Author Topic: Alternator not charging  (Read 7690 times)

1980sdga

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Alternator not charging
« on: 14 April 2011, 03:00 PM »
The 1980 wouldn't start today  :(  I charged the battery and she fired up but I figured I'd check the charging.

I disconnected the battery and got zero voltage at the cables with it running  :(  Everything works with the battery connected but when DCd nada...

I'm thinking voltage regulator because I was having some headlight dimming issues earlier which seemed to straighten out but now this.

Any tips on troubleshooting?

I did notice that the red "battery" light on the dash is not illuminated when the key is turned. It was illuminated with the key in accessory but went off with the car running.

I'll check to see if it's lit with it running.

Please give me some advise because I loathe electrical problems like this  :P

I just checked and the red light is not on at anytime.  Battery hooked or unhooked.

Kind of weird that the light failed at the same time something else did.  Maybe they're related?
« Last Edit: 14 April 2011, 03:23 PM by 1980sdga »
Jon


Little by little I have grown fond of the infamous Auto Temp II we have in our 116's

Big_Richard

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Re: Alternator not charging
« Reply #1 on: 14 April 2011, 03:50 PM »
Koan is the mastermind of such discussions,

but i seem to recall if the alternator bulb is blown the alternator ceases to function.

1980sdga

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Re: Alternator not charging
« Reply #2 on: 14 April 2011, 04:10 PM »
I checked the bulb and it's OK, could be the socket but I kind of doubt it.

Still no light.

I did check the plug at the alternator and I have power to the 2 big wires but the smaller wire looks like someone filled the connector with diaelectric grease or something.  Could be the trouble or at least someone else had similar problems because the plug is a little wonky.
Jon


Little by little I have grown fond of the infamous Auto Temp II we have in our 116's

koan

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Re: Alternator not charging
« Reply #3 on: 15 April 2011, 04:51 AM »
The dash charge indicator light should only be lit when the ignition is on but the engine not running.

Not sure what sort of terminals you have on the back of the alternator, mine has screw terminals, sounds like you might have something different, push on terminals perhaps?

There are only two connections to the alternator but you might have more than one wire on one of the terminals. They should be marked B+ and D+.

The heavy wire(s) on B+ terminal are the alternator output and go to the battery positive terminal and to the light switch, you should have +12 V battery voltage on B+ with the battery connected.

The other smaller terminal D+ comes directly from the charge indicator light. With ignition on +12 V from the battery goes to one side of the light, the other side goes to D+ on the alternator. With the ignition on but the engine not running current is drawn through the light by the alternator and the light glows, this is to supply the initial excitation current to get the alternator to start generating. Once the alternator is generating it is self exciting and the internals of the regulator put 12 V on the D+, the warning lamp now has 12V on both sides and goes out.

An easy test of the dash light and wiring is to remove the wire from the D+ terminal and short the wire to ground, with ignition on the dash light should be lit, if it isn't lit either the lamp is burnt out or there is an open circuit somewhere, possibly the multi-pin connector on the back of the instrument cluster is loose or the contacts are oxidised and need cleaning. if the light does come on problem is most likely the regulator mounted on the back of the alternator.

Not a good idea to disconnect the battery with engine running, on some vehicles the alternator output volts can rise to 18 Volts or more which is not good for the alternator and other components.

Just had a look at the wiring diagram for 79 300 SD and it shows a connection to a seat belt warning buzzer from the D+ side of the light, does you car have a warning buzzer and does it operate correctly?

koan
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koan

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Re: Alternator not charging
« Reply #4 on: 15 April 2011, 04:53 AM »
The dash charge indicator light should only be lit when the ignition is on but the engine not running.

Not sure what sort of terminals you have on the back of the alternator, mine has screw terminals, sounds like you might have something different, push on terminals perhaps?

There are only two connections to the alternator but you might have more than one wire on one of the terminals. They should be marked B+ and D+.

The heavy wire(s) on B+ terminal are the alternator output and go to the battery positive terminal and to the light switch, you should have +12 V battery voltage on B+ with the battery connected.

The other smaller terminal D+ comes directly from the charge indicator light. With ignition on +12 V from the battery goes to one side of the light, the other side goes to D+ on the alternator. With the ignition on but the engine not running current is drawn through the light by the alternator and the light glows, this is to supply the initial excitation current to get the alternator to start generating. Once the alternator is generating it is self exciting and the internals of the regulator put 12 V on the D+, the warning lamp now has 12V on both sides and goes out.

An easy test of the dash light and wiring is to remove the wire from the D+ terminal and short the wire to ground, with ignition on the dash light should be lit, if it isn't lit either the lamp is burnt out or there is an open circuit somewhere, possibly the multi-pin connector on the back of the instrument cluster is loose or the contacts are oxidised and need cleaning. if the light does come on problem is most likely the regulator mounted on the back of the alternator.

Not a good idea to disconnect the battery with engine running, on some vehicles the alternator output volts can rise to 18 Volts or more which is not good for the alternator and other components.

Just had a look at the wiring diagram for 79 300 SD and it shows a connection to a seat belt warning buzzer from the D+ side of the light, does you car have a warning buzzer and does it operate correctly?

koan

EDIT: Sorry for the double post, finger trouble on my part
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1980sdga

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Re: Alternator not charging
« Reply #5 on: 15 April 2011, 09:33 AM »
Thanks a million!  I'm out of town today but I'll check everything out this evening when I get home.  I ordered a voltage regulator which will be in next week. Probably just a good idea to change it even if it's not bad.

I did have a seatbelt light which stayed on all the time so I just removed the bulb. (I don't really need a little lamp to tell me to buckle up  ;D)  Could have something to do with it...

Thanks again for the advise! I really appreciate it!

I friggin' love a car that will run with ZERO electricity  :D Strange huh?
Jon


Little by little I have grown fond of the infamous Auto Temp II we have in our 116's

1980sdga

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Re: Alternator not charging
« Reply #6 on: 15 April 2011, 07:56 PM »
Thanks Koan!  I got home and checked it out.  Power at B+, power at D+ with the ignition on.  I grounded D+ and the battery light was illuminated.

Regulator on order.

So, I guess my regulator is just too crispy to even illuminate the warning lamp.
Jon


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koan

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Re: Alternator not charging
« Reply #7 on: 16 April 2011, 02:40 AM »
Thanks Koan!  I got home and checked it out.  Power at B+, power at D+ with the ignition on.  I grounded D+ and the battery light was illuminated.

Regulator on order.

So, I guess my regulator is just too crispy to even illuminate the warning lamp.

Ahhh, another satisfied customer (I do hope the new regulator fixes it!).

koan
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M110COUPE

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Re: Alternator not charging
« Reply #8 on: 19 April 2011, 02:03 AM »
The bosch regulator has two carbon brushes that run against the commutator, these wear down until they cant do their job, and your battery runs flat as its not being charged.

You can actually just relace the carbon brushes on the regulator, this is how auto electricians do it, just a few dollars of parts and its fixed.However you can also pull the alternator out and pull apart, put the main shaft in a lathe and lathe the commutator down smooth as the carbon brushes wear a groove in them. A lot of auto electricians then deem this as a recoditioned unit, clean it up and charge a small fortune for it. Some aussie has a youtube vid showing just this, search bosch alternator rebuild or something like that and check it out.


koan

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Re: Alternator not charging
« Reply #9 on: 19 April 2011, 04:30 AM »
The bosch regulator has two carbon brushes that run against the commutator, these wear down until they cant do their job, and your battery runs flat as its not being charged.

Yeah, you're dead right. Had a think about it after I posted. The D+ terminal goes directly to the field winding (rotor) via one of the brushes, as well as to the electronics of the regulator. I started to think not so much worn brushes but open circuit field winding, you could be right about brushes though.

Here's a circuit of a Bosch regulator:


Click for big picture.

The top D+ terminal connects internally inside the alternator to the extra three diodes that provide the excitation once the alternator is generating.

koan
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TJ 450

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Re: Alternator not charging
« Reply #10 on: 19 April 2011, 04:45 AM »
I like to keep an eye on the brushes just as a matter of course. I had an alternator fail on a Volvo in that way, and it left me stranded 200km from home.

That's very good info. 8)

Tim
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koan

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Re: Alternator not charging
« Reply #11 on: 19 April 2011, 10:44 AM »
left me stranded 200km from home.

I've been stranded twice, both have been due to alternator failures.

koan
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1980sdga

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Re: Alternator not charging
« Reply #12 on: 29 April 2011, 11:26 PM »


New vs old. The brushes looked OK but changing it seemed to fix it. My batt light is now on with the key to on and the light is off with the engine running.

The batt light was always off before. I'll run it at night to make sure everything is OK.

Question...   The old regulator was larger and covered more of the "hole" in the back of the alternator.  I'm assuming there is supposed to be a big rectangular opening under the regulator?  Cooling I guess?

Thanks again Koan! So far so good...

I noticed that the old one wasn't screwed down very tight...
Jon


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koan

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Re: Alternator not charging
« Reply #13 on: 30 April 2011, 01:07 AM »
Question...   The old regulator was larger and covered more of the "hole" in the back of the alternator.  I'm assuming there is supposed to be a big rectangular opening under the regulator?  Cooling I guess?

Just evolution of electronics has allowed the thing to be made smaller, a bit more airflow in and out of the alternator won't hurt.

koan
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