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  #1  
Old 02-10-2018, 01:55 PM
fatal_chemical
 
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83 om617 charging issues in my wrangler

I have an83 om617 in my wrangler. I just put a new alternator in it and it still won’t charge. If anyone else has done this swap can you please run me through where the wires go that pertain to charging? I have one from battery to alt, one from battery to starter, and one from battery to the distribution doodad. I’m reading only 12 volts.

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Old 02-10-2018, 02:09 PM
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I'm not familiar with jeeps or om617s but I do know many alternators of that era require a 12v exciter wire, which usually is in series with the alternator warning lamp on the dashboard. Without the exciter circuit, the alternator will not produce any output.
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Old 02-10-2018, 02:27 PM
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Quote:
Originally Posted by Fatal_chemical View Post
I have an83 om617 in my wrangler. I just put a new alternator in it and it still won’t charge. If anyone else has done this swap can you please run me through where the wires go that pertain to charging? I have one from battery to alt, one from battery to starter, and one from battery to the distribution doodad. I’m reading only 12 volts.
Assuming you have the stock Alternator with the connector that as 2 wide slots and one slot that is narrow.

The Narrow Slot on the Mercedes would go to the charging (idiot Light) and the Light Bulb needs to be at least 3 watts (some sources say 4 watts) and that provides enough resistance to excite the Alternator to charge. The Wire that goes to that on my Car is a thin blue colored wire.

Also part of the Alternator Circuit appears to go into the Head Light Switch. However, I don't know how that works or effects the charging.

The 2 fat red wires (that go to the 2 large slots on the connector) appear to both eventually end up connected to the + Battery voltage.

If someone could post a free online site of the Mercedes Manual and you could look at the wiring diagram.
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Old 02-10-2018, 03:30 PM
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Right idea, horrible explanation. The D+ (Exciter) wire provides bootstrap current and does indeed go to the dash light. But the light doesn't simply “provide resistance.” As weird as it sounds, the bulb provides POWER. It does this because the other leg of the bulb is connected to a source of switched 12v+. Power flows from the battery to the ignition switch to the bulb, and the bulb grounds through the alternator’s internal regulator via the D+ connection. Once the alternator begins charging, it provides its own power to D+. As a result, the bulb will have power on both leads, and it will go out.

To test this, all you need to do is start the car and “flash” d+ by momentarily touching a test lead between D+ and 12V+ (DO NOT ground). Just a touch will bootstrap the alternator and get it charging.

To fix this permanently, you can either set up an indicator light as described, or you can set up a connection between D+ and any switched 12v source. If you choose not to have a light, then include a diode in-line, otherwise the alternator can be damaged under certain circumstances.
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Old 02-10-2018, 07:54 PM
fatal_chemical
 
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I thank you folks greatly for helping me out! The issue i soon after i posted this thread was a blown fuse. I must have skipped over that one in the panel. Anyways, all of your information will be helpful in the future.
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  #6  
Old 02-10-2018, 11:36 PM
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If the blue wire from the alt to the dash isn't pluged into something. The care won't charge
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Old 02-11-2018, 12:36 PM
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Originally Posted by Mxfrank View Post
Right idea, horrible explanation. The D+ (Exciter) wire provides bootstrap current and does indeed go to the dash light. But the light doesn't simply “provide resistance.” As weird as it sounds, the bulb provides POWER. It does this because the other leg of the bulb is connected to a source of switched 12v+. Power flows from the battery to the ignition switch to the bulb, and the bulb grounds through the alternator’s internal regulator via the D+ connection. Once the alternator begins charging, it provides its own power to D+. As a result, the bulb will have power on both leads, and it will go out.

To test this, all you need to do is start the car and “flash” d+ by momentarily touching a test lead between D+ and 12V+ (DO NOT ground). Just a touch will bootstrap the alternator and get it charging.

To fix this permanently, you can either set up an indicator light as described, or you can set up a connection between D+ and any switched 12v source. If you choose not to have a light, then include a diode in-line, otherwise the alternator can be damaged under certain circumstances.
I make up all of the things I post; none of it is real.

However, the charging light indeed has a resistance to it.
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Old 02-11-2018, 01:20 PM
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Good job fixing it, well done.

In the future, I hugely suggest a Delco 1 wire alternator. The stocker on these cars is mediocre at best by modern electrical system needs. Delco 1 wire is reliable, ubiquitous, and available in sizes all the way up to semi truck for relatively little money. Bracketry is easy to fab and it's not like you're keeping the vehicle or engine original at this point anyway.
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Old 02-11-2018, 05:22 PM
fatal_chemical
 
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I realize now i should have been way more specific. It's not the original alternator, it's a 150 amp aftermarket bosch, which has one battery cable and one small wire that went to the fuse panel, which had a blown fuse which somehow i looked over. The only major thing left to do on her is figure out how to hook up the vacuum lines in order to shut it off properly
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  #10  
Old 02-12-2018, 11:57 AM
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Quote:
Originally Posted by Mxfrank View Post
Right idea, horrible explanation. The D+ (Exciter) wire provides bootstrap current and does indeed go to the dash light. But the light doesn't simply “provide resistance.” As weird as it sounds, the bulb provides POWER. It does this because the other leg of the bulb is connected to a source of switched 12v+. Power flows from the battery to the ignition switch to the bulb, and the bulb grounds through the alternator’s internal regulator via the D+ connection. Once the alternator begins charging, it provides its own power to D+. As a result, the bulb will have power on both leads, and it will go out.

To test this, all you need to do is start the car and “flash” d+ by momentarily touching a test lead between D+ and 12V+ (DO NOT ground). Just a touch will bootstrap the alternator and get it charging.

To fix this permanently, you can either set up an indicator light as described, or you can set up a connection between D+ and any switched 12v source. If you choose not to have a light, then include a diode in-line, otherwise the alternator can be damaged under certain circumstances.
Well I have a Boach Alternator Book wich of course I cannot find when I need it so I am stuck looing on the internet for info.

https://blog.*******.com/the-bosch-alternator-how-it-works
In order to begin charging, a small current has to be available at the rotor windings from the get-go. Nowadays, this may be computer controlled, but in the olden days, a very clever solution was put into place. Earlier Bosch systems involved a battery light indicator on the dash board that was in series with a point on the voltage regulator that would provide an initial current to the rotor. As the engine started up and the stator windings began producing a voltage, the difference in voltage between the windings and the battery would drop, eventually turning out the battery light. However, if a failure was present somewhere in the system, and the stator windings stopped producing adequate voltage, the voltage differential would light the warning indicator lamp, letting you know that your battery was not charging. This is indeed a very elegant solution to a serious problem! Many systems also had a resistor in parallel with the lamp. This is so that the alternator could still charge if the battery indicator lamp had burned out (a real problem with my '93 Volvo 940).”

The above if the best description I could find right away. Notice how if the charging light bulb burns out the resistor works to continue charging. That also indicates that in the end it is resistance that gets the alternator to charge.

My 1984 has no resistor in the circuit so it is the charging light bulb that supplies the resistance.

If the filiment in a light bulb did not cause resistance it would not get hot and glow.
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Old 02-12-2018, 06:52 PM
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The bulb is there for 2 functions: 1: To act as a current limiter on the alternator "flash" circuit.

2: To indicate faults in the charging system.

The resistance is not actually required, it is there to act as a current limiter to merely "boot up" the voltage regulator, you can short 12V directly to the terminal on the alternator and it'll work fine although it can put some extra stress on the regulator. If the bulb burns out in the Mercedes vehicles, the alternator will still function, the rest of the idiot lights feed through diodes into the same circuit to provide a "backup" flash source. If that fails too, the alternator will still self-flash once it gets some RPM.
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Old 02-12-2018, 08:34 PM
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Quote:
Originally Posted by Diseasel300 View Post
The bulb is there for 2 functions: 1: To act as a current limiter on the alternator "flash" circuit.

2: To indicate faults in the charging system.

The resistance is not actually required, it is there to act as a current limiter to merely "boot up" the voltage regulator, you can short 12V directly to the terminal on the alternator and it'll work fine although it can put some extra stress on the regulator. If the bulb burns out in the Mercedes vehicles, the alternator will still function, the rest of the idiot lights feed through diodes into the same circuit to provide a "backup" flash source. If that fails too, the alternator will still self-flash once it gets some RPM.
If that's true, why does the owner's manual tell you to drive to the dealer immediately when the charge indicator light stops working?
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Old 02-12-2018, 08:49 PM
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Originally Posted by funola View Post
If that's true, why does the owner's manual tell you to drive to the dealer immediately when the charge indicator light stops working?
Because usually if that bulb fails to light, it isn't the bulb that's failed, it's a problem with the alternator (worn brushes, failed regulator, open connection, etc). If the bulb fails to light, it can point to a charging issue. It's there as a diagnostic aid.
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  #14  
Old 02-12-2018, 09:08 PM
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Originally Posted by Diesel911 View Post
Many systems also had a resistor in parallel with the lamp. This is so that the alternator could still charge if the battery indicator lamp had burned out (a real problem with my '93 Volvo 940).”

The above if the best description I could find right away. Notice how if the charging light bulb burns out the resistor works to continue charging. That also indicates that in the end it is resistance that gets the alternator to charge.
Resistance isn't essential. You could put a piece of wire in place of the bulb and the alternator would still function normally. In fact, a lot of shade tree installations are done just that way. The resistor is suggested because in the event of a shorted battery cell (for example), the current would rise to infinity and burn out the alternator trio or D+ wiring without some sort of protection. The OP was using a fuse for this purpose.
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Old 02-13-2018, 01:58 AM
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Originally Posted by Mxfrank View Post
Resistance isn't essential. You could put a piece of wire in place of the bulb and the alternator would still function normally. In fact, a lot of shade tree installations are done just that way. The resistor is suggested because in the event of a shorted battery cell (for example), the current would rise to infinity and burn out the alternator trio or D+ wiring without some sort of protection. The OP was using a fuse for this purpose.
"Many systems also had a resistor in parallel with the lamp. This is so that the alternator could still charge if the battery indicator lamp had burned out..."

And yet the aritlcle has it that the altnator could still charge (if the bulb was out) implying that if the Bulb was burned out and there was no resistor (and there is no resistor in my year and model only the Bulb) the Alternator would not charge.

I know when I made the below test cord it worked with the Bulb in the test cord circuit.

Please note that I supplied info beyond my opinion on the subject. I hope my Book will turn up so I can see exactly what Bosch has to say the function of the light is.

I know on the older AC Delco Alternators with the internal votage regulator if you had a Voltmeter instead of the charging light on your car inside of the Alternator is a resistor. If your Car has the charging light the Alternator will not have the resistor inside. But that alternator works on differenlty then the Bosch one does.
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83 om617 charging issues in my wrangler-alternator-test-cord-drawing-feb-10.jpg   83 om617 charging issues in my wrangler-alternator-test-cord-bulb-feb-10-18.jpg  

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Last edited by Diesel911; 02-13-2018 at 02:12 AM.
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