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Old 09-05-2010, 04:10 PM
jmmcalpin jmmcalpin is offline
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Red face Alternator won't charge batteries

While riding yesterday the alarm sounded under the dash and I notice the volt meter dropped to 12 volts (from a little over 13). I replaced one of the batteries since I knew it was not holding a good charge any more and put a volt meter on the battery and alternator.
The battery read a little over 12 volts and when I checked the alternator while running it read .34 volts at 1k rpm, interesting it read 0 when the engine was not running, I thought it would read the 12 volts from the battery but it did not. I switch the batteries by turning the battery switch from both to battery 1 and battery 2 and no difference.
Is there anything else that can cause this or is it simply the alternator went bad on me while driving? I can easily change the alternator but want to be sure the battery switch or the black junction block next to it with 3 red wires attached cannot cause this symptom.
Btw, can I go to a automotive parts place and buy a standard car alternator or do I need to wait until my boat dealer opens on Tuesday.

Boat is an Xstar 2004 with an Indimar 350 engine, it says delco remy on the alternator.

Any help appreciated, John
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  #2  
Old 09-05-2010, 06:18 PM
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Wired_Right Wired_Right is offline
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Boat: * Mastercraft * Stars & Stripes * 1985 * 351 Winsor *
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FIRST or LAST: if it comes down to removing the alternator. Bring the alternator to O'reilly's or Kragen or what ever parts store is near you they can bench test the alternator there.
1. with out the engine running try to turn the alternator pulley, If you can the belt is too loose. this will contribute to the alternator not charging.
2. check the connections on the back of the alternator and make sure they are tight and have no corrosion of any kind.
3. Make sure your ground on your engine block is tight with NO corrosion.
4. Make sure your 12V+ wire to your starter relay is tight NO corrosion
6. Check the connections on the battery switch both sides of it for NO corrosion and tight connections
7. Make sure batteries are fully charged.
LAST or FIRST: if it comes down to removing the alternator. Bring the alternator to O'reilly's or Kragen or what ever parts store is near you they can bench test the alternator there.
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Last edited by Wired_Right; 09-05-2010 at 10:39 PM. Reason: update info
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  #3  
Old 09-06-2010, 12:50 AM
jmmcalpin jmmcalpin is offline
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thanks for all the great info, I did check the pulley and belt , they are tight and not slipping. I checked the wires at the alternator, switch and battery all are tight but you emphasize no corrosion of any kind so I will have to go back and check. Some of the connections had a little corrosion but it appeared to be cosmetic on the outside not between the connections . Since they were tight and I got no voltage (.37 volts) at the alternator I assumed they were ok.
One question though, on the Xstar next to the battery switch there is a black box (Guest) with the alternator red wire going to it and 2 red wires coming off it to the switch, could a bad (I will call it a junction box) cause the alternator to not send out the proper voltage?

BTW , the boat starts and runs fine with a fully charged battery, but I only get 12 volts so I assume I am running off the battery and not the alternator. And of course the alarm under the dashboard is screaming.



John
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Old 09-06-2010, 01:01 AM
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mtajpa mtajpa is offline
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In the link below are some basic ways alternators are wired. You should have a Red wire #10 guage or so the is hot all the time from the battery. Make sure your meter or test lite has a good ground connection prior to testing.

http://bpi.ebasicpower.com/charge/alternatorwiring.htm
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Old 09-06-2010, 07:25 AM
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WTRSK1R WTRSK1R is offline
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Marine Alternator ONLY

One of you original questions was about putting an automotive alternator in the boat. You DO NOT want to do that. Marine alternators are protected from producing a spark inside the closed engine area so that the boat does not explode if there are any fumes. I had mine rebuilt locally for about 1/2 the cost on my last boat.
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Old 09-06-2010, 09:15 AM
jmmcalpin jmmcalpin is offline
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Thanks for the help, I do have the Delco alt , it has a purple and read small wires in a harness and a red #10 guage wire that goes to a box (I believe it says "Guest" on it) , that box has 2 red wires coming off of it and go to the battery switch next to it. I do not get any voltage on the red #10 guage wire coming off the alternator when the engine isn't running and only get .24 to .37 volts when the engine is running. I do not know what the box does but what I am thinking is it broke and is not letting the current get from the alternator to the batteries. Does anyone know how to test the black box, I have an ohm meter and can test it for continuity but I don't know what it should read.
John
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Old 09-06-2010, 09:30 AM
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Quote:
Originally Posted by jmmcalpin View Post
Thanks for the help, I do have the Delco alt , it has a purple and read small wires in a harness and a red #10 guage wire that goes to a box (I believe it says "Guest" on it) , that box has 2 red wires coming off of it and go to the battery switch next to it. I do not get any voltage on the red #10 guage wire coming off the alternator when the engine isn't running and only get .24 to .37 volts when the engine is running. I do not know what the box does but what I am thinking is it broke and is not letting the current get from the alternator to the batteries. Does anyone know how to test the black box, I have an ohm meter and can test it for continuity but I don't know what it should read.
John
Post a photo. If it has an ref or orange wire and a purple one, pull the purple one off and turn the key to ON. If it doesn't have ~12V on it, you need to find out why. That wire is the excite lead and is used to create the magnetic field used to generate voltage.

You don't need to buy a new one- have it rebuilt. It needs to be built to marine spec and if you want, you can have it upgraded to about 95 Amps of output current.
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Old 09-06-2010, 09:51 AM
jmmcalpin jmmcalpin is offline
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Thanks , I will go get a photo, it is a black box with 3 screws, each one has a #10 guage red wire attached to it, that is all. one goes to alternatore the other 2 go to the battery switch.
The alternator does have a purple and red wire in a harness going to it. I will check that for 12v with the ignition switch on. Thanks
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  #9  
Old 09-06-2010, 09:57 AM
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TX.X-30 fan TX.X-30 fan is offline
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Quote:
Originally Posted by jmmcalpin View Post
thanks for all the great info, I did check the pulley and belt , they are tight and not slipping. I checked the wires at the alternator, switch and battery all are tight but you emphasize no corrosion of any kind so I will have to go back and check. Some of the connections had a little corrosion but it appeared to be cosmetic on the outside not between the connections . Since they were tight and I got no voltage (.37 volts) at the alternator I assumed they were ok.
One question though, on the Xstar next to the battery switch there is a black box (Guest) with the alternator red wire going to it and 2 red wires coming off it to the switch, could a bad (I will call it a junction box) cause the alternator to not send out the proper voltage?

BTW , the boat starts and runs fine with a fully charged battery, but I only get 12 volts so I assume I am running off the battery and not the alternator. And of course the alarm under the dashboard is screaming.





John




Check the ground on the Alt mine was low on the alt and I guess had water from the bilge on it and was corroded.
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  #10  
Old 09-06-2010, 01:56 PM
jmmcalpin jmmcalpin is offline
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I tried to post a picture of the battery switch and the black box next to it.. The red wire in the middle is from the output of the alternator and I get 0 volts when I read it with the motor off and .34 volts when the motor is running.
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