Exciting the alternator?

Every car has an electrical system. Here's the place to learn all about it.

Moderator: 2088 bob

vwonnos
Posts: 36
Joined: Sun Jan 30, 2011 7:52 pm

Exciting the alternator?

Post by vwonnos » Mon Apr 11, 2011 9:54 pm

I'm installing a used motor in my buggy and the only way I can get the alternator to charge is to hook up a 12 volt wire directly to the warning light terminal. The voltage at the terminal through the warning light is only 12.20 volts. Is that enough voltage or does it need more? I figure as long as the motor runs shouldn't there be enough voltage to excite it. The battery shows 12.30 volts when the car is off.

So far I have tried a bigger light bulb. I've tried 100ohm 1 watt resistor in parrallel to the bulb. The only way I can get it to charge is when I hook up a jumper wire from the oil pressure switch I have that triggers the fuel pump. No oil pressure= no electric fuel pump.

My battery is pretty old. Its a red top optima that is about 7 years old.

User avatar
rostigbug
Posts: 69
Joined: Sat May 01, 2010 11:32 pm
Location: Tucson, AZ & Afghanistan

Re: Exciting the alternator?

Post by rostigbug » Mon Apr 11, 2011 11:17 pm

alternator or generator???
tim "FISH" fisher
Maxx-Pro FSR
camp Stone, Afghanistan
Wine improves with age
the older I get the more I like it

vwonnos
Posts: 36
Joined: Sun Jan 30, 2011 7:52 pm

Re: Exciting the alternator?

Post by vwonnos » Tue Apr 12, 2011 8:54 am

rostigbug wrote:alternator or generator???

Motorola alternator with internal reg. It just seems that it will only start to charge with direct 12v source and it won't charge with a light inline. I've tried the small warning light and two 100 ohm 1 watt resistors and I've tried two lights wired in parallel and it still wont excite it.

User avatar
rostigbug
Posts: 69
Joined: Sat May 01, 2010 11:32 pm
Location: Tucson, AZ & Afghanistan

Re: Exciting the alternator?

Post by rostigbug » Tue Apr 12, 2011 9:13 am

IDK squat 'bout the newfangled internally regulated alts.
BUT I gotta ask...
do you have the big wire that connects the output of the alt to the battery hooked up?It should be a pretty fat one, mebbe' 10 gage?.
also where are you measuring the output??
tim "FISH" fisher
Maxx-Pro FSR
camp Stone, Afghanistan
Wine improves with age
the older I get the more I like it

vwonnos
Posts: 36
Joined: Sun Jan 30, 2011 7:52 pm

Re: Exciting the alternator?

Post by vwonnos » Tue Apr 12, 2011 9:42 am

rostigbug wrote:IDK squat 'bout the newfangled internally regulated alts.
BUT I gotta ask...
do you have the big wire that connects the output of the alt to the battery hooked up?It should be a pretty fat one, mebbe' 10 gage?.
also where are you measuring the output??

Yes, the big wire is going to the back of the starter. I'm pretty sure the wireing is correct being that I just pulled an 1835 and the alternator would charge after I revved it to 2000 rpm. But this is an alternator that came on this motor and the guy said it worked for him. How else can I excite the alternator and still have a warning light?

vwonnos
Posts: 36
Joined: Sun Jan 30, 2011 7:52 pm

Re: Exciting the alternator?

Post by vwonnos » Tue Apr 12, 2011 9:46 am

rostigbug wrote:IDK squat 'bout the newfangled internally regulated alts.
BUT I gotta ask...
do you have the big wire that connects the output of the alt to the battery hooked up?It should be a pretty fat one, mebbe' 10 gage?.
also where are you measuring the output??
I measured the output at the battery posts.

User avatar
Dale M.
Posts: 1606
Joined: Mon Oct 05, 2009 10:09 am
Location: Just a Little Bit West Of Yosemite Valley

Re: Exciting the alternator?

Post by Dale M. » Tue Apr 12, 2011 12:55 pm

Alternator theory is there only needs to be a initial shot of 12 volts to initialize the alternator into operation.... After the initial shot of voltage the alternator (generating electricity process) should be self sustaining....

A idiot lamp wired to D+ terminal excites the alternator. Why Idiot lamp first is lit when you turn key on is because there is a GROUND potential on D+ terminal of alternator and it grounds the idiot lamp circuit. As you spin up alternator it takes the initial excitation charge of 12 volts through idiot lamp circuit and cause alternator to start functioning. As alternator at startup up begins to function the ground on D+ terminal transitions from ground to +12 volts dc and cause idiot lamp to go out because you now have 12 volts standing on both sides of lamp and there is no current flow....

So most any lamp hooked to one side at 12 volts and other side to D+ terminal of alternator should be sufficient to initiate alternator operation. The danger of to big a lamp or resistor in line is you can cause a condition called "run on" where the out put on D+ terminal (through lamp) is actually strong enough to "back feed" ignition system and when you turn key off the engine continues to run and only to stop it is pull wire off D+ terminal...

Some time all you need to is rev motor above about 2000rpm to get system to initialize (if everything is electrically good) .... Both my Bosch AL82 alternators are stubborn about this... At first it appears they will not work but a quick throttle blip initializes them... Think it had to so at idle speed (especially if you have "power pulley") it does not spin alternator fast enough to initialize...

So in the end all the larger bulbs and resisitors really do not help... The little tiny bulb found in speedo it essentially enough....

http://www.mydune-buggy.com/home/dl_fil ... Basics.pdf

Dale
Lives his life vicariously through his own self.
1970 "Kellison Sand Piper Roadster"

vwonnos
Posts: 36
Joined: Sun Jan 30, 2011 7:52 pm

Re: Exciting the alternator?

Post by vwonnos » Tue Apr 12, 2011 1:07 pm

Dale M. wrote:Alternator theory is there only needs to be a initial shot of 12 volts to initialize the alternator into operation.... After the initial shot of voltage the alternator (generating electricity process) should be self sustaining....

A idiot lamp wired to D+ terminal excites the alternator. Why Idiot lamp first is lit when you turn key on is because there is a GROUND potential on D+ terminal of alternator and it grounds the idiot lamp circuit. As you spin up alternator it takes the initial excitation charge of 12 volts through idiot lamp circuit and cause alternator to start functioning. As alternator at startup up begins to function the ground on D+ terminal transitions from ground to +12 volts dc and cause idiot lamp to go out because you now have 12 volts standing on both sides of lamp and there is no current flow....

So most any lamp hooked to one side at 12 volts and other side to D+ terminal of alternator should be sufficient to initiate alternator operation. The danger of to big a lamp or resistor in line is you can cause a condition called "run on" where the out put on D+ terminal (through lamp) is actually strong enough to "back feed" ignition system and when you turn key off the engine continues to run and only to stop it is pull wire off D+ terminal...

Some time all you need to is rev motor above about 2000rpm to get system to initialize (if everything is electrically good) .... Both my Bosch AL82 alternators are stubborn about this... At first it appears they will not work but a quick throttle blip initializes them... Think it had to so at idle speed (especially if you have "power pulley") it does not spin alternator fast enough to initialize...

So in the end all the larger bulbs and resisitors really do not help... The little tiny bulb found in speedo it essentially enough....

http://www.mydune-buggy.com/home/dl_fil ... Basics.pdf

Dale
Yes, I understand. I have reved it to 5000 rpm, didn't start to charge. The light wont go out and it wont start to charge. It only goes out and charges when I hook a direct 12v wire to it with out any resistance inline. Is there a problem with the alternator?

User avatar
VW_Man_87
Posts: 378
Joined: Wed Aug 05, 2009 7:49 pm
Location: Casa Grande, AZ
Contact:

Re: Exciting the alternator?

Post by VW_Man_87 » Tue Apr 12, 2011 4:17 pm

from my experience it sounds like the regulator in the alternator is bad... so i sugest you try to replace it.... just my 2 cents

jeremy
im in need of a new front clip for my 74 ghia, i dont care what year its from but i need one in order to fix my front end, can anyone help out?

vwonnos
Posts: 36
Joined: Sun Jan 30, 2011 7:52 pm

Re: Exciting the alternator?

Post by vwonnos » Tue Apr 12, 2011 4:23 pm

VW_Man_87 wrote:from my experience it sounds like the regulator in the alternator is bad... so i sugest you try to replace it.... just my 2 cents

jeremy

I swapped it out with my old one and it acts the same. Is there a way to test a regulator with a multi-meter?

vwonnos
Posts: 36
Joined: Sun Jan 30, 2011 7:52 pm

Re: Exciting the alternator?

Post by vwonnos » Tue Apr 12, 2011 4:41 pm

Also noticed that the previous owner painted the alt black. Could this cause a bad ground to the alt.? Does it need to be grounded?

User avatar
Dale M.
Posts: 1606
Joined: Mon Oct 05, 2009 10:09 am
Location: Just a Little Bit West Of Yosemite Valley

Re: Exciting the alternator?

Post by Dale M. » Tue Apr 12, 2011 9:43 pm

vwonnos wrote:Also noticed that the previous owner painted the alt black. Could this cause a bad ground to the alt.? Does it need to be grounded?
Yes it needs to be grounded....

You sure its internally regulated?....

Is it like this one?

Image

Dale
Lives his life vicariously through his own self.
1970 "Kellison Sand Piper Roadster"

vwonnos
Posts: 36
Joined: Sun Jan 30, 2011 7:52 pm

Re: Exciting the alternator?

Post by vwonnos » Wed Apr 13, 2011 8:54 am

Dale M. wrote:
vwonnos wrote:Also noticed that the previous owner painted the alt black. Could this cause a bad ground to the alt.? Does it need to be grounded?
Yes it needs to be grounded....

You sure its internally regulated?....

Is it like this one?

Image

Dale
Thats the one. Except this one has a cheap spray paint job on it. How or where do you ground it?

User avatar
Dale M.
Posts: 1606
Joined: Mon Oct 05, 2009 10:09 am
Location: Just a Little Bit West Of Yosemite Valley

Re: Exciting the alternator?

Post by Dale M. » Wed Apr 13, 2011 11:42 am

vwonnos wrote:
Dale M. wrote:
vwonnos wrote:Also noticed that the previous owner painted the alt black. Could this cause a bad ground to the alt.? Does it need to be grounded?
Yes it needs to be grounded....

You sure its internally regulated?....

Is it like this one?

Image

Dale
Thats the one. Except this one has a cheap spray paint job on it. How or where do you ground it?
You can either remove it and clean paint off where it mounts on pedestal, or put a ground wire under the screw ( down on left side)... Seriously doubt it will help though, Its my opinion you have a bad alternator ...

Dale
Lives his life vicariously through his own self.
1970 "Kellison Sand Piper Roadster"

User avatar
david58
Moderator
Posts: 14050
Joined: Sun Oct 23, 2005 8:14 pm
Location: Georgia near Savannah

Re: Exciting the alternator?

Post by david58 » Wed Apr 13, 2011 12:35 pm

Or you could check the ground of the ALT with a digital volt meter. Hook on test lead to the negative battery post, and the other to the ground screw Dale mentioned on the ALT running a ground to. A good ground will show less than 50 Milli Volts on the voltage scale. If it is less than 50 I'm with Dale, if the ALT is wired up right.
Hot, humid air is less dense than cooler, drier air. This can allow a golf ball to fly through the air with greater ease, as there won't be as much resistance on the ball.

Post Reply