it will not allow charging to occur, something to check before you get an new alerantor if the V's are low.

To test for drains on the system disconnect the earth terminal on the battery and wire in the multimeter in series, i.e. connect the +ve terminal of the battery multimeter to the -ve on the battery and the -ve of the meter to the -ve lead of the battery or the earth post on the suspension turret.

Ensure the multimeter is set to read AMPS or mA and the ignition is switched off, all of the doors & boot are closed and bonnet courtesy light disconnected.

If the meter reads more than 0.05A then would have a excessive drain on the system, typically on your car it should read 0.02-3 amps.

If the draw on your car is more than 0.05amps then remove the fuse box cover and remove 1 fuse at a time, each time you remove a fuse wait about 30 seconds to see what change if any occurs on the mA reading, if no change then the drain is not on that circuit and the fuse can be replaced.

If removal of a fuse reduces the mA reading to an acceptable level then one of the items running off that fuse is the possible culprit, if you look in your owners hand book there is a map of the fues box telling you what runs of each fuse.

HTH.

Edited for major correction. Thank you Gruber thumbup


Edited by E30M3SE on Thursday 3rd February 15:54
First of all, thank you so much for your detailed input.

Ok, just got back from work and went out to car with multimeter:

Car off: 11.58 volts at battery

Car wont start; use booster pack: now get 13.58 volts

Now with a load; 2500 rpm, lights and blowers on: 12.80!!!!!

Alternator?
This would not answer the drainage prob though would it?

Thanks again

TROOPER88

Original Poster:

1,092 posts

62 months

[news] 
Thursday 3rd February 2011 quote quote all
E30M3SE said:
2-2.5K RPMS should produce a reading of 13.5-14.4V.

With the electrical circuits loaded you should still see circa 14V, anything less than 13V is an issue.

On the back of the alternator there is a blue wire, often called the 'exciter' wire, if this wire has a poor connection or a break it will not allow charging to occur, something to check before you get an new alerantor if the V's are low.

To test for drains on the system disconnect the earth terminal on the battery and wire in the multimeter in series, i.e. connect the +ve terminal of the battery multimeter to the -ve on the battery and the -ve of the meter to the -ve lead of the battery or the earth post on the suspension turret.

Ensure the multimeter is set to read AMPS or mA and the ignition is switched off, all of the doors & boot are closed and bonnet courtesy light disconnected.


If the meter reads more than 0.05A then would have a excessive drain on the system, typically on your car it should read 0.02-3 amps.

If the draw on your car is more than 0.05amps then remove the fuse box cover and remove 1 fuse at a time, each time you remove a fuse wait about 30 seconds to see what change if any occurs on the mA reading, if no change then the drain is not on that circuit and the fuse can be replaced.

If removal of a fuse reduces the mA reading to an acceptable level then one of the items running off that fuse is the possible culprit, if you look in your owners hand book there is a map of the fues box telling you what runs of each fuse.

HTH.

Edited for major correction. Thank you Gruber thumbup


Edited by E30M3SE on Thursday 3rd February 15:54
Let me make sure I am doing this right (bare with me; I did say my electrical knowledge was bad!)

I removed the battery negative terminal. Then I set the multimeter to 'A' 20. I then place the red lead of the meter on the negative terminal and the black lead on the negative lead/suspension turret (where it earths)???

I tried this and the reading flashes as instantly -3.04 and then goes off and comes back with a figure in the range of minus 4-6!!


????

E30M3SE

7,599 posts

79 months

[news] 
Thursday 3rd February 2011 quote quote all
I would say yes, alternator, so long as your 'exciter' wire is doing its job.

It is possible for alternator to cause the drain, but at 12.8V it is certainly not charging correctly.

Disconnect the alterantor and check for drains to verify the rest of the electrics.

Amps DC is what you want the meter set to.



Edited by E30M3SE on Thursday 3rd February 16:47

GrilledBeans

61 posts

51 months

[news] 
Thursday 3rd February 2011 quote quote all
Common battery drains are the boot light and glove box light staying on after taking the keys out so might as well check them while you're at it.
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