Batteries, voltage & Alternators.

92 735i E32

In my continuing saga of battery drain; I've gotten conflicting information (not
strange really; considering all the places I've sought info)

Here's what I know:

I have a drain, when adding up the mA's across fuses; about a 170ma drain.

If Idrive the car, then stop; the battery has a voltage of just about 12.5-12.8
volts

If I put the battery on a charger, after driving, it jumps to 9 amps and I
measure 14.8 volts at the battery..

Pulling the charger off; I can watch the volts drop slowly, but steadily slowing
down around 12.5. This happens regardless of the battery being connected to the
car or not.

If I let the car "sit" for 2 days; the battery will not be strong enough to
start the car.

the battery is relatively new. (less than 4 months old)

Theories/opinions.

Max battery drain should be no more than 50ma -- I haven't been able to confirm
this anywhere.

at 200ma; the battery should not be dead in 2 days

Possibly the alternator is bad & if the diode is blown; it is draining the
battery when teh car is off.

The battery is bad and not holding a charge.

Questions:

Could the alternator really drain the battery? If so; is there an easy way to
disconnect the alternator? one of the two bolts on teh alternator is 'blocked'
by the oil filter.

Could a bad alternator have killed the battery?

What is a reasonable battery drain (range) to expect from all the computers &
whatnots?

Based on the rapid decline of voltage held in teh battery when disconnected; the
battery is probably shot, correct?

Thanks all!
-josh



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Josh Assing wrote:
> 92 735i E32
>
> In my continuing saga of battery drain; I've gotten conflicting information (not
> strange really; considering all the places I've sought info)
>
> Here's what I know:
>
> I have a drain, when adding up the mA's across fuses; about a 170ma drain.
>
> If Idrive the car, then stop; the battery has a voltage of just about 12.5-12.8
> volts
>
> If I put the battery on a charger, after driving, it jumps to 9 amps and I
> measure 14.8 volts at the battery..
>
> Pulling the charger off; I can watch the volts drop slowly, but steadily slowing
> down around 12.5. This happens regardless of the battery being connected to the
> car or not.
>
> If I let the car "sit" for 2 days; the battery will not be strong enough to
> start the car.
>
> the battery is relatively new. (less than 4 months old)
>
> Theories/opinions.
>
> Max battery drain should be no more than 50ma -- I haven't been able to confirm
> this anywhere.
>
> at 200ma; the battery should not be dead in 2 days
>
> Possibly the alternator is bad & if the diode is blown; it is draining the
> battery when teh car is off.
>
> The battery is bad and not holding a charge.
>
> Questions:
>
> Could the alternator really drain the battery? If so; is there an easy way to
> disconnect the alternator? one of the two bolts on teh alternator is 'blocked'
> by the oil filter.
>
> Could a bad alternator have killed the battery?
>
> What is a reasonable battery drain (range) to expect from all the computers &
> whatnots?
>
> Based on the rapid decline of voltage held in teh battery when disconnected; the
> battery is probably shot, correct?
>
> Thanks all!
> -josh
>
>
>
> --- AntiSpam/harvest ---
> Remove X's to send email to me.

First, an overcharging alternator would kill a battery quickly, but the
14.8 volts you mention is about right. Second, while 170ma is a little
high, it's probably not your problem. Third, measuring across the fuses
only checks the fused loads, you need to pull a battery cable and
measure between it and the battey, Lastly if it's still 170ma and it's
dead in two days, the battery is bad no matter how old it is.

In article >,
Josh Assing > wrote:
> In my continuing saga of battery drain; I've gotten conflicting
> information (not strange really; considering all the places I've sought
> info)

> Here's what I know:

> I have a drain, when adding up the mA's across fuses; about a 170ma
> drain.

That's higher than I would expect.

> If Idrive the car, then stop; the battery has a voltage of just about
> 12.5-12.8 volts

You really need the battery to settle after being on charge to get
anything meaningful from a voltage reading, but if it was this sort of
value the next morning it means a good battery is in a reasonable state of
charge.

> If I put the battery on a charger, after driving, it jumps to 9 amps and
> I measure 14.8 volts at the battery..

That really depends on the output of the charger. But 9 amps at 14.8 volts
suggests a large unregulated charger - if the battery is good. And would
cause it to gas freely. Not good with low maintenance semi sealed designs.

> Pulling the charger off; I can watch the volts drop slowly, but steadily
> slowing down around 12.5. This happens regardless of the battery being
> connected to the car or not.

Sounds like a faulty battery, I'm afraid. A fully charged battery with no
load will 'settle' to about 13 volts overnight.

> If I let the car "sit" for 2 days; the battery will not be strong enough
> to start the car.

What's the voltage then? A good battery should start the car when only
showing 11.5 volts or so.

> the battery is relatively new. (less than 4 months old)

> Theories/opinions.

> Max battery drain should be no more than 50ma -- I haven't been able to
> confirm this anywhere.

> at 200ma; the battery should not be dead in 2 days

Quite; 200 mA is only approx 10 amp/hr over two days, so a fraction of the
battery capacity.

> Possibly the alternator is bad & if the diode is blown; it is draining
> the battery when teh car is off.

You'd be seeing several amps quiescent if that was the case.

> The battery is bad and not holding a charge.

> Questions:

> Could the alternator really drain the battery? If so; is there an easy
> way to disconnect the alternator? one of the two bolts on teh
> alternator is 'blocked' by the oil filter.

> Could a bad alternator have killed the battery?

> What is a reasonable battery drain (range) to expect from all the
> computers & whatnots?

> Based on the rapid decline of voltage held in teh battery when
> disconnected; the battery is probably shot, correct?

First thing to do is to have the battery tested. There are modern testers
which can give the state of the battery regardless of charge (unless
totally flat). Somewhere that sells batteries should have one and do the
test for free.

--
*Succeed, in spite of management *

Dave Plowman London SW
To e-mail, change noise into sound.

>First, an overcharging alternator would kill a battery quickly, but the
>14.8 volts you mention is about right. Second, while 170ma is a little

Actually; that 14.8 is with a charger, not the alternator.. but.....


>high, it's probably not your problem. Third, measuring across the fuses
>only checks the fused loads, you need to pull a battery cable and


Right! Which is why we're thinking the alternator diode might be bad....

>measure between it and the battey, Lastly if it's still 170ma and it's
>dead in two days, the battery is bad no matter how old it is.

Thanks.
-josh


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>You really need the battery to settle after being on charge to get
>anything meaningful from a voltage reading, but if it was this sort of
>value the next morning it means a good battery is in a reasonable state of
>charge.

After a charge, let it settle; it's down to 12.2 or so volts.

>suggests a large unregulated charger - if the battery is good. And would
>cause it to gas freely. Not good with low maintenance semi sealed designs.

I can hear it gas out....

>Sounds like a faulty battery, I'm afraid. A fully charged battery with no
>load will 'settle' to about 13 volts overnight.

That's EXCELLENT news! No need to be affraid... A battery is cheap (actually
free, just have to get off the island... the battery is still under warranty)


>> If I let the car "sit" for 2 days; the battery will not be strong enough
>> to start the car.
>
>What's the voltage then? A good battery should start the car when only
>showing 11.5 volts or so.

10. something...

>> Possibly the alternator is bad & if the diode is blown; it is draining
>> the battery when teh car is off.
>
>You'd be seeing several amps quiescent if that was the case.

Only over the battery -- I do not have a meter capable of that level


>First thing to do is to have the battery tested. There are modern testers
>which can give the state of the battery regardless of charge (unless
>totally flat). Somewhere that sells batteries should have one and do the
>test for free.

Will do.

Thanks
josh


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Josh Assing wrote:
> 92 735i E32
>
> Questions:
>
> Could the alternator really drain the battery? If so; is there an easy way to
> disconnect the alternator? one of the two bolts on teh alternator is 'blocked'
> by the oil filter.
>
> Could a bad alternator have killed the battery?
>

I've just finished fixing a charging/draining issue on my E30. It
turned out to be a bad alternator/regulator which in turn killed one
cell of the battery, which wasn't that old. Replacing both fixed the
problem. If you start the engine and then connect a voltmeter across
the battery terminals, what reading to you get? On mine it was
fluctuating quite a lot, between about 11 and 14 volts. With a new
alternator and battery the reading shows it as charging at a steady 14v
and all is well again.
--
Mark

>I've just finished fixing a charging/draining issue on my E30. It
>turned out to be a bad alternator/regulator which in turn killed one
>cell of the battery, which wasn't that old. Replacing both fixed the

This is; at least, encouraging that I might be on the right track.

>problem. If you start the engine and then connect a voltmeter across
>the battery terminals, what reading to you get? On mine it was
>fluctuating quite a lot, between about 11 and 14 volts. With a new
>alternator and battery the reading shows it as charging at a steady 14v
>and all is well again.

WIll test it today.

Thanks
-josh


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In article .com>,
MarkS > wrote:
> I've just finished fixing a charging/draining issue on my E30. It
> turned out to be a bad alternator/regulator which in turn killed one
> cell of the battery, which wasn't that old. Replacing both fixed the
> problem. If you start the engine and then connect a voltmeter across
> the battery terminals, what reading to you get? On mine it was
> fluctuating quite a lot, between about 11 and 14 volts.

That's certainly a faulty alternator - probably the regulator or even worn
brushes. But 14 v peak won't damage the battery - it's normal.
Occasionally a regulator will fail in a hard on condition and output some
17 volts. This can damage the battery if left too long by 'boiling' it dry.

> With a new alternator and battery the reading shows it as charging at a
> steady 14v and all is well again.

I had to have the alternator on my E34 changed by my dealer after it died
and I had to have the car towed while I carried on to my destination. They
changed the battery too - although it was previously fine. It could be
running it 'flat' because the alternator failed caused it also to fail,
but I'm not convinced.

--
*The problem with the world is that everyone is a few drinks behind *

Dave Plowman London SW
To e-mail, change noise into sound.

I'm sure that the failing alternator did kill the battery in my case,
as it was a strong battery before the fluctuations started and wasn't
very old. I don't think there was ever any serious over-charging, my
readings were never much over 14v, I just considered that it must have
been the frequent fluctuations themselves which killed the cell.

In article .com>,
MarkS > wrote:
> I'm sure that the failing alternator did kill the battery in my case,
> as it was a strong battery before the fluctuations started and wasn't
> very old. I don't think there was ever any serious over-charging, my
> readings were never much over 14v, I just considered that it must have
> been the frequent fluctuations themselves which killed the cell.

It's unlikely given the actual charging DC isn't a smooth voltage but a
series of peaks and troughs.

--
*Did you ever notice when you blow in a dog's face he gets mad at you? *

Dave Plowman London SW
To e-mail, change noise into sound.