Battery drained?

Last week I was driving my 89 325I to work when the headlights and the instrument panel lights started to go dim, then a few blocks down the car dies, i took the battery in to be tested and it was dead, so I had the battery charged and it tested good, I pulled the alternator out and it tested good as well, where should I start looking to find the source of the charging issue?

I was having similar problems with my 540i and tracked it down to my FSU sensor. My sampling fan for the climate control was not turning off and draining my battery down. I ordered one from BMW and installed it and my charging problems were no longer an issue.

With a DMM and ALL systems off (including boot and interior lights, radio and clock) set up and read battery drain current (if there is any). The charging problem could be a bad terminal related to battery charging. A bad terminal can be 'seen' by the alternator as a fully charged battery. Double check and clean all connections. then check charging voltage and current.

certainly will be an issue between or inclusive of the battery and alternator. No E30 curcuit would drain a battery faster than your alternator can charge the car. But i would lean towards the alternator being dodgy, as an E30 will run off just the alternator with no battery installed (i have driven E30s i plan to wreck back from picking them up to my house with no battery installed, just a crash start or jump start), which reflexively means that if the battery was stuffed, the car would not have died while driving. Who tested your alternator?

The alternator and battery were both tested at autozone

When it died on the highway an officer gave mine a rolling start and it ran as long as the rpms were kept on the high side down to the gas station but the whole way there my headlights were dead and my guages were barely lit up

Sounds like a main feed or earth to the whole vehicle. CAREFULLY check major connections. Even if they look good!!! Clean and tighten the terminals and check where the wire goes in, and next to, the crimp(s).

either a bad/loose ground or the alternator is about to crap out

Originally Posted by _Ethrty-Andy_

certainly will be an issue between or inclusive of the battery and alternator. No E30 curcuit would drain a battery faster than your alternator can charge the car. But i would lean towards the alternator being dodgy, as an E30 will run off just the alternator with no battery installed (i have driven E30s i plan to wreck back from picking them up to my house with no battery installed, just a crash start or jump start), which reflexively means that if the battery was stuffed, the car would not have died while driving. Who tested your alternator?

Maybe you meant you have a generator? An alternator is impossible to start with a rolling-start or push without a battery or some electrical power source if thats what you meant by *crash start*.

Originally Posted by Bandem

Maybe you meant you have a generator? An alternator is impossible to start with a rolling-start or push without a battery or some electrical power source if thats what you meant by *crash start*.

there is no generator on an e30. its an alternator. and yes you can start/run a car with a dead battery by crash start. we've done it multiple times with different vehicles, but mainly jeeps.

also i was thinking some more, how does the car run without the headlights on? seem to charge ok?

Originally Posted by downhiller

there is no generator on an e30. its an alternator. and yes you can start/run a car with a dead battery by crash start. we've done it multiple times with different vehicles, but mainly jeeps.

also i was thinking some more, how does the car run without the headlights on? seem to charge ok?

Thats physically impossible. Your battery in that case, was not fully dead. There is no way an alternator can start without an electrical power source. It has no permanent magnetic fields and therefore needs electrical current at certain voltage to excite the fields.

If you were able to start it through a push, it means your battery still had some juice left in it. Maybe even a miniscule amount, not enough to start ignition or run accessories, but enough to get the alternator going.

Even with the headlights off that next day when i checked the battery they said it was at 85% charge, so i put it in and drove it about a mile down to autozone to check the alternator and was told the battery was reading at 60% so they couldnt test it then

Originally Posted by Bandem

Thats physically impossible. Your battery in that case, was not fully dead. There is no way an alternator can start without an electrical power source. It has no permanent magnetic fields and therefore needs electrical current at certain voltage to excite the fields.

If you were able to start it through a push, it means your battery still had some juice left in it. Maybe even a miniscule amount, not enough to start ignition or run accessories, but enough to get the alternator going.

Im not the most auto inclined here but Isn't the battery only needed to supply power to the starter motor that physically cranks the engine to fire it up? In that case a rolling start would bypass the whole need for starter or battery to get it running because the transmission would be acting as the starter motor to crank the engine

You need a small current to excite the alternator but current and voltage that will increase with rotation speed. Push car ONLY replaces starter motor. Running without a battery can blow diodes but it does keep running - for a time. If your battery went from 85 to 60% it is not being charged by the car. Back to checking leads, terminals and connections.

Don't you have Autoelectricians where you live
All you do is connect a serious Amp meter between Positive & terminal, then pull that terminal from the Battery and see the charging or discharging current.
In Africa, any genuine place that sells you Automotive Batteries will check that, as well as Electrolyte and load test on the battery. Normaly they will not even charge you (pun intended), if you do not stand around wasting their time
THEN you eliminate what is wrong
Battery- OK
Alternator OK
Not charging- lookie look for problem
Draining battery with ingnition off- boot light or similar being on when it should not

Thanks for the responses, once this rain clears up here I'll start checking connections and get back with you all

Well it turned out the alternator was going bad, i ended up taking it to my mechanic for a second opinion and he said it was failing under load, so I replace the alternator and it seems to be running fine now with the exception of the idle which is a little choppy and whenever i rev it up a little and let off the gas the engine nearly dies and then the rpms jump back up to around 500, is it possible i messed up zomething when i reinstalled the air box and air flow meter?

Originally Posted by goat88

Im not the most auto inclined here but Isn't the battery only needed to supply power to the starter motor that physically cranks the engine to fire it up? In that case a rolling start would bypass the whole need for starter or battery to get it running because the transmission would be acting as the starter motor to crank the engine

What will be running your electronics? Your spark plugs, your ECU and all the other various array of electronics throughout the car. That's done by the alternator. If your alternator doesn't work, neither can your engine.

Now, in the old days, cars used to have generators, which produced Direct Current. If you have a generator, you don't need a battery to start it, you can push start, or use cranks on front of the car like old cars did. A generator has a permanent magnetic field and converts mechanical energy (from your flywheel) into electrical energy at any time.

New cars use alternators and alternators produce alternating current which is then rectifyed into direct current and uses your battery as a filter (which is also why jump starting without a battery can damage your ECU), but they need a source of current to start the magnetic field before doing so.

Thats why, if you have no battery or no electrical source of outside power, push starting a car with an alternator is not possible. Often times people will claim they can with a dead battery, but the battery isn't actually dead. They think the battery is dead, because the ignition isn't working, but in reality its enough to excited the magnetic fields of the alternator and go.

So to answer your question, part of your battery power is for the starter, and a small part is for the alternator.

goat88 - Check CAREFULLY for leaks/damaged hoses on EVERYTHING you disconnected or 'moved'. Older car hoses crack or split very easily..

Well I checked the vacuum hoses for leaks without any luck and i honestly couldnt hear a leak either, most of the hoses look fairly new, i did retighten the hose attached to the icv after cleaning it out and that seemed to smooth out the idle some but the issue im still stuck on is when i start the car it will fire up like normal but as the rpms slow down to idle it eother seems to struggle with staying running or it dies, it also dies when im driving and i stop at a light when it would normally go down to idle it dies then too

Originally Posted by Bandem

What will be running your electronics? Your spark plugs, your ECU and all the other various array of electronics throughout the car. That's done by the alternator. If your alternator doesn't work, neither can your engine.

Now, in the old days, cars used to have generators, which produced Direct Current. If you have a generator, you don't need a battery to start it, you can push start, or use cranks on front of the car like old cars did. A generator has a permanent magnetic field and converts mechanical energy (from your flywheel) into electrical energy at any time.

New cars use alternators and alternators produce alternating current which is then rectifyed into direct current and uses your battery as a filter (which is also why jump starting without a battery can damage your ECU), but they need a source of current to start the magnetic field before doing so.

Thats why, if you have no battery or no electrical source of outside power, push starting a car with an alternator is not possible. Often times people will claim they can with a dead battery, but the battery isn't actually dead.

So to answer your question, part of your battery power is for the starter, and a small part is for the alternator.

generators were used back in the day when the battery was used for everything. all the generator did was keep the battery charged. until the 50-60s, when accessories were becoming available, is when they went to an alternator, where the battery is only used to get the car started or until the alternator can power everything.

an alternator uses magnetic fields to create power. you dont need power to go through the windings to create electricity, you just need to spin the rotor fast enough to create the power. i havnt tried crash starting to many new cars all because most of the are automatic and i dont own new cars. the only vehicals i have crash started were late 70s early 80s, and mainly jeeps, which the only real electrical to the vehical was the stereo and lights.

They think the battery is dead, because the ignition isn't working, but in reality its enough to excited the magnetic fields of the alternator and go.

we are not talking about hybrids here. first the starter need to spin the motor fast enough so the flywheel can keep the crankshaft moving so the engine can get to idle. there is nothing involving the alternator on starting the engine (except hybrids).

Originally Posted by downhiller

an alternator uses magnetic fields to create power. you dont need power to go through the windings to create electricity, you just need to spin the rotor fast enough to create the power.

Downhiller, I agree with you 99% of the time, but on this you are dead wrong. You can spin an alternator as fast as you want, but until there's excitation voltage it will generate nothing. An alternator has no magnetic field without excitation voltage. No magnetic field= no electrical generation. Generators had permanent magnets and didn't need electrical current to start producing electricity, but alternators absolutely MUST have a magnetic field created by electricity in the windings before they'll do anything at all.

Originally Posted by Bandem

Thats physically impossible. Your battery in that case, was not fully dead. There is no way an alternator can start without an electrical power source. It has no permanent magnetic fields and therefore needs electrical current at certain voltage to excite the fields.

If you were able to start it through a push, it means your battery still had some juice left in it. Maybe even a miniscule amount, not enough to start ignition or run accessories, but enough to get the alternator going.

Originally Posted by hornhospital

Downhiller, I agree with you 99% of the time, but on this you are dead wrong. You can spin an alternator as fast as you want, but until there's excitation voltage it will generate nothing. An alternator has no magnetic field without excitation voltage. No magnetic field= no electrical generation. Generators had permanent magnets and didn't need electrical current to start producing electricity, but alternators absolutely MUST have a magnetic field created by electricity in the windings before they'll do anything at all.

a crash start is putting the car in 2nd gear with the clutch in and letting the vehicle roll down a hill or getting someone to push the car quickly, then you drop the clutch and the car starts. obviously not possible for automatics.

With that said, and my understanding of electronics and past exercises, you are both right. You cannot crash start a car that doesn't have a battery in it. no battery is ever 100% dead, even when shorted out. what you can do however is disconnect the battery once the car is started and it will continue to run.

by the way, when i say car, i mean an E30. other cars may be different.

Wikipedia has a nice entry on alternators which includes a cool animation with rotating magnetic field vectors.

From what ive gathered from various scources an alternator can self excite, when spun above a certain rpm range