Jump to content
amazighman

Replaced alternator still not charging???

Recommended Posts

Hi.

I have been doing some work on my e39 530i and replace oil filter housing gasket and vanos hose, all ok.

I also replaced the alternator as it wasn't charging enough.

Problem is i cant get any charge from new alternator either, my battery died and i am back to square one.

Any ideas? Could it be that my replacement second hand alternator is kaput ? Or there is another issue?

 

Cheers

Share this post


Link to post
Share on other sites

My original alternator was 13.5 engine on but after the engine warms up it drops to between 11-12 v.

 

The replacement second hand with engine on it is about 10.8v 

No I don't have a drain.

14 minutes ago, LukeH said:

What is the voltage at the battery while the engine is running? 

Are you sure you don't have a drain somewhere?

 

Share this post


Link to post
Share on other sites

That's certainly low. When my alternator failed on my 750 I just changed the brush/regulator pack on the back, it was only about £30 from memory. 

 

It it sounds like your original was dying and your replacement is dead sadly. 

Share this post


Link to post
Share on other sites
1 hour ago, LukeH said:

That's certainly low. When my alternator failed on my 750 I just changed the brush/regulator pack on the back, it was only about £30 from memory. 

 

It it sounds like your original was dying and your replacement is dead sadly. 

I had a look at the brushes on the voltage regulator in my old alternator and they seem fine and not worn, but not sure maybe other bits in that voltage regulator may have failed

Share this post


Link to post
Share on other sites

A healthy alternator should keep the battery at 14v while the motor is running. It looks like the original one was weak (it had to work some, in order to raise the voltage to 13.5v) and the replacement is not working at all.

 

It you had similar voltage drops, you might have have suspected a drain somewhere. But it rather looks like you had the misfortune to get a faulty replacement from the breaker.

Share this post


Link to post
Share on other sites

duff 2nd hand ones are common place, and if working are just as bad as the one taken of fin the first place!! Been there, done that, bought a replacement!

Share this post


Link to post
Share on other sites
On ‎28‎/‎10‎/‎2017 at 5:52 AM, LukeH said:

As did mine, there still looked to be plenty of life in the brushes, but once changed it came back to life with no issues. 

The brushes can indeed look ok - until you compare them with new, which will be considerable longer. Had this on wife's 330Ci - flat battery problems, low running voltage at the battery, both disappeared after a brush pack change.

Share this post


Link to post
Share on other sites

You might want to consider testing for voltage drops between the alternator and the battery. That's a lot of cabling, but at least the voltage drop immediately after the alternator is easily testable and could indicate a duff alternator. I had an issue with charging, from battery charger when parked up, and despite having a healthy alternator voltage showing, the battery wasn't charging properly and it was the battery connector clamps that needed sanding down (no visible corrosion but weren't shiny). Without testing it is really guesswork with many variables.

Share this post


Link to post
Share on other sites

+1 to PliSsK's suggestion.

 

Checking voltages around the car would verify the alternator & confirm it isn't rogue resistance - or not for each.  It shouldn't take more than 10 minutes.

 

I'd recommend the following sequence to determine alternator output and whether resistance is causing a low battery charge rate and low car voltage.

 

1) Have a helper start the engine with everything possible switched off, and run it @ ~2,,000 RPM

2) In the trunk, immediately measure between +ve battery post and +ve battery terminal to check for resistance across the joint. Result should be less than 0.01V. You want to catch this while the alternator is trying to recharge the battery for the amps used while cranking; after a minute or so all the amps will be replaced and little current will be flowing into the battery.

3) Immediately, measure between -ve battery post and -ve battery terminal. Result should be less than 0.01V again.

4) Allow the engine to come to temperature, since you've mentioned voltage drops when warm. (It would help if you'd describe exactly where and how you did that measurement)

5) Turn on lots of high amp consumers:, e.g. cabin blower maximum, rear window defogger, headlights including high beam, A/C if warm enough for it to run, windshield wipers, etc. The idea is to maximize amps through the power and ground circuits to load test the alternator and to maximize voltage drops across any rogue resistance & make any problems easier to measure.

6) Have a helper run the engine at ~ 2.500 RPM. At this speed the alternator should be able to generate enough amps to feed all the  consumers turned on in 5) above without drawing from the battery.

7) Measure voltage between the engine jump post and the alternator case/frame, i.e. the voltage the regulator/alternator is generating before any resistance losses toward the battery. BMW specs say it should be between 14.0 & 14.5V (this assumes the connections from the alternator +ve post and the jump post is tight, which should be a good assumption, but subject to checking if later results are confusing)

8 ) Measure between the jump post and the ground lug/nut on the shock tower, which  checks for resistance in the ground strap from engine to chassis. It should be within 0.01V of results from 7) Alternatively measure between alternator case and the ground lug, which should equivalently return less than 0.01V

9) Go to the trunk and measure between the +ve and -ve battery terminals. The result should be no more than 0.5V difference (0.25 would be better) from 7) above. If the delta is more than 0.5V there is excess resistance in the cable or its connections from alternator to battery, or in the short ground strap from body to battery -ve terminal.

 

Let us know what you find.

 

Regards

RDL

Share this post


Link to post
Share on other sites
22 hours ago, rdl said:

+1 to PliSsK's suggestion.

 

Checking voltages around the car would verify the alternator & confirm it isn't rogue resistance - or not for each.  It shouldn't take more than 10 minutes.

 

I'd recommend the following sequence to determine alternator output and whether resistance is causing a low battery charge rate and low car voltage.

 

1) Have a helper start the engine with everything possible switched off, and run it @ ~2,,000 RPM

2) In the trunk, immediately measure between +ve battery post and +ve battery terminal to check for resistance across the joint. Result should be less than 0.01V. You want to catch this while the alternator is trying to recharge the battery for the amps used while cranking; after a minute or so all the amps will be replaced and little current will be flowing into the battery.

3) Immediately, measure between -ve battery post and -ve battery terminal. Result should be less than 0.01V again.

4) Allow the engine to come to temperature, since you've mentioned voltage drops when warm. (It would help if you'd describe exactly where and how you did that measurement)

5) Turn on lots of high amp consumers:, e.g. cabin blower maximum, rear window defogger, headlights including high beam, A/C if warm enough for it to run, windshield wipers, etc. The idea is to maximize amps through the power and ground circuits to load test the alternator and to maximize voltage drops across any rogue resistance & make any problems easier to measure.

6) Have a helper run the engine at ~ 2.500 RPM. At this speed the alternator should be able to generate enough amps to feed all the  consumers turned on in 5) above without drawing from the battery.

7) Measure voltage between the engine jump post and the alternator case/frame, i.e. the voltage the regulator/alternator is generating before any resistance losses toward the battery. BMW specs say it should be between 14.0 & 14.5V (this assumes the connections from the alternator +ve post and the jump post is tight, which should be a good assumption, but subject to checking if later results are confusing)

8 ) Measure between the jump post and the ground lug/nut on the shock tower, which  checks for resistance in the ground strap from engine to chassis. It should be within 0.01V of results from 7) Alternatively measure between alternator case and the ground lug, which should equivalently return less than 0.01V

9) Go to the trunk and measure between the +ve and -ve battery terminals. The result should be no more than 0.5V difference (0.25 would be better) from 7) above. If the delta is more than 0.5V there is excess resistance in the cable or its connections from alternator to battery, or in the short ground strap from body to battery -ve terminal.

 

Let us know what you find.

 

Regards

RDL

Hi.

I changed the alternator again and this time it is a guaranteed recon unit which had little use.

At first i measured the voltage across battery terminal +&- and got just over 14v which i was happy with and it shows alternator working fine.

But after couple of minutes i measued the voltage again and it has dropped 13.5v and then after few more minutes it went down to 12.4v.

I am really puzzled, cant be my 3 alternators are not working.

I believe i have some high resistance somewhere can you shed some more light to what could be the cause?

I dont have any parasitic drain as battery voltage doesnt drop overnight, it just drops with every crank of the starter.

 

Plz help i am scratching my head.

Share this post


Link to post
Share on other sites

This isn't enough to trace closer to root cause.

At what RPM did you take the measurements?

Did you have everything turned off? Or was the car drawing lots of amps?

 

You need to follow the test program I described above. The several voltage readings will help to narrow down toward root cause.

 

On the results posted the most suspect root causes are:

1) the alternator output has fallen to 12.4V due to internal faults,

2) the battery is damaged & absorbing so many amps that the alternator is unable to maintain voltage,

3) too low RPM and a faulty module/component drawing high current making it impossible for the alternator to maintain voltage.

4) resistance is causing a lower voltage at the measuring points. 

 

A bad battery is certainly a potential suspect. Can you feel any heat in the battery or detect any gassing when voltage falls to 12.4V? Either or both would be expected if 2) is the case.

Or could you borrow and battery & set of jumper cables for a test? You needn't even remove your current battery from the car. Disconnect the +ve battery terminal. Use jumper cables to connect the test battery to the car's battery terminals: +ve to +ve and -ve to -ve. Wrap the +ve clamp at the car's terminal in rags or similar to prevent inadvertent shorts. Start the car and check voltages. 

 

If it's excess resistance it could be between the alternator and the under car connection point you measured or in the ground circuit. Resistance at the battery terminals is eliminated.

 

A word of explanation regards 2) & 3). When the current draw exceeds the alternator's capacity laws of electro-magnetics require that output voltage falls. Further alternator amp capacity varies with RPM - it's quite possible to "overdraw" the alternator at idle or low RPM.

 

Regards

RDL

Share this post


Link to post
Share on other sites

I will try a new battery i have in the garage, it is slightly larger and has more Ah but at least i know it is new and i have it fully charged.

I am a bit confused as this is the 3rd alternator.

#The original one was outputting 13.8 when started and drops to 12.4v after few minutes.

# second one was pretty dead with 12.4v 

# third one which looks like new as it is remanufactured  has an output of over 14.0 to 14.2  v at start and then it drops to 12.4 after few minutes...cant be all these alternators are dead.

 

Share this post


Link to post
Share on other sites

Three consecutive bad alternators certainly would be bad luck.

 

More plausible are:

1) bad battery sinking amp that overwhelm the alternator 

2) a module or component that starts drawing excess amps after the engine is started, again overwhelming the alternator

3) a bad connection or frayed cable that increases resistance as it it heated by I2R losses and therefore increases resistance, which would result in the voltage drop you're measuring ... at the points you're measuring. One wonders what the voltage is at the alternator terminals when you see 12.4 V downstream in the circuit.

4) a variation on 2) & 3) above -> modules turn on after a few minutes of running & the increased amp draw increases the voltage drop across the excess resistance in either the ground strap or alternator to battery cable.

 

Regards

RDL

Share this post


Link to post
Share on other sites

I have checked my ground connections and they look fine, the main one from engine block to chassis is quite oily but thats it. None of them is showing signs of burns or anything like that.

I  could connect both bolts at the end of the ground strap in engine bay with a jump leak and see what happens next..

This is a nightmare

 

 

Share this post


Link to post
Share on other sites
48 minutes ago, amazighman said:

I have checked my ground connections and they look fine, the main one from engine block to chassis is quite oily but thats it. None of them is showing signs of burns or anything like that.

I  could connect both bolts at the end of the ground strap in engine bay with a jump leak and see what happens next..

This is a nightmare

 

 

 

Checked with a voltmeter?

Share this post


Link to post
Share on other sites

 

1 minute ago, rdl said:

 

Checked with a voltmeter?

I just returned from the garage.

I did test the voltage from the back of the alternator to the casing and it is about 12.4 v same as at the battery.

 

I hooked a jump lead as a ground strap and the voltage didnt improve .

 

As engine runs longer voltage drops to just over 12.3 v.

Could it be that i bought another bad alternator and that i need a new voltage regulator? They are about 30 pounds same as a salvage alternator.

 

This is turning into a headache.

Share this post


Link to post
Share on other sites

It's got to be either another bad alternator or the car is drawing more amps than the alternator can supply (since the battery has been eliminated with your test of a known good battery.)

 

What RPM is the engine running while you test?

How many electrical loads in the car do you have turned on?

Do you have a 100 DC amp meter available? In-line or clamp-on style?

 

I can think of two ways to check between the alternatives.

If you're lucky enough to have a DC ammeter, measure current in the cable labelled "B+ to car's electrics" in this image of the battery  (ignore the white text, it's left over from the image I borrowed for this post) With the engine running, of course.

With everything else in the car turned off, it shouldn't be drawing more than 20 or 30 amps.

BatterySafetyTerminal.jpg.5f206fdbee79c18c62e28364d815d518.jpg

 

If no ammeter, there is a backyard mechanic alternative that isn't fully conclusive but almost so.

Disconnect the "B+ to car's electrics" cable from the battery terminal.

Take your spare battery and use jumper cables to connect -ve post to the car's -ve terminal.  Leave the -ve terminal connected to the car battery -ve post.

Again with jumper cable, connect the spare battery's +ve post to the  "B+ to car's electrics" cable. Now the alternator is connected to the car's battery only, while the spare battery supplies the car's electrics, including the DME, fuel pump, etc. so the engine can run.

Start the engine and check voltage. If voltage stays ~14V, something in the car is consuming more amps than the alternator can supply. If the voltage drops to 12.4V, the alternator is the likely problem.

 

This test doesn't actually prove the alternator is good or bad. The alternator might simply be weak and able to maintain battery voltage but not supply the car's electrical load. But that means you've had 3 weak alternators in a row. It's much more reasonable to conclude the car is the problem, not the alternator.

 

Regards

RDL

Share this post


Link to post
Share on other sites

I will try your see method when off work Monday Tuesday. Thanks for that RDL.

I was also thinking about using my daily driver car to act as an alternator for my BMW.

I tought if a i hook the jumps from my Mercedes 3.2 litres  to the jump points on BMW E39 , Start Mercedes and let it replace amps lost from starter, then start the BMW ,measure voltage in various points,then disconnect BMW live alternator cable ,theory my BMW should run off my Mercedes alternator generated power. If i get good voltage at the battery then my alternator is dead, if it still goes low means i have an electrical problem somewhere.

 

Cheers

Share this post


Link to post
Share on other sites

Running the alternator while it is disconnected from the battery risks damaging the alternator.

 

Every source for auto electrics diagnosis and repairs that I've ever seen very specifically warns against this. With no amps flowing, the regulator may/will not be able to respond quickly enough to avoid voltage spikes that could damage windings, diodes or the regulator itself. The battery acts as an accumulator that smooths out voltage spikes and gives the regulator time to adjust before damage.

 

Share this post


Link to post
Share on other sites

I decided to enlist a help of a more knowledgeable person in car electrics, we did test the wiring, and the battery health and found no issues there, he suggested may be the crankshaft pulley is split , i marked both parts of it and revved the engine for a while and marks still line up fine.

He suggested i have a dead alternator  so i ordered a brand new recon unit with 12 months warranty, if that doesn't solve the problem then i dont know

Edited by amazighman

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


×